Sensitivity of space-borne SAR data to forest parameters over sloping terrain. Theory and experiment

Abstract

Recently, SAR data proved to be useful for the retrieval of forest biomass. However, the eVects of terrain slope must be addressed towards the generalization of biomass retrieval for varied forest and environmental conditions. To this aim, we developed experimental and theoretical approaches allowing the study of multi-frequency/multi-polarization forest backscatter of a given forest type, as a function of forest parameters and SAR local incidence angle over the relief. The experimental results showed that the sensitivity of SAR data to biomass was similar to that obtained over a at terrain, only if the backscatter data were calibrated for slope eVects. Moreover, the backscatter must also be corrected for its angular decrease, which can be removed using a simple angular model developed under assumptions of theoretical equations. The highest correlation of corrected backscatter with forest parameters related to aboveground biomass (such as stand age and bole volume) was achieved at L-HV 55°(R2=0.8 ) with results similar to those for at terrain. Modelling results validate the semiempirical model developed to remove the angular decrease of forest backscatter, which is due to variable optical depth with terrain slope. Results also indicated that the simple angular model may encounter problems for forested areas with low optical depth (t<0.5) located over extreme topographic conditions ( local incidence angle <10°or >80°).*

Improving the Estimation of Above Ground Biomass Using Dual Polarimetric PALSAR and ETM+ Data in the Hyrcanian Mountain Forest (Iran)

“…Therefore, we performed radiometric terrain correction to compensate for the ground-topography influence on backscattering coefficient. The corrected backscatter in gamma-nought ° format can be obtained from the sigma-nought ° value according to Equation (3) [71,72]. A flat = PALSAR pixel size for a theoretical flat terrain, A slope = true local PALSAR pixel size for the mountain terrain, = local incidence angle, = radar incidence angle at the image center.…”

A National, Detailed Map of Forest Aboveground Carbon Stocks in Mexico

“…30 × 30 m 2 pixel size (0.000278° posting in geographic coordinates). The dependence of the backscatter, σ°, on the local incidence angle, θ i , was normalized with respect to the incidence angle, θ (i.e., the local incidence angle over flat terrain) with [57,58]:…”

Assessment of Aboveground Woody Biomass Dynamics Using Terrestrial Laser Scanner and L-Band ALOS PALSAR Data in South African Savanna

“…This is applicable to the current study area, and so the authors did not carry out noise filtering. Topographic normalization was then applied to the backscatter intensity images [65,66]. The final resultant geocoded and terrain corrected backscatter SAR images had a ground resolution of 12.5 m. …”