Post-launch Radiometric and Spectral Calibration Assessment of NPP/CrIS by comparing CrIS with VIIRS, AIRS, and IASI

Transcription

1 Post-launch Radiometric and Spectral Calibration Assessment of NPP/CrIS by comparing CrIS with VIIRS, AIRS, and IASI Likun Wang 1, Yong Han 2, Denis Tremblay 3, Fuzhong Weng 2, and Mitch Goldberg 4 1. CICS/ESSIC/University of Maryland, College Park, MD; Likun.Wang@noaa.gov 2. NOAA/NESDIS/STAR, College Park, MD 3. Earth Resources Technology, Inc., Laurel, MD 4. NOAA/NESDIS/JPSS Program Office, Greenbelt, MD 2012 CalCon, Logan, Utah; 08/29/2012 1

2 Motivation It is very hard to assess calibration accuracy after launch No truth on orbit. Instrument status can change onorbit Inter-calibration Examine relative differences between CrIS with similar instruments (AIRS/Aqua and IASI/MetOp-A) or instruments sharing the same spectral range (VIIRS/NPP) Track the difference varying with time y(t 2 ) True y? p(t 2 ) p(t 1 ) y(t 1 ) 2

3 From Hank Revercomb 3

4 CrIS overlapped with VIIRS CrIS spectrum is overlapped with VIIRS SRFs for M13, M15, and M16 4 d S d v S R L i i i ) ( ) ( ) ( 10.8 µm 12.0 µm 4.05 µm

5 Updates on CrIS SDR calibration Main Changes of CrIS Calibration Engineer Package V34 Thermal drift threshold values Uploaded on June New FIR digital filter Uploaded On April Geolocation coding errors are found in CrIS SDR processing software 3.5 km in scan and 2.7 km in track direction will be corrected in October, 2012 CrIS SDR data: produced by ADL 3.1 Geo-location correction Engineer Package V34 6-day s data: May and July

6 Simultaneous Nadir Overpasses (SNO) Obtain SNO prediction data Download SDR dataset Collocate CrIS (nadir) with IASI/AIRS Collocated VIIRS with CrIS SNO FOVs Polar orbiting satellites intersect each other at high latitudes. This occurs for satellites even in very different orbits. When the SNO occurs, the radiometers from both satellites view the Earth and the atmosphere at the same place and same time but from different altitudes. Re-sample spectra onto common grids Filter out inhomogeneous Scenes Average the spectra (all, FOV or Scan) Make a comparison Courtesy of image from Changyong Cao 6

7 Collocate VIIRS Pixel with CrIS (1) CrIS FOV footprint (ascending) Satellite Direction VIIRS Scan Direction CrIS Scan Direction FOR 1 FOR 14 FOR 30 7

8 Collocate VIIRS with CrIS (2) Identify uniform scenes VIIRS Pixels CrIS FOV footprint CrIS FOV Spatial Response 50% Histogram of VIIRS M16 in CrIS FOV 8

9 Collocating VIIRS with CrIS (3) Identify uniform scenes Scene homogeneity causes uncertainties for comparison, we define homogeneity ratio: R =STDEV(Rad viirs )/Mean(Rad viirs ) M is used as a cut-off value to identify uniform CrIS FOVs. (50% data are cut off) When average spectra, homogeneity ratio is used as weight. 9

10 Resample IASI to CrIS Fourier Transform 1) De-Apodization 2) Truncation 3) Apodization CrIS IASI Re-sampling error very small Inverse Fourier Transform 10

11 A total of 86 SNO cases Time Difference: <= 120 seconds Pixel distance difference: <=(12+14)/4.0 km = 6.5 km Angle Difference: ABS(cos(a1)/cos(a2)-1) <=

12 IASI and CrIS SNO case CrIS IASI CrIS - IASI 12

13 SNO Spectra:727 samples Weighted average North (344) South (383) 13

14 CrIS vs. IASI: CrIS Band 1 North Pole South Pole IASI CrIS CrIS-IASI CrIS-IASI BT differences are scene-dependent and get larger when scene temperature are low

15 CrIS vs. IASI: CrIS Band 2 North Pole South Pole CrIS IASI CrIS IASI CrIS-IASI For band 2 at water vapor absorption region, CrIS and IASI are consistent to each other and the difference is less than 0.1 K.

16 CrIS vs. IASI: CrIS Band 3 North Pole South Pole CrIS IASI CrIS IASI CrIS-IASI At South Pole, the noise is large at low temperature, and the differences are less than 0.1 K in most region at North Pole

17 Scene-dependent Bias 700 cm cm cm cm cm cm-1 17

18 Separate with FOVs: North Pole 18

19 Separate with FOVs: South Pole 19

20 AIRS and CrIS SNO cases 20

21 Resampling CrIS into AIRS AIRS Spectrum is convolved with CrIS SRFs (three bands) at each AIRS spectral grid Resampling CrIS into highresolution data (e.g. 2^15) and then they are convolved with AIRS SRFs After that, AIRS and CrIS spectra are processed at AIRS spectral grids CrIS AIRS Dark: Original AIRS Blue: Re-sampled CrIS Pink: AIRS convolved with CrIS SRF CrIS-AIRS

22 AIRS vs. CrIS: North Pole CrIS AIRS CrIS-AIRS 22

23 AIRS vs. CrIS: South Pole CrIS AIRS CrIS-AIRS Cold scene, large NEdT 23

24 CrIS vs. VIIRS: for SNO FOVs NEdT large at low temperature Scene-temperature dependence can be seen at Band M15 CrIS is warmer than VIIRS at M15 and M16 but is colder at M13 CrIS-VIIRS BT difference for SNO cases are consistent with the whole orbital data (presented before). 24

25 Conclusion For Band1 CrIS-IASI/AIRS BT difference is scene-dependent and the difference get large when scene temperatures are low. CrIS is warmer than IASI around K CrIS agrees well with AIRS at window region for warm scene (>270K) but warmer than AIRS at the CO 2 region ( K). For band 2, at water vapor absorption region, CrIS and are consistent to both IASI and AIRS. For Band 3, at the South Pole, the noise are large at low temperature, and the differences are less than 0.1 K in most region at North Pole. CrIS-VIIRS inter-comparison results are consistent with previous findings: 1) M15: Scene-dependent bias; 2) M16: CrIS warmer than VIIRS ( K); 3) M13 is CrIS colder than VIIRS ( K) The comparison results indicate that CrIS meets the designed specification, but we still need to further investigate the root causes of BT difference between CrIS and AIRS/IASI. 25

26 287K From Hank Revercomb 26

27 Thank you 27

28 For all SNO case (North Pole) CrIS IASI CrIS-IASI 28

29 For all SNO cases (South Pole) CrIS IASI CrIS-IASI Cold scene, large NEdT 29