Overview of Post-launch CrIS SDR Calibration and Validation

Transcription

1 Overview of Post-launch CrIS SDR Calibration and Validation Yong Han NOAA/ Center for Satellite Applications & Research and CrIS SDR Team CALCON Technical Conference Aug. 27 Aug. 30, 2012 Logan, Utah 1

2 CrIS SDR Science Team NOAA Y. Han (team lead), D. Tremblay, X. Jin, Y. Chen, L. Wang and C. Barnet NASA D. Johnson Space Dynamics Laboratory/Utah State University (SDL) D. Scott, G. Bingham, M. Esplin, V. Zavyalov and M. Greenman University of Wisconsin (UW) H. Revercomb, D. Tobin, B. knuteson, J. Taylor and L. Borg University of Maryland Baltimore County (UMBC) L. Strow, S. Hannon, H. Motteler and P. Schou Massachusetts Institute of Technology/Lincoln Labs D. Mooney Exelis (ITT) J. Predina, M. Cromp and L. Suwinski Northrop Grumman Aerospace Systems (NGAS) D. Gu, D. Hagan, L. Wang and C. Wang Raytheon W. Ibrahim 2

3 Outline CrIS Performance Specification and SDR Algorithm Modules Post-launch Calibration and Validation Milestones Post-launch Calibration and Validation Results Summary 3

4 Related Presentations Inter-Calibration of AIRS with IASI and CrIS Larrabee Strow CrIS On-orbit Spectral and Radiometric Performance Denise Hagan Performance of CrIS on NPP Dave Tobin CrIS Calibration and Validation Larrabee Strow Post-launch Radiometric and Spectral Calibration Assessment of NPP CrIS by comparing CrIS with VIIRS, AIRS and IASI Likun Wang Assessment of CrIS Raiometric Accuracy using Community Radiative Transfer Model and Double Difference Approach Yong Chen Cross-track Infrared Sound (CrIS) Instrument In-flight Performance - Vladimir Zavyalov Preliminary Comparison of Radiometric Calibration Performance among CrIS, AIRS and IASI Using GSICS GEO-LEO Inter-calibration Fangfang Yu CrIS Sensor Temperature Effect on CrIS Radiometric Performance Mark Esplin 4

5 NPP CrIS Sensor Data Record (SDR) Requirements Band Spectral range (cm -1 ) N. of chan. Resolution (cm -1 ) FORs per Scan FOVs per FOR NEdN@287K mw/m 2 /sr/ cm -1 Radiance Uncertainty (%) Spectral uncertainty ppm Geolocation uncertainty km LW MW SW ppm part per million FOV Field OF View FOR Field OF Regard CrIS SDR spectra are un-apodized 5

6 Scan, FOR & FOV Position North (~50km, nadir) FOV Field OF View FOR Field OF Regard FOV (14km, nadir) - Swath is 2200 Km (FOR1 to FOR 30). - CrIS acquires 1 scan line every 8 seconds. - CrIS measures 8.7 million spectra per day. 6

7 CrIS Space Segment Processing Cross-track Infrared Sounder (CrIS) Volume: < 71x80x95 cm Mass: 146 kg Power: < 110 W RDR - Raw Data Record All calibration parameters are included in Engineering packet embedded in downlink data streams 7

8 CrIS SDR Algorithm & Software RDRs: Interferograms 8 sec science Telemetry 4 min Engineering packet Geometric data Pre-Process RDR FFT to spectrum FCE handling Nonlinearity correction Radiometric Calibration SDR Geolocation Residual ILS removal Selfapodization removal Spectral resampling to user grid Post calibration filter CrIS SDR Processing Software Interface Data Processing Segment (IDPS) - operational code Algorithm Development Area (ADA) - an offline IDPS code Algorithm Development Library (ADL) - Linux version IDPS code Team member science codes: Exelis SDR code UW/UMBC CCAST (CrIS Calibration Algorithm & Sensor Testbed) MIT/LL SDR code For development and CalVal 8

9 CrIS CalVal Activity Category Early sensor checkout and optimization (completed) CrIS performance characterization (ongoing) SDR software update and algorithm improvement (ongoing) Radiometric calibration NEdN, nonlinearity, ICT model and etc (ongoing) Spectral calibration (ongoing) Geolocation calibration (ongoing) CrIS performance trending and monitoring (ongoing) 9

10 CalVal Milestones January 18 th 2012: CrIS was powered up; team started instrument checkout and optimization. February 8 th : Engineering packet v32 was uploaded (PGA setting and bit trim mask updates). February 22 nd : Full spectral resolution RDRs (0.8 cm maxopd for all bands) were collected. April 11 th : Engineering packet v33 was upload (spectral calibration parameters, nonlinearity coefficients and ICT emissivity table updates). April 18 th : A new FIR digital filter was uploaded to replace the corrupted one. May 15 th : CrIS SDR product reached Beta maturity level. June 27 th : Engineering packet v34 was uploaded (temperature drift limit updates) Provisional product: October, 2012 Validated product: 2013 Jan. 25: First light image, 900 cm -1 BT 20-Jan :54 to 23:57 UTC from CCAST SDR processing system, UW/UMBC 10

11 NEdN MW FOV7 is known to have excess NEdN Noise Equivalent Difference Radiance (NEdN) is much better than specification (Dashed lines) 11

12 On-board FIR Digital Filter Change In-orbit data analysis revealed sweep direction bias (~0.1 K). Diagnostic data analysis, simulations and ground testing indicated the root cause is the defective on-board FIR digital filter. The bias was eliminated by uploading an improved filter. 12

13 Nonlinearity Correction Coefficient Adjustment for Radiometric Calibration Nonlinearity correction coefficient (a 2 ) is used in the factor (1-2a 2 V int ) to scale the spectrum for nonlinearity correction for each detector. Some LW and MW detectors have significant nonlinearity. Method: Analysis of in-orbit Diagnostic Mode data. Further a 2 adjustments using normal mode Earth scene observations. Verify/assess results with SNO and double obs-calc comparisons with IASI and AIRS Results: FOV-to-FOV radiometric performances approach uniformity. Radiometric uncertainties are significantly reduced. 13

14 Comparison to AIRS before and after a 2 Updates LW Band Before a 2 updates After a 2 updates ~300 mk ~175 mk ~75 mk ~45 mk FOV-to-FOV difference is reduced from 300 mk to 75 mk. Radiometric uncertainty is reduced from 175 mk to 45 mk. 14

15 ILS Parameter Adjustment for Spectral Calibration Neon bulb wavelength and detector focal plane position parameters are key Instrument-Line-Shape (ILS) parameters for spectral calibration. Methods Adjust detector positions until all 9 detectors on each focal plane exhibit the same frequencies in observed radiance (FOV overlay). Adjust Neon bulb frequency until observed upwelling radiances agree with computed radiances via cross-correlation of Observation with Calculations. Results: On-orbit spectral accuracy achieved: ~1ppm Specification: 10 ppm. 15

16 Excellent Neon/Metrology Laser Stability Laser frequency variation 2 month Neon/Metrology laser stability: 1 ppm 16

17 ppm from FOV5 ppm from FOV5 ppm from FOV5 LW Inter-FOV Spectral Calibration Analysis ADL with pre-launch ILS parameters CCAST with new ILS parameters, derived using CCAST ~8ppm spread ADL with new ILS parameters Orbit Feb 24 th 2012 Main spread removed, but all FOVs ~1.5 ppm off from FOV5 The new ILS parameters have greatly improved the spectral calibration. 17

18 Radiance Bias Assessed with RTM after Nonlinearity and ILS Parameter Adjustments (1) Black: before a2 and ILS parameter updates Blue: after a2 updates but before ILS parameter change Red: after both a2 and ILS parameter updates BIAS ( Obs CRTM ) ( Obs CRTM ) i FOVi CRTM Community Radiative Transfer Model used at Numerical Weather Prediction (NWP) centers FOV all Total clear sky observation points ~ The achieved uniformity of the spectral and radiometric calibration cross the 9 FOVs allows the NWP centers to assimilate more radiance data 18

19 Radiance Bias Assessed with RTM after Nonlinearity and ILS Parameter Adjustments (2) Standard deviation (over 9-FOVs) of Bias vs Radiative Transfer Model (RTM) simulated radiances after a2 and ILS parameter adjustment Overall bias < 0.1 K 19

20 Δ SNO Radiance Difference between CrIS and IASI (Preliminary) CrIS IASI CrIS-IASI North Pole, 344 samples 20

21 Geolocation Errors Estimated Using Co-located VIIRS Scatter plot of CrIS and VIIRS BTs + + Original Collocation at (0, 0) 21 Cost function as Root Mean Square Errors (RMSE) of CrIS-VIIRS BT difference Findings from 18 data sets (VIIRS M13, M14, M16 and I5) Mean CrIS Geolocation Bias: Crosstrack: 4.5 pixels (±1 pixel) ~ 3.5 km (± 776m) Alongtrack: -3.6 pixels (±1 pixel) ~ -2.7 km (± 742 m) Collocation after shift at minimum of cost function (5, -4)

22 Geolocation Error Root-cause and Correction A coding error was found that caused the geolocation error Before and after the coding error correction Before After Geolocation uncertainty after the correction: < 1 km 22

23 New Quality Flag Based on the Imaginary Radiance The SDR product includes both real and imaginary parts of the spectra Good radiance spectra have near zero imaginary radiances Add a bit flag to indicate the spectrum is Invalid if any imaginary channel in the range exceeds the thresholds: LW: upper limit 1.5, lower limit -1.5, in the range cm -1 MW: upper limit 0.5, lower limit -0.5, in the range cm -1 SW: upper limit 0.05, lower limit -0.05, in the range cm -1 Invalid spectrum example Hit threshold to make the bit flag turned on Range of interest 23

24 Summary The instrument is very stable. NEdNs are much better than specification. Spectral calibration uncertainty is about 1-2 ppm, better than specification (10 ppm). Overall radiometric uncertainty is about 0.1 K and FOV-to-FOV radiometric performance difference is about 0.05K. The geolocation uncertainty is better than 1km. 24