Title: DC-8 Lidar Atmospheric Sensing Experiment (LASE) Data [NASA] CONTACTS: Dr. Edward Browell (PI) MS 401A NASA Langley Research Center Hampton, VA 23681 Voice: 757-864-1273, Email: email@example.com Dr. Syed Ismail (Co-PI) MS 401A NASA Langley Research Center Hampton, VA 23681 Voice: 757-864-2719 Email: firstname.lastname@example.org Dr. Richard Ferrare (Co-I) MS 401A NASA Langley Research Center Hampton, VA 23681 Voice: 757-864-9443 Email: email@example.com 1.0 DATA SET OVERVIEW NASA's Lidar Atmospheric Sensing Experiment (LASE) system was operated during the International H2O Project (IHOP_2002) field experiment from May 23 through June 14, 2002. IHOP_2002 was conducted over the Southern Great Plains (SGP) of the United States from 13 May to 25 June 2002. The chief objective of IHOP_2002 was to improve the characterization of the four-dimensional (4-D) distribution of water vapor and its application to improving the understanding and prediction of deep convection. The IHOP_2002 region, in the central United States, was an optimal location due to existing experimental and operational facilities, strong variability in moisture, and active convection initiation. 2.0 INSTRUMENT DESCRIPTION 2.1 Instrumentation LASE is an airborne DIAL (Differential Absorption Lidar) system used to measure water vapor, aerosols, and clouds throughout the troposphere. This system uses a double-pulsed Ti:sapphire laser, which is pumped by a frequency-doubled flashlamp-pumped Nd:YAG laser, to transmit light in the 815-nm absorption band of water vapor. The Ti:sapphire laser wavelength is controlled by injection seeding with a diode laser that is frequency locked to a water vapor line using an absorption cell. LASE operates by locking to a strong water vapor line and electronically tuning to any spectral position on the absorption line to choose the suitable absorption cross-section for optimum measurements over a range of water vapor concentrations in the atmosphere. During IHOP_2002, LASE operated from the NASA DC-8 using strong and weak water vapor lines in both the nadir and zenith modes, thereby simultaneously acquiring data below and above the aircraft. The strongly absorbing, temperature insensitive water vapor line at 817.2231 nm (12236.5603 cm-1) with a line strength of 4.060E-23 cm, linewidth of 0.0839 cm-1, and lower energy state of 224.838 cm-1 was used during IHOP_2002. Line strength accuracy is estimated to be 2% and linewidths have agreed with other measurement to within 2% giving an overall accuracy of absorption cross-section of less than 3% (Ponsardin and Browell, 1997). Effective absorption cross-section profiles were calculated at the on-line and off-line wavelengths and the side-line positions, and corrections for Doppler broadening, pressure shift, water vapor line width, spectral purity, molecular density, and aerosol scattering ratio were used in water vapor mixing ratio retrievals (Ismail et al., 1989). Absolute water vapor distributions will be derived from the LASE measurements across the troposphere from 0-12 km over a mixing ratio range of about 20 g/kg to 0.01 g/kg; however, the initial data submitted to the archive contained only the nadir water vapor distributions. The LASE nadir water vapor profiles have a vertical resolution of 330 m and a temporal averaging period of 3 minutes, which corresponds to a horizontal distance of about 42 km. Other temporal averaging periods can be produced upon request. Previous water vapor comparisons have shown the LASE water vapor mixing ratio measurements have an accuracy of better than 6% or 0.01 g/kg, whichever is larger, across the troposphere (Browell et al., 1997). In addition to measuring water vapor mixing ratio profiles, LASE simultaneously measures aerosol backscattering profiles at the off-line wavelength near 815 nm. Profiles of the aerosol scattering ratio, defined as the ratio of aerosol scattering to molecular scattering, are determined by normalizing the scattering in the region containing enhanced aerosol scattering to the expected scattering by the "clean" (molecular only) atmosphere in that same region. For these IHOP_2002 nadir measurements, the LASE nadir aerosol scattering ratio profiles have a vertical resolution of 60 m and a horizontal resolution of 6 seconds (~1.4 km) for all flights except LASE Flights 06 and 11. For Flight 06, LASE horizontal resolution was 6 seconds (~1.4km) until 19:58 UT, then operated with a horizontal resolution of 3 seconds (~0.7km) for the remainder of Flight 06. For Flight 11, LASE horizontal resolution was 3 seconds (~0.7km) until 16:00 UT, then operated with a horizontal resolution of 6 seconds (~1.4km) for the remainder of Flight 11. 3.0 DATA COLLECTION AND PROCESSING LASE was operated from the NASA DC-8 aircraft in the nadir and zenith modes simultaneously. Six dedicated DC-8 flights were made in the IHOP 2002 region. In addition, there were two transit flights from/to the NASA Dryden Flight Research Center (DFRC) where LASE operated while transiting into and out of the IHOP region on 23 May and 14 June 2002. During the return to Dryden, an additional 5 hours was used in a coordinated sampling experiment in the IHOP_2002 region. LASE collected profile data over more than 40 flight hours. Data Intervals Water vapor and aerosol horizontal data interval is 6 seconds or ~1.4 km. For portions of Flight 06 and 11 (described above), the horizontal data interval was 3 seconds or ~0.7 km. Water vapor and aerosol vertical data interval is 30m. Data Resolution (Averaging Interval) Nadir water vapor horizontal resolution is 3 minutes or 42 km Nadir water vapor vertical resolution is 330 m Nadir aerosol scattering ratio vertical resolution is 60 m . 4.0 DATA FORMAT AND FILE NAMING 4.1 Data Format Data file archive format Format specification for Data Exchange by Steve E. Gaines and R. Stephen Hipskind found at cloud1.arc.nasa.gov/solve/archiv/archive.tutorial.html. LASE uses format number 2310. IDL 2310 format read code The following IDL program (attached), "rd_ihp_2002_2310.pro" will read the 2310 formatted LASE aerosol and water vapor profile data. 4.2 File Naming conventions Data Files bnYYYYMMDD.txt, [aerosol scattering ratio, YYYY= year, MM= month, DD= day] wnYYYYMMDD.txt, [water vapor, YYYY= year, MM= month, DD= day] Flights 01, 02, and 03 were test flights at NASA Dryden Flight Research Center. Flight 04 - Transit: DFRC to Oklahoma City - May 23, 2002 Flight 05 - Convective Initiation #1 - May 24, 2002 Flight 06 - Boundary Layer mapping #1 - May 30, 2002 Flight 07 - Nocturnal Lower Level Jet - June 02, 2002 Flight 08 - Convective Initiation #2 - June 03, 2002 Flight 09 - Low Level Jet & Convective Initiation #3 - June 09, 2002 Flight 10 - Convective Initiation #3 - June 11, 2002 Flight 11 - Boundary Layer Evolution & Transit to DFRC - June 14, 2002 5.0 DATA REMARKS LASE IHOP_2002 URL: The LASE IHOP_2002 campaign images are located at: asd-www.larc.nasa.gov/lidar/ihop/ihop.html. The LASE aerosol, water vapor profile data, and images are archived at UCAR URL: www.joss.ucar.edu/ihop/dm/archive/. LASE IHOP_2002 data set release history a. "Quick-look", preliminary data These data were produced and distributed during the IHOP_2002 field mission during May - June 2002. These data sets are for "quick-look" purposes only. b. Processed data These data completed post-processing in January 2003 and contained only nadir aerosols and water vapor profiles. Zenith aerosols and water vapor are still undergoing post-processing and will be archived in the near future. Algorithm for data reduction Water vapor employs the DIAL technique, which is explained at asd-www.larc.nasa.gov/lidar/concept.html and instrument description (item 2.1 above). Aerosol scattering ratio computations are described in instrument description (item 2.1 above).6.0 REFERENCES
Ismail, S., E. V. Browell, 1989: Airborne and spaceborne lidar measurements of water vapor profiles: A sensitivity analysis, Appl. Opt., 28, 3603-3615.
Ponsardin, P.L. and Browell, E.V., Measurements of H216O Linestrengths and Air-Induced Broadenings and Shifts in the 815-nm Spectral Regions, Journal of Molecular Spectroscopy 185, 58-70(1997), Article No. MS977354.