Sodar and RASS

Vertical profiles of the wind speed, turbulence components, and the temperature in the lower regions of the atmospheric boundary layer can be determined by performing active acoustic and radioacoustic sounding with ground-based devices. This chapter introduces two types of instruments — sound detection and ranging (sodar) devices and radioacoustic sounding systems (RASS) — that can be used to carry out such measurements. While sodars can provide quantitative vertical wind and turbulence profiles and qualitative mixed-layer height and inversion height data, RASS can provide that as well as quantitative temperature profiles. Both types of instruments have a typical height range of several hundreds of meters, and their vertical resolution is on the order of 20m.