Aircraft detection and tracking with high frequency radar

Sustained research and development at Memorial University of Newfoundland has led to an operational High Frequency Ground Wave Radar (HF-GWR) system for coastal surveillance. This radar system has demonstrated over-the-horizon detection of targets such as vessels, ice hazards and low-flying aircraft, and performed ocean parameter measurements over a large area. The industrial developers of offshore hydrocarbon reserves in ice infested regions have an urgent requirement for the long range detection and tracking of icebergs from their production platforms. However, due to space restrictions, a rig- or ship-based system can only accommodate a compact antenna array. The uniform trajectory and low velocity of icebergs is ideal for Reciprocal Synthetic Aperture Radar (RSAR) processing with long target dwell times. The proven ice detection capability of HF-GWR systems, coupled with the compact antennas suggested by the RSAR technique, can be used to develop a rig- or ship-based all-weather surveillance device for ice hazards. It is also anticipated that the results of this research will allow the use of shorter antenna arrays for many other applications. Preliminary results using real data from the operational HF-GWR system are presented.

Traditionally, radar signals have been analysed in either the time or the frequency domain. Joint time–frequency representations characterise signals over a time–frequency plane. They thus combine time-domain and frequency-domain analyses to yield a potentially more revealing picture of the temporal localisation of a signal's spectral components. Therefore, for air target returns with time-varying frequency content, joint time–frequency representations offer a powerful analysis tool. A concise review of time–frequency transforms is provided as background and is needed to appreciate how time–frequency processing methods can improve conventional time or frequency processing methods. The authors use time–frequency analysis techniques for the detection of a manoeuvring aircraft using high frequency (HF) radar in heavily cluttered regions. They compare the ability of different time–frequency transforms to resolve several experimental aircraft returns. The relative speeds of the different transforms are also quantitatively studied. The results clearly demonstrate that time–frequency analysis techniques can significantly improve the detection performance of the HF radar and add considerable physical insight over what can be achieved by conventional Fourier transform methods currently used by HF radars.

Raytheon Systems Canada Limited, in association with Northern Radar Inc (NRI), have designed and built two long-range High Frequency Ground Wave Radar (HFGWR) facilities at Cape Race and Cape Bonavista, NF, Canada. Even though these systems can routinely monitor offshore target activity, the data stream for target detection can also be used to generate surface currents. Since each station is capable of providing estimates of the radial components of the surface current field, the vector current field can be reconstructed from the radial data via geometric considerations. To explore this possibility, sample datasets from both stations were collected in June of 2000 and subjected to a dual station analysis scheme. The treatment presented here will discuss some of the statistics associated with the radial current data as well as the dual station technique used to generate the surface current field. Finally, the radar current estimates will be compared with current meter data collected near the Hibernia platform.

To reduce the floor space of receiving antenna arrays, the Radio Ocean Remote SEnsing (RORSE) laboratory of Wuhan University developed a circular receiving array for a multi-frequency high frequency (MHF) radar system in 2014, consisting of seven uniformly spaced antenna elements positioned on a circle with a diameter of 5 m. The new system, which is abbreviated MHF-C radar, adopts frequency modulated interrupted continuous wave (FMICW) chirps and is capable of simultaneously operating at a maximum of four frequencies in the band of 7.5–25 MHz, and providing current, wave and wind maps every ten minutes. The phase direction-finding method is utilized to estimate the directions of the current signals, and array phase uncertainties are also taken into consideration in the signal model. This paper introduces the system in detail and investigates the performance of current measurements using MHF-C radars installed at Shengshan and Zhujiajian along the coast of the East China Sea. Radial current measurements derived from 8.27 MHz and 19.20 MHz at the same range are compared. Observations and comparisons between MHF-C radars and acoustic Doppler current profilers (ADCPs) are also presented in this paper. The results preliminarily demonstrate that the MHF-C radar system is capable of maintaining the same performance for current measurements whenever it steers to any other azimuth in the coverage and has a good ability to measure currents.

High Frequency (HF) ground wave radar is widely used in maritime target detection and marine environment observation. Its performance is often degraded by co-frequency interference of the HF band. It is necessary to detect the environmental radio frequency for a HF radar to select the proper operation frequency. In this paper, a radio frequency detecting module is designed and equipped on a double-frequency all-digital multi-input and multi-output (MIMO) HF radar. The operational frequency bands are scanned in the operation of the radar to help select an unoccupied frequency in the band. The application of this module reduced the influence of RF interference on the HF radar. The improvement in the signal quality is obvious.

For the frequency modulated continuous wave (FMCW) radar, the angle resolution of the generated point cloud map (PCM) is limited by both the number of receiver antennas and the interference of multi-target environments. This paper proposes an improved scheme for high-resolution PCM generation based on a 77 GHz FMCW radar system. The scheme consists of a method to synthesize an equivalent virtual array based on the time-division multiplexing (TDM) multiple-input multiple-output (MIMO) technique and an improved target detection algorithm based on multi-channel fusion. The results show that the proposed scheme could suppress the noise floor and improve the accuracy of target detection by 1.33 times compared to a conventional constant false alarm rate (CFAR) detector in a multi-target environment. Moreover, by applying the proposed scheme, the angle resolution of the PCM generated by the radar system reaches to 1.3022 degrees.

As an improvement of regular frequency-modulated continuous-wave (FMCW) radar in transmitter-receiver isolation, frequency-modulated interrupted continuous-wave (FMICW) radar has many advantages such as high range resolution, low peak power and high duty cycle. However, the false targets introduced by range aliasing may interfere with radar performance when it comes to long-range detection. In this paper, a range aliasing elimination method for FMICW radar is proposed based on batch Poisson disk sampling (BPDS) and sparse reconstruction. The received echoes are sampled by the newly developed BPDS pattern, which consists of uniform sampling bursts and Poisson disk inter-burst delays, so that the echoes from the maximum unambiguous range can be collected. Taking advantages of the excellent spectrum anti-aliasing performance of BPDS, the range aliasing phenomenon can be effectively eliminated and the range-Doppler spectrum containing multiple targets can be accurately reconstructed by the Iterative Soft Thresholding like (IST-like) algorithm. Compared with the existing signal processing methods for FMICW radar, the proposed method can obtain a larger maximum detection range without range aliasing. The effectiveness of the proposed method is verified by simulations and experiments on real FMICW radar data.

The tutorial provides an introduction to the fundamental principles of high frequency over-the-horizon (OTH) radar, including sky-wave and surface-wave systems as well as other bi-static HF radar architectures. The main challenges of operating in the HF environment are described and connected to motivate and explain the architecture and design of existing OTH radar systems. From this viewpoint, the most influential characteristics of the HF propagation medium, and those of different HF signals received by OTH radar, are described in detail. The essential properties of various radar sub-systems, including antenna, transmitter, and receiver, are also explained. This is followed by a description of the central features of conventional and adaptive signal processing methods in OTH radar. In addition to the theoretical aspects, the tutorial also contains numerous examples of practical results obtained from actual HF radar systems, new insights for the way ahead, and a comprehensive list of references. For this reason, it is expected to benefit scientists and engineers, either starting out in this field, or those wishing to gain a more complete understanding of the most critical OTH radar concepts.

Suffering from multiform time-variant and fluctuant clutter in High Frequency Radar(HFR), uniform target detection, tracking and clutter mitigation methods will result in false alarm or missing alarm. To select optimized detection and clutter mitigation method in the region of interesting, a method maximizing the separability of the resultant classes in amplitude of range-Doppler map is used for segmentation in multi-level detection background. Statistical and qualitative analysis is operated on the result of clutter extraction. Real data indicated that the proposed method can extract clutter region and adapt for various echo spectral maps for HFR as well, which can offer more accurate prior knowledge for target detection and clutter mitigation.

As a special system of early warning radar, high-frequency sky-wave over-the-horizon (OTH) radar usually needs to detect sea and airborne targets in the same direction simultaneously. However, the long coherent integration time (CIT) required by the sea target makes the echo data about high-speed moving airborne target in the same direction incompletely coherent, which is not conductive to the detection and tracking of airborne target. To overcome this problem, this paper proposes a novel track-before-detect (TBD) algorithm for airborne target. Firstly, the motion prior knowledge of the airborne target is utilized to select the number of pulses in the CIT to perform coherent integration processing. Then TBD based on dynamic programming (DP-TBD) technique is used to realize the noncoherent integration for the detection and tracking of the airborne target. Simulation results show that compared with the traditional method, the proposed algorithm effectively improve the detection and tracking performance of the airborne target.

Frequency-modulated continuous wave (FMCW) radar system synchronization using external clock signals can cause repeated Range-Doppler (R-D) map corruption when clock signal asynchronization problems occur between the transmitter and receiver. In this paper, we propose a signal processing method for the reconstruction of the corrupted R-D map owing to the FMCW radar's asynchronization. After calculating the image entropy for each R-D map, the corrupted ones are extracted and reconstructed using the normal R-D maps acquired before and after the individual maps. To verify the effectiveness of the proposed method, three target detection experiments were conducted: a human target detection in an indoor environment and a wide place and a moving bike-rider target detection in an outdoor environment. The corrupted R-D map sequence of observed targets in each case was reconstructed properly and showed the validity by comparing the map-by-map range and speed changes in the detected target with the ground-truth information of the target.

Passive radar permits inexpensive and stealthy detection and tracking of aerospace and geoscience targets. Transmitters of opportunity such as commercial FM broadcast, DTV broadcast, and cell phone towers are already illuminating many populated areas with continuous power. Passive radar receivers can be located at a distance from the transmitter, and can sense this direct transmission as well as any reflections from ground clutter, aircraft, ionospheric turbulence and meteoroids. The 100% duty cycle allows for long coherent integration, increasing the sensitivity of these instruments greatly. Presented here is a new passive radar receiver designed to analyze any transmission of opportunity with frequencies up to 1.5 GHz without the use of a front end analog downconverter. The receiver centers around a Reconfigurable Open Architecture Computing Hardware (ROACH) board developed by the Collaboration for Astronomy Signal Processing and Electronics Research (CASPER) group. The radar is designed for mobile operation. It fits within a 19 rack, it is equipped with solid state hard drives, and can run off an uninterruptible power supply (UPS) for up to 1 hour of continuous operation. In this paper we describe technical details of the hardware, firmware, and software of the system including the use of polyphase filtering in lieu of traditional digital downconversion. We describe the use of the cross-ambiguity function as a detection mechanism. We present preliminary results of detections from this radar. In stationary operation, the same helicopter has been detected using two different DTV transmissions. We present early results of mobile operation, in which the doppler-spread ground clutter and possible detection of aircraft can be seen, again with the use of DTV broadcast. Finally, we detail future developments to exploit the full capabilities of this versatile new system.

High frequency surface wave radar (HFSWR) is becoming accepted as an important remote sensing device for sea state monitoring, and the frequency-modulated continuous wave (FMCW) has been widely used as the radar transmitted waveform. However, the performance of HFSWR may be significantly impacted by unwanted echoes, of which ionospheric clutter is one of the main sources. During transmission, a portion of the radar radiation may travel upwards to the ionosphere from the transmitting antenna. This may be partially reflected back to the receiving antennas directly or via the ocean surface, the latter being refered to as ionosphere-ocean propagation. The purpose of this paper is to investigate the physical mechanism of how the ionosphere clutter might be analytically characterized within the radar backscatter spectrum. The first-order HF radar clutter power and its radar cross section of ionosphere-ocean propagation for an FMCW source will be derived theoretically, and then simulated and compared for a variety of ionosphere velocities and wavelengths.

This paper discusses the implementation of GNU radio-based software defined radio (SDR) for designing a frequency modulated continuous wave (FMCW) radar to detect stationary and moving targets. The use of SDR system in which its components are implemented by means of software is to reduce cost and complexity in the design and implementation. Whilst the signal processing of FMCW radar is carried out using Matlab R® with triangular linear frequency modulation (LFM) waveform to obtain the target distance and the target relative speed for stationary and moving target, respectively. From the result, it is shown that the radar is successfully implemented using GNU radio-based SDR with the capability in distance target detection of 14.79km for a moving target away from the radar with the relative speed of 50m/s.

This paper proposes a distributed target fusion detection method based on underwater sensor network, which mainly solves the problem of passive detection of underwater targets. A target detection system based on a distributed underwater sensor network is established, which adopts a parallel distributed information fusion structure with a fusion center. Energy of the received signal is utilized on local nodes to obtain the test statistics. Then the corresponding false discovery rate (FDR) is calculated for each node. The fusion center uses the FDR to control the detection threshold and figure out the global decision, which can realize the adaptive adjustment of the detection threshold of local nodes with different received signal-to-noise ratios. The proposed method is conducive to improving range and probability of underwater passive target detection.