S. Kushuwaha

ABSTRACT Synthetic Aperture Radar (SAR) polarimetry is an uprising and nascent area of research in radar remote sensing and it has proved its potential in the area of forest biophysical parameter retrieval. The key intention of the present study was to develop SAR polarimetry based semi-empirical model for Stem volume and Aboveground biomass estimation of forest area and check its reliability in implementation to the study area for the relationships between these forest biophysical parameters and Polarimetric SAR (PolSAR) decomposition components. Five scenes of Quadpol SLC ALOS PALSAR data which has been acquired over Southern Gujarat forest area covering portions of Surat, Valsad, The Dangs and Dadra & Nagar Haveli districts in March, April and May 2010 are used. A field calculated circumference at breast height and height of trees in 0.1 hectare plots designed using stratified random sample method has been collected from Forestry and Ecology Department, IIRS. This field data was utilized for plot-wise stem volume density and aboveground biomass estimation. Coherency matrix based decomposition was carried out, yielding three components and resultant generated restoring polarimetric information. Coherency matrix was utilized for polarization orientation angle shift compensation which demonstrated acknowledgeable overestimation of volume scattering mechanism and underestimation of double bounce scattering mechanism unaltering the odd bounce scattering information after decomposition. Coherency matrix was utilized for Radar Vegetation Index and backscattered HH, HV and VV polarimetric channels generation. HV backscattered polarimetric channel and volume scattering component were found to be best correlated with forest parameters. Radar Vegetation Index was correlated with the field retrieved stem volume density and aboveground biomass resulting coefficient of determination i.e., R 2 = 0.573 and R 2 = 0.617 respectively, which resulted in stating moderate potential for study area into consideration. Semi-empirical Water Cloud Model was implemented for execution of parameter retrieval using the field estimated stem volume and aboveground biomass which proved its potential by illustrating higher coefficient of determination. I. INTRODUCTION Forest parameter retrieval is a very tedious and time consuming job using traditional methods especially for dense forests and forests which are not easily accessible for human beings. In spite of the availability of radar data under any weather conditions, the retrieval of biophysical parameters has been frequently carried out using optical data, mainly because the interaction between the radar signal and the vegetation is more complex than with the optical signal. The SAR image understanding and processing is a challenge as well. It is more difficult to establish the biophysical relationships between the SAR information and the targets with which it interacts due to its mathematical calculation complexity. Thus, more work is required in the retrieval of biophysical parameters using radar satellite data which have been limited by the type of data. Hence, SAR polarimetry is being implemented for forest parameter estimation. Previous studies have analysed the potential of single and dual polarized SAR data in stem volume density (SVD) and aboveground biomass estimation (AGB) [27], [28]. Present study intends to study the potential of SAR polarimetry in SVD and AGB retrieval. SAR has operational advantages over optical sensors for rapid disaster assessment because of its day/night acquisition capability, the ability to "see through" smoke, clouds and dust, and the side-looking viewing geometry, which is an advantage as whenever data collection directly above the site would prove dangerous [16]. Integration of radar and optical sensor data also demonstrated the potential to improve AGB estimation as it reduced the mixed pixels and data saturation problems [23]. For accomplishment of the study purpose, SAR fully polarimetric data in Single Look Complex (SLC) format has to be decomposed for extraction of the polarimetric information in all scattering mechanisms like Braggs surface scattering, double bounce scattering and Fresnel's volume scattering. The slope variability of terrain, the structure and the shape of different scatterers under radar beam encounter the orientation angle shift which gives rise to over estimation of volume scattering and hence forest types. Huynen (1970) is the pioneer of orientation angle. The orientation angle is