Abstract
Measuring the absolute calibration constant is crucial for the radiometric calibration of synthetic aperture radar (SAR) systems. However, it is expensive to monitor the calibration constant continuously using manmade calibrators, and it is regionally restricted using the rainforest as the calibration field. In this study, the stability of SAR backscattering for common objects on the earth surface was analyzed, expecting to find the stable backscattering feature that could be used for maintaining absolute radiometric calibration. A database was established using Sentinel-1 dataset, and a classification model based on neural networks was proposed to extract the image slices of proper objects. Based on these, a temporal stable backscattering feature with a standard deviation of 0.19 dB was obtained from urban areas, and it was proved to be even more stable than the rainforest. Finally, the calibration scheme was given using this stable feature as a reference, which provided a new means of monitoring the SAR radiometric calibration constant.
Highlights
The measurement of the absolute calibration constant is vital to the radiometric calibration of synthetic aperture radar (SAR) systems, which influences the quantitative application of SAR, such as soil moisture mapping, marine parameters measurement, and biomass retrieval [1,2,3,4]
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We analyzed the stability of C-band backscattering using a σ0 sample database and determined that the median center of the backscatter coefficients in urban areas would be a statistically stable feature
Summary
The measurement of the absolute calibration constant is vital to the radiometric calibration of synthetic aperture radar (SAR) systems, which influences the quantitative application of SAR, such as soil moisture mapping, marine parameters measurement, and biomass retrieval [1,2,3,4]. Like transponders, corner reflectors, and ground receivers, are commonly used to measure the calibration constant. They have known radar cross sections (RCSs) with a high radiometric accuracy (better than 0.2 dB) [5,6,7]. Monitoring of the constant is usually undertaken by the measurement of Amazon rainforest, which is a temporal stable and azimuthally isotropic natural target [8,9,10]. The measurements of Radarsat-1 show that, if it chose a suitable area in Amazon, the backscatter coefficients of rainforest in C-band SAR are concentrated on −6.5 dB with a standard deviation of less than 0.3 dB [11].
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