Friday, 8 August 2003: 5:30 PM
Requirements Analysis for Snowfall Measurements over Canada from Space
The Global Precipitation Mission (GPM) is a proposed follow-on mission to the Tropical Rainfall Measurement Mission (TRMM) with a launch date of 2008. It is a joint NASA-NASDA mission which will include high frequency radiometers and dual frequency active radar (14GHz, 35GHZ) in addition to the TRMM instrument package. Using the passive microwave instruments, GPM will provide coverage up to 83o latitude compared to the 40o limit of TRMM and will provide near-global coverage of precipitation with a 3 hour update at high spatial resolution. The GPM radars are used for algorithm development and validation. They have a sensitivity of around 17 dBZ or about 0.4 mm/h of water equivalent. ESA is proposing to participate in GPM through the contribution of a satellite with microwave radiometers. Preliminary climatological analysis of surface snow fall measurements and vertical profiles of radar data was conducted for Canada to determine the radar specifications and indicate the need for much greater sensitivity. Analysis of surface snowfall measurements indicate that light precipitation (below ~0.5 mm/h water equivalent) contributes substantially to the total precipitation in Canada and that this contribution roughly increases with latitude. Analyses of vertical profiles of reflectivity provide greater precision to this estimate and support that conclusion. It also indicates that a blind layer of 500 meters is tolerable. The analysis also provides information on the distribution of snowfall with reflectivity and shows that the probability distribution of occurrence is highly skewed. As a result, the Canadian Space Agency is considering a proposal to jointly fund the development of high sensitivity 35GHZ radar to fly on the ESA satellite. The proposal is to add the ESA option of a 35 GHz radar with a sensitivity of around 0 dBZ using available radar technology in Canada. The paper will describe the snowfall measurement requirements analysis for precipitation measurements in Canada.