Quantitative Precipitation Estimates
The degree to which a radar can detect precipitation targets depends upon a variety of factors. Most important are:
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Radar characteristics
- Distance from radar to precipitation
- Atmospheric conditions
- Target characteristics - Radar Reflectivity
- Particle size (diameter)
- Particle concentration (number per m3)
- State (frozen, liquid or mixture)
- Shape (round, flat, elongated)
- Particle size (diameter)
Because the atmosphere is a dynamic target, comprising innumerable possibilities of characteristic variations, radar reflectivity values received must be based on several assumptions.
Radar characteristics are known, and their effects upon returned signal strength from a precipitation echo will be examined. Additionally, the effect of target range on returned signal strength is known and will be discussed.
The big unknown for a radar operator concerns the precise characteristics of the precipitation target itself. What is the particle size distribution, and how does that affect the degree of backscatter? How much of the precipitation is in a frozen state? The radar operator needs to be aware of the assumptions made concerning these factors since displayed reflectivity levels and derived precipitation intensities are based to a large degree, on these assumptions.