Modifications to the SSMIS Unified Preprocessor for Use With Climate and Precipitation (UPP-CP) Joe Turk Jet Propulsion Laboratory, California Institute of Technology Pasadena, CA USA Hilawe Semunegus NOAA/National Climate Data Center Asheville, NC USA Steve Swadley Naval Research Laboratory, Marine Meteorology Division Monterey, CA USA Bill Bell ECMWF, Reading, UK With comments and suggestions from many others

Purpose SSMIS datasets have been available since 2003, but have not yet achieved substantial usage in the climate and precipitation (C&P) community Open questions on data quality have been addressed by several user groups, most notably via the SSMIS Unified Preprocessor (UPP) jointly developed by NRL-Monterey and the UK Met Office (NWP SAF) The analysis showed that the sensor is affected by three main phenomena, much of which cannot be accounted for by traditional inter-sensor calibrations The goal is to adapt the UPP into a form suitable to needs of C&P community (UPP-CP), essentially to provide a s/w package capable of producing sensor data records (SDR) at the native SSMIS scan grid of each channel

DMSP Sun-Synchronous Orbit click to animate SatelliteLaunchCurrent LTAN 1 F-13Mar F-14Apr F-15Dec F-16Oct (drifting earlier) F-17Nov (fairly stable) F-18Aug (drifting later) F F SSMISSMIS 1 As of Oct 2010 F-13 recorder #2 failed Nov 2009 F-14 RDS transmitter failed Aug 2008 F-15 RADCAL beacon since Aug 2006 F-16 operating with single gyro for attitude control

SSMIS Channel Sets

SSMIS Scan Geometry 1707-km SSMIS 1400-km SSMI

Three Types of Corrections to the SSMIS TDR files Scan Non-Uniformity (all satellites) Applied to each beam position from non-uniformity files Radiometer Gain (F16 all year, F17 at high solar elevation angles in spring and summer) Corrects for solar intrusions into warm load In UPP Version 1 this was done by flagging intrusions with precalculated solar geometry calculations In UPP Version 2 this is done with NGST provided gain files (one file for each TDR file) Reflector Emission (F16 and F17, but applied for all) Requires knowledge of reflector temperature T refl and frequency-dependent emissivity ε

GenRemapLASBufr GenTDRdata Reads TDR file and fills each set (IMA, ENV, LAS, UAS) GetSCANCoeffs Reads scan nonuniformity coefficients for sensor and channel set DoScanCorrection Apply scan uniformity to IMA, ENV, LAS GetGAINdata Read gain file (N x 24 size) if provided for Gain Ratio DOGAINCorrection Apply gain ratio to each channel set T scene = T cosmic + (T obs -T cosmic )*GR CalSolZenAndAz Calculate solar zenith and azimuth Add to IMA structure DetectSolarIntrusions GenTAnt Reflector temperature extraction ProcessLASTDR_v2 Remap to LAS and apply TB corrections UPP: Averages all channels to LAS resolution (N/3 X 60), then calls CorrectTB to apply correction for (frequency dependent) reflector emission and spillover factor (read from external coefficient files) For UPP-CP: Apply correction for reflector emission and spillover at native resolution, output data in NCDC user format IMA (6) ENV (5) LAS (8) U A S (5) Native: UPP Version 2 UPP Version 1

Reflector Emission K= spillover factor for each channel Degradation of the Al coating on the reflector has resulted in an emissive reflector, notably for F16 and F17 Once per orbit the sensor enters Earth shadow for ≈ 10 minutes, and the reflector cools by ≈80 K, then warms rapidly when exiting shadow If the reflector temperature T refl and emissivity ε are known the scene temperature can be reconstructed F16: thermistor located on reflector rim, T refl based on “lagged-derivative” approach F17-F20: thermistor moved to back to reflector, gives better estimate of T refl F18 uses improved reflector with lower reflector emissivity, F19-F20 similar

F16 SSMIS Solar Intrusions 1 June 2010 Rev Y-axis: 1-(Gain_Original/Gain_Filtered), range to X-axis: scanline, range Solar intrusions into the warm load occur 2-4 times per orbit

150H GHz Original TDR file 150H GHz (TDR – UPP) 24 March 2010 F16 Ascending Most notable changes are when is in shadow

183±1 GHz Original TDR file 183±1 GHz (TDR – UPP) 24 March 2010 F16 Ascending

150H GHz Original TDR file 150H GHz (TDR – UPP) 1 June 2010 F16 Ascending

183±1 GHz Original TDR file 183±1 GHz (TDR – UPP) 1 June 2010 F16 Ascending

150H GHz Original TDR file 150H GHz (TDR – UPP) 1 October 2010 F16 Ascending

183±1 GHz Original TDR file 183±1 GHz (TDR – UPP) 1 October 2010 F16 Ascending

Current Status The UPP is essentially a collection of Fortran90 subroutines that compile under Linux (gfortran under MacOS X works also) that read in a TDR file and its associated gain file, and outputs a BUFR file with all 24 channels at a remapped LAS resolution Currently have adapted various UPP subprograms to write out each channel set (IMA, ENV, LAS, UAS) at native resolution after correction for spillover and reflector emissivity (simple ASCII to plot up results) Code needs to be polished so that UPP-CP acts as a “filter” between the input TDR and the output “TDR”, with no changes to format, only to TB values (although after all these corrections, the output is really an SDR) NOAA/NESDIS/NCDC currently negotiating with US Navy (FNMOC) to access gain files NCDC will make UPP-CP versions available for users via CLASS