Radiometric calibration of high resolution UAVSAR data over hilly, forested terrain

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Title: Radiometric calibration of high resolution UAVSAR data over hilly, forested terrain
Author: Riel, Bryan Valmote
Abstract: SAR backscatter data contain both geometric and radiometric distortions due to underlying topography and the radar viewing geometry . Thus , applications using SAR backscatter data for deriving various scientific products (e .g . above ground biomass ) require accurate absolute radiometric calibration . The calibration process involves estimation of the local radar scattering area through knowledge of the imaged terrain , which is often obtained through DEMs . High resolution UAVSAR data over a New Hampshire boreal forest test site was radiometrically calibrated using a low resolution SRTM DEM , and different calibration methods were tested and compared . Heteromorphic methods utilizing DEM integration are able to model scattering area better than homomorphic methods based on the local incidence or projection angle with a resultant backscatter calibration difference of less than 0 .5 dB . Additionally , the impact of low DEM resolution on the calibration was investigated through a Fourier analysis of different topographic classes . Power spectra of high -resolution airborne lidar DEMs were used to characterize the topography of steep , moderate , and flat terrain . Thus , errors for a given low resolution DEM associated with a particular topographic class could be quantified through a comparison of its power spectrum with that from the lidar . These errors were validated by comparing DEM slope derived from SRTM and lidar DEMs . The impact of radiometric calibration on the biomass retrieval capabilities of UAVSAR data was investigated by fitting second -order polynomials to backscatter vs . biomass plots for the HH , HV , and VV polarizations . LVIS RH50 values were used to calculate biomass , and the process was repeated for both uncalibrated and area calibrated UAVSAR images . The calibration improved the $R^2 $ values for the polynomial fits by 0 .7 -0 .8 for all three polarizations but had little effect on the polynomial coefficients . The Fourier method for predicting DEM errors was used to predict biomass errors due to the calibration . It was revealed that the greatest errors occurred in the near range of the SAR image and on slopes facing towards the radar .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2010 -12 -2452
Date: 2011-02-10

Citation

Radiometric calibration of high resolution UAVSAR data over hilly, forested terrain. Master's thesis, University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2010 -12 -2452 .

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