B. IMPACT OF CLUTTER ON SENSOR PRFORMANCE IN LAND COMBAT
The Longbow program was further along than any others; the Longbow approach
used information provided by its high range resolution radar return from the stationary
target as opposed to a Doppler-shifted return from a moving target.
As a follow-on to the work modeling radar clutter for engagement of air targets,
STD got a study from the Army’s Model Improvement and Simulation Management
Agency to look at how clutter affected engagement of stationary ground targets. The
Longbow program was at that time further along than any other at trying to exploit highrange-
resolution radar signals to do detection and identification of stationary targets. It
was selected as the technology development on which to focus.
Tactical radars have low resolution in azimuth and elevation, limited by antenna
size. The resolution in range is limited by bandwidth and can be much higher. “High
range resolution” means that the radar “pixel” size (in the downrange direction) is small
compared with targets of interest. For a Longbow-sized antenna operating in K-Band,
with a 1 GHz bandwidth, the radar could distinguish “spots” on the ground about 100 m
wide and 15 cm deep. Typically, one would group these range cells, looking for “hot
spots,” then process the individual cells. A ground patch of about 30 range resolution
cells (even numbered cells in blue, odd numbered clear) with a tank in the middle might
The task for the clutter-suppression algorithm is to use the 30 or so returns, called
a “range profile,” from the wide, thin ground patches to determine whether a target of
interest is present. This is very challenging for a number of reasons:
• Each range cell has much more nontarget area than target area. Therefore, the
return may not be dominated by the target.
• The target may overlap adjacent patches, either in range or in cross range.
• The target orientation is unknown.
• For a turreted vehicle, the turret chassis angle will be unknown.
• The returns will vary rapidly with viewing angle. For example, there is no
reason to believe there will be any similarities in target returns between the
situation below and the one above.
Note that in the application of the high-range resolution technique to the air-to-air
environment, all these challenges are substantially mitigated or nonexistent.