1. Development of a L-band On-orbit Calibration Reference Model for the Marie-Byrd Antarctic Region: Application to Aquarius, SMOS and SMAP Shannon Brown and Sidharth Misra Jet Propulsion Laboratory, California Institute of Technology
2. L-band Radiometer Calibration Calibration at L-band has become an important issue: SMOS, Aquarius, SMAP These radiometers use an internal calibration approach; internal switches and noise diodes Requires external end-to-end calibration reference – pre-launch and on-orbit Calibration techniques developed for radiometers on-board satellite altimeter missions applicable Altimeter radiometers also employ internal calibration For Jason series radiometers, calibration referenced to stable on-Earth references 2
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4. Used on-Earth references to remove long-term drift, instrument temperature dependence and antenna pattern correction errorsHot Reference Targets
5. AMSR-E De-polarization Developing On-Earth TB Calibration References at L-band Natural targets for L-band radiometer calibration over on-Earth dynamic range Calm, flat ocean scenes – Cold reference Ice sheets: Antarctica (e.g. Dome-C), Greenland – Mid-range reference Land areas: flat, dry deserts; homogeneous heavily vegetated regions – Hot reference Use to assess absolute calibration, monitor stability and assess residual instrument calibration errors 37 V-H 23 V-H 18 V-H 10 V-H 6 V-H
6. Use match-ups between Aquarius and ocean altimeters to identify observations over calm seas Compare Aquarius to modeled TB Calm ocean surface reduces model uncertainty – nearly specular emission Model inputs (e.g. SST, SSS) from ancillary data sources Sort comparisons to identify residual errors in corrections (e.g. solar, galactic, ionosphere) Significant number of match-ups with minimal temporal and spatial difference (1 hr/100km) 5 Cold TB Reference Number of match-ups per 1o bin – all horns
7. Cold Scene Stability Monitoring Used simulated data to assess resolution of method Compare TBs to model to look for jumps/drifts 6 TBV – Model : Horn 1 Inter-channel double difference : Horn 1 Over range of 0 < WS < 5 m/s Assumes 0.5C SST knowledge and 0.5psu SSS knowledge
8. Antarctic Calibration Reference Recent work has shown Dome-C as suitable candidate for an on-Earth L-band reference (Floury et al., 2002; Macelloni et al. 2006 ; Macelloni et al. 2007) Region is heavily instrumented and studied, but small in size Particularly for Aquarius, larger site desired due to fixed independent radiometer beams Used AMSR-E to search for other suitable Antarctic calibration sites Identified other regions with low spatial and temporal variability of surface and deep ice temperature Aquarius 3-beams
32. Time Series Comparison Monthly averaged SMOS TB at 55o incidence angle compared to AMSR-E 6.9 GHz channel for June 2010 to June 2011 Observed annual signal at L-band higher than expected 21 AMSR-E 6.9 GHz and SMOS V-pol AMSR-E 6.9 GHz and SMOS H-pol
33. Conclusions and Future Work Marie-Byrd region identified as a candidate L-band calibration site in West Antarctica Large in extent, thermally stable Complementary to Dome-C site Analysis of AMSR-E indicates good long term stability of region Developing model to transfer calibration from higher frequency radiometers (e.g. AMSR-E, WindSat) to L-band over region Next steps Evaluate several radiative transfer models, constrain using AMSR-E Inter-compare Aquarius and SMOS over region
37. Additionally, constrain solution to minimize slope of RMS error vs. instrument temperatureSSM/I 37.0 GHz V-pol – H-pol TB Hot Reference Targets
38. Salinity Retrieval Validation Form database of Aquarius co-locations with in situ data Argo float array, the Shipboard Sensor Database (SSD) and the Global Temperature-Salinity Profile Program (GTSPP). Analyze global mean differences between Aquarius retrieved salinity and in-situ measurements Assess over time and instrument temperature Analyze regional differences Assess antenna pattern correction, faraday rotation correction and atmospheric and roughness corrections 25
39. Faraday Rotation Correction Dual-frequency altimeter match-ups also useful for assessing Faraday rotation correction Match-ups cover large range of TEC values 26
42. Calibration Approach for Aquarius Monitor instrument level parameters and diagnostics Objective is to identify the cause of any observed calibration or retrieval error or instability in order to apply a suitable correction at the appropriate level of processing Compare retrievals to in situ ground truth or models Compare brightness temperatures to natural on-Earth reference targets
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44. Radiative Transfer Model Used simple radiative transfer model to estimate L-band TB from estimated temperature vs depth Snow is assumed to be dry and pure Density was varied from 0.3g/cm3 to 0.916 g/cm3 to fit with AMSR-E values Simple empirical scattering correction 0.17 K peak to peak 1.4 GHz 6.8 GHz 10.7 GHz 18.7 GHz 36.5 GHz
