Visible and Near IR Lidar (VIRL) Measurements Taken Onboard the NASA DC-8 During the TOGA COARE Intensive Observing Period
Entry ID:
COARE_cm_dc8.virl
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Summary
DATA ACCESS
The NASA/TOGA COARE Data Archive
http://daac.gsfc.nasa.gov/fieldexp/TOGA/
The VIRL data are available from the NASA GSFC/DAAC via ftp from
ftp://disc1.gsfc.nasa.gov/data/toga_coare/aircraft/nasa_dc8/virl/
For more ... information contact Pat Hrubiak at hrubiak@daac.gsfc.nasa.gov.
BACKGROUND
TOGA COARE was a multidisciplinary, international research effort that
investigated the scientific phenomena associated with the interaction
between the atmosphere and the ocean in the warm pool region of the
western Pacific. The field experiment phase of the program took place
from 1 November 1992 through 28 February 1993 and involved the
deployment of oceanographic ships and buoys, several ship and land
based Doppler radars, multiple low and high level aircraft equipped
with Doppler radar and other airborne sensors, as well as a variety of
surface-based instruments for in-situ observations.
The NASA component of TOGA COARE, while contributing directly to
overall COARE objectives, emphasized scientific objectives associated
with the Tropical Rainfall Measuring Mission (TRMM) and NASA's cloud
and radiation program.
INSTRUMENT INFORMATION
The Visible and near Infrared Lidar (VIRL) measures the backscatter
cross-sections of cloud and aerosol particles at 1.064 and 2.036 um
and was used in TOGA COARE primarily to profile clouds. The 1.064 um
lidar return is split into signals that are parallel and perpendicular
to the outgoing laser radiation, thereby providing polarization
sensitive data principally for cloud phase detection. The 2 um
measurement was an experimental test of lidar performance and
scattering at that wavelength region. The lidar can be pointed in the
nadir or zenith direction by rotating the telescope. Therefore, it
can measure cloud base heights when flying under clouds and cloud tops
when flying over them. It can also provide vertical profiles of
backscatter cross-section that show extended structure into cirrus and
other thin clouds.
The principal application that was planned for the DC-8 lidar was the
study of radiative heating and cooling rates for tropical cirrus,
especially in the case of dense anvil cirrus. The integrated
attenuated backscatter cross-section, from optically thin to thick
clouds, when plotted against cloud base thermal brightness data, also
acquired from the DC-8, is typically asymptotic. This gives a measure
of effective backscatter-to-extinction ratio and leads to calculation
of cloud base emittance profiles.
The lidar also gathers data on boundary layer heights and aerosol
backscatter cross-sections. From the distribution of cloud base
heights in and around the marine boundary layer, an estimate of the
LCL (Lifting Condensation Level) is obtained. When combined with the
sea surface temperature this may provide a measure of the moisture
content. From the intensity and depolarization of the lidar return,
estimates of cloud density and phase discrimination are possible.
Principles of Operation: The VIRL system is based on a Nd:YAG laser to
produce the 1.064 um signal. The parallel and perpendicular polarized
components of the lidar return are stored in separate channels. An
Optical Parametric Oscillator (OPO) was used to convert the 1.064 um
output of the Nd:YAG laser to generate a pulse around 2 um. The system
employs incoherent signal detection. VIRL has a 12-bit digitizer that
resolves data that varies over 4 orders of magnitude. Linear
amplifiers are used which allow precise resolution of very small
signals. The basic pulse rate of the laser is 50 Hz, but data is
recorded as a sum of 10 shots at 5 Hz. The data system acquired
navigation data (DADS) from the DC-8 in real time and appended it to
each lidar return data record as it was written to 8 mm
tape. Navigation data is processed to account for aircraft banks,
rolls and pitches during turns and climbs. Appropriate altitude
corrections were made and were verified by comparing with the very
large lidar return from the ocean surface when the instrument was
pointing down. A cleaned dataset is available as 1 sec averages which
translates to about 200 m along the flight track. In the vertical
direction, the profiles have a 75-m resolution.
In order to calibrate the data, the 1.064 um return was initially
fitted to a molecular backscatter cross-section profile in a clean
region. A relative target calibration was used to obtain the
backscatter cross-section profiles at 2.036 um, and the calibration
ratio of the parallel and perpendicular channels. In addition to a
hard target (at NASA Ames), an experimental procedure to use the ocean
surface as a target was attempted. An effort is underway to use the
aerosol backscatter component from the perpendicular channel to
generate aerosol cross-sections at 1.064 um for "apparently" clean
cases in the upper troposphere. The effect of the Pinatubo volcanic
eruption was very prominent in zenith viewing data. The enhanced
aerosol backscatter in the stratosphere was very pronounced for the
TOGA COARE observations.
DATA ORGANIZATION
The VIRL data currently comprise two types of files:
a) ASCII data files which contain the cloud boundary information. They
have an approximate volume of 14 MB and file size ranges from 33 K to 1
MB.
b) Associated GIF Images of backscatter cross-section. They have an
approximate volume of 6 MB and a file sizes range from 70 K to 200 K.
ASCII data: In acb93025.f1b "acb" denotes ascii cloud boundary, 93
refers to 1993, 025 refers to the Julian Day when the DC8 flight
originated from Townsville, Australia, and f1b uniquely identifies
each flight segment from that sortie based on when the lidar was
turned on and off. The various parameters which are included in the
acb93XXX.FXX file are indicated by the headers of each column, as
shown in the sample below
-----------SAMPLE CLOUD HEIGHT FILE-FROM ACB93025.F1B------------------------
IV DAY HR MI SE PLNHT G CTOP1 CBOT1 CTOP2 CBOT2 CTOP3 CBOT3 RLAT
2 26 2 17 19 8.705 2 11.975 11.696 17.052 12.183 0.000 0.000 -1.71
2 26 2 17 20 8.705 2 11.981 11.702 17.000 12.121 0.000 0.000 -1.70
SECTION BEYOND COLUMN 80
RLONG PITCH ROLL
151.71 1.70 -21.90
151.71 1.70 -21.60
IV indicates Lidar View (2=UP,1=Down)
DAY is the Julian DAY for that data point
HR MI SEC denote UTC hour, minute, and second
PLNHT is the Plane Height in km above sea-level
G indicates ground stroke and is not relevant for uplooking data
CTOP1, CBOT1, CTOP2, CBOT2, CTOP3, CBOT3 give the heights (km)
of the tops and bottoms of the first 3 cloud layers from the DC8.
RLAT and RLONG provide the decimal latitude and longitude in degrees.
PITCH and ROLL provide the aircraft pitch and roll in degrees.
Image file format: The image file 0260217a.gif displays a
cross-section image of the lidar data. The 026 refers to the JULIAN
DAY at the beginning of that image; 0217 denotes the UTC START TIME of
the image. The duration of the image is evident from the X-Axis which
gives the Elapsed Time in minutes. The START and END TIMES of each
"gif" image are present in the title at the top of the image. In this
case the image is for the entire flight line acb93025.f1b but for
longer flight lines the images are often broken up into shorter
sections. The letter "a" refers to attenuated aerosol backscatter and
is the prevalent type of gif image. In some cases the letter "t" is
used to denote total backscatter cross-section images, while the
number "1" or "2" is used to indicate that only channel 1 (1064 nm
Perpendicular) or channel 2 (1064 nm Parallel) data are displayed. In
any case the legend at the top of each image describes the data type,
location and the duration. It is a good idea to use the image in
conjunction with the cloud boundary file. This is especially
important when there are thick clouds present at or near the plane
altitude. This makes identification of the second and third cloud
layer boundaries more difficult.
Geographic Coverage
Spatial coordinates
| N: 10.0 |
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S: -20.0 |
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E: 180.0 |
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W: 140.0 |
Data Set Citation
Dataset Creator:
TOGA COARE
Dataset Title:
Visible and Near IR Lidar (VIRL) Measurements Taken Onboard the NASA DC-8 During the TOGA COARE Intensive Observing Period
Online Resource:
http://daac.gsfc.nasa.gov/fieldexp/TOGA/
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Temporal Coverage
Start Date:
1993-01-01
Stop Date:
1993-02-28
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Location Keywords
Science Keywords
ISO Topic Category
Platform
Instrument
Project
Ancillary Keywords
Originating Center
Data Center
Distribution
Distribution Media:
On-line
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Personnel
GES DISC HELP DESK SUPPORT GROUP
Role:
TECHNICAL CONTACT
Phone:
301-614-5224
Fax:
301-614-5268
Email:
help-disc at listserv.gsfc.nasa.gov
Contact Address:
Goddard Earth Sciences Data and Information Services Center
Code 610.2
NASA Goddard Space Flight Center
City:
Greenbelt
Province or State:
MD
Postal Code:
20771
Country:
USA
JAMES
D.
SPINHIRNE
Role:
INVESTIGATOR
Phone:
301-614-6274
Email:
James.D.Spinhirne at nasa.gov
Contact Address:
NASA Goddard Space Flight Center
Mailstop 613.1
City:
Greenbelt
Province or State:
MD
Postal Code:
20771
Country:
USA
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Related URL
Link:
GET DATA
Description:
Access the DC8 TOGA COARE VIRL Data.
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Publications/References
Spinhirne, J.D., S. Chudamani and J.F. Cavanaugh, 1991: Visible and
Near IR Lidar Backscatter Observations on the GLOBE Pacific Survey
Missions, Symposium on Meteorological Observations and Instrumentation
and Special Sessions on Laser Atmospheric Studies, J261-J264, American
Meteorological Society.
...
Spinhirne, J.D. and W.D. Hart, 1990: Cirrus Structure and Radiative
Parameters from Airborne Lidar and Spectral Radiometer Observations:
The 28th October 1986 FIRE Study, Monthly Weather Review, V. 118 (11),
2329-2343.
TOGA COARE International Project Office (TCIPO), 1992: TOGA COARE
Operations Plan, Working Version September 1992. University
Corporation for Atmospheric Research, Boulder, CO 80307, 138 pp.
TOGA COARE International Project Office (TCIPO), 1993: TOGA COARE
Intensive Observing Period Operations Summary. University Corporation
for Atmospheric Research, Boulder, CO 80307, 505 pp.
TOGA COARE International Project Office (TCIPO), 1994: Summary Report
of the TOGA COARE International Data Workshop, Toulouse, France, 2 -
11 August 1994, University Corporation for Atmospheric Research,
Boulder, CO 80307, 170 pp.
Webster, P.J., and R. Lukas, 1992: TOGA COARE: The Coupled Ocean-
Atmosphere Response Experiment. Bull. Am. Meteol. Soc. 73, 1377-1416.
World Climate Research Programme (WCRP), 1985: Scientific Plan for the
TOGA Coupled Ocean-Atmosphere Response Experiment. WCRP Publications
Series, No. 3 Addendum, World Meteorological Organization, Geneva, 96 pp.
Creation and Review Dates
Last DIF Revision Date:
2008-12-15
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Links
