Title: DC-8 Lidar Atmospheric Sensing Experiment (LASE) Imagery [NASA]


CONTACTS:

Dr. Edward Browell (PI)
MS 401A
NASA Langley Research Center
Hampton, VA 23681

Voice: 757-864-1273,
Email: e.v.browell@larc.nasa.gov


Dr. Syed Ismail (Co-PI)
MS 401A
NASA Langley Research Center
Hampton, VA 23681

Voice: 757-864-2719
Email: s.ismail@larc.nasa.gov


Dr. Richard Ferrare (Co-I)
MS 401A
NASA Langley Research Center
Hampton, VA 23681

Voice: 757-864-9443
Email: r.ferrare@larc.nasa.gov


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

  GIF Image Files 
 
     Log scale :   ihp_NN_asr_logY.gif,  [image, NN = DC-8 flight number, Y = image segment 
                   consecutive number, (no number indicates entire flight image)] 
 
     Linear scale : ihp_NN_SSS_linY.gif,  [image, NN = DC-8 flight number,  SSS = asr scattering
                    ratio or SSS = h2o, water vapor, Y = image segment consecutive
                    number, (no number indicates entire flight image)]
                   
     Note:  Aerosol images are presented on both a log and linear scale. Water
     vapor images are presented on a linear scale.  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