Spotlight mode SAR stereo technique for height computation

Abstract

This paper examines the feasibility of extracting three-dimensional (3-D) or topographic information in spotlight mode stereo synthetic aperture radar (SAR). A display of a SAR (intensity) image has two axes: range and cross-range. Elevated scatterers appear closer in range; this phenomenon is called radar image layover. How the height of each scatterer can be computed from the difference in its layover between two images is investigated. This is analogous to computing height from disparity distance (triangulation) in optical stereo. The same procedure can be applied on pixel by pixel basis for terrain elevation mapping. A general expression is derived for the accuracy of the height estimate as a function of the range resolution and the angular difference between the image planes. Accuracy increases as the angle between the image planes increases, but the bright scatterers in one image tend to fade in the other image. This limited angular persistence of radar scatterers is also discussed. Trajectories for data collection are examined that provide near-optimal height estimates while eliminating the scatterer persistency problem.

The possibility of isolated target 3-D position estimation and optimal receiver position determination in SS-BSAR

“…If the 3-D information of the target scene can be generated, 3-D imagery has the potential to greatly benefit applications such as 3-D topographic mapping, target detection and object classification. In order to recover 3-D information of a target, one must have multiple apertures available at different look angles, thereby enabling interferometric [3,4] , stereo [5] or curvilinear SAR [6] processing. All the techniques require the images to lie on different image planes (slant range planes).…”

Three-dimensional surface reconstruction from multistatic SAR images

“…2(c) to the actual scatterer height, yielding an RMS height estimation accuracy of 30.6 cm. Inserting the parameters shown in Table I into (17) predicts an accuracy of centimeters, where has been assumed to be zero. In practice, both the simulated and predicted performance would be worsened by the effects of scintillation and image decorrelation.…”

“…This is based on the assumption that phase scintillation is due in some degree to the interference of multiple scatterers within a resolution cell. The RMS height estimation accuracy expected, given a phase uncertainty of , is simply (17) The images of Fig. 2(a) and (b) contain point scatterers with a signal-to-noise ratio of 30 dB.…”

“…Earlier works involving multiple monostatic apertures have illustrated methods for height estimation, including interferometric SAR [14]- [16] and stereo SAR [17], [18]. Interferometric SAR typically involves coherent processing of a pair of images formed from data collected by two separate antennas on the same data collection platform and has proven to be effective at forming topographic ground maps of smoothly varying terrain.…”

On the design of SAR apertures using the Cramer-Rao bound

“…In a sense, this is an aperture adjustment, requiring the use of multiple antennas, multiple platforms, or multiple passes. Reference [11] describes a technique where a curved flight path with sufficient angular diversity creates a stereo pair in spotlight mode that is then used to measure scatterer height and resolve layover. This too is an aperture adjustment that provides vertical excursion of the radar platform for scatterer height estimation.…”