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Glossary

Glossary
 

This glossary has been compiled by Sky Eye for those who may be unfamiliar with some of the terms associated with aerial photography. It is a mixed dictionary of the definitions, acronyms and jargon used in aerial photography and the many other disciplines associated with it, including digital photography, computer science, aviation, meteorology, geography, electronics and graphic design.

Should you feel there are any significant omissions or inaccuracies, we would welcome an email with your suggestions to improve the glossary. Thank you.


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Aberration - Inability of a lens (ie a fault) in which light rays are scattered, causing distortions in the recorded image. There are 6 main types of aberrations: chromatic, spherical, coma, distortion, astigmatism and field curvature.

Absolute temperature - The temperature at which all molecular movement is considered to cease. Often referred to as absolute zero (-273.16 degrees centigrade). It forms the base point of the Kelvin scale, used in photography to measure the 'colour temperature' of light.

Achromatic lens - A lens constructed of different types of glass to minimise chromatic aberration.

Aerial perspective - Term, often used by non-aerial photographers, to describe the distance or depth effect caused by atmospheric haze. Haze creates large amounts of extraneous ultra-violet light, to which all photographic films are sensitive. This produces an overall density in the image that obscures detail and produces tone differences from the foreground through to the horizon.

Aerial survey - There are many different types of surveys, depending on the objective of the information gathering process. Surveys generally consist of capturing images of large areas of the ground from an aircraft or other airborne platform in a systematic way to later collate, interpret and produce reports of various kinds. Examples include pipeline surveys, large construction sites using conventional photography or infrared thermographic (IR) surveys using thermal imaging cameras to detect and measure heat loss from structures.

AGL - Above Ground Level (see also Datum).

Air frost - Temperature below 0 degrees centigrade, measured at a height of 1 - 2 metres above the ground.

Air mass - A large body of air with nearly uniform temperature and moisture content. There are 6 recognised air masses that affect the British Isles, denoting their source region and subsequent track (eg Polar Maritime and Tropical Continental).

Airbrushing - Traditional and specialised method of retouching photographs to remove unwanted areas or change certain aspects of the image using a very fine spray gun. Retouching is now performed mainly as a computer manipulation using specialised software.

Airstream - A significant body of air flowing in the same general circulation.

Air-to-air photography - Photography of an aircraft in flight, taken from another aircraft.

Air-to-sea photography - Photography of a ship, other vessel or the sea from the air.

Aliasing - Visibly jagged steps along an angled line, seen at high magnification of a digital image, caused by sharp tonal contrasts between adjacent pixels. This effect can be reduced by 'anti-aliasing'.

Altimeter - Devise for measuring height (eg of an aircraft, relative to mean sea level).

Altitude - Height expressed as the distance above a known reference level, usually mean sea level or ground level (see also Datum).

Ambient light - Naturally occurring daylight or other light sources available to the photographer (ie not supplied by the photographer with a flash gun or other lights).

Anemometer - An instrument that measures wind speed.

Angle of incidence - When light strikes a surface it forms an angle with an imaginary line, often known as the 'normal', which is perpendicular (90 degrees) to the surface. The angle that is created between the 'incident ray' and the 'normal' is called the 'angle of incidence'. In aerial photography this is important, as the photographer may need to alter the angle of incidence (of the aircraft he is shooting from) to avoid unwanted reflections from water or other reflecting surfaces.

Angle of reflectance - a law in physics states that the angle of reflectance equals the angle of incidence. This is important for aerial photographers to know as it can help avoid unwanted reflections from water and other surfaces. See also Angle of Incidence.

Angle of view - the proportion (measured in degrees) of a scene that can be captured by a particular lens. The focal length of the lens determines the angle of view. (eg a 24mm wide-angle lens allows a greater angle of view to be captured than a 400mm telephoto lens).

Anti-aliasing - Removal of the jagged, pixelated edge in a digital image, by averaging adjoining pixels to create a smooth blend of colour or edge.

Anticyclone - A region of relatively high pressure where air is descending through the atmosphere normally bringing dry and settled weather. Winds on the surface of the Earth blow clockwise around it in the northern hemisphere (and anti-clockwise in the southern hemisphere).

Aperture - In most lenses, the aperture is an adjustable circular hole that allows light to enter the camera and be recorded on film or a digital camera's CCD.

Aperture priority - A programme mode on an automatic camera that, when a specific aperture is selected, it ensures the camera automatically selects an appropriate shutter speed to give a correct exposure.

ASA - See ISO.

Aspect ratio - Ratio of width to height, either of a photograph, negative, digital CCD (eg: a 35 mm negative with a 3:2 ratio will produce a full size print of 6 inches wide by 4 inches high or 12 x 8 inches etc).

ATC - Air Traffic Control.

Atmosphere - The mass of air immediately surrounding the Earth. It is made up of different layers, each with different properties and temperature structure etc. These properties differ throughout the year and the over different continents. The troposphere is the lowest region, varying between 16 km near the equator and 9 km over the poles. (Mt. Everest is about 10 km). It contains about 80% of the atmosphere by weight and it is where most of the 'weather' occurs. The upper limit of the troposphere is the tropopause (about 8 miles). The layer above the troposphere is the stratosphere, which extends to about 50 km (30 miles) above the earth's surface. Most long-distance aircraft fly in the lower stratosphere to avoid adverse weather systems.

Atmospheric pressure - Pressure asserted by the mass of the column of air directly above any specific point. (Also called air pressure and barometric pressure).

Attachment - A file, of any type or format, attached to an e-mail and delivered at the same time as the e-mail message. Low-resolution photographs are often sent as attachments.

Autofocus (AF) - A camera system that describes the automatic focusing of a modern film or digital camera on the subject targeted by the photographer.

Average scene brightness - A reflectance rate of 18% is considered to be the average scene brightness. Most meters are calibrated to provide correct exposure for a subject of average brightness, but can be 'fooled' by subjects with higher or lower values.

Azores high - A semi-permanent area of high pressure, often centred around the Azores in the mid-Atlantic. It is caused by the air at high levels moving out from the equatorial regions, slowing down at about 30 degrees North and descending. (Good news for British aerial photographers!)

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Back-lit - When the subject is illuminated from behind (eg by the sun), it may be under-exposed unless the photographer compensates for this by adjusting the camera settings. Sometimes, however, this is a desirable effect.

Backup - A second or additional copy of a computer file or program, stored for safety in case the hard-drive fails and all the information on it is un-retrievably lost.

Barometer - Instrument for measuring atmospheric (air) pressure.

Barrel distortion - A common lens aberration where shape of the image is distorted. Straight lines, particularly at the edge of the field, are bent into the shape of a barrel.

Basic Scale - The scale at which a survey is undertaken. Ordnance Survey uses 3 basic scales (1:1250 for urban mapping, 1:2500 for urban and rural and 1:10 000 for mountain and moorland).

Bathymeter - Instrument used to measure the depth of water in seas or lakes.

Baud - Bits per second. A measurement used in data transfer via telephone lines.

Bearing - Angles measured in degrees against the National Grid. They are measured clock-wise from grid North (0/360 degrees). For example, a bearing of 90 degrees is due East, 180 degrees due South and 270 degrees due West.

Beaufort Wind Scale - Traditional system used to classify wind speed. Range used is from 0 (calm: less than 1 knot) - 12 (hurricane force: more than 75 knots). For instance, balloon aerial photographers usually work in the range of 1 - 3 (gentle breeze: 7 - 10 knots, ie when light flags are extended).

Bench Mark - A survey point on a fixed object, the altitude of which has been surveyed in relation to Ordnance Datum (or applicable local datum), which in turn is related to mean sea level.

Biplane - Aircraft with a pair of wings on each side of the fuselage.

BIPP - British Institute of Professional Photography.

Bit - A binary digit. The smallest unit of digital data. A bit is either a 1 or 0.

Bitmap - An image composed of a grid of pixels produced by digital cameras. The colour of each pixel is defined by the specific number of bits it contains.

Bleed - Term used to describe where printed matter runs across the white borders of a page for effect and off the edge of the page after it is trimmed.

Blimp (Helium balloon) - A large, tethered (captive) balloon, which is filled with high-grade helium used for low-altitude aerial photography. Because helium is lighter than air, the balloon, with remote cameras suspended below it, rises gently to the height allowed by the length of tether cable. Photographs can then be taken at specific heights and in all directions, controlled by a pan and tilt mechanism. The photographs are composed using a TV camera mounted beside the stills camera and the images are observed on a TV monitor on the ground. A blimp is often the only method of taking certain photographs at specified heights, especially in built-up locations.

Blur - Unsharp image area, created by movement of the subject or camera, or by inaccurate focussing.
Occasionally, blurring is produced intentionally to create an artistic effect or the impression of speed and movement.

Bookmark - A marker stored by a web browser that acts as a future shortcut to a web address. A good way of keeping useful websites to hand for regular use. (Bookmarks are called 'Favourites' in Internet Explorer).

Border - The edge of a photographic print beyond the image area, either left white or sometimes printed black.

Bracketing - Method for overcoming uncertainties in exposure in difficult lighting situations. By making progressive, additional exposures, above and below the estimated 'correct' exposure, the photographer is more confident that one of the series will be the correct exposure.

Buffer - Memory in the camera that stores the digital image data before it can all be written to the removable memory card. (This allows the photographer to keep shooting pictures at a faster rate than the card can accept and store the data).

Byte - The measurement for standard computer file sizes. Contains 8 bits. A byte can have any value between 1 - 255. (1 Kilobyte (KB) = 1,024 bytes, 1 Megabyte (MB) = 1,000 Kilobytes, 1 Gigabyte (GB) = 1,000 Megabytes, 1 Terabyte (TB) = 1,000 Gigabytes).

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CAA - Civil Aviation Authority. This is the official organisation that controls and regulates air movements and air space in the UK. (Also, an acronym for 'Computer Applications in Archaeology', an annual international archaeology conference, which includes aerial photography issues).

Cable release - Flexible cable used for remotely firing the camera's shutter. Particularly useful when any camera movement is to be avoided.

CAD - Computer-Aided Design. Software programs for the design, drafting and presentation of graphics. Originally designed for producing architectural drawing etc, but now highly sophisticated CAD programs are now widely used in mapping and other graphic-based projects.

Camera angles - Various positions of the camera, relative to the subject being photographed, each giving a different viewpoint and perspective.

Camera shake - Unintentional and unwanted (usually) movement of the camera during exposure, causing the image to be less sharp than it would have been if the camera was not moving, or if a faster shutter speed had be selected.

Candela - Measurement unit that expresses the luminous intensity of a light source.

Canon - A leading camera, lens and photographic equipment manufacturer. Produces professional equipment used by many aerial and other photographers (eg EOS IDs Mark II series of digital camera).

CCD - Charged Coupled Devise. The component in a digital camera that essentially replaces film to capture the light and ultimately create the image. It is a light sensitive chip containing a grid of special pixels, each of which produces an electrical output proportional to the amount of light striking it.

CD-R (CD-Rom) - Compact Disc used for storing digital data for use in computers. It can hold about 650 MB of data and is 'non-reWritable'. There are reWritable CDs called CD-RW. See also DVD.

Ceiling - The height above ground of the base of the lowest layer of cloud, when the cloud cover is over 60% of the sky.

Centigrade - Scale of temperature in which freezing point of water is equal to 0 degrees and boiling point equals100 degrees.

Cessna - Small, high-winged aircraft, popular for aerial photography, as the wings attached to the fuselage above the cockpit, giving the photographer good visibility of the ground.

CGI - Computer Generated Image - A graphic representation of (usually) a proposed building, structure or property development) for illustrating to the client or planning authority what the end result will look like when built. Aerial photographs of the general surrounding area are often commissioned so that the CGI can be digitally inserted into an actual photographic image to make the whole effect look more realistic.

Chrominance - The colorimetric difference between a given colour in a digital or video picture and a standard colour of equal luminance (brightness or light intensity)

Clearance - Authorisation from ATC (Air Traffic Control) for an aircraft to proceed as requested or instructed (eg Cleared for take-off and Cleared to descend etc).

Close-up - General term to describe an image taken close to the subject. It will need qualifying by the person commissioning the photography, as it can be interpreted in different ways by different people. For example, it could mean more-or-less filling the frame with the subject, with some surrounding scenery etc left in the frame, or it can mean really close, with perhaps the edges or the subject left out, in order to capture as much detail as possible.

Cloud amount - The portion of the sky (measured in eighths or 'octas') covered by cloud.

Cloud base - Basically, the lowest level in the atmosphere where cloud particles are visible.

Cloud cover - The proportion of the sky covered by clouds, measured in octas (eighths). More than 4/8 cover makes aerial photography risky if 'sunny' shots are required, especially without cloud shadows.

Cloud shadows - When viewed from the air, the shadows caused by areas of dense cloud on a partially sunny day. Sometimes cloud shadows cause a distracting effect on an aerial photograph.

Cloudy day - At least 6/8ths of the sky covered with cloud all day.

CMOS - Complementary Metal-Oxide Semiconductor. One of the few main types of image sensors currently used in digital cameras (same basic function as a CCD).

Coated lens - Lens with air-glass surfaces that have been coated with magnesium fluoride to reduce lens flare.

Cold colours - Colours at the 'blue end' of the colour temperature spectrum.

Cold front - The leading edge of a colder mass of air that displaces a warmer mass.

Colour (bit) depth - The number of bits used to represent each pixel in an image. (1-bit colour = black and white image with no greys or colour. 8-bit colour = 256 colours or greys. 24-bit colour = 16.7 million colours, the maximum number computers can deal with, giving photo-realistic colour images.

Colour balance - Adjustment in colour photographic or computer software processes ensuring, subjectively, that a faithful representation of the original colours of the subject matter, taken by the photographer, is reproduced in the final output (eg photograph or digital image etc).

Colour cast - When an image displays an unwanted (usually) bias towards one particular colour.

Colour management - The complex process of trying to ensure consistent colours are displayed and reproduced throughout all the devises used to produce the end product of photography (the 'workflow'). The different mechanisms used in the various devises in this process, including the digital camera, computer, scanner and printer etc, all have the ability to change the colours of the original image, so systems for colour management are adopted to minimise these changes. Calibration of all devises should be regularly carried out and 'colour profiles' produced for each devise to ensure consistency through the workflow. Digital images can then have a colour profile embedded into the image which can then be 'read' and utilised by the viewer or printer to print the correct 'colour balance'.

Colour saturation - Purity or strength of colour, due to the relative absence of black, white or grey.

Colour sensitivity - The response of a sensitive material to colours of different wavelengths.

Colour space - A Colour space describes how the red, green and blue primary colours are combined to form a given hue in the colour spectrum. As it is not possible to artificially represent every colour in the visible spectrum precisely by mixing different amounts of red, green and blue, colour spaces allow the modification of red, green, blue and white to get the best colour reproduction possible in digital photography. By slightly modifying primary colours, it is possible to maximize how many colours can be accurately represented on monitors and in printers by matching the colour space closely to what the specific device is capable of reproducing. See also Embedded Profiles.

Colour temperature - Colour, of any light source, is determined by its wavelength and its position on the electromagnetic spectrum. The spectrum ranges between 2,000K (eg 'warm' candlelight) - 20,000K (eg 'cold' blue skylight), measured in degrees Kelvin. Photographers set the 'white balance' on their cameras to the colour temperature of the light source they are using. If colour temperature is difficult to ascertain, cameras are often set on 'automatic white balance', where in-built computers calculate the colour temperature. Most 'daylight colour films' are balanced at an arbitrary, but generally accepted, colour temperature of 5,400K, considered as the average colour temperature of direct sunlight at midday in Washington DC - 'Mean Noon Sunlight'.

Commission - An order for something, especially a work of art or set of photographs, to be produced specially for the client, who is to pay for it.

CompactFlash™ - A common type of digital camera memory card used by professional photographers. Cards can hold up to about 8GB of data or more, allowing many high-resolution shots to be taken on a shoot without downloading the images or needing to use another memory card.

Compression - A process which reduces the number of bits of information in an image to reduce storage space, or so that it can be transmitted over the Internet more quickly. The JPEG image file format is the most popular one that uses compression. There are many degrees of compression that can be used, depending on the need. Popular compression software for files includes WinZip for PCs and Stuffit for Apple Macs.
Contact sheet - A print or sheet of all (or selected) images taken of a particular photographic shoot, as a convenient visual reference to the digital files supplied on a CD or DVD.

Contour - A line drawn on a map joining locations of equal height above datum.

Contract - A legally binding document that, when signed by both parties, holds the photographer and the commissioning person or organisation to the terms agreed to and stated in the contract. A simple contract is required for most aerial photography commissions to ensure what is ordered and to be provided is clear to both parties.

Contra-jour - A term for taking a photograph into the light source or sun.

Contrast - Difference in brightness between adjacent tones. Too little contrast often means a photograph looks 'muddy', whereas too much contrast causes some loss of half-tones and detail and unnatural.

Control points - Sometimes referred to as ground control points or tie points. These are points visible on aerial photographs for which an exact spatial reference is known, which can be used to help in the rectification of the image.

Cookie - A packet of data sent be an Internet server to a browser, which is returned by the browser each time it subsequently accesses the same server. Used to identify the user or track their access to the server.

Coordinates - Pairs on numbers expressing vertical and horizontal distances along the respective axes on a scaled map.

Copyright law - The law that governs the legality of ownership of a particular photograph or artwork. It is based currently on the Copyright Designs and Patents Act 1988 and provides (among other things) that a photograph is an artistic work protected by copyright, and that the copyright owner is the photographer (author), not his client, whether is was commissioned or not. Copyright forbids any illegal copying, reproduction or inclusion into a database or website of an image without the written consent of the author. The duration of copyright protection (for photographs taken after 1 August 1989) is 70 years from the end of the year in which the author dies.

Correction filter - A filter used in front of the lens to correct the differences between the colour temperature of the subject and the particular film being used. They may also be used with digital cameras.

Crop marks - Patterns in growing crops that appear in aerial photographs as shapes, colour, height or reflectance differences that reveal buried features of archaeological or geological origin.

Cropping - Removal of unwanted areas of an image to improve the composition.

Cross platform - Software able to be used on different types of computer and operating systems (eg PC and Mac).

CUCAP - Cambridge University Committee for Aerial Photography.

Cyan - The blue/green colour that absorbs red and transmits blue green. White light minus red.

Cyclone - A low pressure system in which winds spin inward in an anti-clockwise direction in the northern hemisphere (and clockwise in the southern hemisphere).

CYMK - Cyan, Yellow, Magenta and Black. The colour system commonly used in inkjet printers and by commercial printers to produce magazines and books etc.

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D2X - A high-end professional digital camera, made by Nikon and used by many aerial and other professional photographers. It incorporates a sophisticated CMOS sensor for image capture.

Dark room - A light-tight room used for processing films and printing photographs in the traditional method. It is usually illuminated by a 'safe-light' suitable for the materials involved. Many photographers now process their digital images in normally-lit rooms or studios - 'Light rooms'
.
Data - Generic name for any digital information used by a computer.

Datum - Short for 'Ordnance Datum'. A fixed, known reference point from which all height information used in the National Grid is relatively measured. Datum, in the UK, is a fixed point on the harbour wall in Newlyn, Cornwall, England.

Decompression - The expansion of compressed digital image or other computer files.

Definition - The subjective effect of clarity and sharpness and the provision of detail in an image.

Depth of field - Effectively, the distance between the foreground and the background that is acceptable sharp. Depth of field is increased when the aperture in decreased (smaller f/stop) and decreased when the aperture in increased (larger f/stop).

Derived map - A map that has been produced by reference sources of information other than primary survey data.

Differential focus - Choosing a wide aperture (eg f/2,8 or f/4) in order to render certain parts of the image out of focus and slightly blurred (to accentuate other parts remaining in sharp focus).

Digital Terrain Model - A 3-dimensional representation of the Earth's surface, constructed from different layers of survey data including aerial photography.

DIN - See ISO.

DNG™ - Digital Negative. A publicly available, archival format for raw files generated by digital cameras. Produced by Adobe, this is hoped to become a standard format for raw camera data to help ensure all software can read it in the future.

Download - The transfer of data from one source (eg the Internet) to another (eg a computer's hard drive).

DPI - Dots Per Inch. The measurement of a printer's or computer monitor's resolution. Not to be confused with PPI (Pixels Per Inch) used to state the resolution of a camera's digital image.

Dry mounting - Method of attaching photographic prints to a mounting surface by heating shellac tissue between the print and the mount.

DSLR - Digital Single Lens Reflex. (Camera design - see SLR).

DVD - Digital Versatile Disk. A standard, single-layer, single-sided DVD can store 4.7GB of data, approximately 7 times the amount of a similarly looking CD, which holds about 650 MB. When 'High Definition' DVDs become available, they are likely to store about 6 times more than conventional DVDs.
See also CD.

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Edge numbers - Reference numbers (printed by light) at regular intervals along the edge of 35mm and roll films during manufacture to identify individual frames after the film is processed.

EIS - Electronic Image Stabilizer. A devise that helps minimise the unwanted effects of camera shake.

Embedded profile - An ICC (International Colour Consortium) profile stored within a digital image that defines the 'colour space' in which the image data are interpreted.

Emulsion - The light-sensitive coating of a film (basically silver halides in a gelatin-like substance) that records the image.

Encryption - The use of specialised software for converting data so that it cannot be read by anyone other than the intended recipients, who have the same software installed to decode the encrypted data.

Enlargement - An image (usually a print) that is larger than the negative or capture media used to produce it. (Most prints are therefore enlargements, but most people consider print sizes of 8 or 10 inches and above as enlargements).

Enprint - A small, enlarged print of a fixed ratio size, produced commercially and automatically by film processing companies.

EOS 1Ds Mk II - A high-end professional digital camera, made by Canon and used by many aerial and other photographers. Incorporates a CMOS sensor for image capture.

ETA - Estimated Time of Arrival. The time an aircraft is calculated to touch down at an airport.

Exposure latitude - The difference in exposure which can be made, from the minimum necessary to record a full range of shadow and highlights detail, to the maximum exposure before detail is lost. Some films, especially transparency film (reversal film, diapositive film, slides), have less latitude than others.

Exposure value (EV) - The calculated combination of shutter speed and aperture setting at any given light level (eg 1/500th at f/8 or 1/250th at f/5.6).

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F/stop (F number) - The notation used for describing relative aperture sizes (eg: f/4, f/5.6, f/8 etc). The larger the f/stop number, the more light enters the aperture. It is the focal length of the lens divided by the diameter of the aperture.

False colour - Computerised translation of visible or invisible wavelengths to colours within the visible spectrum to enhance visibility and interpretation.

FAQs - Frequently Asked Questions. A list of common and useful questions and answers found on informative websites.

Fast film - Film which has a high ISO rating (eg ISO 400 and above), which is very sensitive to light, and therefore can be used in low light situations and still capture the scene acceptably well without additional lighting, eg flash light etc.

Fast lens - Lens with a wide maximum aperture (low f/stop number, eg f/2.8) to allow fast shutter speeds to be used when necessary.

File format - The way digital information is stored (eg Jpeg, Tiff, Raw etc)

Film speed - See ISO.

Filtre - Tinted optical glass, or other transparent material, fitted in front of the lens that alters the characteristics of the light passing through it to cause a beneficial effect on the image. In aerial photography, UV filters are often used to reduce atmospheric haze and other unwanted effects.

FireWire - A type of cabling technology for rapidly transferring data between digital devices. Faster than USB connections, and used by many photographers to transfer images from memory card to computer.

Fish-eye lens - A very wide-angle lens, with an angle of view in excess of 100 degrees and sometimes 180 degrees. Causes a characteristic and extreme barrel distortion.

Fixed-wing aircraft - An aircraft with non-movable wings attached to the fuselage (ie not a helicopter).

Flare - Caused by bright light (eg the sun, when shooting in a southerly direction, when in the northern hemisphere) entering the lens and producing unwanted (usually) effects on the image and often reduced colour and contrast. A usually unavoidable effect when taking a series of photographs in sunny conditions for 360 degree panoramas.

Flatbed scanner - A devise incorporating a flat transparent plate on which original images are placed for scanning (copying). The scanning process is linear rather than rotational, as in a drum scanner.

Floppy disk - a low cost, low capacity storage medium that can hold up to 1.4 MB of data.

Focal length - Basically, the distance in millimetres (mm) between the film plane and the optical centre of the lens, when focused on infinity.

Fog - A cloud of water droplets suspended in air that descends to ground level giving a horizontal visibility of less than 200 metres.

Foreground - The area in an image that is closer than the main subject matter.

Freezing fog - Fog with a temperature below 0 degrees Centigrade that deposits rime (frost) on contact with objects
.
Front (weather) - The boundary between two different air masses.

FTP - File Transfer Protocol. A common method of transferring data across the Internet.

Fuselage - The body of an aircraft or helicopter.

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Gale - A wind reaching a mean speed of 39 mph (34 knots) or gusts of 49 mph (8 on the Beaufort Scale).

Gamut - The range of colours and tones a printer or other device is capable of recording or reproducing (ie the colour space). The human eye can sense many more colours than can be reproduced on a computer monitor in any particular colour space.

Geodata - Information that identifies the geographical location and characteristics of natural or man-made features and boundaries of the Earth's surface.

Geometric transformation - The correction of spatial distortion into recognised map projection.

Geophysics - The study of the Earth by a wide range of physical techniques, some of which involve aerial surveys.

Geostationary satellite - A satellite orbiting at about 38,000 kilometres above the Earth over the equator. It orbits the Earth once daily so stays approximately stationary above a specific point. These satellites are used for many purposes, included weather forecasting and GPS navigation.

GIF - Graphics Interchange Format (bitmap graphics format).

Gigabyte - Measurement of file size of 1,024 megabytes (1,073,741,824 bytes).

GIS - Geographic Information System. A system (computer software) for capturing, storing, integrating, manipulating, analysing and displaying data spatially related to positions on the Earth's surface. Used for complex mapping projects, where different layers of data hold information about different physical features.

Glossy paper - Photographic printing paper with a smooth, shiny surface to display maximum detail and tonal range.

GMT - Greenwich Mean Time. The time zone based on the meridian of Greenwich, in London and used as the prime basis for standard time throughout the world. Sometimes called Universal Time (UT) or Zulu Time (ZT).

GPS - Global Positioning System. A satellite-based navigation system allowing accurate determination of any point on the Earth's surface or in the atmosphere. Based on radio transmissions from a series of US Defence satellites.

Graininess - The subjective impression of visible clumps of particles (silver halide crystals), seen in fast films, which may have to be used in low-light conditions.

Greyscale - A continuous monochrome scale consisting of up to 256 tones of black and grey.

Grid Coordinates - A plane-rectangular coordinate system based on, and mathematically adjusted to, a map projection in order that geographic positions (ie latitudes and longitudes) can be transformed into plane-coordinates for surveying.

Ground frost - A temperature of 0 degrees centigrade or below recorded on a thermometer placed on short grass.

Gust - A sudden, brief increase in wind speed lasting for at least 20 seconds. Aerial photographers don't like them!

Gyro-stabiliser - Electrically powered support for hand-held or mounted cameras that incorporates a gyroscope to reduce the effects of aircraft vibration and movement.

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Hail - Pieces of ice that form in layers in the updrafts of thunderstorms.


Hard drive (disk) - A built-in (to computer) or off-line fixed storage medium (ie external hard drive) that holds large amounts of data (eg up to 1000 GB) that can be rapidly accessed by the computer.

Hardware - All physical 'hard' parts of a computer system that are not 'software' (ie not programs/applications). Hardware includes printers and scanners etc.

Harr - A term used mainly in NE England and Scotland for fog and low cloud along the North sea coast.

Hasselblad - A major camera manufacturer, specialising in professional medium-format film and digital equipment.

Haze - Particles of fine dust and pollutants suspended in the air that limit visibility. It includes ultra-violet light.

Helium - A safe, lighter-than-air, gas used to lift balloons (and the payload attached beneath them), into the atmosphere. Helium weighs 0.1785 grams/litre (compared with air which weighs about 1.25 grams/litre) and is inert (non-inflammable). Hydrogen weighs less than helium (0.8988 grams/litre) but is not used now used in balloons as it highly inflammable and dangerous, so the slightest spark can cause it to explode.

Helium balloon (Blimp) - A large, tethered (captive) balloon, which is filled with high-grade helium used for low-altitude aerial photography. Because helium is lighter than air, the balloon, with remote cameras suspended below it, rises gently to the height allowed by the length of tether cable. Photographs can then be taken at specific heights and in all directions, controlled by a pan and tilt mechanism. The photographs are usually composed using a TV camera mounted beside the stills camera and the images are observed on a TV monitor on the ground. A helium balloon is often the only method of taking certain photographs at specified, low-altitude heights, especially in built-up locations.

High key - Image in which light or pale tones predominate, rather than dark, deeper tones associated with 'low key'.

High resolution (High-res) - See Resolution.

High-level oblique - The type of aerial photograph taken with a view of the subject at an oblique angle (of about 75 degrees off the vertical) and includes the horizon and the sky.

High-wing aircraft - Aircraft with the wings attached to the top of the fuselage, allowing better visibility for the aerial photographer shoot downwards towards the ground (eg Cessna).

Hire fee - In this photographic context, the charge made by an image library to use a photograph from a stock library for a specified use.

Histogram - A graphic representation of the range of tones, from dark to light, in a photograph. Histograms are displayed in professional digital cameras to allow checking of correct exposure and other parameters.

Hit rate - The number of times a website has been viewed by an Internet user.

Hoar frost - Ice crystals deposited on objects below 0 degrees centigrade, or dew that freezes after formation.

Hue - The name for a colour or shade.

Humidity - A measure of water vapour content of the air.

Hyperlink - A part of a web page (usually a single word, phrase or image), that, when clicked, automatically transfers the user to another point, either within the same web site or to an entirely different web site.

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ICC profile - International Colour Consortium is an industry group that has endorsed a standard format for 'device profiles' so that digital files can be interpreted by any devise 'reading' it and reproduce the same colour and other characteristics of an image to those when it was created. An example of a commonly used ICC profile is 'Adobe (1998)'. This has become the de facto standard within the industry for colour profiles when shooting images digitally.

Icon - In computer language, a graphic symbol used to represent a file or folder. It is opened by the user clicking on it. In architectural terminology, it is often used to mean a building or structure with special merit and representative of its time.

Image - Two-dimensional representation of a real object or scene produced, in the case of a photograph, by focusing rays of light.

Image (Photograph, Stock) library - A large collection of images (either owned by a photographer or an organisation), available for hire by anyone wanting to use or publish the image.

Image enhancement - The technique of altering an image with computer software to improve its appearance or accentuate its tonal and textural qualities.

Incident light - Light falling on to a surface, not reflected by it.

Indian summer - A period of warm, settled weather in mid-late autumn. Aerial photographers like them!

Infinity - Focus setting at which the lens gives a sharp image of a very distant object, such as the horizon.

Infra-red radiation - Electromagnetic radiation emitted by hot bodies (longer in wavelength than light: 730 nanometers - 1 mm). (See also Thermography).

Interpolation - Increasing the number of pixels in a digital image, or filling in missing colour information by averaging the values of neighbouring pixels. This 'up-sampling' process is used by many digital cameras and photo-manipulation software packages.

Intranet - A private computer network within an organization that uses the same protocols as the Internet, but is not necessarily connected to it.

ISO - ISO (International Standards Organization) is an arithmetically progressive sensitivity rating of a film to light (For example, ISO 200 film is twice as 'fast' as ISO 100). This 'speed' rating system allows photographers to calculate and achieve relative combinations of shutter speeds and aperture combinations in different lighting conditions. Alternative systems include ASA (American Standards Association) and DIN (Deutsche Industrie Norm), all now largely replaced by ISO. Digital photographers use the term 'sensitivity', which has been set to be roughly equivalent to ISO ratings.

Isobar - A line on a weather map (synoptic chart) that joins places with the same atmospheric pressure. The closer the isobars are together, the stronger the wind is. Wind blows almost parallel to the isobars.

Isotherm - A line on a weather map (synoptic chart) that joins places with the same temperature.
It is done with the aid of computer software and requires the photographs to be taken carefully (ideally with a tripod), with a suitable amount of overlap, so that a near perfect join can be made which is undetectable at a close viewing distance with the human eye. Aerial photographs can, in some cases, be stitched together, but not always, due to the movement of the camera.

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JPEG - Joint Photographic Experts Group. The most popular image file format than can store over 16 million colours and therefore is good for storing and transmitting photographic images. It is a 'lossy compression format', so if the image is to be opened on a frequent basis, degradation of the image will eventually occur. (Saving the image as a TIFF file will avoid loss of quality). When images are saved as jpegs, it is usually possible to select from a range of 12 file compression settings, starting with the highest compression (ie smallest file size and lowest quality) using the Quality 1 setting, through to the lowest level of compression (largest file size and highest quality) using Quality setting 12. JPEG 2000 is the new International JPEG compression standard that is supposed to be used in new digital cameras and software. It features higher compression but with less image quality loss.

Joule - The SI (International System of Units) unit of energy. Equivalent to the work done to produce power of one watt continuously for one second.

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Kelvin - Unit of measurement used to describe the 'colour temperature' of the various forms of light (eg daylight and fluorescent light etc). The standard unit of thermodynamic temperature, calculated by adding 273 to degrees centigrade. Most daylight colour films are balanced at an arbitrary, but generally accepted, colour temperature of 5,400K (degrees Kelvin), supposedly being the average colour temperature of direct sunlight at midday in Washington DC - 'Mean Noon Sunlight'. The Kelvin scale ranges between 2,000 -10,000K.

Knots - A measurement of distance expressed in nautical miles per hour. (Approx 1.855 km/hour or 1.15 mph).

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Landmark - A significant object or place on the ground which can easily be seen from the air to allow the pilot/photographer to identify his position, relative to the subject to be photographed.

Landsat - A series of satellites that produce images of the Earth. Developed by NASA.

Landscape - A rectangular image that is taken or displayed in the horizontal orientation (ie longest side in the horizontal position). Opposite to 'Portrait' orientation. Landscape also refers to the visible features of an area of land or countryside.

LCD monitor - Liquid Crystal Diode monitor. Small colour screen found on the back of most digital cameras and videos for previewing and reviewing images and other information.

LED - Light-Emitting Diode. Type of indicator light that is similar in function to a single LCD.

Lens hood - Circular shade attached to the front of a lens to reduce the amount of unwanted light entering the lens and causing flare, especially when shooting into the direction of the sun.

LiDAR - (Light Detection And Ranging). A sophisticated airborne remote sensing technique for producing high-resolution, coloured 3D images. Uses include detailed surveys of difficult-to-access terrain, shallow coastal waters and salt marshes etc.
Light room - Recently introduced term given to a digital photographic processing studio, where darkness is no longer a necessity (as it is when processing exposed film in 'dark rooms'). Also the name of some software used for digital photography.

Li-ion - Battery power source (Rechargeable) for modern digital cameras.

Long range forecast - A weather forecast extending past 10 days ahead.

Lossy compression - A form of digital file compression (as used with Jpeg files) that removes image data and therefore may reduce image quality.

Low altitude - A vague term sometimes used to describe heights lower than an aircraft can legally fly, but at which aerial photographs can be taken with non-aircraft methods (eg helium balloons and telescopic masts).

Low clouds - Clouds with a cloud base of less than 7,000 feet.

Low key - Image in which dark tones predominate, rather than light, paler tones associated with 'high key'.

Low-level oblique - The type of aerial photograph taken at a height below about 1,500 feet and view of the subject at an oblique angle (at about 45 degrees off the vertical). This usually does not include the visible horizon or the sky.

Lumen - Unit of light intensity falling on to a surface.

Luminance - Measurable amount of light (intensity), which is emitted by or reflected from a source.

Luminosity - Brightness or intensity of either a light source or reflective surface.

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Mac - Apple Macintosh computer (preferred by many photographers, designers, graphic artists and printers as an alternative system to the 'PC').

Magenta - The complimentary colour to green. Composed of equal amounts of blue and red light. It is the 'M' in CYYK.

Mapping - Transcription and interpretation of physical features observed on aerial photographs.

Mast (Tower, Pole) - Telescopic mast. A convenient method of elevating a camera to take 'low-altitude' aerial photographs. A series of aluminium sections of different diametres, which, when retracted, are stored within each other. When the mast is extended (by compressed air), the camera can be elevated to about 20 - 25 metres (65 - 80 feet) or even higher, where it is operated remotely. The higher masts are usually installed semi-permanently on a 4 x 4 or other suitable vehicle or sometimes mounted on trailers. Shorter masts can be hand-carried and stabilised with a tripod.

Matte - A non-reflective, non-textured surface (often referring to photographic paper). Also an American term for a cardboard mount that surrounds a photograph before it is framed.

MB - Megabyte. A measurement of storage data equal to 1,024 kilobytes (KB).

Mean Noon Sunlight - Most daylight colour films are balanced at an arbitrary, but generally accepted, colour temperature of 5,400K (degrees Kelvin), supposedly being the average colour temperature of direct sunlight at midday in Washington DC - 'Mean Noon Sunlight'.

Media - Material that information/data is written to and stored on. Digital photography storage media includes CompactFlash cards and CDs etc. Also can refer to the newspapers and television news.

Medium format - The format (size) of 6 x 6 cm (or 6 x 4.5 cm) roll film. Also called Professional format, being larger than 35 mm wide (3.5 cm), the format used by most amateur photographers still using film.

Medium range forecast - A weather forecast for 3 - 10 days ahead.

Megabyte - Just over one million bytes (1,048,576 bytes).

Megapixel - A CCD chip containing one million pixels. Professional aerial and other photographers tend to use digital cameras with at least a 12 megapixel chips to achieve high quality images and these are increasing in size all the time.

Memory - Can either be referring to the memory of a camera's storage chip (removable media), for recording the digital images on, or the computer's memory (either the hard disk or RAM).

Metadata - Information about information. In this context, it is the information about a digital image which is stored within the image file when shot on professional digital cameras. A great deal of data (eg exposure data and the time/date the image was shot) is automatically stored when the image is taken. Other data can be added by the photographer afterwards (eg copyright ownership and the name and description of the image etc). This can be read by certain software (eg Photoshop) and is important that image users are aware of this.

Midtone area - An area on an image that contains 'average' colour and tonal values.

Millibar - A metric unit of air pressure equal to 1 hectapascal.

Mist - A horizontal visibility of more than 200 metres but less than 6 miles. Caused by water droplets in suspension in the atmosphere.

Mode - The programmed operating function of automatic cameras etc (eg aperture priority mode or manual mode).

Modem - Devise for facilitating computers to communicate using telephone lines.

Monochrome - Single coloured. Usually applied to black and white photographs.

Montage - Composite picture made from a number of photographs.

Moral rights - Moral rights which remain with the author of a photograph, irrespective of what happens to the copyright (eg even if the author sells his copyright). This aspect was introduced in the Copyright Designs and Patents Act 1988 and applies to all photographs protected by copyright (See Copyright law). Moral rights cannot be assigned, in the way copyright can be assigned, and include a number of different and specific rights. One particular moral right (Paternity right) nearly always asserted by photographers is that the author has a reasonably prominent printed credit and acknowledgement whenever his images are commercially published or displayed in any form, including electronically on the Internet.

Motor-drive - Power-driven, often externally fitted, film wind-on mechanism allowing a photographer to shoot multiple images at high speed (eg 6 frames per second), with a single press of the shutter button. 'Continuous shooting' modes are available with a built-in form of motor-drive.

Multimedia - Any combination of sound, graphics, text, still or video images.

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Nadar - Name adopted by the first known 'aerial photographer', Gaspard-Felix Tournachon (1820-1910), who took his first photograph from a captive balloon near Paris in 1858.

NASA - National Aeronautics and Space Agency (American).

Nautical mile - a distance of 1,852 metres. I nautical mile per hour equals I knot.

Near vertical - (see also Vertical). An image taken almost vertically above the subject, but not that accurately and with the special equipment needed to qualify as a 'true vertical' for scaling and mapping purposes.

Near-Infrared - That part of the electromagnetic spectrum between 700 - 1200 nanometres.

Negative - The material image produced on a photographic emulsion, after exposure to light and processing, in which the tones of light and dark and all the colours are reversed to that of the original subject.

Newton's rings - Rings of coloured light produced when two glass or transparent surfaces are in partial contact. Often observed in transparency (slide) glass mounts.

NiCad (Ni-Cd) - Nickle Cadmium battery (Rechargeable). Have a disadvantage of a 'memory effect', which led them to believe they were full when recharged after only partial use.

Niepce, Joseph Niecephore - Frenchman (1765 - 1833) widely credited as the inventor of photography, being the first person to have created a 'permanent' image made directly by the action of light (a faint image on bituminized pewter plate in a camera obscura, following an eight hour exposure). His first picture (heliograph) was probably taken in 1822 - 1824, but was not until many years later that the 'invention' of photography was made public. It was, however, Louis Jacques Mande Daguerre who is acknowledged as the first person to develop a more practical process (Daguerreotype), announced in 1839.

Nikon - A leading camera, lens and photographic equipment manufacturer. Produces professional equipment used by many aerial photographers (eg Nikon D2X digital camera).

NiMH - Nickle Metal Halide battery (Rechargeable). Greater capacity than NiCads and do not have the unwanted 'memory effect'.

Noise - In digital photography, it is unwanted electrical interference causing degraded picture quality. Noticed mostly in low light conditions when the camera is set at a high ISO sensitivity.

Normal (Standard) Lens - Lens with a focal length equal to the diameter of the film (or digital CCD) format. It produces an image that appears to have a normal perspective and angle of view, comparable to the human eye. (For instance, on 35mm cameras, this is usually 50mm).

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Oblique - An aerial photograph that is not aligned vertically to the ground surface (See Vertical). There are basically 2 types of obliques: A Low oblique is when the picture does not include the horizon (eg taken with the camera inclined about 30 degrees or so from the vertical). A High oblique is when the picture includes the horizon (eg the camera is inclined about 60 degrees or more from the vertical).

Operating system - The program that controls a computer system.

Ortho-rectified - The removal of distortions from an aerial photograph, that occur as a result of imperfect optical lenses and sensors, the tilt of the camera/aerial sensor (relative to the ground), and other aspects of capture methodology. If an image is not ortho-rectified, it is not possible to use it for mapping and take accurate scaled measurements from it.

OS - Ordnance Survey. Great Britain's national mapping agency. OS produces a large number of different scaled mapping information from these data, including the widely available Landranger map series (Scale 1:50 000, 2.0 cm to 1 km) and the Explorer series ( 1:25 000, 4 cm to 1 km). Many other variations of scaled mapping are available for professional use.

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Pan and Tilt - The action of moving a camera horizontally and vertically.

Panchromatic film - Film that is sensitive to all the colours of the visible light spectrum.

Panning - A smooth rotation of a stills camera so as to keep a moving subject continuously in frame. A video camera pan is to capture a horizontal panoramic view. (Opposite direction to Tilt).

Panoramic camera - Camera with a special type of scanning lens that rotates (on its rear nodal point) and produces an image of the scanned area on a curved film.

PAPA - Professional Aerial Photographers Association.

PDF - Portable Document Format. A document standard produced by Adobe, used for e-mailing attachments in their original form.

Pentax - A camera manufacturer.

Perspective - The use of converging lines, differences in scale, or changes in tone with distance to give an impression of depth in pictures.

Photogrammetry - A mapping technique using a compilation of stereo images to produce accurate digital models and site plans. Following an aerial photographic survey of a site, digital images are downloaded to a computer where modelling software can produce the resultant model very rapidly.

Photograph (Image, Picture, Stock) library - A large collection of images (either owned by a photographer or an organisation), available for hire by anyone wanting to use or publish the image.

Photoshop - The industry-standard image processing and manipulation software.

Photosites - Groups of pixels within a digital camera's CCD that form the colour sensitive part of the image-capturing process.

Pixel - Picture element. The smallest element of a digital image. Also, the tiny points of light that make up the picture on a computer screen.

Pixelation - In computer graphics, pixilation is an effect caused by displaying a bitmap image at such a large magnification as to make individual pixels (square, single-coloured elements that make up a bitmap image) visible with the naked eye. ('Anti-aliasing' is a technique employed to improve the appearance of low-resolution images to make pixilation less obvious).

Polarization - Restriction of the direction of vibration of light. Normal light vibrates at right angles in every plane to its direction of travel. A polarizing (plane-polarizing) filtre restricts the vibration to one plane only. When rotated in front of the lens appropriately, it helps to eliminate reflections from water and non-metallic surfaces. It can also make the sky a darker, more saturated blue.
Port - An electrical connection point on the computer into which a cable (specific to that type of port) can be plugged, in order that the computer can communicate with another devise (eg a printer, scanner or modem etc).

Portfolio - A collection of photographs, either taken as a commission for a client or for a display to show a potential client.

Portrait - A rectangular image that is taken or displayed in the vertical orientation (ie longest side in the vertical position). Opposite to 'Landscape' or 'View' orientation.

Positive - In photography terms, prints or transparencies in which light, dark and colours correspond to those in the original subject.

Primary colours - Red, blue and green. (When mixed together equally form white light and called additive primary colours).

Prime lens - A photographic lens of a fixed focal length (ie not a zoom lens, which has a variable focal length). Sometimes considered as having slightly superior optical quality, but tend not to be as versatile in situations such as aerial photography.

Professional format - Description of a format (size) of film large than 35mm (as used by most amateur photographers). For example, 6 x 6 cm square roll film is called medium-format.

Programmetric survey - Transcription and rectification of features observed on photographs.

PTZ - A housing unit containing a camera (usually video), which can be operated remotely to pan, tilt and zoom.

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Quadrant - Each of 4 quarters of a circle.

QuarkXpress - A leading professional desktop publishing software package.

Quotation - A formal written statement setting out clearly the costs to be charged for providing a specified service or product, along with the terms and conditions. Quotations should be supplied to all clients who commission aerial photography so that both parties are in agreement as to exactly what is being provided and paid for. Usually, a simple, but legally binding, contract is signed by the client to confirm their acceptance of the quotation and associated terms and conditions.

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RADAR - Radio Detection And Ranging. An active sensor system (using microwave and radio wavelengths) that transmits its own energy to illuminate and receive back a signal from the ground or other object.

RAM - Random Access Memory. The computer memory where the machine stores software and other data while it is in use. Insufficient RAM causes the computer to work more slowly than it otherwise could.

Raw (Format) - The original and uninterpolated digital data collected directly from the camera's CCD image sensor, before any processing by the camera. (eg NEF is Nikon's own version of RAW format, short for Nikon Electronic Format).

Reconnaissance - A preliminary survey of a site to be photographed to see the features and check for any issues that may be involved. Usually shortened to 'Recce'.

Rectification - Removal of geometric distortion from an image or map.

Remote control (RC) - A system to control a camera or other types of machine's actions when the machine is distant from the operator and unable to be controlled manually. The control is usually by means of signals transmitted from a radio or other electronic device.

Remote sensing - The science of obtaining information from an object without making physical contact with it. For instance in archaeology, it applies to aerial photography and satellite-based sensors.

Removable media - Digital storage devices (eg a CompactFlash card) that can be removed from the camera (equivalent to the film in a traditional, non-digital camera).

Resize - Changing the resolution, file size or physical size of an image.

Resolution - An extremely complicated subject, as there are many interpretations of this term. Essentially, the measurement of the amount of information contained in an image. If measurement if of a 'capture' devise, (eg a digital camera or scanner) then the units are ppi (pixels per inch), whereas if the devise is an 'output', the units are dpi (dots per inch). Generally, it is meant to describe the quality of a digital image, in terms of how many pixels a set size image contains. For instance a professional DSLR camera taking images set at 300 ppi is considered as 'High resolution'. Low resolution is generally accepted at 72 ppi and medium resolution between 72 and 300 ppi. Professional aerial photographers would always take high-resolution images. See also Screen resolution.

Resolution, interpolated - A process of enlarging or increasing the apparent quality of an image by artificially added pixels.

Resolution, optical - The true resolution of an image, without interpolation.

Retouching - The act of improving or altering an image. Usually undertaken with computer software now.

RGB - Red, Green and Blue. A sophisticated combination of these 3 colours are used to represent all colours in a digital image. The additive system of colour filtration used by colour computer monitors.

Rights Managed (RM image) - Usage rights by the client for a specific, declared use only of an image.

Roll film - Type of film used in medium-format cameras (eg 6 x 6 cm size).

Rolleiflex - A major typed of medium-format camera, made by the German manufacturer, Rollei.

Rotary-wing aircraft - Helicopter.

Royalty - A payment made to the copyright holder of an image for its use by a third party.

Royalty-free (RF image) - A stock photography licence where the client pays a one-time fee for multiple use of an image.

RPS - Royal Photographic Society.

RT - Radio Transmission (method for remotely controlling a camera, aerial photography platform or devise, such as a model helicopter, kite or balloon).

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Saturation (of colour) - Purity of colour, due to the absence of other colours, including black, white or grey.


Scanner - A machine (input device) that uses a passing light to read and capture information, (eg photographs, transparencies, negatives, text, graphics and bar codes etc) and transfers it to a computer after converting it to digital data. There are various types including flatbed scanners (similar action to a photocopier) and drum scanners (for professional use to create high resolution output).

Screen (Display) resolution - The physical number of columns and rows of pixels creating the display. These can be changed on the computer to many different settings, such as 800 x 600 (low) to 1280 x 1024 pixels (high). The higher the screen resolution, the higher the quality of the images displayed on it.

SCSI port - Small Computer System Interface (pron. Scusy). A port that facilitates data transfer faster than serial or parallel ports, but slower than USB and FireWire ports.

SD card - Secure Digital card. A type of removal media for digital cameras.

Sepia - Reddish-brown colour, particularly associated with monochrome photographs of the 19th and early 20th centuries. (Brown pigment prepared from the black fluid secreted defensively from cuttlefish).

Sheet lightning - Cloud to cloud lightning.

Shoot - An assignment (usually commissioned) to take the required photographs for a client.

Shutter - Mechanism in the camera which controls the period of time that light is allowed to fall on the film or digital CCD.

Shutter lag - The time delay between pressing the shutter on a camera and the capture of the image.

Shutter priority - A programme mode on an automatic camera which, when a specific shutter speed is selected, ensures the camera automatically selects an appropriate aperture (f/stop) to give a correct exposure.

Sleet - Precipitation consisting of rain and snow mixed.

Slide - Alternative name for transparency film (or diapositive). Opposite to a negative.

Slow film - A film having an emulsion with a relatively low sensitivity to light (typically ISO 50 or less). Has very fine grain and therefore gives very good quality detail when prints are produced.

SLR - Single Lens Reflex. Camera design, using a hinged mirror to divert the light, that allows the focused image to be previewed, exactly how the lens sees it.

Smog - Air pollution caused by a mixture of smoke and fog.

Soft focus - An effect, often created artificially by the photographer, to give a slightly diffused (but not out of focus) effect to the image. It creates an evocative, sometimes romantic, feel to the image, although this is not generally used in aerial photography. It can be achieved at the capture or processing stage.

Software - Computer instructions. There are 2 main types: 1. 'System software' which includes the operating system and all the utilities a computer needs to operate. 2. 'Application software', the programs that do the work, such as word processors and spreadsheets etc.

Solar table - Tabulated information showing the position of the sun for any given time and day of the year.

Solstice - Time of the year when the sun is the farthest north or the farthest south (Summer Solstice about June 21 and Winter Solstice about December 21).

Spatial resolution - The ability of a sensor to differentiate between closely spaced objects, usually on the ground. This term is sometimes incorrectly used to describe the pixel spacing of a digital image.

Spot meter - An exposure meter that measures reflected light over a small, precise angle of view.

Squall - A heavy shower and/or thunderstorm often accompanied by strong and gusty winds. Aerial photographers don't like them!

Stereoscopy - Method of creating a 3-dimensional effect on 2-dimensional surface. Produced by using a pair of images taken from slightly different viewpoints, and then viewed through special stereo-viewers.

Stills camera - A camera that takes only still images (ie not a 'movie' camera).

Stitching - The process of joining 2 or more images together to make a wider or panoramic image.

Stop - The aperture of a camera or enlarging lens.

Stopping down - Reducing the size of the aperture (increasing the f/stop), and therefore the light entering the camera, usually to increases the depth of field. To compensate and maintain the correct exposure, it is necessary to halve the shutter speed for every stop reduced.

Storage media - A term generally referring to the removable cards (eg CompactFlash or SD cards) which are inserted into digital cameras to store the images (so-called 'digital film'). These cards are then downloaded onto a computer for processing.

Stuffit - A computer file compression system, commonly used on Macintosh computers.

Sub-contract - A legal contract undertaken by one party to fulfil the obligations of another party. For example, in the case of aerial photography, if a client contacts an aerial photographer to arrange some work and that photographer cannot for some reason carry out the work himself, he could 'sub-contract' the work out to another photographer. The client's contract, however, is with the original photographer, and not the one who does the actual work.

Subject - The person or object being photographed (ie the main reason for taking the shot).

Symmetry - A photographic composition made up of exactly similar parts facing each other or around an axis, often making a pleasing effect of perfect proportions.

Synoptic chart - A weather chart/map (characterised by the presence of 'isobars') on which data and analyses are presented that describe the state of the atmosphere over a large area at a given time.

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Telescopic mast - See Mast.

Terabyte - 1,000 Gigabytes. See Bytes.

Tethered balloon - A captive, helium-filled balloon for elevating a camera to take aerial photographs. Classified as an aircraft by the Civil Aviation Authority (CAA).

Thermograph - An instrument that produces a trace or image of the varying temperature of infra-red radiation over an area during a period of time.

Thermal - a bubble of warm, buoyant air rising through the atmosphere.

Thermal Infrared - The portion of the electromagnetic spectrum between 3 and 50 micrometres where the radiance of an object is dominated by emittance rather than reflectance.

Thermogram - A record made by a thermograph.

Thermography - The measurement of mid-infra-red radiation. The use of thermograms to study heat distribution in structures of the ground (eg to detect underground fires or the heat caused by the build up of methane in landfill sites). Aerial photographers are commissioned to elevate thermal-imaging cameras and scanners to obtain the height necessary for heat detection over a wide area.

Thumbnail - A small, low-resolution image from a larger file used to quickly and conveniently display images, either on a computer screen, digital camera LCD monitor or as a printed version.

TIFF - Tagged Interchange File Format. An industry-standard raster data format that stores digital data in an uncompressed form. (A 'lossless' compression form, LZW, is also available).

Tilt - The action of moving a camera upwards and downwards. (Opposite directions to Panning).

Trough - An elongated low-pressure system that enhances showers into longer spells of rain or snow.

TTL (Through-The-Lens) meter - Exposure meter, built in to the camera, which measure the light falling on the image capturing media (film or digital CCD).

TWAIN - A software protocol for exchanging information between image-capture devises such as digital cameras and scanners.

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USB - Universal Serial Bus. A cross-platform interface for the connection of peripheral devises (eg scanners) to computers.

UV (Ultra-violet) radiation - Electromagnetic radiation from 13 - 397 namometres, shorter in wavelength than light. Most films, unlike the human eye, are sensitive to UV light.

UV filter - Filtre used by many photographers, especially aerial photographers, to absorb UV radiation to reduce the effects of atmospheric haze.

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Vector - A method of displaying spatial information as a series of points, lines and polygons.

Vertical - (True Vertical) A term to describe a photograph taken with the camera pointing directly down (+/- 3°), so that all the 4 corners of the ground framed in the viewfinder are equidistant from the film plane, to show a map-like perspective. This allows the resultant photograph to be 'scaled' and measurements taken from it. Verticals are necessary for translation into mapping. (See also Near Vertical).

Videographer - A photographer who uses a video camera, rather than a stills camera.

View - A rectangular image that is taken or displayed in the horizontal orientation (ie longest side in the horizontal position). Opposite to 'Portrait' orientation. Also means what can be seen from a particular place or viewpoint.

Viewfinder - Simple optical devise in the back of a camera for viewing the subject.

Visibility - The greatest distance at which one can see and identify objects on the horizon.

VRAM - Video Random Access Memory. A graphics card in the computer that controls how many colours can be displayed on the screen.

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Warm colours - Colours at the red end of the colour temperature spectrum.

Warm front - The leading edge of a mass of warmer air that displaces a mass of colder air.

Watermark - In photography terms, a visible or often invisible mark embedded in a digital image (displayed on the Internet) to protect the image from unauthorized copying and use (ie being stolen). Sophisticated invisible watermarking allow images to be tracked and identified by the copyright holder whenever they appear in the public domain. It is the method by which 'internet image thieves' are prosecuted under international copyright laws.

Wavelength (of light) - The distance between adjacent peaks in a wave of light. This distance determines the colour of the light. It is the method for describing precise position along the continuum of the electromagnetic spectrum.

Weather front - the boundary between two dissimilar air masses. (The resulting winds associated with a passing front can help clear the atmosphere and improve air quality).

Wide-angle lens - Lenses (with a short focal length) with an angle of view wider than that considered, subjectively, as normal by the human eye (ie more than about 50 degrees).

WinZip - Compression software used by PCs.

Word - A popular, near universal, word-processing software package.

www - World Wide Web. Major part of the Internet.

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Zoom lens - Lens with a continuous variable focal length over a certain range. It is generated by differential movement of the lens elements.

Zulu time - Alternative name for Greenwich Mean Time (GMT) and Universal Time (UT).

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