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The Radiometric Measurement Quantity for SAR Images

Döring, Björn and Schwerdt, Marco (2013) The Radiometric Measurement Quantity for SAR Images. IEEE Transactions on Geoscience and Remote Sensing, PP (99). IEEE - Institute of Electrical and Electronics Engineers. doi: 10.1109/TGRS.2012.2234128. ISSN 0196-2892.



A Synthetic Aperture Radar (SAR) system measures among other quantities the terrain radar reflectivity. After image calibration, the pixel intensities are commonly expressed in terms of radar cross sections (for point targets) or as backscatter coefficients (for distributed targets), which are directly related. This paper argues that pixel intensities are not generally proportional to radar cross section or derived physical quantities. The paper further proposes to replace the inaccurate term radar cross section by equivalent radar cross section as the radiometric measurement quantity for SAR images. The measurement procedure as such remains unchanged. Two problems are seen with using radar cross section as the radiometric measurement quantity for point targets. First, the radar cross section is frequency and/or angular dependent for many targets, whereas a SAR system operates not at a single set but through a range of frequencies and aspect angles. This begs the question of which radar cross section within this two-dimensional range should actually be taken as the measurement result. Second, the pixel intensities seen in SAR images are the output of a filtering process, which is affected by the complex transfer function of the point target. Radar cross section, on the other hand, does not depend on phase. The equivalent radar cross section expresses the reflectivity in terms of the radar cross section of an equivalent conducting sphere which would result in the same pixel intensity as the one observed if the sphere were to replace the actual target in the scene. This distinction is crucial in defining the measurand for radiometric SAR measurements in principal, and hence it is important for radiometric SAR calibration. It is furthermore of particular practical importance for current and emerging wideband, high-resolution, and high-accuracy SAR systems.

Item URL in elib:https://elib.dlr.de/83291/
Document Type:Article
Title:The Radiometric Measurement Quantity for SAR Images
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Döring, BjörnUNSPECIFIEDhttps://orcid.org/0000-0002-4257-1413UNSPECIFIED
Date:February 2013
Journal or Publication Title:IEEE Transactions on Geoscience and Remote Sensing
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:Yes
Publisher:IEEE - Institute of Electrical and Electronics Engineers
Keywords:synthetic aperture radar; radiometric measurements; calibration
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - Projekt TerraSAR-X Kalibration und Projektunterstützung (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Microwaves and Radar Institute > Spaceborne SAR Systems
Deposited By: Döring, Björn
Deposited On:08 Jul 2013 16:04
Last Modified:29 Nov 2023 12:50

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