Propagation of infrared radiation in the evaporation duct

In the air close to the sea surface there often exist strong vertical gradients of temperature and humidity, which may in turn cause strong gradients of atmospheric refractive index. Such gradients may have important effects on the propagation of electromagnetic radiation over the sea. The refractive index of air at infrared wavelengths are compared with that at radio wavelengths. Meteorological models of the air-sea boundary layer are used to compute vertical profiles of temperature and water vapour. From these are derived profiles of refractive index at infra-red and radio wavelengths. Raytracing is used to illustrate the contrasting propagation behaviour in the two frequency bands