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 January 5 and February 23, 1993 under the direction of Principal Investigator Jim Wang of NASA/Goddard Space Flight Center.
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, 174, 178 and 181 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 ~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 averaged over a few samples 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 ~4 seconds.
3.1 General Characteristics 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 1 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 data set, also available on FTP (See Section 4, DATA ACCESS).
The files are named Fdddhhmm where ddd is the Julian day, hh is the hour and mm is the minute when the instrument began recording.
The following table relates AMMS data files to ER-2 and DC-8 flight numbers and dates for the 13 mission flights of the NASA/TOGA COARE campaign. The AMMS data set contains two files (F0041728 and F0051913) that were generated on ferry flights to Townsville and hence are not included in the table. The objectives column is included for the convenience of the user; the mission objective defaulted to Radiation unless Convection was forecast in the target area.
| Date(UTC) | ER-2 Flight | DC-8 Flight | AMMS File | Objective |
|---|---|---|---|---|
| Jan 11-12 | 93-053 | 93-01-06 | F0112041 | Radiation |
| Jan 17-18 | 93-054 | 93-01-07 | F0172208 | Convection |
| Jan 18-19 | 93-055 | 93-01-08 | F0191245 | Convection |
| Jan 25-26 | 93-056 | 93-01-09 | F0252226 | Radiation |
| jan 31-Feb 1 | 93-057 | 93-01-10 | F0312107 | Radiation |
| Feb 4 | 93-060 | 93-01-11 | F0350139 | Convection |
| Feb 6 | 93-01-12 | F0371331 | Convection | |
| Feb 7 | 93-061 | |||
| Feb 8-9 | 93-062 | 93-01-13 | F0391722 | Convection |
| Feb 10-11 | 93-063 | 93-01-14 | F0411759 | Convection |
| F0420049 | ||||
| Feb 17-18 | 93-01-15 | F0481750 | Convection | |
| Feb 20-21 | 93-065 | 93-01-16 | F0511810 | Convection |
| Feb 22-23 | 93-066 | 93-01-17 | F0531812 | Convection |
| Feb 23-24 | 93-067 | 93-01-18 | F0541909 | Radiation |
3.2 Data Format
The data files are formatted as follows:
4.1 AMMS Data Online
5.1.1 Times. All times are in UTC. The instrument clock was synchronized with the aircraft clock at the beginning of each flight.
5.1.2 Geo-referencing information was acquired from the aircraft's DADS system.
5.2 Noise. The noise threshold for this instrument is 4 Kelvin. Saturation did not occur during this campaign.
5.3 Calibration. 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 ~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 in 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.
For NASA/TOGA COARE user services, please contact:
AMMS data on
FTP.
Pat Hrubiak
EOS Distributed Active Archive Center(DAAC)
Code 610.2
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
Internet: hrubiak@disc.gsfc.nasa.gov
(301) 614-5165 (voice)
(301) 614-5268 (Fax)
For detailed information about the sensor or data, please contact
Principal Investigator:
James R. Wang
Code 975
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Internet: wang@sensor.gsfc.nasa.gov
(301) 286-8949 (voice)
(301) 286-1761 (FAX)
Co-Investigator:
Paul Racette
Code 975
NASA Goddard Space Flight Center
Greenbelt, MD 20771
(301) 286-9114 (voice)
NASA/TOGA COARE Science Data Workshop II Proceedings, March 15-17, 1994, page 4.
J. R. Wang 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.
J.R. Wang, 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.
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