Vogel, J. L. | Search NASA

NASA NTRS1981

Sampling problems

Precipitation estimates from satellites are subject to a number of uncertainties involving design characteristics, satellite positioning, natural variability of precipitation, and the noncontinuous acquisition of data. The sources and sizes of these uncertainties are in need of proper evaluation and estimation. The present sampling and estima-theory seems to be adequate for some measurement problems (e.g., determining precipitation at a point), while others require further theoretical work (e.g., determining the time history of precipitation over large areas).

Flueck, J. A.↗

NASA NTRS1981

Raingage network sampling statistics

Sampling problems raise large difficulties for the precipitation measurements from space. In the tropics rainfall processes are organized in scales which are hardly resolved by the microwave radiometers on board of satellites. Even in the cloud clusters, which mark significant, large extended signals in the visible and infrared images, the precipitation areas cover only a small region. Our analysis of the cloud clusters over the W Pacific Ocean revealed that more than 50% of the area of a typical Western Pacific cluster are without rain. The radar observations during GATE generally confirmed those results. The rainfall was calculated from Nimbus V microwave data at 19.35 GHz and the results were compared with the GATE radar rainfall. The results are improved if the rain areas within the field of view are determined by additional observations and lead to a correction of the microwave brightness temperature.

Vogel, J. L.↗