Report on VIIRS / CrIS Participation Paul Menzel March 2002

1. Report on VIIRS / CrIS Participation Paul Menzel March 2002 With Jeff Key, Steve Ackerman, Richard Frey, Eva Borbas, Youri Plokhenko, Kathy Strabala, Graeme Stephens

2. Raised concerns about VIIRS spectral selection Jan 01

3. VIIRS, MODIS, FY-1C, AVHRR CO2 O2 O3 H2O O2 H2O H2O H2O O2 H2O H2O CO2

4. VIIRS MODIS Earth emitted spectra overlaid on Planck function envelopes

5. Issues 1. No channels are sensitive to CO2 2. No channels are sensitive to UTH 3. No channel pairs can detect low level T inversion, since all channels view surface Suggested Changes 1. Consider 1.88 instead of 1.38 um (better for separating high thin clouds from snow in polar regions) 2. Add 6.7 um (can detect inversion in polar regions to help identify clear from cloud, UTH also) 3. Add noisy 13.3 and 13.6 um channels (CO2 slicing for high thin clouds, helps CrIS with cloud clearing)

6. Highlighted VIIRS problems with semi-transparent clouds Feb 01

7. VIIRS needs an absorbing channel for accurate Cloud Height Determination For semi-transparent clouds (N<1 or E<1) IRW window underestimates height by 300 to 400 hPa Semi-transparent clouds occur in 45% of HIRS obs, 50% of MODIS obs Height correction algorithms include CO2 slicing or H2O intercept technique GOES and MSG demonstrated H2O semi-transparency correction to assign cirrus to correct cloud height Cloud height EDR will not be met with current VIIRS for more than half of the cloud observations

8. clouds are found in 75% of all observations (they cover about 69% of 65N to 65S) global preponderance of semi-transparent clouds (about 45%) ITCZ shows high frequency of cirrus (greater than 50%) more cirrus in summer than winter in each hemisphere

9. H2O Intercept and CO2 slicing compare reasonably well IRW, CO2, and H2O height assignments for clouds using VAS from 20 to 50N and 50 to 100W for 29-31 Jan 92 (199 cases) __________________________________________________ All Mean CTP Scatter wrt RMS Deviation (hPa) (hPa) Mean (hPa) wrt CO2 wrt H2O IRW 416 102 109 141 CO2 344 87 -- 85 H2O 314 65 85 -- __________________________________________________ Nieman et al., 1993: JAM, 32, 1559-1568

10. Studying effects of surface reflection on IR soundings over land Feb 01

11. Average absolute temp diff (solution with and wo sfc reflection vs raobs) Spatial smoothness of temperature solution with and wo sfc reflection standard deviation of second spatial derivative ( multiplied by 100 * km * km)

12. LW & SW emissivity estimated with RT model & GOES Obs on 06/01/00 at 10 UTC 1.0 LW 0.8 1.0 SW 0.8

13. Made the case for a H2O channel on VIIRS Mar 2001

14. VIIRS needs a water vapor channel for Fine scale WV depiction Experience with MODIS has revealed fine scale moisture details that are important for global PW understanding (GWEX) * continuity of these data will be important Cloud identification HIRS and MODIS reveal polar winter cloudy vs clear skies by searching for inversions * forty percent of polar night is clear but thought to be cloudy without WV channel Cloud Height determination GOES and MSG demonstrated semi-transparency correction to assign cirrus to correct cloud height * avoid IRW mistakes of 300 - 400 hPa Polar Wind tracking MODIS loops reveal opportunity for improved polar winds * fills a global observing system hole for NWP Cloud clearing within CrIS FOV MODIS-AIRS will be demonstrating cloud clearing of high spectral resolution sounder with high spatial resolution imager * UTH and cloud clearing for CrIS is improved

15. MODIS 1 km resolution reveals fine-scale structure

16. IRW-WV channels combine to detect polar inversions BT6.7 (sees mid-trop) is warmer than BT11 (sees sfc) BT11-BT6.7 (from HIRS) versus strength of temperature inversion (from raobs) Ackerman, 1996: Global satellite observations of negative brightness temperature differences between 11 and 6.7 um. JAM, 53, 2803-2812.

17. 40% of HIRS obs for 1 - 5 Jul 2000 show inversions of > 5 C; these clear sky obs would be called cloudy without WV channel

18. Jun % time BT11-BT6.7 < -10C Jul Aug Sep

19. Clouds Indicated by BT11-BT6.7 Test MODIS BT11 Image MODIS 11 µm measurements from Antarctica near the South Pole 8 Sep 2000. Warmer temperatures are darker. Brightness temperatures vary from approximately 187K to 237K. Clear areas are lighter (colder). Clouds are indicated in white. From the operational MODIS cloud mask algorithm. IRW test alone would have declared warmer temps clear; the opposite is true

20. Winds from MODIS: An Arctic Example Water vapor winds from MODIS for a case in the western Arctic. The wind vectors were derived from a sequence of three images, each separated by 100 minutes.

21. Positive impact of two weeks of polar winds in ECMWF Fcst Model

22. Explored Advantage of 1.88 vs 1.38 um for Polar Cirrus Mar 01

23. MODIS 1.38 um channel is saturating over clear sky in Arctic

24. 1.88 um clear sky reflectance would be less than 1.38 um

25. Clear sky and ice cloud contrast would be maintained

26. The case for 1.88 um channel on VIIRS 1.88 um band alleviates problems with cirrus detection over snow in very dry atmospheres, e.g., Antarctica. Advantages of 1.88 include (a) both new and old snow are darker at 1.88 than 1.38 um and (b) the 1.88 um MAS band gives better cloud mask results than the 1.38 um MODIS band. While ice clouds are more absorbing at 1.88 um, the contrast between clear and cloudy reflectances, at least over snow, is similar. Thus for polar applications, if the same signal-to-noise ratio can be obtained as that specified for the 1.38 um band, it appears that it would be advantageous to replace the 1.38 um band with a 1.88 um band.

27. Identified VIIRS Polar Night Cloud Mask Problems Dec 2001

28. VIIRS vs MODIS Cloud Mask Comparison • VIIRS will not have .945, 6.7, or 13.9m bands • This affects: • High thick cloud detection (6.7 and 13.9m threshold tests) especially over land at night. • Polar cloud detection at night (11-6.7m BTDIF inversion test). • Sunglint regions (less tests performed ). • Daytime and Nighttime land - fewer groups can push result into different clear category (Cloud/Uncertain threshold is .67)

29. VIIRS sees too many clouds over Antarctica 23:40 UTC 4 June 2001 MODIS Cloud mask MODIS Band 31 VIIRS Cloud mask (No 11-6.5m test) green – clear; white – cloud; red - uncertain

31. What happens if you add back the 6.7 m band? • VIIRS cloud mask looks very similar to the original MODIS cloud mask. • Why? : • High thick clouds can now be found with a straight 6.7 m BT threshold test. • Polar clouds are more accurately determined at night using 11-6.7m BTDIF inversion test. • Sunglint regions will use 4 group tests instead of 3 -just as the MODIS cloud mask does.

33. Cloud mask comparison: Polar Night - Antarctica 23:40 UTC 4 June 2001 MODIS Cloud mask MODIS Band 31 VIIRS Cloud mask (wo 11-6.7m test) VIIRS Cloud mask (with 11-6.7m test) green – clear; white – cloud; red - uncertain

34. Assisted drafting NPP Cal / Val Plan Nov 2001

35. Draft National Polar-orbiting Operational Environmental Satellite System [NPOESS] Preparatory Project [NPP] NPP Calibration and Product Validation Plan December 30, 2001 NATIONAL POLAR-ORBITING OPERATIONAL ENVIRONMENTAL SATELLITE SYSTEM (NPOESS) INTEGRATED PROGRAM OFFICE and the NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

36. Studying combined GPS and CrIS retrievals Dec 01

37. IR: HIRS CrIS Simulation of GPS improvements (RMS) on 700 temperature (first column) and humidity (second) retrievals derived from HIRS/CrIS (IR), AMSU (MW) and surface data. Retrievals with AMSU (upper panels) and without (lower panels) are shown. AMSU improvements on temperature retrievals (upper third panel). GPS + HIRS + AMSU (dashed line) and GPS+ CrIS + AMSU (solid line) bias and RMS errors wrt RAOBS are shown as a reference in lower third panel. Temperature (K) Humidity (%) Presented at 1st CHAMP Science Meeting, GFZ Potsdam, January 22-25, 2002 by Eva Borbas

38. Exploring sensitivity of CrIS radiances to CO2 amounts Dec 01

39. In a wet atm changes to spectra for CO2 increase of 10 (red) and 20 (blue) ppm

40. In a dry atm changes to spectra for CO2 increase of 10 (red) and 20 (blue) ppm

41. From Engelen et al., 2001 (Right) Maximum level at any level in every temperature retrieved when CO2 is prescribed as a single monthly mean value. (Left) Zonal-height cross-section of the temperature retrieval errors when CO2 is prescribed as a single monthly-global mean value

42. Proposal Stephens, Kumer, Menzel Carbon Dioxide measurements from an airborne spectrometer in support of operational temperature soundings and the study of the Carbon Cycle. Development of NPOESS Airborne CO2 Spectrometer System (NACOOSS) proposed for ER2 deployment to measure CO2 profiles and impact on NAST-I temperature and moisture retrievals.