The fine structure of elevated refractive layers: Implications for over-the-horizon propagation and radar sounding systems

Radar and acoustic sounder data are compared with in situ turbulence and meteorological data collected with fast response sensors on a carriage traversing a 300-m tower. The carriage data reveal a fine structure of sharp laminae within elevated inversions that is associated with laminated echoes in the sounder records. The zones of sharp gradient contain narrow regions of enhanced structure parameters of temperature and humidity that presumably account for the radar and acoustic returns from those zones. In these cases the temperature and humidity profiles are remarkably close (negative) replicas of each other, greatly simplifying the interpretation of radio refractive index from temperature data. A model of specular reflection is compared with a Bragg backscatter model, and it is concluded that specular contributions from the observed gradients can exceed the Bragg return even for back-scatter if radar wavelengths greater than a few meters are used. For bistatic configurations the specular contributions should commonly exceed the tropospheric scatter contribution when elevated stable layers are present.