Airborne Miltichannel Microwave Radiometer (AMMR)

AMMR data on FTP.

1. GENERAL INFORMATION

The AMMR radiometer package was part of the NASA/TOGA COARE Campaign. It was flown onboard the DC-8 between January 12 to February 24, 1994 under the direction of Dr. Jim Wang of NASA Goddard Space Flight Center.

2. Instrument Information

2.1 Instrument Mission and Objectives. AMMR measures thermal microwave emission (in degrees Kelvin of brightness temperature) from surface and atmosphere. For TOGA COARE, the AMMR (with frequencies between 10 and 100 GHz) was used for measurements of hydrometeors associated with tropical convective systems. Radiometers at 18, 21, 37 and 92 GHz are comparable to the frequencies on the Special Sensor for Microwave/Imager (SSM/I) onboard the Defense Meteorological Satellite Program (DMSP) satellite. Where aircraft flights coincide with SSM/I overpasses over the COARE domain, comparisons between satellite and AMMR sensors at different resolutions are proposed to study beam filling effect.

2.2 Instrument Geometry. The AMMR package is made up of AMMR-1 and AMMR-2. AMMR-1 consists of single-beam, microwave radiometers operating at 18.7, 18.7, 21 and 37 GHz, all viewing through a nadir port of the aircraft, therefore withan incidence angle of 0 when the aircraft was on level flight. The two channels at 18.7 GHz should be seeing the same scene and brightness.

AMMR-2 also consists of single-beam, microwave radiometers operating at 10, 21, 37 and 92 GHz. These radiometers were installed in the left windows of the DC-8 aircraft and viewed the scene at an incidence angle of 45 degrees in level flight.

2.3 Principles of Operation. The 37 and 92 GHz radiometers were dual-polarized. Georgia Institute of Technology operated the 92 GHz radiometer and is responsible for the calibration of the data. The 92 GHz data will be included in this AMMR data set when they are submitted to the Goddard DAAC.

The spatial resolution of the data is between 1.5 to 2 Km. The temporal sampling is 1 scan per second. Following are the key components of these sensor assemblies and their characteristics:

3. Data Organization

3.1 General Characteristics. The AMMR instruments were operational for all thirteen mission flights of the DC-8 during the TOGA COARE Campaign yielding twenty six ASCII data files (13 each for AMMR-1 and AMMR-2). The total data volume is 45 MB.

AMMR files are named Adddhhmm.AR1 (for AMMR-1) and Gdddhhmm.AR2 (for AMMR-2) where ddd is the Julian day, hh is the hour, and mm is the minute the instrument was turned on for the flight.

The following table relates ESMR data files to ER-2 and DC-8 flight numbers and dates for the 13 mission flights of the NASA/TOGA COARE campaign. 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.

3.2 Data Format

There are 10 parameters in each file:

• Scan number
• Month
• Day
• Hour
• Minute
• Second
• Brightness temperatures in degrees Kelvin at 18.7 GHz, 18.7 GHz, 21 GHz, and 37 GHz

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 AMMR data files are formatted as follows:

4. Data Access

4.1 AMMR Data Online

AMMR_1 data on FTP.

AMMR_2 data on FTP.

DC-8 DADS data on FTP.

5. Quality Assessment

The calibration of the radiometers is based on pre-flight and post-flight surface measurements by pointing the antennas at a nearly perfect absorber (emissivity ~ 1) at room and liquid nitrogen temperatures and the in-flight ocean surface observation with dropsondes. The radiometric accuracy is estimated to be about +/- 3 K, which is adequate for rain rate measurements.

The data producers consider the second 18.7 GHz channel of AMMR-1 (column 8 of the data file) and the second 10 GHz channel of AMMR-2 (column 8 of the data file) to be sufficiently noisy that they may be disregarded.

The noise threshold for the AMMR is 1 degree Kelvin. Noise saturation did not occur during the TOGA COARE mission.

Radiative transfer calculations were made (using code developed by Colorado State University) with assumed hydrometeor profiles to match the brightness temperatures measured by AMMR (at 20 km), AMMS (at 11 km) and AMMR-1 (at 11 km) over precipitating regions on January 19, 1993. Calculated results matched the measurements well.

6. Points of Contact

 For TOGA COARE user services, please contact: 

	GES DISC User Services 
        Code 610.2, NASA Goddard Space Flight Center 
        Greenbelt, Maryland 20771
GES DISC User Services
	(301) 614-5224

For detailed information on instrument and data, please contact:
        Principal Investigator:  
        James R. Wang
        Code 975, NASA Goddard Space Flight Center
        Greenbelt, MD 20771
wang@sensor.gsfc.nasa.gov
        (301) 614-5655 (voice)
        (301) 614-5558 (FAX) 
     
        Co-Investigator:
        Paul Racette
        Code 975, NASA Goddard Space Flight Center
        Greenbelt, MD 20771
per@meneg.gsfc.nasa.gov
        (301) 286-9114 (voice)
        (301) 286-1762 (Fax)

7. References

NASA/TOGA COARE Science Data Workshop II Proceedings, March 15-17, 1994, FIRE Project Office, NASA Langley Research Center, Mail Stop 483, Hampton, VA 23666.

J. R. Wang and A. Chang, 1990: Retrieval of water vapor profiles from microwave radiometric measurements near 90 and 183 GHz. J. Appl. Meteor., 29(10), 1005-1013.

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