Principles of Modern Radar - Volume 2 1891121537

392 CHAPTER 8 Interferometric SAR and Coherent ExploitationWar, the system can image terrain and detect and geolocate ground moving vehicle targetsfrom substantial standoff ranges. Figure 8-31b shows an example Joint STARS GMTI dataproduct [75]. Each of the black or white dots represents a ground moving target detectedby the system, geolocated, and overlaid onto an image of the terrain. The online colorversion provides additional detail.8.9 SUMMARYThis chapter has shown how pairs of complex SAR images can be combined to generateseveral useful remote sensing products. The focus has been primarily on digital elevationmaps, but it has also introduced ways to measure temporal changes in the profile or reflectivityof a scene on both short and long time scales using along-track interferometry,coherent change detection, and temporal motion mapping. All of these techniques rely onmeasurements of interferometric phase differences between images, differing in whetherand how much those images are separated along spatial and temporal baselines. Becausethey all rely on IPD as the fundamental measured quantity, they share many commonsignal processing steps: subpixel image coregistration; two-dimensional phase unwrappingor its equivalent; filtering and multilook averaging for maximizing coherence; andorthorectification and geocoding to provide useful final data products.These mission concepts and processing techniques continue to be active researchareas: InSAR is expanding into true 3-D imaging using Fourier, tomographic, and othermethods, while ATI is expanding into combined GMTI and SAR. More advanced SARsensors and the advent of formation and constellation sensor systems continue to expandthe menu of measurement configurations. These developments mark progress toward acapability for timely, high-quality earth resources data acquisition as well as military andsecurity surveillance, both on a global scale.8.10 FURTHER READINGAn excellent first introduction to the concepts and issues in InSAR is given by Madsenand Zebker in [51]. Detailed tutorial developments of InSAR with an airborne radarperspective are given in the spotlight SAR textbooks by Jakowatz et al. [20] and Carraraet al. [14]. An analysis from a spaceborne radar perspective is given in the book byFranceschetti and Lanari [33]. The tutorial paper by Rosen et al. [24] also emphasizesspaceborne systems and provides a good overview of space-based InSAR applicationsas well as an extensive bibliography. Bamler and Hartl [36] is another excellent tutorialpaper, again with a spaceborne emphasis. Additional tutorial sources are [76,77]. Earlyattempts at interferometric radar are described in [78-80]. The first descriptions of the useof coherent imagery for InSAR were reported in [81,82]. The first InSAR-related patentapplication was apparently that of D. Richman, then at United Technologies Corp. [83].The application was filed in 1971 but was placed under a secrecy order and was not granteduntil 1982 [51].While not tutorial in nature, a comprehensive set of papers describing virtually allaspects of a modern remote sensing satellite system is the special issue on TerraSAR-Xof the IEEE Transactions on Geoscience and Remote Sensing [65]. The papers in thisissue describe in detail the mission, satellite design, ground system design, calibrationprocedures, and early application results.