Radio Acoustic Sounding Systems (RASS) are remote-sensing systems for the measurement of the temperature profile in the (lower) atmosphere. The RASS system uses backscattering of radio waves from an acoustic wave front to measure the speed of sound at various heights above the ground. From the speed of sound, the temperature of the air in the planetary boundary layer can be computed. These are used in conjunction with wind profiler instruments (see link to wind profiler instrument record for details on those instruments).