New Space Radar system

The U.S. Air Force, National Reconnaissance Office,
and National Geospatial-Intelligence Agency are developing
a new radar reconnaissance satellite?-known as Space
Radar?-to produce images of the Earth's surface using
synthetic aperture radar (SAR) techniques and to detect
moving targets on the ground, among other missions.
The first launch of what would eventually be a constellation
of Space Radar satellites is now planned for about
2015.
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The Space Radar system is intended to carry out four
missions for members of the military and the intelligence
community:
- Synthetic aperture radar imaging?-using transmitted
microwaves to produce images of the Earth's surface
(somewhat akin to photographs produced by optical
imaging).2 By providing their own illumination,
radars can produce images day or night, and microwaves
have the advantage of being able to penetrate
obscuring layers of clouds (although heavy rain or
snow can reduce the quality of the images). However,
radar images can be more difficult to interpret than
pictures produced with visible light.
- Ground moving-target indication?-detecting moving
targets on the surface of the Earth using special radar
techniques. Radar signals that reflect off objects in
motion have a different Doppler shift (the change in
the frequency of a signal caused by the relative motion
of the source and receiver) than do signals that reflect
off the surface around them. Through careful signal
processing, that Doppler shift can be detected and
used to highlight the locations of moving targets.
GMTI is used to conduct surveillance of large areas. It
typically provides the operator with an indication of
moving targets, which can be superimposed on a map
or image.
- Provision of high-resolution terrain information?-
making precise measurements of surface elevation. If
two observations of the same piece of terrain are collected
from slightly different angles, small differences
in timing between the returning radar signals used to
form the two images can be used to estimate the terrain's
height (through a technique known as interferometric
SAR).
- Open-ocean surveillance?-observing wide areas of the
oceans to monitor the movement of ships.
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