The new approach of evaluating differential signal of airborne FMCW radar-altimeter

The paper describes the new approach for evaluating the altitude using airborne radar-altimeters based on frequency modulation. Present radar-altimeters evaluate altitude by direct measurement of differential frequencies. The method is significantly influenced by methodical measurement error as a result of discrete processing of the differential signal. The altitude is a continuously changing value whilst the measured signal by altimeter is represented by discreet steps. The fundamental idea of evaluating the altitude by this approach is based on evaluation of the period of the differential signal, which carries altitude information as well but it is changing continuously. To verify this new approach, the RV-UM radar-altimeter was subjected to an experiment. The results have proven the validity of this approach whereby the accuracy of this radar-altimeter has been increased substantially, from ± 4.4   m stated by the manufacturer up to ± 0.6   m achieved through the new approach. By applying this approach the centimeter level of accuracy can be obtained using radar-altimeters.