Observation stations within the RASS station network transmit their observations in the form of a RASS message. The RASS network 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.Hourly observations from around 120 stations distributed globally, and the report is transmitted at 6-hourly intervals at the standard hours of observation which are: 0000, 0600, 1200, and 1800 UTC. The RASS message contains measurements of parameters such as wind speed and temperature.