AMMS
The Advanced Microwave Moisture Sounder (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 secon ds (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. Additional information available at "http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/TOGA/amms.html" [Summary provided by NASA]
Profilers/Sounders