Matched Filter Processing Research Articles

Estimates of the bottom reflection coefficient involving vector sensor

Estimates of the bottom reflection coefficient made in the frequency range of 4–8 kHz, as part of the Targets Reverberation Experiment (TREX) are presented. The TREX experiment took place in the Gulf of Mexico, near Panama City, FL, in waters 20 m deep. At the measurement site the sediments are loosely classified as fine sand. The reflection coefficient R is estimated over the nominal grazing angular range 1 to 20 deg., using measurements made at ranges 50 to 800 m and received on a vertical line array (length 1.6 m). The arrival time and magnitude of the bottom reflection is determined by the matched filtered output of a frequency modulated signal, 4–8 kHz. In addition, the match filter processing technique is applied to the vector sensor data (measured simultaneously and co-located with the line array.) This allows for an extraction of the active intensity contribution associated with the bottom reflection, and provides a vector intensity-based estimate of the bottom reflection coefficient. The estimates of the bottom reflection arrival time are also used to time-gate simultaneously transmitted cw tones (1–4 kHz) to analyze the Lloyd’s mirror pattern associated with seabed reflection. [Research supported by ONR, with partial support from ONRG.]

Space–time interference analysis and suppression for airborne passive radar using transmissions of opportunity

This study presents the space–time snapshot models for the interfering passive signals received by the airborne passive radar which uses a ground-based stationary non-cooperative transmitter. The random range sidelobes couplings of the direct path and of the strong clutter signals into further range cells are major concerns in moving target detection performance. The least squares-based adaptive interference cancellation technique is proposed to efficiently suppress the direct path, strong clutter and Doppler-shifted strong clutter signals present at each antenna element prior to matched filter processing. In mitigating the interfering signals, their corresponding random range sidelobes will also be suppressed by the same amount. Ground-based moving passive radar trials were conducted to validate and ascertain the effectiveness of the proposed adaptive interference cancellation algorithm.

Performance analysis of single-frequency MPPSK integrated system for ranging applications.

The dual-frequency MPPSK-MODEM is a flexible platform. When ranging accuracy request is low or platform is particularly limited by power, the platform would perform both data transmission and range measurement with single-frequency modes. In this paper, the ranging resolution of MPPSK pulse waveforms with the match filter and impacting filter processing are discussed, respectively. Also, the parameter selection of MPPSK modulator for ranging is considered. In particular, requirements that allow for employing such special parameter values for range measurements with high accuracy and high range are investigated. Moreover, high repetition frequency (HRF) biphase code MPPSK pulse train base on m sequence is presented, and the ranging accuracy of the proposed signal with the match filter processing is deduced. In addition to theoretical considerations, the paper presents system simulations and measurement results of single-frequency MPPSK integrated systems, demonstrating the high-performance of ranging applications.

Toward real-time spectral imaging for chemical detection with a digital micromirror device-based programmable spectral filter

Hyperspectral imaging sensors have proven to be powerful tools for highly selective and sensitive chemical detection applications, but they have significant operational drawbacks including slow line-scanning acquisition, large data volume of the resulting images, and a detection time lag due to the computational overhead of the matched-filter analysis. We have recently developed and demonstrated a high-speed, high-resolution, programmable spectral filter based on the Texas Instruments DLP® digital micromirror device (DMD) that is capable of performing matched-filter image processing across a two-dimensional (2-D) field-of-view directly in the optical hardware and will enable real-time chemical detection without slow scanning, large data volumes or expensive postprocessing requirements. Based on traditional optical techniques, our spectral filter encodes the spectral information orthogonal to the spatial image information, enabling the DMD to encode matched-filter information into the spectral content of the scene without disturbing the underlying 2-D image. With this new technology, everything from simple multiband filters to very complicated hyperspectral matched filters can be implemented directly in the optical train of the sensor, producing an image highlighting a target signature within a spectrally cluttered scene in real time without further processing. We will first describe the implementation of a DMD as a multiplexing spectral selector for a 2-D field-of-view, discuss its utility as a multiband spectral filter, and show how the DLP’s® duty cycle-based grayscale capability enables the direct measurement of the adaptive matched filter. We will also show examples of multispectral and hyperspectral matched-filter images recorded with our visible spectrum prototype.

High-Resolution Radar Imaging Through a Pipe Via MUSIC and Compressed Sensing

Techniques for high-resolution radar imaging through a pipe are explored. To improve the angular resolution imposed by the pipe diameter, two high-resolution processing methods, MUSIC and compressed sensing (CS), are adapted for through-pipe radar imaging. First, the signal model, for propagation through the pipe, is formulated such that MUSIC and CS can be used. Then, methods for forming radar images from scattering collected through a pipe are derived. The methods are then demonstrated through electromagnetic simulation and verified with measurement data. It is shown that both methods provide high angular resolution in comparison with matched filter processing. The primary difference between the methods is that MUSIC requires multistatic data collection, while monostatic data collection is sufficient for CS. The performance of the two methods in terms of the number of targets and the signal-to-noise ratio is also evaluated. It is found that both methods can be used to image a complex scene composed of multiple point scatterers. CS, however, requires fewer number of data points than MUSIC. On the other hand, MUSIC is found to be less susceptible to noise than CS.

New Antivelocity Deception Jamming Technique using Pulses with Adaptive Initial Phases

An effective electronic counter-countermeasures (ECCM) technique for a moving target indication/pulsed Doppler (MTI/PD) radar system against velocity deception jamming is proposed. A novel radar signaling strategy is outlined based on variations of the initial phases of the transmitted pulses in pulse repetition interval (PRI) domain. It makes the Doppler spectrum of the false targets, created by a digital radio frequency memory (DRFM) repeat-back jammer, form a notch around the Doppler frequency of the true one. The penalty function and corresponding algorithm for designing adaptive initial phases are given. We also present an approach of the multi-channel matched filter processing to estimate the manner, by which a DRFM repeat jammer operates, and the parameters of the false targets. The working flow of an MTI/PD radar for countering velocity deception jamming is investigated. Simulation results show the effectiveness of the above methods.

Inverse filtering of radar signals using compressed sensing with application to meteors

Compressed sensing, a method which relies on sparsity to reconstruct signals with relatively few measurements, provides a new approach to processing radar signals that is ideally suited to detailed imaging and identification of multiple targets. In this paper, we extend previously published theoretical work by investigating the practical problems associated with this approach. In deriving a discrete linear radar model that is suitable for compressed sensing, we discuss what the discrete model can tell us about continuously defined targets and show how sparsity in the latter translates to sparsity in the former. We provide details about how this problem can be solved when using large data sets. Through comparisons with matched filter processing, we validate our compressed sensing technique and demonstrate its application to meteors, where it has the potential to answer open questions about processes like fragmentation and flares. At the cost of computational complexity and an assumption of target sparsity, the benefits over pulse compression using a matched filter include no filtering sidelobes, noise removal, and higher possible range and Doppler frequency resolution.

Bio-sonar signal processing

An ideal sonar for biological observations in the ocean should employ very long signals for Doppler resolution, wide bandwidth for time resolution and pulse compression properties for gain in order to reduce sound pressure levels to mitigate marine mammal concerns. Signal spread in time and Doppler (leakage) must also be eliminated so that direct arrival and reverberation signals do not leak and swamp bio-signal returns when operation in a continuous transmit and receive mode. Orthogonal codes would help multi-static applications. Here two types of signals and processing are presented and analyzed; 1) M-sequences with matched filter processing and 2) Inverted binary sequence with matched- inverse processing. Ambiguity diagrams of conventional active sonar signals are compared with the two candidate signals. Then the two methods are compared by numerical simulation for propagation in shallow channels with zero Doppler returns and moving bio-scatterers. It is shown that for realistic conditions leakage from direct and zero Doppler reverberation can be eliminated not just reduced. Limits on temporal coherence times of shallow water propagations channels are discussed. These approaches improve Figure of Merit of conventional active sonar by 10 to 15 dB and displays in the time Doppler plane simplify the interpretation of clutter.

Autonomous underwater vehicle localization using the acoustic tracking system

Operator peace-of-mind during Autonomous Underwater Vehicle (AUV) missions is dependent on the ability to localize the vehicle. During launch and recovery phases this capability is particularly important. Defence R&D Canada (DRDC) Atlantic has designed and built a long-range tracking system for the International Submarine Engineering Explorer class AUVs. The acoustic tracking system (ATS) enables an operator on a loud icebreaker platform to determine the position of the AUVs at ranges up to 30 km. An acoustic projector, mounted on the AUV, emits a hyperbolic frequency modulated (HFM) chirp at a preset time interval. A small, directional, acoustic receiving array mounted near the stern of the icebreaker, accurately synchronized with the remote projector, receives signals from the distant AUV. Matched filter processing is used to determine the time of flight of the transmitted chirp. A beamforming algorithm applied to the data provides bearing and elevation angle estimates for the received signals. A ray tracing algorithm then uses this information, along with the sound velocity profile, to determine the position of the AUV. Moreover, ATS uses different HFM chirps to provide a basic one-way AUV state messaging capability. We conclude with a brief discussion of ATS data collected during in-water trials.

Adaptive Range Oversampling to Achieve Faster Scanning on the National Weather Radar Testbed Phased-Array Radar

Abstract This paper describes a real-time implementation of adaptive range oversampling processing on the National Weather Radar Testbed phased-array radar. It is demonstrated that, compared to conventional matched-filter processing, range oversampling can be used to reduce scan update times by a factor of 2 while producing meteorological data with similar quality. Adaptive range oversampling uses moment-specific transformations to minimize the variance of meteorological variable estimates. An efficient algorithm is introduced that allows for seamless integration with other signal processing functions and reduces the computational burden. Through signal processing, a new dimension is added to the traditional trade-off triangle that includes the variance of estimates, spatial coverage, and update time. That is, by trading an increase in computational complexity, data with higher temporal resolution can be collected and the variance of estimates can be improved without affecting the spatial coverage.

Acoustic pulses in the atmosphere: An outdoor teaching laboratory.

For the past two years, the Penn State Acoustic Data Measurements and Analysis course has incorporated several outdoor-sound exercises. One of these exercises is particularly amenable to illustrating concepts in acoustic propagation, signal design, and signal detection. Using relatively inexpensive hardware, student-designed pulse sequences are transmitted, received, and recorded in various outdoor environments. The advantages and disadvantages of large-bandwidth pulses are readily apparent. The students can perform replica correlation or matched filter processing and compare the achieved results to theoretical performance. The effects of the transmitting transducer on pulse shape are seen easily. Variability in the atmospheric propagation path, multipath, and upwind/downwind effects can be demonstrated as well as the impact of ambient noise on pulse detection. In addition, pulses can be reflected from moving objects (buses, for example) either for analyzing Doppler shift or for experimenting with Doppler-tolerant detection. Waveform types range from simple sinusoidal pulses to frequency-modulated pulses and frequency- or phase-shift coded maximum-length sequences to reproductions of animal vocalizations. In the fall of 2010, 40 students participated in this exercise: 20 resident students and 20 distance-education students.

The advantage of FM slide signals for active acoustic systems used for fisheries studies.

A key requirement for many active acoustics systems used for fisheries or biological oceanographic data collection is to provide high spatial resolution while maximizing the range for which useful data are obtained. Unfortunately, most systems in use today use cw pulse transmit signals for which the user must trade‐off range resolution with output signal‐to‐noise, which determines the maximum useful range at which data can be collected. This paper describes the application of a different type of signal, the FM slide or chirp, for fisheries and oceanographic acoustic assessment. Compared to the cw pulse based systems, acoustic systems that use FM slide signals with the corresponding matched filter processing can achieve significantly better spatial resolution without sacrificing maximum range. The explanation of why the FM slide signal achieves this improved performance as well as a discussion of some of the factors that must be considered when implementing this signal type are described. Laboratory measurements and field results are presented that show the advantages of the FM slide for real world assessment studies.

Remote sensing of Carhuarazo volcanic complex using ASTER imagery in Southern Peru to detect alteration zones and volcanic structures – a combined approach of image processing in ENVI and ArcGIS/ArcScene

A combined approach to detect hydrothermal alteration zones and their mineral distribution is proposed for a relatively remote area around the Carhuarazo volcanic complex in southern Peru encompassing 2222 km2. In this region, tertiary volcanic structures associated with hydrothermal alteration are well known to host epithermal ore deposits. We make an attempt to detect and to quantify alteration minerals based on spectral analysis using ASTER reflectance data product provided by LP-DAAC. Besides commonly used ratio images, mineral indices (MI) and relative band depth images (RBD), we also extracted endmember spectra using Pixel-Purity-Processing preceded by minimum noise fraction transformation. These spectra are thought to represent the spectrally purest pixel of the image and show the typical absorption features of the main constituents. Based on this assumption, we used different spectral analysis methods in order to extract the most important alteration minerals for such an environment. These minerals were then used for matched filter processing in areas showing high values in MIs and RBDs. Using this method, we detected and mapped argillic alteration and variations in the distribution of important minerals like alunite, kaolinite or nacrite. There were no indications for the presence of propilitization at ASTER spatial resolutions. Our method can be applied easily to any ASTER scene and provides information about the intensity of alteration and the character of alteration zones. The intensity is highest in the centre of the Carhuarazo volcanic complex and is mostly argillic with a high content of alunite, dickite and other clay minerals.

On overloaded vector precoding for single-user MIMO channels

We address the possibility of overloaded vector precoding in single user MIMO channels, i.e. the number of data streams is larger than the minimum of the number of antennas at transmitter and receiver side.We find that the convex vector precoding introduced in [1] allows for overloading while, with a certain probability, keeping the received signal free of interference. We find that the probability that overloading is not possible decays exponentially with the size of the system as long as the number of data streams is less than twice the minimum number of antennas. We give an explicit formula to calculate this probability for any antenna configuration in presence of correlated Rayleigh fading. Although overloading comes with the need for increased transmitted power, we show by means of the replica method that overloading up to 22% yields better spectral and power efficiency than without overload and spatial matched filter processing at the receiver.

Interference suppression for code-division multiple-access communications in an underwater acoustic channel

In a code-division multiple-access communications network, the signal from a nearby user often creates a strong interference for the signal from a distant user. This is known as the near-far problem. Power control of source levels is ineffective in an underwater acoustic channel due to the slow sound speed. Interference rejection based on code orthogonality is ineffective using matched-filter processing due to the fact that multipath arrivals effectively destroy the code orthogonality and that the signal arrival times between different users are not synchronized. An algorithm, called hyperspace cancellation by coordinate zeroing, is used in this paper to remove/suppress interference. Using a fast Walsh-Hadamard transform (FWHT) based on the interferer's code sequence, the interference signal is enhanced and removed by coordinate zeroing. The residual signal is transformed back using an inverse FWHT. The filtered data, with the interference signal largely removed, are processed using the desired signal code sequence. Two methods previously developed for direct-sequence spread-spectrum communications in an underwater channel are used to extract the transmitted symbols. Low bit error rate (<10(-2)) is found with the at-sea data for signal-to-interference ratio as low as -8 to -11 dB.

Coherent interferometric imaging for synthetic aperture radar in the presence of noise

This paper shows that the coherent interferometric imaging strategy originally proposed in the context of passive or active arrays of antennas can be implemented for synthetic aperture radar, in which a single antenna is used as an emitter and as a receiver at successive positions along a trajectory. The idea is to backpropagate the cross correlations of the recorded signals over selected frequency-spatial windows rather than the signals themselves. The theoretical analysis shows that the signal-to-noise ratio can be enhanced dramatically compared to the standard matched filter processing, without any loss of resolution. This holds true when the fluctuations of the recorded signals have a spatial correlation (along the antenna trajectory) that is larger than the distance between two successive positions of the antenna and smaller than the length of the antenna trajectory. As a result, a good compromise between resolution and deblurring can be achieved by an appropriate choice of the spatial window size.

Mapping mineralogical alteration using principal‐component analysis and matched filter processing in the Takab area, north‐west Iran, from ASTER data

The Takab area, located in north‐west Iran, is an important gold mineralized region with a long history of gold mining. The gold is associated with toxic metals/metalloids. In this study, Advanced Space Borne Thermal Emission and Reflection Radiometer data are evaluated for mapping gold and base‐metal mineralization through alteration mapping. Two different methods are used for argillic and silicic alteration mapping: selective principal‐component analysis and matched filter processing (MF). Running a selective principal‐component analysis using the main spectral characteristics of key alteration minerals enhanced the altered areas in PC2. MF using spectral library and laboratory spectra of the study area samples gave similar results. However, MF, using the image reference spectra from principal component (PC) images, produced the best results and indicated the advantage of using image spectra rather than library spectra in spectral mapping techniques. It seems that argillic alteration is more effective than silicic alteration for exploration purposes. It is suggested that alteration mapping can also be used to delineate areas contaminated by potentially toxic metals.

Determining tomographic arrival times based on matched filter processing: Considering the impact of ocean waves

Reflection of high-frequency acoustic signals from an air-sea interface with waves is considered in terms of determining travel times for acoustic tomography. Wave-induced, multi-path rays are investigated to determine how they influence the assumption that the time of the largest matched filter magnitude between the source and receiver signals is the best estimate of the arrival time of the flat-surface specular ray path. A simple reflection model is developed to consider the impact of in-plane, multi-path arrivals on the signal detected by a receiver. It is found that the number of multi-path rays between a source and receiver increases significantly with the number of times the ray paths strike the ocean surface. In test cases, there was always one of the multi-path rays that closely followed the flat-surface specular ray path. But all the multi-path rays arrive at the receiver almost simultaneously, resulting in interference with the signal from the flat-surface specular ray path. As a result, multi-path arrivals due to open ocean surface waves often distort the received signal such that maxima of matched filtering magnitudes will not always be a reliable indicator of the arrival time of flat-surface specular ray paths.

Distribution of hydrothermally altered rocks in the Reko Diq, Pakistan mineralized area based on spectral analysis of ASTER data

The Reko Diq, Pakistan mineralized study area, approximately 10 km in diameter, is underlain by a central zone of hydrothermally altered rocks associated with Cu–Au mineralization. The surrounding country rocks are a variable mixture of unaltered volcanic rocks, fluvial deposits, and eolian quartz sand. Analysis of 15-band Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data of the study area, aided by laboratory spectral reflectance and spectral emittance measurements of field samples, shows that phyllically altered rocks are laterally extensive, and contain localized areas of argillically altered rocks. In the visible through shortwave-infrared (VNIR + SWIR) phyllically altered rocks are characterized by Al–OH absorption in ASTER band 6 because of molecular vibrations in muscovite, whereas argillically altered rocks have an absorption feature in band 5 resulting from alunite. Propylitically altered rocks form a peripheral zone and are present in scattered exposures within the main altered area. Chlorite and muscovite cause distinctive absorption features at 2.33 and 2.20 μm, respectively, although less intense 2.33 μm absorption is also present in image spectra of country rocks. Important complementary lithologic information was derived by analysis of the spectral emittance data in the 5 thermal-infrared (TIR) bands. Silicified rocks were not distinguished in the 9 VNIR + SWIR bands because of the lack of diagnostic spectral absorption features in quartz in this wavelength region. Quartz-bearing surficial deposits, as well as hydrothermally silicified rocks, were mapped in the TIR bands by using a band 13/band 12 ratio image, which is sensitive to the intensity of the quartz reststrahlen feature. Improved distinction between the quartzose surficial deposits and silicified bedrock was achieved by using matched-filter processing with TIR image spectra for reference.

Distortion of a received radar pulse due to high target velocity

This paper presents a method to determine the signal received for the general radar problem, i.e., velocity, translation/rotation, displacement, and modifications caused by the target. In addition to the velocity and spatial/rotation, displacement effects of the radar receiver are included. The narrow-band restriction of the signal does not apply. Once the received signal is determined, it can be compared to the original transmitted signal and the changes in the radar parameters can be determined. These changes are incorporated in the matched filter processing to produce the same output wave forms as if the transmitted wave form was not modified by the motion of the target. The method uses the Poincare transform and a mathematical representation of the reflection and modifications created by the moving target. The solution for the monostatic radar case is presented in detail. Three examples are given to demonstrate the use of the method in the monostatic radar case.