A revised radiometric normalisation standard for SAR

Abstract

Improved geometric accuracy in SAR sensors implies that more complex models of the Earth may be used not only to geometrically rectify imagery, but also to more robustly calibrate their radiometry. Current beta, sigma, and gamma nought SAR radiometry conventions all assume a simple "flat as Kansas" Earth ellipsoid model. We complement these simple models with improved radiometric calibration that accounts for local terrain variations. In the era of ERS-1 and RADARSAT-1, image geolocation accuracy was in the order of multiple samples, and tiepointfree establishment of the relationship between radar and map geometries was not possible. Newer sensors such as ASAR, PALSAR, and TerraSAR-X all support accurate geolocation based on product annotations alone. We show that high geolocation accuracy, combined with availability of high-resolution accurate elevation models, enables a more robust radiometric calibration standard for modern SAR sensors that is based on gamma nought normalised using an Earth terrain-model. A REVISED RADIOMETRIC NORMALISATION STANDARD FOR SAR ABSTRACTImproved geometric accuracy in SAR sensors implies that more complex models of the Earth may be used not only to geometrically rectify imagery, but also to more robustly calibrate their radiometry. Current beta, sigma, and gamma nought SAR radiometry conventions all assume a simple "flat as Kansas" Earth ellipsoid model. We complement these simple models with improved radiometric calibration that accounts for local terrain variations. In the era of ERS-1 and RADARSAT-1, image geolocation accuracy was in the order of multiple samples, and tiepointfree establishment of the relationship between radar and map geometries was not possible. Newer sensors such as ASAR, PALSAR, and TerraSAR-X all support accurate geolocation based on product annotations alone. We show that high geolocation accuracy, combined with availability of high-resolution accurate elevation models, enables a more robust radiometric calibration standard for modern SAR sensors that is based on gamma nought normalised using an Earth terrain-model.

Terrain-flattened gamma nought Radarsat-2 backscatter

“…Translation of the recorded backscatter values into the sigma nought (s 0 ) or gamma nought (g 0 ) conventions requires the use of an Earth model, either a simple ellipsoidal Earth (Rosich and Meadows, 2004;ESA, 2007), or a more detailed DEM. In the former case, the subscript E can be used to indicate the use of an Ellipsoidal Earth model (r 0 E and c 0 E ), while in the latter case, the subscript T can be used (r 0 T and c 0 T ) to indicate the use of a terrain model (Small et al, 2009a). The radiometric look-up tables (LUTs) included with Radarsat-2 (R2) products (MDA, 2008) were generated using an ellipsoidal Earth model.…”

Analysis of multi-dimensional SAR for determining the thickness of thin sea ice in the Bohai Sea

“…The gamma coeffi cient γ was used to remove the effects of different incidence angles (Small et al, 2009) because the ALOS PALSAR and ENVISAT ASAR images for 20 December 2008 have signifi cantly different incident angles. The γ was defi ned with respect to the area orthogonal to the incident ray from the radar.…”

Research on a Dem Coregistration Method Based on the Sar Imaging Geometry

“…The terrain has a strong influence on the geometric and radiometric characteristics of a SAR image (Wegmuller 1999;Loew et al 2007;Small et al 2009;Frey et al 2013). Given a SAR imaging geometry, SAR backscatter images (i.e., DEM intensity images) from two DEMs in geographic coordinates can be simulated.…”