期刊名称：ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences
印刷版ISSN：2194-9042
电子版ISSN：2194-9050
出版年度：1992
卷号：XXIX Part B1
页码：212-222
出版社：Copernicus Publications
摘要：Recent advances in calibration techniques havemade calibrated SAR images, in which the datarepresents radar cross-section (0') or normalizedradar cross-section (0'0), a reality. In this paper,some of these recent advances are discussed inthe context of their impact on SAR sys'temdesign, and in terms of the errors associatedwith each technique.The main sources of error in radiometriccalibration of SAR data are fluctuations in thetransmitted power, receiver gains, system noiseand the illumination pattern of the antenna.Internal calibration loops can be used to ensurethe stability of the transmitters and receivers.The noise level can be measured by turning offthe transmitters and operating in a receive-onlymode. One of the more difficult problemsremaining is then to determine the appropriateantenna pattern illumination for each pixel onthe ground. This can be achieved by a variety oftechniques: first, the normal antenna pattern canbe measured using a suitable uniform,distributed target such as the Amazon RainForest; second, the roll angle of the antenna canbe measured by using some form of echotracker;then the elevation angle for each pixelcan be determined if the terrain heightvariations in the image are known or can bebounded. For aspaceborne SAR, a curved earthmodel gives a good approximation for the longrange at which spaceborne SAR's must operate.For an airborne SAR, a Digital Elevation Model(DEM), registered to the SAR image, may benecessary. The DEM can be derived from astandard topographic data set, registered usingtie-poin ts to the SAR image, or frominterferometric SAR height maps which areautomatically registered to the SAR image, or bymonopulse techniques, which are also in thesame reference frame as the SAR image.Additionally, these three techniques may beused to determine the local incidence angle foreach pixel, so that measurements of 0' may beconverted to 0'0.To verify radiometric calibration, andparticularly to ensure that the data is absolutelycalibrated, known calibration targets such ascorner reflectors or transponders, are often used.These suffer from their own calibrationuncertainties, which may be a limiting factor inthe overall radiometric calibration.
