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Why can radio-based EDM work in fog and heavy rain?

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surveying Figure 1: Photogrammetric photographs from two short, overlapping flight strips arranged for supplying mapping details. Photo-control points are shown on only one photograph; shading indicates a typical terrain feature such as a lake (see text).

In the context of civil engineering and surveying, radio-based electromagnetic distance measurement (EDM) utilizes ultrahigh-frequency radio beams to determine distances. Unlike light-based EDM, which requires a clear line of sight, radio-based systems can effectively penetrate atmospheric obstructions such as fog, haze, heavy rain, dust, and sandstorms.1

This capability exists because these systems operate using longer wavelengths compared to light or infrared radiation. While scattering losses occur when airborne particles have diameters similar to the signal's wavelength, radio frequencies typically used in these surveying instruments are less susceptible to the scattering effects caused by the water droplets found in fog and heavy rain. Consequently, these radio beams maintain signal integrity through adverse weather conditions that would otherwise disrupt optical measurements.12