Patent ID: 7122820
Filing Date: 2006-10-17
Classification: G01N

Abstract:
1. A method for determining visibility, amount of precipitation and type of precipitation comprising the steps of: illuminating a defined spatial area by using an intensity modulated light transmitter of selected wavelength and adapted intensity; receiving light which is scattered by aerosol conglomeration and, in the case of precipitation, additionally by single precipitation particles of liquid or non-liquid types from an angle range of 20° to 40° to a radiation axis of the light transmitter by a light receiver in a suitable visual field, in a narrow band and with adapted sensitivity for creating a first reception signal, whereas spatial overlap of a viewing field of the light receiver and a light transmitter beam defines a measurement volume MV; receiving light which is scattered by aerosol conglomeration and, in the case of precipitation, additionally by single precipitation particles of the liquid or non-liquid types from an angle range of 70° to 120° to the radiation axis of the light transmitter by a light receiver in the suitable visual field in a narrow band and with adapted sensitivity for creating a second reception signal, whereas spatial overlap of the light receiver viewing field and the light transmitter beam defines a measurement volume which is similar to the measurement volume MV; detecting precipitation particles which are passing the measurement volume MV by evaluating the first reception signal which derived from light which is obtained at 20° to 40° to the radiation axis of the light transmitter, said first reception signal having a mean value and a spontaneous value, in such a way that the mean value of said first reception signal is compared to the spontaneous value of the first reception signal, and a corresponding particle detection signal is given to a processing unit, as long as the spontaneous value of the reception signal exceeds the mean value of the first reception signal; determining a dwell time of each detected precipitation particle in the measurement volume MV by the processing unit utilizing the duration of the particle detection signal; determining a maximum signal value Amax( determining a signal average Aav( determining a maximum signal value Amax( determining an extinction component which is not caused by precipitation based on the signal average Aav( determining whether a detected precipitation particle is of liquid or non-liquid type based on comparison of Amax(