Tuesday, 11 January 2005
Detection of arctic cloud ice properties using submillimeter-wave radiometers
Radiometric brightness temperatures near 20 and 31 GHz have been used operationally for several years to retrieve integrated vapor water and cloud liquid water path. Theoretical studies indicate that radiometric brightness temperatures at submillimeter wavelengths may be sensitive to ice within clouds, suggesting the possibility of retrieving integrated ice water path. During the recent Arctic Winter Water Vapor Intensive Operating Period 2004 (WVIOP'04) campaign, the Ground-based Scanning Radiometer (GSR) of the NOAA/Environmental Technology Laboratory was deployed in Barrow, Alaska. The GSR is a multi-frequency scanning spectrometer operating at radiometric bands ranging from 50 to 380 GHz, with eleven channels in the 50-56 GHz oxygen band, dual linearly polarized channels at 89 and 340 GHz, seven channels around the 183.31 GHz water vapor absorption line, and three channels around the 380.20 GHz water vapor line. The main goal of the WVIOP'04 experiment was to demonstrate the capability of millimeter wavelength radiometers to improve water vapor observations during the Arctic winter. One of the secondary goals included evaluation of the sensitivity of millimeter-wave window channels to Arctic clouds. A 340 GHz radiometer was one of the operating channels used to determine the potential for discrimination between liquid and ice clouds using polarimetry. Based on active data from the cloud radar and lidar, case studies of the GSR zenith brightness temperatures were analyzed over the periods when mixed-phase clouds and ice clouds were present. By using estimates of ice water path (IWP) from the 35 GHz radar retrievals, the sensitivity of several millimeter and submillimeter-wavelength channels to IWP is presented.
Supplementary URL: http://www.etl.noaa.gov/technology/gsr/