Its short history

Radar was developed in the 1940s for the detection of aircraft, and the effects of precipitation on the received signal were originally seen as an inconvenient source of interference. However, even in the late 1940s it was recognised that radar could be used to measure precipitation. Kurtyka (1953) remarked that ‘In the last five years, the necessity of adequate precipitation instruments to calibrate radar for precipitation measurement has pointed to the primitiveness of the present-day rain gauge.’ He went on to say that ‘In all likelihood, the rain gauge of the future may be radar, for even in its present developmental stage, radar measures rainfall more accurately than a network of one rain gauge per 200 square miles.’ But radar has not replaced raingauges, and while it has advanced greatly over the years, it still relies on in situ data from telemetering raingauges to calibrate the system, although this need may eventually be overcome.

Principle of operation

One of the great advantages of radar is that it gives an areal estimate of precipitation rather than a single-point measurement, and the area covered is quite large, typically about 15,000 km2 for each station. It also has the advantages of giving data in real time and of not needing anything to be installed in the area, or even access to the area.

In a weather radar system, the dish alternately transmits a pulse of microwaves and then switches to receive the returned (or more correctly ‘scattered’) pulse.