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Comparison of CALIPSO, GLAS, and LITE CFLOS Statistics for Use In DWL Mission Design and OSSEs

Analyzing CALIPSO, GLAS, and LITE data to study cloud-free line-of-sight statistics for Doppler Wind Lidar design, optimization, and comparisons. Focus on aerosol backscatter distributions, instrument trade studies, and other relevant aspects.

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Comparison of CALIPSO, GLAS, and LITE CFLOS Statistics for Use In DWL Mission Design and OSSEs

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  1. Comparison of CALIPSO, GLAS, and LITE CFLOS Statistics for Use In DWL Mission Design and OSSEs S. Greco and D. Emmitt WG SBLW Wintergreen, VA June 17, 2009

  2. CALIPSO/LITE ROSES07 study The ROSES07study is using both LITE and CALIPSO data to address the following four major issues: • Cloud free line-of-sight (CFLOS) statistics for laser beam footprints (with particular interest in contiguous laser shot integration intervals), • Global aerosol backscatter distributions with particular interest in their correlation with cloud and atmospheric dynamics, • Conversion of observations at CALIPSO wavelengths to those pertinent to GWOS, the hybrid wind lidar (.355 and 2.01 microns); validation of aerosol backscatter distributions being used in NASA/NOAA OSSEs. • Instrument trade studies relevant to the GWOS instrument concept using an existing Doppler Lidar Simulation Model

  3. Overview • Develop a state-of-the-art set of cloud free line-of-sight (CFLOS) statistics and atmospheric optical properties for space-based Doppler Wind Lidar (DWL) design using both LITE and CALIPSO data and use the Doppler Lidar Simulation Model (DLSM) to conduct basic trade studies that relate directly to laser design and scanning options. • Effort is focused upon issues that are unique to the hybrid (coherent and direct detection combined) Doppler Wind Lidar being considered for the first USA mission. In particular, deriving 2 micron coherent performance from .532/1.06 µm CALIPSO data is non-trivial and is being modeled by Bowdle (UAH). • Our revisit to the LITE data is in recognition of the fact that LITE was the most powerful backscatter lidar ever flown in space. Since the weak aerosol distributions are being investigated, the LITE data appears to be most useful. • Simpson Weather Associates’ (SWA) study of the CFLOS statistics from the ICESat GLAS (Geosciences Laser Altimeter System) data sets provides the motivation and methodology behind this work as well as data for comparison

  4. Planning and Strategy • All Calipso Level 2 cloud products (333m, 1km and 5km) would be investigated but the focus would be on the 1 km product - Cloud top, Cloud base, Number of Layers - Surface elevation/detection • August 2007 was selected as the case study • Data obtained from the NASA Langley Atmospheric Science Data center • Comparison with existing results from LITE and GLAS

  5. Laser and Data Features • LITE (September 1994) - 532/1064 nm - 530 mJ@532; 470 mJ@1064 - 740m horizontal; 15 m vertical • CALIPSO (August 2007) - 532/1064 nm - 110 mJ per channel - 333m horizontal;30-60m vertical • GLAS (November 2003) - 532/1064 nm - 35 mJ @532; 75 mJ @1064 - 170m horizontal; ~ 70 m vertical

  6. Previous Results: LITE CFLOS study The general conclusions of the LITE data analyses of cloud porosity for lasers were that: • The 532nm beam provided a ground return more often (~60 - 65%) than the current cloud climatologies based upon passive imagers suggested (~30-40%). • More than 50% of the time that the lidar beam intercepted a cloud it also provided a ground return. In other words the porosity of the clouds to the LITE beams was on the order of 50%. • Study by Berthier et al. found global cloud cover to be ~ 70%

  7. Previous Results: GLAS • SWA found that 70 - 80% of the GLAS lidar samples involved some return from clouds (assumed that “no cloud/no ground returns” intercepted thick layers of optically thin clouds). Other work by BERTHIER also found global cloud cover between 65-80% • 75 - 80% of the GLAS lidar samples detected the earth’s surface (adjusted for smooth water returns) • When clouds were present, 25 – 40% of the time at least two layers were detected. (http://esto.nasa.gov/adv_planning_studies_archive.html ).

  8. CALIPSO RESULTS(for August 8 – 14)

  9. Shot Resolution/Distribution • CALIPSO - 333 m – single shot - 1 km - (3 shots) - 5 km – (15 shots) • GLAS - Full resolution (170 m) - High resolutions (8 shots over 1.36 km) - Medium resolution (40 shots over 6.8 km)

  10. CALIPSO: 333m vs 1km vs 5km product

  11. CALIPSO: 333m vs 1km vs 5km product . Numbers in parentheses reflect cases where there were clouds.

  12. CALIPSO: 333m vs 1km vs 5km product

  13. CALIPSO: 1 KM Product

  14. CFLOS Statistics • Cloud-Free-Line-Of-Sight (CFLOS) - Does the lidar shot (product) make it down to a certain level without any cloud detection? • Pass Through - Is there a ground return or cloud returns below a certain level? • Integration Distances for 1 km product - 25 KM (25 products/75 shots) - 50 KM (50 products/150 shots) - 75 KM (75 products/225 shots)

  15. CFLOS Statistics –Why? • Trade studies on lidar technology or sampling strategies - Efficiency needed - Integration length - Efficiency vs EAP vs Integration length • How many consecutive shots have either a CFLOS or, despite clouds, made it to a lower level?

  16. 100% Pass Through Efficiency for 50 KM Integration Length. 80% Pass Through Efficiency for 50 KM Integration Length.

  17. 100% CFLOS Efficiency for 50 KM Integration Length. 80% CFLOS Efficiency for 50 KM Integration Length.

  18. Effects of Integration Distance

  19. Effect of Integration Distance -100% Pass Through Efficiency Effect of Integration Distance -50% Pass Through Efficiency

  20. Effect of Integration Distance -100% CFLOS Efficiency Effect of Integration Distance - 50% CFLOS Efficiency

  21. CALIPSO and GLAS Comparisons

  22. Comparison with GLAS: 100% CFLOS Efficiency at 50 KM Comparison with GLAS: 50% CFLOS Efficiency at 50 KM

  23. Tropical vs Mid-Latitude(1 KM Product)

  24. 100% CFLOS Efficiency for 50 KM Integration Length. 80% CFLOS Efficiency for 50 KM Integration Length.

  25. Continuing Work • Utilize the latest data release to extend statistics to entire month (August 2007) and for all three cloud products (333 m, 1 km, 5 km) • Currently examining CALIPSO overpasses of TPARC/TCS08 cases where P3DWL was scanning both up and down. • Phenomological/Synoptic Studies • Backscatter portion of study is in progress. Exploring ways to determine distribution of “background” vs “enhanced” aerosol regions.

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