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 phase of surface features 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 stability of 1 dB (3σ) in all operation modes. This is a more stringent radiometric stability than previous ESA SAR missions.
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 while external calibration makes use of ground targets of known backscatter coefficients to ensure an end-to-end calibration of the SAR system.