An ultrasonic ranging and data telemetry system determines a surveyor's position and automatically links it with other simultaneously taken survey data. An ultrasonic and radio frequency (rf) transmitter are carried by the surveyor in a backpack. The surveyor's position is determined by calculations...http://www.google.es/patents/US4924450?utm_source=gb-gplus-sharePatente US4924450 - Ultrasonic ranging and data telemetry system
