It is a well established fact that radio waves can detect aircraft over short distances. Since the demonstration by Robert Watson-Watt and Arnold Wilkins in 1935 detecting a Handley Page Heyford aircraft by using radio signals from BBC Daventry, radar systems are now used around the world for aircraft detection and tracking. In this technical paper we demonstrate how WSPR signals can detect aircraft over short distances like radar.
During the 3rd November 2023 a total of nine flights were analysed with commercial aircraft including Boeing, Airbus, Embraer and Canadair flying at altitudes between 7,350 feet and 37,000 feet in the vicinity of the transmitter W8AC. Eight of the nine flights were detected with a total of 13 SNR anomalies. In two cases flights were additionally detected by frequency drift anomalies.
Sometimes the presence of the aircraft would make reception possible, by deflecting the transmitted ray to the receiver. When the aircraft track aligned to the WSPR propagation path, we observed multiple SNR anomalies in successive two minute WSPR time slots. In five cases there were multiple transmissions at different frequencies in the same two minute WSPR time slot resulting in one or more SNR anomalies in the same time slot.
WSPR can act as a multi-static and multi-frequency passive radar system over short distances. In a subsequent technical paper, we will demonstrate how WSPR signals can detect aircraft over long distances using ionospheric propagation around the globe. In this paper we show how a single WSPR link can detect aircraft, in the next paper we will show how multiple WSPR links can combine to detect aircraft with a higher confidence level.
The technical paper can be downloaded here