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 i- cluding next to polar also equatorially orbiting tandem POL-IN-SAR sensors.