Terrain-flattened gamma nought Radarsat-2 backscatter

Abstract

Radarsat-2 offers a variety of new modes and capabilities. We present results from rigorous application of geometric and radiometric calibration to backscatter values, enabling comparisons between different modes. First, the system's a priori geometric accuracy was tested (tiepoint free) by comparing the measured positions of corner reflectors in ultrafine images with predicted locations calculated based on the satellite state vectors and radar timing annotations. Second, the geometric accuracy of the dualpol ScanSAR SCNB mode was tested by correlating each backscatter image to a radar image simulation calculated using the same product annotations. Third, the radar image simulation was used to normalize the backscatter values in both polarisations, generating terrain-flattened gamma nought values that were then terrain geocoded. Fourth, the available ascending and descending SCNB image pair was overlaid with and without such radiometric terrain correction applied. The advantages gained by using terrainflattened gamma nought are discussed. Abstract. Radarsat-2 offers a variety of new modes and capabilities. We present results from rigorous application of geometric and radiometric calibration to backscatter values, enabling comparisons between different modes. First, the system's a priori geometric accuracy was tested (tiepoint free) by comparing the measured positions of corner reflectors in ultrafine images with predicted locations calculated based on the satellite state vectors and radar timing annotations. Second, the geometric accuracy of the dual-pol ScanSAR SCNB mode was tested by correlating each backscatter image to a radar image simulation calculated using the same product annotations. Third, the radar image simulation was used to normalize the backscatter values in both polarisations, generating terrain-flattened gamma nought values that were then terrain geocoded. Fourth, the available ascending and descending SCNB image pair was overlaid with and without such radiometric terrain correction applied. The advantages gained by using terrain-flattened gamma nought are discussed.Résumé. RADARSAT-2 offre une variété de nouveaux modes et fonctionnalités. Nous présentons les résultats obtenus par l'application rigoureuse de la calibration géométrique et radiométrique sur les valeurs de rétrodiffusion, permettant de comparer les différents modes. Premièrement, la précision géométrique a priori du système est testée (sans points de soutien) en comparant les positions de réflecteurs trièdres mesurées sur les images ultra-fines avec les positions prévues, ces dernières étant calculées à partir des annotations contenant les vecteurs d'état du satellite ainsi que les paramètres temporaux du radar. Deuxièmement, la précision géométrique du mode ScanSAR en polarisation double (appelé SNCB) est testée en corrélant chaque image de rétrodiffusion avec une image radar simulée, générée en utilisant les vecteurs d'état et les paramètres temporaux extraits des annotations en combinaison avec un MNT. Troisièmement, ...

COSMO-skymed, TerraSAR-X, and RADARSAT-2 geolocation accuracy after compensation for earth-system effects

“…For RADARSAT-2, some preliminary results were reported in [6]. Since then, four additional UF products were acquired over another test site; the geolocation accuracies are similar to those previously reported.…”

SAR backscatter multitemporal compositing via local resolution weighting

“…An example of an ascending/descending (A/D) overlay is presented in [15]. Although the method generally performs well in flattening the radiometry of images acquired even in steep terrain such as the Swiss Alps, it is unable to improve upon the locally available geometric resolution at each coordinate.…”

“…The local illuminated areas computed during the radiometric terrain correction are shown in (a) and (b). The original ground range versions and geometrically-terrain-corrected (GTC) backscatter values can be seen in [15]. The RTC γ T 0 estimates for the asc.…”

“…Two R2 ScanSAR narrow (SCN) images of Switzerland were acquired within 12 hours of each other on April 26-27, 2010. Terrain-flattening [14] was applied to the VV & VH backscatter measurements and reported in [15]. The products are used in this paper to illustrate application of the local-resolution-weighting (LRW) technique.…”

An Improved Sar Radiometric Terrain Correction Method and Its Application in Polarimetric Sar Terrain Effect Reduction

“…Tilley and Bonwit [26] and Bolter et al [27] proposed to normalize the brightness values of SAR image pixels in foreshortening and layover areas by dividing the value equally among all ground patches contributing to that particular SAR pixel. Small et al [17,28] proposed a correction method by normalizing the backscatter coefficient with the local illuminated area projected onto the plane perpendicular to the radar line of sight. For polarization distortion, researchers proposed to perform the correction through polarization orientation angle shift compensation [12][13][14]29].…”