Infrared propagation in the air-sea boundary layer
Abstract
Over the oceans and other large bodies of water the structure of the lowest layers of the atmosphere is often strongly modified by evaporation of water vapor from the water surface. At radio wavelengths this layer will usually be strongly refracting or ducting, and the layer is commonly known as the evaporation duct. However, the refractive index of air at infrared wavelengths differs from that at radio wavelengths, and the effects of the marine boundary layer on the propagation of infrared radiation are examined. Meteorological models of the air-sea boundary layer are used to compute vertical profiles of temperature and water-vapor pressure. From these are derived profiles of atmospheric refractive index at radio wavelengths and at infrared wavelengths in the window regions of low absorption. For duct propagation to occur it is necessary that the refractivity of air decreases rapidly with increasing height above the surface. At radio wavelengths this usually occurs when there is a strong lapse of water vapor pressure with increasing height. By contrast, at infrared wavelengths the refractive index is almost independent of water vapor pressure, and it is found that an infrared duct is formed only when there is a temperature inversion.
- Publication:
-
In AGARD
- Pub Date:
- March 1990
- Bibcode:
- 1990apuv.agarS....L
- Keywords:
-
- Air Water Interactions;
- Atmospheric Boundary Layer;
- Atmospheric Refraction;
- Infrared Radiation;
- Marine Meteorology;
- Temperature Inversions;
- Evaporation;
- Infrared Spectra;
- Oceans;
- Vapor Pressure;
- Water Vapor;
- Communications and Radar