SAR Acquisition Modes
Five ways a radar trades resolution against coverage, shown in 3D. Drag to orbit, scroll to zoom. The beam projects down to the ground and the imaged footprints accumulate as the platform flies along-track. The strip underneath shows when each part of the swath is being illuminated: that timing, not the ground picture, is where burst modes pay their price.
drag · scroll · right-drag pans
platform / ground track
active beam
imaged footprint (darker = overlap)
receive sub-beam / squint
sub-swath edge
Where the gaps really are. In ScanSAR and TOPS the antenna footprint is longer than the distance the platform moves during one full sub-swath cycle, so consecutive bursts on a sub-swath overlap on the ground and the coverage is contiguous. What each target loses is
time: it is recorded for only part of its footprint crossing, which shortens the synthetic aperture and coarsens azimuth resolution. SweepSAR has no bursts, but it does have gaps, in
range: the radar cannot receive while it transmits, so each transmit event blanks a band of the swath. NISAR moves those bands by dithering its PRF so that the missing samples can be filled (
Freeman et al. 2009;
Villano et al. 2014;
Kellogg et al. 2020).