NAMMA DC-8 Dropsonde
Table of Contents
Introduction
The DC-8 dropsonde system uses an integrated, highly accurate, GPS-located atmospheric profiling dropsonde, which measures and records current atmospheric conditions in a vertical column below the aircraft. The dropsonde, also known as dropwindsonde or parachute radiosonde, is a small, lightweight (less than 1 lb) cylindrical instrument that falls freely through the atmosphere, slowed somewhat by a small inflatable parachute. This type of instrument offers atmospheric researchers a complete solution for accurate in-situ measurement of the atmosphere.
A unique square-cone parachute is used to reduce the initial shock load and to slow and stabilize the descending dropsonde. The parachute is deployed immediately on exit from the launch chute and takes about five seconds to be filled by ram-air. The square-cone parachute is very stable during the descent, reducing or eliminating any pendulum motion of the dropsonde.
Once deployed, the launch crew does not expect to see the instrument again. The cost of recovering a dropsonde would likely exceed its value. Also, since they are mostly launched over water, the probability of finding them would be low.
Additional information about dropsondes can be found here: http://www.eol.ucar.edu/rtf/facilities/dropsonde/ and here: http://www.vaisala.com/weather/products/dropsonde.html.
Campaign
These data files were generated during support of the NASA African Monsoon Multidisciplinary Analyses (NAMMA) campaign, a field research investigation sponsored by the Science Mission Directorate of the National Aeronautics and Space Administration (NASA). This mission was based in the Cape Verde Islands, 350 miles off the coast of Senegal in west Africa. Commencing in August 2006, NASA scientists employed surface observation networks and aircraft to characterize the evolution and structure of African Easterly Waves (AEWs) and Mesoscale Convective Systems over continental western Africa, and their associated impacts on regional water and energy budgets. For more information about the NAMMA Campaign, go to the NAMMA web site: http://namma.nsstc.nasa.gov/
Instrument Description
The dropsonde instrument is ejected from a tube in the underside of the DC8 aircraft. As the dropsonde floats to the surface on a parachute, it continuously measures and transmits via a 400 MHz meteorological band telemetry link, pressure, temperature and relative humidity, as well as GPS-based wind formation data, to the receiving system onboard the aircraft. Sensitive atmospheric sensors and computer electronics inside the dropsonde can measure changes in temperature to within 0.2 deg C, 2% variations in moisture, and wind speeds to within 0.5 m/s. The winds are computed using the Global Positioning System (GPS) and thus the dropsonde also contains a special antenna to track the progress of these satellites. The dropsonde is designed and manufactured through a partnership between the National Center for Atmospheric Research (NCAR) and Vaisala, Inc.
During the NAMMA field campaign two different versions of the dropsonde were used. The Rev.D dropsonde, also referred to as GPS121, is an older version. The newer Rev. F version dropsonde uses a GPS receiver based upon u-Blox GPS receiver technology. It is a full up code correlating receiver providing a 12 channel receiver with significant improved tracking performance and reliability over the previous codeless GPS receiver used in the Rev D dropsonde. The new GPS receiver module also provides superior latitude, longitude, and altitude information.
File naming convention
There are three files associated with each dropsonde released during the experiment:
- EOL format data files
- World Meteorological Organization (WMO) code files
- Image files
These files are named respectively, following the GHRC naming convention:
NAMMA_DROP_yyyymmdd_nnnnnn_PQC.eol
NAMMA_DROP_yyyymmdd_nnnnnn_P.txt
NAMMA_DROP_yyyymmdd_nnnnnn_P.png
where,
yyyymmdd = year, month and day
nnnnnn = the dropsonde sequence number
P = preliminary
QC = quality controlled
eol = data file in eol format
txt = WMO code file
png = plotted image
Data Format
Quality Controlled Data Files
These data files are in a new "EOL file format", which is similar to the "CLASS format" that has been used in the past, but improved to include a revised header with more detailed sounding information. Section III of the NAMMA dropsonde readme file describes this new EOL file format in detail, and can been found here: ftp://ghrc.nsstc.nasa.gov/pub/doc/namma/namdrop/readme.NAMMA2006.radiosondes.pdf
WMO Code Files
These files contain the coded temp drop code, and are in the format specified by the World Meteorological Organization. Decode information can be found at this hurricane hunter's web location, http://www.hurricanehunters.com/, or in this word document: ftp://ghrc.nsstc.nasa.gov/pub/doc/namma/namdrop/TEMP_DROP_CODE.doc
Figure 1 below is a sample temp drop (WMO) file.
UZNT13 KNHC 072009
XXAA 57202 99473 70900 15470 99001 19259 19008 00010 19259 19508
92675 14861 27002 85384 09856 34517 70973 03872 34030 50564 11569
30543 40732 21982 29544 30936 38369 29057 25059 46370 28080 20205
529// 28597 88999 66197 28598 418//
31313 09608 81949
61616 AF001 WXWXA TRAIN OB 99
62626 SPL 4723N08983W 2002 MBL WND 18007 AEV 20605 DLM WND 30032
001217 WL150 19507 075 =
XXBB 57208 99473 70900 15470 00001 19259 11944 15862 22850 09856
33818 07857 44807 07664 55754 03262 66743 04667 77689 04288 88594
01381 99471 14770 11426 17985 22375 25180 33296 38569 44293 40369
55243 47970 66224 513// 77212 505// 88197 533//
21212 00001 19008 11922 28502 22889 34510 33850 34517 44814 35016
55795 33514 66742 35022 77655 32534 88358 29047 99197 28598
31313 09608 81949
61616 AF001 WXWXA TRAIN OB 99
62626 SPL 4723N08983W 2002 MBL WND 18007 AEV 20605 DLM WND 30032
001217 WL150 19507 075 =
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Figure 1
Image Files
These image files are skew-T diagrams in PNG format. They show the temperature, dewpoint, and vertical wind profiles measured during the flight of the dropsonde. Date, time of release, and mission ID are given in the title of the image. Figure 2 below is an example of one of the skew-T diagrams.
Figure 2
Contact Information
The data producer is:
Gerald Heymsfield
NASA Goddard Space Flight Center
Greenbelt, MD 20771
heymsfield@agnes.gsfc.nasa.gov
To order these data or for further information, please contact:
Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: support-ghrc@earthdata.nasa.gov
Web: http://ghrc.nsstc.nasa.gov/
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