P - R
The Division of Atmospheric Research took part in ARM's TOGA COARE (Tropical Ocean Global Atmosphere/Coupled Ocean Atmosphere Response Experiment.) PROBE experiment at Kavieng, New Guinea (2.5S, 150.8W) in January - February, 1993. This afforded an opportunity to use the new radiometer alongside the CSIRO Mark II radiometer in a direct comparison. The Division's 0.532 m lidar was also used, and the data obtained on cirrus clouds, as well as some altocumulus, will be analyzed with the LIRAD method. The PROBE will also provide excellent radiosonde data every six hours, together with continuous microwave data of water vapour column and cloud liquid water column observations from the National Oceanic and Atmospheric Administrations's (NOAA) Wave Propagation Laboratory (WPL). The water vapour column data will be invaluable in allowing for any variations in water vapour radiance and transmittance at times between radiosonde observations. A preliminary analysis of the data indicates the variability of the cirrus and its considerable geometrical depth at times and also the persistence of the cirrus cover. Particularly interesting was an apparent diurnal variation in both the cirrus cover and the optical depth with a maximum at about midday. The ARM filter radiometer was run for about 70% of the time on the 8.62 m filter; however, for some periods, the radiometer was run with the 10.86 m filter enabling a direct comparison with the Mark II radiometer which used a 10.84 m filter. As the input radiance is chopped against a 40C blackbody, the zero radiance when viewing liquid nitrogen actually gives a large negative signal; whereas, the zero voltage occurs when the input radiance is from a 40C blackbody. The responses of the two radiometers to various clouds are quite evident. The water vapour radiance is large, which is typical for the tropics. Periodically, there are either cirrus radiances or larger cumulus radiances superposed. Also evident is the superior behaviour of the new ARM radiometer. The two radiometer apertures were equal in the comparison; however, the ARM and Mark II time-constants were 1 second and 5 seconds, respectively. By looking at the signal and noise levels during the calibration episodes in! more detail, we calculate the minimum detectable radiances (MDR) of the two instruments as 4.9 x hz-1/2(ARM) and 6.8 X hz-1/2(CSIRO Mark II). Contact: C. Martin Platt (Lead Scientist) mplatt&#64net2000.com.au For more information, link to "http://www.arm.gov/docs/iops/past/afteriop_probe1993.html" [Summary provided by ARM]
PROBE