Critical assessment of the historical development of radar polarization technology towards radar polarimetry culminating in fully polarimetric-interferometric SAR

In this historical assessment of the development from polarization radar systems technology towards fully polarimetric POL-SAR airborne, high-altitude drones and satellite sensors, the at times slow and stepwise advances in step with -polarization device manufacture are critically analyzed. The main contributions from Kennaugh's fundamental polarization radar optimal null postulates of 1952 and its verification by Poelman in the 1970'ies with the first full polarimetric radar at SHAPE-TC will be highlighted, resulting with the chance discovery of Huynen's dissertation of 1970 in a thorough re-assessment of optimal polarization theory derived from Sinclair's scattering matrix formulation. With the introduction of the correct transformation matrix operators by Kostinski & Boerner 1982 for polarization basis transformation plus proper reduction of the 4×4 to the 3×3 reduced covariance and coherency matrices by Lueneburg & Boerner of the 1980'ies, it was possible to derive novel covariance matrix decomposition theories either based on physical reasoning by Durden & Freeman or on optimal eigenvalue theories by Cloude & Pottier during the 1990'ies. Hand in hand with digital SAR processing advances, polarimetric SAR systems technology enjoyed successful airborne (AIR-SAR, E-SAR, Convair-580 & PI-SAR) of the 1990ies, shuttle (SIR-C/XSAR) 1994, and satellite (ALOS-PALSAR, RADARSAT-II & Terra-SAR-X) verification of the past ten years, resulting in the first tandem satellite formation of TanDEM-X 2010. Although various incomplete dual-pol and compact-pol SAR implementations were and are still being pursued, the irreversible quest for fully polarimetric POL-IN-SAR decomposition theories of Yamaguchi with its verification by multi-band airborne, high-altitude drones and satellite sensors is highlighted. The succinct overview will be concluded with a comprehensive assessment of its plethora of steadily increasing applications including next to polar also equatorially orbiting tandem POL-IN-SAR sensors.