Precipitation, such as rain, hail, fog, or snowfall, may be detected by radar. For example, in meteorology, the intensity of precipitation may be determined via radar, in that a directed antenna emits electromagnetic radiation in the form of a pulse in the microwave range. A radar system that emits radar beams having a wavelength of approximately 3 to 10 cm may be used for this purpose. If the radiation strikes a particle in the atmosphere whose diameter is larger than approximately 0.2 mm, the radiation is reflected by it. The wavelength of the radiation does not change in the process. Part of this radiation is detected by a radar receiver and the reflectivity is measured. If certain assumptions are made about the particle and drop size distribution of the precipitation respectively, it is possible to calculate the intensity of the precipitation from the reflectivity. Then a conversion takes place using a so-called Z-R relationship, Z standing for reflectivity and R for the intensity of the precipitation.
International Patent Application No. WO 1993002370 A1 describes a method for detecting rain. In this instance, multiple radar signals are emitted. Backscattered signals are received in order to generate a Doppler spectrum. A reduced amplitude in the Doppler spectrum, in particular in the regions near the edges of the spectrum, indicates rain.
European Patent No. EP 1229348 describes a system for detecting rain or hail using a weather radar. For that purpose, different standard deviation and reradiation intensity cards are combined with one another.
Japanese Patent No. 07248380 describes a device for correcting a calculated rain intensity in conjunction with a radar.
Japanese Patent No. JP 10048333 A describes a radar device that detects snowfall or rain by receiving a reflected signal and measuring its level.