and high-resolution photographs taken from satellites orbiting high
above the Earth are available for all locations in the UK and elsewhere
in the world. These can be acquired from certain licensed, subscription-based
sources and can be purchased, often at reasonable cost. Low-resolution
images are also available from some sources at low or no cost, but
while they provide a fascinating perspective of the world, the quality
is usually of insufficient resolution for professional use.
High resolution satellite images for specific locations and at specific
scales and magnifications can be acquired through us, if commercially
there are thought to be about 300 satellites orbiting the Earth,
but in the next decade or so, many more will be operating or are
planned to be launched. With hundreds of different types of instruments
on board, they will increase the already vast amount of data and
photographs being transmitted to Earth, some of which will be available
commercially to the non-scientific community.
from dedicated defence and surveillance satellites, many of the
other satellites have meteorological and environmental observations
are their primary objective, providing weather and climatic photographic
data for national agencies. Other satellites provide a diverse range
of other information such as telecommunications, scientific measurements
and other commercially useful data.
well as conventional 'visible' photographs, satellite images can
be produced in the form of Infrared,enhanced infrared, composite
visible/infrared, composite satellite/surface maps and water vapour
addition to satellites operated by major governmental agencies,
privately-owned and operated satellites provide a large amount of
the photographs available commercially. One particular new satellite
weighs about 725 kg and orbits the Earth once every 98 minutes at
an altitude of approximately 400 miles (680 km). It is in a sun-synchronous
orbit so it will pass a given longitude at about the same local
time each day 10:30 a.m. The satellite orbit exactly repeats every
since the sensor is capable of viewing land mass far from the area
directly below the path of the satellite, a site can be imaged almost
daily, although not always at 1-metre resolution. The satellite
produces a number of different types of images (black and white
include 1-meter resolution panchromatic, 1-metre resolution pan-sharpened,
multispectral and 4-metre resolution multispectral (colour) images,
which can be used for a wide variety of applications. These represent
the highest resolution satellite imagery currently commercially
TYPES OF SATELLITE ORBITS
described by their inclination (the angle between their orbital
plane and the equatorial plane).
Orbits (GEO, Geosynchronous):
orbit over the equator (zero degree inclination) at the same rate
the Earth rotates, once every day. They orbit at a height of about
22,300 miles (36,000 km) above a fixed spot on the Earth's surface.
This precise positioning allows continuous and consistent monitoring
of a specific area. Geostationary satellite's cameras transmit their
pictures in 'real time' and therefore provide an instantaneous record
of the Earth, its geographical features and weather. A series of
these photographs can also be displayed in continuous sequence to
produce a movie effect.
Earth Orbits (LEO) Heights of approx 300 - 1000 km
and Medium Earth Orbits (MEO) Heights of approx 10,000 km.
example of a LEO is a Polar Orbit. This closely parallel
the earth's 0/180 meridian line (c. 90 degree inclination) and orbit
at a much lower altitude of about 530 miles (850 km) providing more
detailed information. They pass over the North and South poles each
revolution. As the Earth rotates to the East beneath the satellite,
each pass monitors an area to the West of the previous pass. These
'strips' of data can be pieced together to produce a picture of
a very large area.
Orbits: This follows an oval-shaped path and takes about 12
hours to circle the planet, with an inclination of about 64 degrees.
images can show any proportion of the earth from a full view of
one whole side of the planet down to close-up views of individual
buildings. It is also possible to overlay a number of different
feature sets on the image for specific analytical purposes.
choice of images available is wide, but limited to the stock made
available by NASA and the other international organisations for
commercial use. High magnification images (ie down to street and
building level) may not always be accessible for all areas and sometimes
can be relatively expensive.
HEIGHT RANGE:400 - 23,000 miles, depending on the type of satellite
and its orbit.