This radiometer is a new device capable of measuring profiles of temperature, water vapor and liquid water (at more limited vertical resolution) at time intervals of about 10 min. Profiles can be determined to about 10 km AGL, and vertical resolution of the measurements is greatest at low levels. Detailed information on its capabilities and accuracy is documented in Soldheim and Godwin (1998) and Soldheim et al (1998); additional information and examples are available at the Radiometrics Web Site. The 12 channel radiometer measures atmospheric emissions around the water vapor absorption band (5 channels, 22-30 GHz) and the oxygen absorption band (7 channels, 51-59 GHz). The measured brightness temperatures are converted to temperature and water vapor using neural network techniques described in Solheim et al (1998). The system has a mirror that cycles through a tip cycle of selectable elevation angles to calibrate the water vapor measurements and enhance vertical resolution of T and rv. The vertical resolution is proportional to height; thus the atmosphere is sampled at best resolution below several kilometers within and just above the boundary layer. The system also includes an infrared pyranometer that measures cloud base temperature down to -60 C. For uniform cloud layers, this capability extends the cloud base coverage of the ceilometer (7.5 km) to -60 °C for typical late spring to early summer temperature profiles. For temperature profiling, radiation intensity is measured at points along the low-frequency side (51-59 GHz) of the oxygen absorption band centered near 60 GHz. By scanning in downward in frequency from the center, where the opacity is greatest, low level temperature information is estimated. Higher temperature levels are obtained by stepping down in frequency from the peak in the oxygen band. Water vapor profiles are obtained in a similar fashion using the water vapor absorption band near 22 GHz. In this case, the radiometer tunes the 22-30 GHZ range to determine water vapor profiles. Limited resolution cloud liquid water profiles are obtained by taking advantage of the asymmetry in liquid water absorption centered near 60 GHz. Cloud water, if present, contributes more to the 60-75 GHz frequency side than to the 45-60 GHz low frequency side. The system also includes surface meteorological sensors that measure surface temperature, relative humidity and pressure. To improve measurements of water vapor and cloud water density profiles, cloud base temperature (and hence altitude) information is obtained with an infrared pyranometer. (Recall that the MIPS will also derive cloud base altitude from the lidar ceilometer.) The radiometer is controlled by a microprocessor and firmware, which are in turn controlled via RS232 ports by FORTRAN software on a portable notebook computer. The RS232 link also allows remote control and data archival by a modem and local network. Archived data includes profiles of T, rv and rc, and brightness temperatures for each channel.