Instantaneous doppler signature extraction from within a spectrogram image of a VHF band

Abstract

Aircraft tracking based on the Doppler shift of radio sources of opportunity presents one approach to avert or reduce tragedies like the lost flight MH370. Systems like this are based on simultaneous observation of the Doppler shift caused by aircraft from multiple common radio sources and many listeners, for example by capturing Doppler signals from spectrogram images. In the current article, a mathematical model of instantaneous Doppler curve extraction from within a VHF spectrogram image is presented and exploited with three receiving and one transmitting stations. The model is based on a priori knowledge of the probability density function (pdf) of the first-order derivative of the Doppler shift (FODDS), and on a system of blocks for identifying, classifying, and predicting the Doppler signal in a one-scan-at-a-time fashion. Tracing capabilities of such a model are tested in an off-line experiment with 21 TV signal recording sessions. The system was able to trace 73.8% of observed Doppler signatures; its stability was proven with various scenarios of Doppler curve appearance within the recorded sessions and simulated synthetic data.