Classification of Birds and UAVs Based on Radar Polarimetry

Abstract

This letter aims to show the potential of using polarimetric parameters to distinguish between large birds and unmanned aerial vehicles (UAV) of comparable size in the context of a modern long range air defence radar. Time is a critical resource in such systems and techniques for robust noncooperative target recognition (NCTR) not relying on spatial resolution or long dwell times are highly desired. Furthermore, methods less dependent on target micro-motion are in many cases required. Methods exploiting polarimetric features are shown to have potential in both cases. An experiment in S-band shows that a simple Nearest-neighbor classifier can achieve good separation between UAVs and birds both with and without detectable micromotion based on a set of polarimetric parameters alone.

10th European Conference on Radar in Meteorology and Hydrology (ERAD 2018) : 1-6 July 2018, Ede-Wageningen, The Netherlands

“…PSWR is a dual polarization, X-band, 1D phased array radar. Dualpolarization is a current standard in weather radar industry and can be used to improve target classification (Torvik et al, 2016). PSWR in its current configuration is able to perform simultaneously a full 360 degree mechanical scan in the azimuth and a 90 degree (ground to zenith) electronic scan in the elevation.…”

Review of radar classification and RCS characterisation techniques for small UAVs or drones

“…Torvik, et al [42] studied how polarimetry could be exploited to aid in the classification between four classes of both birds and drones, these are already known to exhibit very similar RCS characteristics [43]. The work employed up to 12 extracted vectors from the radar signature across multiple domains as features for classification.…”

“…However, at high elevation angles vertical and cross polarisation combinations are shown to provide improved SNR. Low frequency measurements at L Band are established to be not as useful as S Band, nevertheless classification performance is improved [42] [69]. In the context of a real drone surveillance radar, very high elevation angles would be uncommon as, drones typically operate at low to medium altitude (below 100 m).…”

Interference of Radar Detection of Drones by Birds

“…Air surveillance radars (ASRs) are not fit for detecting drones at low altitude because the mission of ASR focuses on searching for aircraft that have a large radar cross section (RCS) in the sky, not at low altitude [6,7]. Besides, detection of drones with high range resolution radar profiles (HRRPs) is problematic because subcentimeter resolution is needed to capture the longitudinal structure of targets less than 100 cm in length [8,9]. Therefore, most radar systems being used to detect and identify birds and drones have a low range profile.…”

“…The researches on the differentiation between flying birds and small drones by radar are relatively new. Yet, the common view is that birds become the major jamming of radar detecting drones because of the similarity in RCS [14,15], motion pattern [9,16,17], and even similar micro-Doppler features [18]. Moreover, Ritchie et al reported that various birds will interfere with micro-drones in comparable signature within the time domain and similar RCS values, and the discrimination between birds and drones is needed to avoid significant false alarm rates [19].…”