The effect of scattering from buildings on interferometric SAR measurements

Abstract

The determination of elevation models of buildings using interferometric synthetic aperture radar (IFSAR) is an important area of active research. The focus of this paper is on some of the unique scattering mechanisms that occur with buildings and how they affect the IFSAR height measurement and the coherence. We will show by theory and examples that the various data products obtained from IFSAR can be used to aid in interpreting building height results. We will also present a method that we have used successfully in mapping buildings in Washington D. C.

A null-steering viewpoint of interferometric SAR

“…The decorrelation gets worse with narrower nulls (larger baselines) and larger target separation (e.g., taller buildings). This result was found in [6], [7] as well. One implication here is that an additional antenna element would allow us to steer a separate null at one of the targets while retrieving the IFSAR phase, or steering another null, at the other target.…”

“…This case has been evaluated for IFSAR previously using the van Cittert-Zemike theorem [6], [7] However, the nullsteering viewpoint adds intuition into the issue. Figure 3 shows that one of the problems in the two target case is that we have only a single null to steer at two separate targets.…”

“…The minimization of equation (5) Rcwi =~iWi (6) Equation (5) is minimized by choosing the Lagrangian multiplier as the minimum eigenvalue of R=. The result is that the optimal weights, to within a constant amplitude and phase, are:…”

Collection and processing data for high quality CCD images.

“…This is related to the "front-porch" problem in IFSAR height measurements. 8 Ultimately, for good CCD performance, the degree to which squint angles need to match depends on the topography of the scene being imaged, both the elevation differences within the scene and the elevation gradients within the scene. Anecdotal evidence suggests that for scenes with significant topography, even 2 degrees of squint angle difference will cause noticeable degradation in the CCD product, unless suitably compensated.…”

Interferometric SAR coherence classification utility assessment

“…Tree canopies can exhibit lower coherence due to the target's extended ensemble of reradiators [2,6]. This drop in coherence and relatively high intensity returns from tree canopies provides the ground work for a simple classifier without training sites and maximum likelihood calculations.…”