Near-field radiometry of smoothly-inhomogeneous media

For a smoothly-inhomogeneous media with the permittivity /spl epsiv/=/spl epsiv/(z), using the expression for a fixed component of the transversal wavenumber spectrum, it is possible to obtain the general expression for the effective brightness temperature of received (by a matched antenna) near-field emission. Then, using the mean value theorem and the condition of unity normalization of the kernel, we have a simple formula that can be expressed in the form similar to the well-known solution of the emission transfer equation. This theory was applied to near-field measurements at wavelength 31 cm, similar to those presented in, but for water at zero salinity with a strong dependence /spl epsiv/(T) using the developed exact theory for smoothly-inhomogeneous media.