Research and Development Studies for a Low-Level Free-Air Velocity Measuring System

This report describes the development effort involved in creating an instrument capable of measuring the speed (0 to 50 fps) and direction of an air-flow vector at any selected point ranging from 0 to 1000 ft above the earth's surface. The sensitive instrument element was an electrically heated thermistor rod producing an electrical signal variation as a result of the convective cooling action of the measured air flow. The electrical signal from the elevated instrument station was conveyed to the ground readout station by a transmission cable. The instrument was stably supported and selectively positioned in the air flow by a tethered kite-type balloon. The development resulted in a complete and practical field measuring instrument having good accuracy and response.