<title>Passive millimeter- and submillimeter-wave imaging for atmospheric research</title>

Abstract

In recent years there has been considerable advancement in millimeter and submillimeter wave radiometry applied to atmospheric remote sensing. Contributing to this advancement are the measurements made by the Millimeter-wave Imaging Radiometer (MIR) and subsequent analysis of the data. The MIR is an imaging radiometer designed to fly aboard the National Aeronautics and Space Administration's (NASA) ER-2 high altitude aircraft with nine frequency channels between 89 and 325 GHz. Since its maiden flight in May 1992, the MIR has flown over 80 sorties comprising more than 300 flight hours. In addition, the instrument has participated in several ground-based experiments yielding hundreds of hours of data. The MIR data have been used for comparing atmospheric water vapor profiles derived from different measuring techniques. Images of the atmosphere reveal these frequencies are sensitive to the presence of liquid and ice clouds; analysis of the data suggests that characteristics of the clouds may be extracted from the data. The instrument has been used to support calibration and validation studies of satellite sensors. Analysis indicates ground-based radiometric observations near the 183 GHz water vapor absorption line may be useful for obtaining accurate ground-based measurements of low values (less than 1.0 cm) of precipital water vapor. This paper describes the application and utility of millimeter and sub-millimeter wave radiometric imaging for atmospheric research in the context of accomplishments attained with the MIR.