Air Surveillance by Doppler Tracking

Earlier this year Lappeenranta University of Technology (LUT) was granted the sum of 100 000 euro for one year project, called ‘Doppler tracking of distant targets’, by Scientific Advisory Board of Defence (MATINE). Additional funding of 67 500 euro was provided by LUT itself. The research group consists of eight people among which there are researchers, programmers, specialists and technicians. As the first year of the project is coming to the end it is a time for conclusions and setting goals for the future.

The goal of the project was to recognize possibilities of air surveillance with use of bistatic radar configuration. This radar configuration differs from conventional monostatic one as transmitter and receiver are at different locations, very often hundreds of kilometres apart. In the case of this project, transmitters of opportunity were used such as radio/tv stations. Bistatic radar as the monostatic one uses the same physical phenomenon – Doppler effect. Because of the geometry of bistatic configuration tracking aircraft is much more demanding. However, by using an inverse approach one can track aircraft with fine precision. The estimated trajectories are validated with use of information provided by flightradar24.com portal. Moreover, retrieved radio signal can be used to estimate aircraft size. With a limited number of observations that were recorded during this year the system was able to classify aircraft into three size-dependent groups.

Another goal was to create coverage maps for different receiving antennas. As the project evolved more antennas were erected. Currently there are three places of reception: west and east of Joensuu and LUT. Total of 7 antennas, each directed to different transmitter makes the tracking and classifying system quite efficient. Total area of observation includes Karelia region of Finland and neighboring region of Russian Federation, see figure. Besides the indicated coverage map the figure depicts the trajectories based on which the map was created. The lower subfigure gives an histogram information on the types of aircraft flying through the region.

The choice of the equipment used for preprocessing was yet another target. At the beginning of the year, the equipment used was the one currently in possession by the radio operator. The price for such equipment is rather high. To attract new volunteers for receiving station we needed reasonably priced and reliable solution. Raspberry Pi and radio stick configuration acts as a fully operational solution at LUT node these days.

The results of the findings were published in IEEE Transactions on Aerospace and Electronic Systems as three separate papers and presented at three conferences. Moreover, the researcher managing the project based his doctoral thesis on those developments and received one with distinction.