SMAP Version 4.0 Radiometer Calibration Summary:
Steps Forward for Salinity Continuity Activities
[27-Aug-2018] Misra, S. and Brown, S.
Presented at the 2018 Ocean Salinity Science Team and Salinity Continuity Processing Meeting
We will present a summary of the SMAP radiometer calibration activities undertaken by the SMAP science team and project team for the recent Version 4.0 data release. SMAP recently completed three years of operation in space with a fairly stable daily average NEDT of 0.96 K and an overall drift of less than 0.1K.
We provide an assessment of the calibration quality of the L1B TB data. Key innovations made in the SMAP radiometer are an (1) Improved reflector emissivity value, (2) Concurrent antenna pattern/noise-diode/reference-load calibration, and (3) improved galaxy correction model over the ocean that takes into account varying wind-speeds. We find that SMAP radiometer calibration compares favorably with SMOS over land, ocean and ice with overall differences of <0.4K.
Table 1. Performance of SMAP Radiometer Level 1B Brightness Temperature Data
Table 1 from the SMAP L1_TB Assessment report shows the current performance of the data with respect to the requirements.
Going forward there are still outstanding calibration issues that impact high precision salinity measurements. This includes reflector and radome temperature, radome paint degradation issues, SMAP ocean TA model adjustment used to achieve version 4 calibration, antenna asymmetry observed at coastal crossings, sub-band to full-band calibration differences, concurrent SMAP drift and eclipse correction done during the first year of orbit, scan dependent biases observed during cold-sky maneuvers etc. All of these issues, though subtle are expected to have a systematic impact on derived salinity data.
The presentation will discuss outstanding issues impacting potential salinity retrievals in addition to version 4 summary and performance.