Microwave radiometric sensing of the marine boundary layer

An experiment in 1975 demonstrated that 22 GHz microwave radiometers could detect, and localize in altitude, long-period (3-15 min) internal gravity waves on low-level atmospheric inversion layers. A second experiment in June 1976 examined atmospheric structure in finer detail by using two 3 deg beamwidth antennas. This has resulted in the first observation and correlation between microwave radiometer beams of short-period (1-2 min), Kelvin-Helmholtz waves. In addition, during slowly varying synoptic conditions, the radiometers followed changes in the height of the inversion base with an average sensitivity of 25 m/deg K. Using an atmospheric quiet period to determine the radiometer noise level, the resulting vertical resolution of the radiometer is shown to be approximately + or - 1 meter, comparable to active sensors. The observed sensitivities were unaffected by the presence of stratus clouds beneath the inversion. On 19 June 1976, a 5.5 hour sequence of 10 to 11-minute period waves showed recurring internal (gravity) wave propagation from 3 to 4 directions. The corresponding radiometer undulations shifted time-phase 180 deg with the microbarograph surface pressure undulations when the direction of wave propagation changed. Calculation of wave phase velocities based on meteorological soundings favor 2d mode wave propagation, in agreement with the observed wave velocities and microbarograph periodicities.