C Kidd

Algorithms for the Retrieval of Rainfall from Passive Microwave Measurements.

The retrieval of rainfall intensity from radiances measured by spaceborne microwave radiometers can be understood in terms of well established physics. At frequencies below about 40 GHz over an ocean background the relationship between the rainfall and the observations is particularly well understood. In this part of the spectrum, the radiances are principally determined by the liquid hydrometeors with only a modest amount of ambiguity. In very intense convection, ice aloft may increase this ambiguity somewhat. At high frequencies, such as the 85.5 GHz channel of the SSM/I, scattering by the frozen hydrometeors becomes more significant and quantitative rainfall retrieval becomes more problematic. In spite of the ambiguities, the use of the higher frequencies is desirable on a number of counts including: applicability over land, spatial resolution and dynamic range. n nA total of 16 algorithms were submitted for the PIP‐1. These include algorithms that are based on high frequency (scattering) measurements and low frequency (emission) measurements with a few combinations and variations on these themes. The calibration of the algorithms varies from mostly empirical to essentially first principles with most falling somewhere in‐between. All of the algorithms retrieved rainfall and one also retrieved a profile of the liquid and frozen hydrometeors.

Daily Precipitation over Southern Africa: A New Resource for Climate Studies

This paper describes a new high-resolution multiplatform multisensor satellite rainfall product for southern Africa covering the period 1993–2002. The microwave infrared rainfall algorithm (MIRA) employed to generate the rainfall estimates combines high spatial and temporal resolution Meteosat infrared data with infrequent Special Sensor Microwave Imager (SSM/I) overpasses. A transfer function relating Meteosat thermal infrared cloud brightness temperatures to SSM/I rainfall estimates is derived using collocated data from the two instruments and then applied to the full coverage of the Meteosat data. An extensive continental-scale validation against synoptic station data of both the daily MIRA precipitation product and a normalized geostationary IR-only Geostationary Operational Environmental Satellite (GOES) precipitation index (GPI) demonstrates a consistent advantage using the former over the latter for rain delineation. Potential uses for the resulting high-resolution daily rainfall dataset are discussed.

A new instrument with rainfall monitoring potential

Abstract The new Special Sensor Microwave Imager (SSM/I) is introduced, and its global data acquisition pattern illustrated. Through an image for the morning of 29 July 1987 covering north-western Europe in general, and southern Britain in particular, its rainfall monitoring potential is illustrated and explained. An initial comparison with digital outputs from the FRONTIERS radar system of the U.K. Meteorological Office is presented, revealing very promising spatial correspondences between SSM/I and radar-derived rain areas.

The first WetNet Precipitation Intercomparison Project (PIP-1): reflections on the results

The First (algorithm Intercomparison Project) (PIP-1) was organised by the Precipitation Working Group of the NASA-led WetNet Project. Focussed on the months of August, September, October, November 1987, results from passive microwave (MW) infrared (IR), and combined MW and IR imagery, MW soundings, a numerical weather prediction (NWP) model and surface raingauge data sets were intercompared. This paper summarises the results, reflects on them, and reaches concluding recommendations for subsequent activities of similar and supporting kinds.

Microwave monitoring of rainfall: results and implications of radar/satellite studies over southern England

This paper begins with a review of present passive microwave satellite algorithms, and remarks on their perceived strengths and weaknesses. It continues with a report of studies undertaken between SSM/I data and digital multiparameter radar observations of precipitation, over parts of southern England.