Absolute radiometric calibration and time-series analysis using Sentinel-1A

Absolute radiometric calibration is crucial in remote sensing, ensuring that raw satellite data, like that from Sentinel-1A, are accurately converted into physical units representing Earth’s surface. Sentinel-1A, part of the ESA’s Copernicus program, is equipped with a Synthetic Aperture Radar (SAR) Sensor that captures high-resolution images in all weather conditions. SAR’s ability to penetrate clouds makes it invaluable for long-term monitoring and time-series analysis. Accurate time-series analysis requires consistent radiometric values across images to detect real changes, such as deforestation or urban expansion. Calibration converts radar backscatter values to normalized radar cross-sections, adjusting for sensor and atmospheric biases. This study applies time-series backscatters from Sentinel-1A to assess the stability of the calibration process over Rosamond, California, using data from 2 corner reflectors and 17 images. The findings will support radiometric calibration for Taiwan’s future SAR mission.