Low level range coverage performance prediction for VHF radar
Abstract
A VHF radar frequencies the range coverage is not strictly limited by the quasi-optical horizon like at microwave radar frequencies but is extended due to diffraction propagation. This effect, here called beyond-the-horizon (BTH) detection capability is strongly dependent on the propagation path and thus on the terrain structure. The availability of digital terrain maps gives way to the use of computerized methods for the prediction of radar range coverage in real environment. In combination with wave propagation models suitable for diffraction at terrain structures, digital terrain data can even be used for the prediction of BTH target detectability at VHF radar. Here the digital landmass system (DLSS) terrain database was used in combination with a multiple-knife-edge diffraction model to predict the diffraction attenuation between the radar and the potential target positions, especially beyond the optical horizon. The propagation paths extracted from the database are modeled as a sequence of diffraction screens suited for the application of a Fresnel-Kirchhoff algorithm yielding the knife-edge-diffraction attenuation. This terrain related propagation model was verified by a large number of measurements at different frequencies. Implemented in a fast computer system, this prediction model can be used for mission planning of air operations. Considering hostile VHF radar coverage and terrain condition for flight path optimization or, on the other hand it can assist in siting mobile radars for gap filling according to the actual threat situation. Calculations of the diffraction propagation using the prediction model, yield range coverage patterns in real terrain situations, allowing to quantify the BTH detection advantage of VHF radar compared to microwave radar. An experimental large wavelength radar LARA (VHF) built flying targets beyond the close horizon. Here, especially the detection of hiding helicopters by exploiting diffractive wave propagation was examined. Measurements at different VHF frequencies were carried out, to validate the results obtained by simulation.
- Publication:
-
In AGARD
- Pub Date:
- September 1989
- Bibcode:
- 1989odae.agarR....K
- Keywords:
-
- Diffraction Propagation;
- Flight Paths;
- Mapping;
- Mathematical Models;
- Performance Prediction;
- Radar Range;
- Terrain;
- Very High Frequencies;
- Wave Propagation;
- Algorithms;
- Computer Techniques;
- Digital Data;
- Digital Systems;
- Helicopters;
- Microwaves;
- Radar Detection;
- Radar Targets;
- Communications and Radar