A sensing device includes a piezoelectric vibration sensor mounted to a surface for producing an analog signal proportional to raindrops striking the surface, an amplifier, an analog-to-digital converter, and a processor for calculating the rain rate based on an exponential probability density function...http://www.google.com/patents/US6936985?utm_source=gb-gplus-sharePatent US6936985 - Sensing device for determining a rain rate
