Analysis of seasonal effects on forest parameter estimation of Indian deciduous forest using TerraSAR-X PolInSAR acquisitions

TerraSAR-X/TanDEM-X form the first space-borne interferometer providing full-PolInSAR acquisitions with a near-zero temporal gap. This paper explores the potential of X-band SAR data for forest height estimation over tropical Indian forests. Unique TanDEM-X data sets with varied spatial baselines are acquired over a tropical, deciduous Indian forest. Multiple dual polarimetric and fully polarimetric acquisitions are analysed and the best performance is achieved using fully polarimetric data acquired over both high- and low-biomass forests (r2 = 0.86 and r2 = 0.80 respectively). It is shown for the first time that, for deciduous Indian tropical forests, seasonal changes such as leaf-fall affect the PolInSAR based height inversion performance. For species exhibiting leaf-fall, acquisition during leaf-on season provides better height inversion accuracy (r2 = 0.75) than for leaf-fall season (r2 = 0.65). Results show consistent PolInSAR height inversion performance for both high- and low-biomass forests in both natural and managed forest tracts. Spatial baseline is a critical factor for selection of suitable acquisitions for PolInSAR based height estimation. The effect of spatial baseline on height inversion performance is also discussed.