1. WP120 External Calibration of Spaceborne Microwave Remote Sensing System Sensors Objective:Evaluation of external calibration needs for a variety of microwave sensors, emphasizing those planned for Sentinel 1 and Sentinel 3 Report: CALIB-TN-WP120-001-BRIX Iss P4 Author: Robert Gray BRIX Systems, Ottawa, Canada

2. WP120 External Calibration of Spaceborne Microwave Remote Sensing System Sensors Report CALIB-TN-WP120-001 BRIX P4 Document Organization Chapters 1Introduction 2Document Structure 3Calibration and Validation – Concepts and Constraints 4Synthetic Aperture Radar 5Microwave Radiometers 6Altimeters

3. WP120 External Calibration of Spaceborne Microwave Remote Sensing System Sensors 3Calibration and Validation – Concepts and Constraints - Generally applicable to all three types of microwave instruments considered - Addresses instrument calibration types and phases – pre-flight, - onboard internal, - onboard external, - validation - Differentiates ‘External Calibration’ and ‘Validation’ in a calibration framework - Discusses constraints imposed by external targets on spaceborne sensors – temporal and spatial access to target regions from orbit, - instrument field of view, - characterisation of target at time of measurement (local variability) - Ionospheric propagation effects for microwave instruments

4. WP120 External Calibration of Spaceborne Microwave Remote Sensing System Sensors 4 Synthetic Aperture Radar –Overview of spaceborne SAR systems and key parameters –Identification of SAR external calibration parameters –Extended external target choices – Rain Forests –Point target identification and purpose – transponders and passive reflectors –Cross calibration among SAR systems

5. WP120 External Calibration of Spaceborne Microwave Remote Sensing System Sensors 5 Microwave Radiometers –Design and calibration considerations for microwave radiometers –Representative spaceborne microwave radiometers –External calibration and calibration targets Cold sky measurements Earth surface calibration measurements –Cold land areas –Rain forests –Hot deserts –Sea surfaces –Sun and moon –Model usage –Cross calibration with other radiometers

6. WP120 External Calibration of Spaceborne Microwave Remote Sensing System Sensors 6 Altimeters –General considerations for spaceborne microwave radar altimetry –Representative spaceborne radar altimeter systems –Altimeter waveforms and measurements –External calibration information required for spaceborne altimetry Precise orbit knowledge Propagation delay corrections Sea height biases Geoid shape and tidal models Independent sea surface characterization – tide guages and ocean buoys Geophysical parameter incorporation –Calibration error budget –External calibration sites –Validation

7. WP120 External Calibration of Spaceborne Microwave Remote Sensing System Sensors Recommendations for External Calibration of Sentinel 1 & Sentinel 3 Microwave Instruments - Both the Sentinel 1 SAR and the Sentinel 3 Altimeter are intended for mission continuity. They are required to be similar to existing operational instruments flown by ESA. - Consequently their external calibration and validation should use the same external calibration sites and methods that are currently established for the ENVISAT ASAR and RA2, and for Jason-1 instruments to: - maximize use of existing knowledge and investment, - facilitate integration of Sentinel 1 & 3 SAR and altimeter operations into existing operations and dataflows - This includes cross-calibration with existing instruments

8. WP120 External Calibration of Spaceborne Microwave Remote Sensing System Sensors Sentinel 1 SAR Calibration Accuracy Requirements CharacteristicParameterTargetRequired Accuracy Point Target Response- Gain - IRW - PSLR - ISLR Transponder or Corner reflector 1 dB 10% 1 dB 0.5 dB Antenna Pattern- Azimuth - Elevation - Transponder - Amazon Rain Forest 1 dB 0.5 dB RadiometryGain ConstTransponder0.5 dB Polarization-|S HH |, |S VV | -|S HV |, |S VV | Amazon R.F. and Transponder TBD GeolocationPoint Target LocationCorner Reflector or Transponder or Precisely Located Natural Feature 5 m

9. WP120 External Calibration of Spaceborne Microwave Remote Sensing System Sensors Sentinel 3 Altimeter Error Budget based on ENVISAT RA-2 SourceUncorrected Effect cm Residual Error After Corrections cm Notes Instrument2.4measured Orbit3DORIS precise orbit Sea State Bias0 - 202SWH 4 m Dry Troposphere2300.2 - 2 Wet Troposphere0 - 301 - 2Using real time MWR data Total (RSS)4.4 – 5.2