Balloon-Borne Radio Altimeter

This work describes an accurate pulse radar altimeter which is simple and light enough to be carried aloft by a regular sounding balloon. The altimeter uses a single superregenerative stage serving as both the receiver and the transmitter. This stage is used in a feedback system in such a way that the period between transmitted pulses is a measure of altitude. The relatively slow rate of change of altitude allows the averaging of many returns with corresponding improvement in signal-to-noise ratio. Accurate geometric altitude of a meteorological balloon can improve atmospheric sounding. It can also replace either temperature or pressure measurements through the use of the hydrostatic equation. Geometric altitude is essential in floating superpressure balloons, where, together with a pressure measurement, it yields the necessary reference pressure. Analysis of the altimeter and details of the instrumentation are given, along with results of flight tests. Altitudes up to 20 km were measured in balloon flight tests over Lake Michigan. At midrange, the rms value of the random error was smaller than 0.07 percent. Height readings were available every 2 seconds during both the ascent and descent of the balloon payload. The peak power of the altimeter was one watt.