Vaisala Oy

Jan Lonnqvist

Horst Huttmann

The invention relates to an apparatus and method for measuring visibility and present weather. The apparatus includes a light source (1) for directing a light ray toward the object (9) to be measured, a detector (3) for measurement of light which is forward scattered from the object (9), and computing elements (12-15) adapted to differentiate the signal representing the forward scattered light from signals representing stray or ambient light. The apparatus may include a pulsed light source, a receiver (19) for receiving directly backward reflected/scattered light pulses, and computing elements (11) for computing the propagation delays of the different backward reflected components in the received pulse-shaped optical signal.

Apparatus and method for measuring visibility and present weather

The invention concerns a method and device for measuring the meteorological visibility and the scattering of light. A light pulse is emitted into the atmosphere via an optical transmit system, the backscattered light returns via the optical transmit system after which its intensity and delay are measured. The waveform of the optical transmit pulse generated at the instant of its launching from within the apparatus is sensed in a manner that excludes any backscattered light originating from outside the measurement system, this signal is scaled for both its magnitude and phase so as to achieve a suitable feedback signal relative to the actual measurement signal and said feedback signal is subtracted from said measurement signal to avoid overloading of the receiver.

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Espoo, Finland

Jan Lonnqvist