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Development, Test and Evaluation of an Automated Present Weather Observing System.

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Final rept. 26 May 83-24 May 86,

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A need exists for an Automated Present Weather Sensor APWOS for use at unmanned weather stations, or stations that are not manned on a round-the-clock basis. An APWOS has been developed by HSS Inc which utilizes a microprocessor to expand the measurement capabilities of a Model VR-301 Visibility Meter. The VR-301 is a forward-scatter nephelometer with a sample volume of 400 cu. cm. The size and velocity of each particle of precipitation passing through the sample volume is measured and stored in a precipitation recognition matrix which has 20 size increments and 16 velocity inrcrements. The various types of precipitation rain, snow, drizzle, hail, etc. are identified by pattern recognition algorithms based on the sizevelocity distribution of particles. Amount of precipitation is determined from the size and number of particles passing through the sample volume in the sample time interval. The APWOS is 10 times more sensitive than a tipping bucket rain gauge, and a linear response to rain-rates up to 6 inches per hour has been demonstrated. The measuring precision is 0.001 inhr for rain and 0.0001 inhr for snow. Current algorithms identify rain as rain 98.8 of the time and snow as snow 92.4 of the time in the ambiguous temperature between 23 F. and 41 F. The APWOS also measures visual range and can determine the presence of fog during any form of precipitation.

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  • Meteorology

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