Calibration is the process of quantitatively defining the system response to known controlled signal inputs. Calibration tasks are executed throughout the mission to ensure the normalised radar cross-section and the phase of the individual pixels are provided with stability and accuracy. Calibration of the entire SENTINEL-1 system is critical to guaranteeing product quality for operational demands. The SAR system must perform within an absolute radiometric accuracy of only 1 dB (3σ) in all operation modes. This is a higher radiometric accuracy than any other SAR mission before it.
Calibration can be divided into two forms:
Internal calibration provides an assessment of radar performance using internally generated calibrated signal sources, in particular from pre-flight testing.
External calibration makes use of ground targets of known backscatter coefficients to render an end-to-end calibration of the SAR system.