The AMMS data are available from the NASA GSFC DAAC via ftp from daac.gsfc.nasa.gov in subdirectory pub/toga_coare/aircraft/nasa_dc8/amms or ftp://disc1.gsfc.nasa.gov/data/toga_coare/aircraft/nasa_dc8/amms. To request data on tape, contact the DAAC ... User Services Office. 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 AMMS instrument, which was mounted on NASA's DC-8 aircraft for the TOGA COARE Field Experiment, is a scanning radiometer that measures brightness temperatures in degrees Kelvin. It was operational during 16 mission flights of the DC-8 between 5 January and 23 February 1993.
The AMMS was designed to profile atmospheric water vapor and was mainly used for this purpose in the past. It is also sensitive to cloud cover and precipitation. Because the weighting functions of its four frequency channels peak at different altitudes, depending on water vapor density and profile, AMMS has the potential of estimating the height of frozen hydrometeors associated with a convective storm. For TOGA COARE the sensor was combined with other radiometers in the same aircraft to measure the radiometric response of convective rainfall systems in the frequency range of 10-183 GHz.
AMMS is a 4-channel, mechanically scanned, imaging microwave radiometer operating at 92, 183.3+/-2, 183.3+/-5, and 183.3+/-9 GHz. It has a 15-cm aperture giving an angular resolution of about 2 degrees at 92 GHz and 1 degree at 183 GHz. After every 6 scans, the beam is directed to view heated (330 K) and cooled (250 K) external calibration targets for 2 seconds each, resulting in a total frame time of approximately 30 seconds (including slewing time). The radiometric signals and the measured physical temperatures from these calibration targets form the basis for the derivation of the scene brightness temperatures. The calibration accuracy is on the order of 1 K in the 250-300 K brightness temperature range. The temperature sensitivity (delta T) of the sensor has gradually deteriorated over the past 10 years. For water vapor profiling, averaging of up to 50 radiometric samples is needed to meet the requirement of delta T of <= 1 K. The microwave signatures from precipitation are much stronger than water vapor at the AMMS frequencies, and data from this sensor will be sufficient to derive important information about the hydrometeors.
The beam is scanned in 50 steps of 1.8 degrees from nominally 45 degrees to the right through nadir, and to 45 degrees to the left with a total scan time of approximately 4 seconds. For TOGA COARE, only the left half of the scan (25 steps, from nadir to the left of the aircraft) is useful because of the geometry of nadir port in which it is mounted in the aircraft.
DATA
One data product consisting of 16 ASCII files of calibrated brightness temperatures in degrees Kelvin was produced by the AMMS instrument during the TOGA COARE Field Experiment. Each file contains data from 1 flight. File size ranges from 2.8 to 4 MB. The total data volume is 55 MB. There are 10 parameters in each file. Latitude, longitude, altitude and aircraft attitude information are not present in these quick-look data files, but may be obtained from the DC-8 DADS dataset, also available on FTP.
NASA TOGA COARE Project Office, 1993: Mission Summary Reports, TOGA COARE. NASA Langley Research Center, Mail Stop 483, Hampton, VA 23666.
NASA TOGA COARE Project Office, 1994: NASA/TOGA COARE Science Data Workshop II Proceedings, Albuquerque, New Mexico, March 15-17, 1994, NASA Langley Research Center, Mail Stop 483, Hampton, VA 23666, 4 pp.
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.
Wang, J.R., and L.A. Chang, 1990: Retrieval of water vapor Profiles from microwave radiometric measurements near 90 and 183 GHz. J. Appl. Meteor., 29(10), 1005-1013.
Wang, J.R., W.C. Boncyk and A.K. Sharma, 1993: Water Vapor Profiling over Ocean Surface from Airborne 80 and 183 GHz Radiometric Measurements Under Clear and Cloudy Conditions IEEE Transactions on Geoscience and Remote Sensing, 31(4), 853-859.
Webster, P.J., and R. Lukas, 1992: TOGA COARE: The Coupled Ocean- Atmosphere Response Experiment. Bull. Am. Meteorol. 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.
