New High-Frequency Microwave Radiometer Provides Improved Sensitivity

Published: 31 October 2006

A microwave radiometer (MWR) is essentially a sensitive microwave receiver that is tuned to measure the microwave emissions of vapor and liquid water molecules in the atmosphere at specific frequencies. All of the ARM sites include a 2-channel MWR operating at 23.8 and 31.4 GHz as part of their measurement suite. On October 18, a new high-frequency MWR (MWRHF) was deployed at the ARM Southern Great Plains (SGP) site’s Central Facility. Operating at frequencies of 90 and 150 GHz, measurements from the new radiometer are more sensitive to the presence of liquid water than the currently deployed MWRs. By combining measurements from the both instruments, more accurate estimates of the amount of liquid water (i.e., the liquid water path or LWP) in thin clouds can be obtained than can be achieved using the 2-channel MWR alone. Accurate measurements of LWP are necessary to accurately model the contributions of thin clouds to radiative feedback processes.

A representative from Radiometer Physics, Gmbh (the instrument manufacturer in Meckenheim, Germany) traveled to the SGP site to direct the installation of the new radiometer, carry out its initial calibration, and provide training on its operation and maintenance to the instrument mentor and local operations staff. Once the radiometer completes acceptance testing and evaluation at the SGP site, it will be deployed at the ARM North Slope of Alaska site in Barrow, Alaska, where thin clouds are prevalent. A second MWRHF is planned for deployment with the ARM Mobile Facility during the Convective and Orographic Precipitation Study (COPS) to be held in Germany in 2007.