Abstract
Abstract. Forests play a pivotal role in synchronizing earth’s carbon cycle by absorbing carbon from the atmosphere and storing it in the form of biomass. Researchers today are trying to understand the climatic variations, especially those occurring due to destruction of forest and its corresponding biomass loss. Hence, quantification of various forest parameters such as biomass is imperative for evaluating the carbon. The objective of this research was to exploit the potential of C-band Radarsat-2 Polarimetric Interferometric Synthetic Aperture Radar (PolInSAR) technique for analysing the relationship between complex coherence and field-estimated aboveground biomass. Association between the backscatter and the aboveground biomass was also established in the process. To serve our objective, Radarsat-2 interferometric pair dated 4th March, 2013 (master image) and 28th March, 2013 (slave image) were procured for the Barkot Reserve Forest region of Dehradun, India. Field sampling was done for 30 plots (31.62 m x 31.62 m) and stem diameter and tree height were measured in each plot. The study emphasized on the application of POLINSAR coherence instead of using conventional method of relying on backscatter values for retrieving forest biomass. Coherence matrices were utilized for generating complex coherence values for different polarization channels and were regressed against field estimated aboveground biomass. Results indicated a negative linear relationship between complex coherence and aboveground biomass with the cross – polarized coherence showing the highest R2 value of 0.71. Further, the backscatter mechanism when studied with respect to aboveground biomass indicated a positive linear relationship between backscatter values and field estimated aboveground biomass with R2 value of 0.45 and 0.61 for slave and master image respectively. The results suggest that PolInSAR technique, in combination with different modelling approaches, can be adopted for estimating forest biomass.
Highlights
The long term net carbon flux between terrestrial ecosystems and the atmosphere has been dominated by changes in forest area and changes in forest biomass per hectare (Houghton, 2005).Terrestrial biosphere serves as the crucial component in carbon cycle with most of the carbon present in forest
Previous researches have analysed the potential of single and dual polarized SAR data in aboveground biomass and other biophysical parameters quantification(Kushwaha et al.,2000 and Pandey et al.,2010).While if fully polarimetric dataset is employed in the study it allows to extract information on all scattering parameters(surface, double bounce and volume scattering) from a single SAR resolution cell
Backscatter mechanism increases with increasing forest biomass, but this function saturates at a wavelength dependent biomass density, which limits its usefulness for biomass mapping (Imhoff,1995).Coherence which does not saturates till 350t/ha, proves to be a potential approach for quantifying bio-physical parameters
Summary
The long term net carbon flux between terrestrial ecosystems and the atmosphere has been dominated by changes in forest area and changes in forest biomass per hectare (Houghton, 2005).Terrestrial biosphere serves as the crucial component in carbon cycle with most of the carbon present in forest. Forests contain about 50% of the world’s terrestrial organic carbon stocks, locking up 335-365 Gt of carbon each year, making them a potential carbon source Changes in this component brought about by various anthropogenic activities such as land use change, together with fossil fuel burning are assumed to be dominant drivers of the climate change. Previous researches have analysed the potential of single and dual polarized SAR data in aboveground biomass and other biophysical parameters quantification(Kushwaha et al.,2000 and Pandey et al.,2010).While if fully polarimetric dataset is employed in the study it allows to extract information on all scattering parameters(surface, double bounce and volume scattering) from a single SAR resolution cell. Present study intends to exploit the potential of fully polarimetric C-band dataset for analyzing the relationship between complex coherence and field estimated aboveground biomass.
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