Microwave radiometric sensing of the marine boundary layer


  • C. I. Beard,

  • L. U. Martin


An experiment performed 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° beam width antennas. This has resulted in the first observation and correlation between radiometer beams of short-period (i.e., 1 to 2 min), Kelvin-Helmholtz waves. In addition, during unchanging synoptic conditions, the radiometers would follow changes in the height of the inversion base with an average sensitivity of 25 m/K. Using an atmospheric “quiet period” to determine the radiometer noise level, the resulting vertical resolution of the radiometer is shown to be approximately ±1 m, comparable to active sensors. The observed sensitivities were found to be unaffected by the presence of stratus clouds beneath the inversion. A 5.5-hour train of 10- to 11-min period waves on 19 June 1976 showed recurring internal (gravity) wave propagation from three or four directions. The corresponding radiometer undulations shifted time-phase 180° with the microbarograph surface pressure undulations when the direction of wave propagation changed. Calculation of wave phase velocities based on meteorological soundings favor second-mode wave propagation, in agreement with the observed wave velocities and microbarograph periodicities.