Spectrum Difference Function technique for measuring velocity
In radar applications, target velocity is commonly determined using the Doppler effect. By comparing the transmit-receive differential frequency the Doppler frequency shift can be measured and as a result the target velocity can be determined. The Tasman International Geospace Environment Radars (TIGER) form part of an international network of similar HF radars called Super Dual Auroral Radar Network (SuperDARN) which explore the impact of solar disturbances on Earth by monitoring the location of aurora and related phenomena occurring in the ionosphere. These radars utilise an Auto Correlation Function (ACF) to measure the changing phase of the ACF between lag times to determine the Doppler frequency and the target velocity. This paper presents a novel method to measure Doppler shifts with high resolution and accuracy in radar applications. In the proposed method, a comparison of the transmit and receive signal spectrums is performed to determine the Spectrum Difference Function (SDF). It is shown that the gradient of SDF in the vicinity of the carrier frequency is proportional to the target Doppler shift. Therefore, by examining the SDF, the target velocity can be detected with a high level of accuracy.