High Accuracy Velocity Measurement Based on Keystone Transform Using Entropy Minimization

In Pulsed Doppler radar, when wideband signals are used and the target radial velocity is high, linear range migration occurs and cannot be neglected. The migration misaligns the range profiles within a coherent processing interval and degrades the coherent integration gain eventually. Keystone Transform is a method used for range migration compensation of fast moving targets. In this paper, diminishing effect of range migration by utilizing Keystone Transform in a realistic sea clutter environment is studied. For this, a realistic sea clutter environment is generated.

This study considers the coherent integration problem for detecting a manoeuvring target, involving range migration (RM) and Doppler frequency migration (DFM) within the coherent processing interval. An efficient coherent integration method based on keystone transform (KT) and Lv's distribution (LVD) is proposed. It can not only correct the RM effect by KT and fold factor phase compensation, but also remove the DFM effect and achieve the coherent accumulation via LVD. Compared with the moving target detection, Radon‐Fourier transform, and Radon‐fractional Fourier transform algorithms, the proposed method can obtain better detection ability under low signal‐to‐noise ratio environment. Finally, several simulations are provided to demonstrate the effectiveness.

1. Behavioral measures of target velocity discrimination, Doppler shift discrimination, and Doppler shift compensation are described for the fish-catching bat,Noctilio leporinus. These bats echolocate using a short constant frequency/frequency modulated (short-CF/FM) sonar pulse. 2. Two bats, trained by operant conditioning, performed an in-flight discrimination between sequentially-presented targets which differed in the velocity of movement in the line of the bat's flight path. Both bats discriminate target velocity differences as low as 40 cm/s. This discrimination ability is independent of the absolute speed or direction of target movement. 3. These same bats were subsequently trained by operant conditioning to discriminate between the presence or absence of an upward frequency (simulated Doppler) shift in artificial echoes of their sonar pulses. The smallest frequency shift that can be discriminated is 570 Hz, corresponding to the Doppler shift produced by a relative velocity of 170cm/s. 4. Since these bats cannot detect the Doppler shift associated with moving targets at the threshold of target velocity discrimination, we conclude that Doppler information is not used to make velocity measurements. Target velocity discrimination must instead be based upon range-rate information obtained from the wide band FM component of the sonar pulse. 5. Three of four bats partially compensate for Doppler shifts of their echoes produced by their flight velocity. During flight, the frequency of their sonar emissions is lowered enough to compensate for about 50% of the flight-induced Doppler shift. None of the bats compensate for target-induced Doppler shifts. 6. The functional significance of short CF signals and the echolocation of moving targets byNoctilio and other bats are discussed.

Interferometric Synthetic Aperture Radar (InSAR) is a microwave imaging system with all-weather earth observation. Because of its wide observation area, high precision, day and night operational capabilities, it has a significant advantage in monitoring large-scale surface deformation. Phase unwrapping is a key step in InSAR data processing. The core of Goldstein traditional branch unwrapping method is the establishment of branch-cutting lines. The shorter the overall length of the branch line, the solution is more accurate. Based on the idea of solving the shortest path of Travelling Salesman Problem (TSP), a new algorithm combining ant colony algorithm and genetic algorithm is proposed. Based on the advantages of these two algorithms, we avoid the disadvantages of excessive parameters, slow calculation speed and low efficiency in ant colony algorithm, reduce the time consumed by ant colony algorithm in solving local optimal solution, improve the local search ability of ant colony algorithm, establish shorter branch line than traditional branch method, prevent islanding effect and improve the precision of phase unwrapping. The tests performed on real and simulated interferometric SAR data confirm the validity of the proposed method.

Keystone Transform (KT) and Radon Fourier Transform (RFT) are two popular methods proposed to overcome range migration in radars. A major concern in these methods is the computational complexity for real time operations. In this paper, a low complexity implementation of recurrent chirp-z transform (CZT) is offered in order to be employed in fast KT with no loss in performance. Additionally, a novel RFT implementation utilizing recurrent CZT is proposed to take advantage of the fast execution of repeated CZT. A mathematical analysis and simulation results are presented to show the performance and efficiency of the proposed techniques.

Filtered Rayleigh scattering is an optical diagnostic technique that allows for simultaneous planar measurement of velocity, temperature, and pressure in unseeded flows. An overview of the major components of a filtered Rayleigh scattering system is presented. In particular, a detailed theoretical model is developed and discussed with associated model parameters and related uncertainties. Based on this model, results for two experimental conditions are presented: ambient room air and a Mach 2 freejet. These results include two-dimensional, spatially resolved measurements of velocity, temperature, and pressure derived from time-averaged spectra. ILTERED Rayleigh scattering (FRS), a recently developed flow diagnostic technique,1'2 achieves large suppression of background scattering allowing planar flowfield visualization and obtains quantitative measurements of velocity, temperature, and density in unseeded gaseous flows. This technique makes use of Rayleigh scattering from molecules in the flow and is driven by a high-power, narrow linewidth, tunable, injection seeded laser. When imaging the scattered light onto a charge-coupled device (CCD) camera, unwanted background scattering from stationary objects may be filtered out by tuning the frequency of the narrow linewidth laser to coincide with an atomic or molecular absorption line and by placing a cell containing the atomic or molecular species between the camera and the flow. This cell acts as a notch filter, absorbing all background scatter at the laser frequency. Scattered light that is Doppler shifted, however, passes through the filter and is imaged on the camera. Quantitative measure of flow properties is achieved by measuring the total intensity, Doppler shift, and spectral profile of the Rayleigh scattered light. The total intensity is directly proportional to density; the Doppler shift is directly proportional to velocity; and the spectral profile is a function of temperature and pressure. The scattering intensity, Doppler shift, and spectral profile are determined by passing the scattered light through the notch absorption filter and then by imaging it onto an intensified CCD camera. Because the filter absorbs light in a narrow frequency band, it converts the spectral information contained in the Doppler shift and Rayleigh profile into intensity information at the camera. By collecting data (camera pixel intensity) for varying conditions, v, T, and P may be determined. Previous work has concentrated on the use of this technique for background suppression when visualizing flows and for the measurement of velocity. The background suppression feature of FRS has been used to image flowfields that otherwise would be completely obscured by the strong scattering from wind-tunnel surfaces. The authors have used this technique to image the flowfield inside a Mach 3 inlet and to generate volumetric images of the crossing shocks and boundary layer.3 Elliott et al.4 have also used this technique to observe structures in compressible mixing layers. The use of FRS to measure velocity was initially demonstrated using scattering

Traditional space-time (ST) adaptive processing (STAP) theory is based on the assumption of narrowband or “zero-bandwidth,” where the decorrelation within the ST snapshot is ignored. However, with radar bandwidths increasing, this assumption becomes invalid due to the deteriorated decorrelation of the received signals within the ST snapshot. The decorrelation directly causes the dispersion of the received signals in both spatial and temporal domains, leading to the spreading of the clutter spectrum in the 2-D frequency (Doppler-spatial frequency) domain. With the spreading of the clutter spectrum, the clutter suppression notch in the traditional STAP filters is widened, resulting in a relative poor ability to detect slow-moving targets. In this article, we focus on the clutter suppression for wideband radar STAP. A generalized signal model of the ground clutter is first established for the wideband array radar. Using this outcome, we analyze the influence of bandwidth on the characteristics of the ground clutter and quantitatively describe the 2-D spreading of the ground clutter on the Doppler-spatial frequency plane. Moreover, the model of clutter covariance matrix for wideband STAP (W-STAP) is established. Finally, a 2-D keystone transform (KT) algorithm, referred to as ST KT (ST-KT), is proposed to eliminate the spreading of the ground clutter in the 2-D frequency domain caused by increasing bandwidths. Simulation results are employed to validate the theoretical analysis and verify the overperformance of the ST-KT based W-STAP method in terms of the output signal-to-clutter-plus-noise ratio (SCNR) of moving targets.

Detecting and estimating the velocity of slowly moving targets from a moving platform is difficult due to the Doppler broadening of the ground clutter. The latest MTI (moving target indicator) technique employs STAP (space time adaptive processing) to reduce the clutter's signal and thus is able to detect the target's speed. This technique has proven to be very effective for detecting high-speed targets and also for some slower moving targets such as helicopters. If, however, the target's speed is small, such as ground targets, the target's signal is reduced along with the clutter, again rendering the detection of the target's speed difficult. The techniques described in this paper utilize the signals from a multiple sensor system and are based on the correlation of the scattered waves of the target. The Doppler shift of the correlation function is then used to obtain the target's velocity. Unlike conventional MTI radar, our technique makes use of the Doppler shifted phase of the correlation of the scattered waves. Controlled experiments were conducted with an X-band radar and good agreement was obtained with numerical simulations.

Direct target localization and vector-velocity measurement method based on bandwidth synthesis in distributed high frequency surface wave radar

A series of Acoustic Doppler Velocity (ADV) measurements were made in a highly mobile sand bed channel with riprap side slopes and suspended sediment. The velocity measurements, in conjunction with sediment load data, are useful in determining the sediment load carrying capacity of the channel under different hydraulic conditions. The ADV data shows that for plane bed conditions a nearly logarithmic velocity profile exists. For ripple and dune bed conditions the velocity profile is kinked, consisting of a flatter sloped inner boundary layer and a steeper sloped outer boundary layer. Both the inner and outer boundary layers have a logarithmic velocity distribution. Above the outer boundary layer there is a nearly constant velocity zone that occasionally has a velocity dip near the free surface. The various types of velocity profiles are documented, and bed conditions are described with the Coles wake trength parameter.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation A. D. Sharma, A. K. Sharma, N. Thakur; Explosively generated shock wave processing of metal powders by instrumented detonics. AIP Conf. Proc. 3 June 2013; 1536 (1): 1169–1170. https://doi.org/10.1063/1.4810654 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

In order to improve capability of passive measurements, a novel approach is presented, which increase the medium wave and long wave infrared radiant information in the traditional bearings-only measurements equation. We explain the proposed mathematics model and modified covariance extend kalman filter algorithm in much detail in the full paper. Then the proposed model is used to estimate the position and velocity of aerial target by its angular information and infrared radiant information. Finally we give a simulation example. The results show that the passive measurements model proposed by us not only relax restriction of airplane motion, but also enhance the pace and precision of location, which looks promising for making passive measurements of position and velocity of target.

2-D phase unwrapping (PU) is a critical image processing step in many interferometric measurement technologies. To avoid the discontinuous phase gradient error spreading from the noisy region to the high-quality region of input interferogram, a skillful PU method should keep the congruency between input phase fringes and rewrapped phase fringes of the PU result as much as possible. However, traditional PU methods often fail in case input interferogram contains "bad" regions, in which the phase information should not be trusted. Under this condition, it is desired that the PU method instinctively keeps the fringe-congruency in the high-quality area and reasonably modifies the input phase fringes in the low quality area. In other words, the PU method with an extra adaptive filtering function would be preferred in practice. Based on this perspective, a novel minimum infinity-norm-based PU method, referred to MIN, is proposed in this letter. Both theoretical analysis and experiments demonstrate that the MIN method is an effective PU method.

The determination of airflow parameters is essential to the research of critical information on environment monitoring, chemical kinetics, and aerodynamic and propulsion applications. During the past few decades, tunable diode laser absorption spectroscopy has become a common and efficient tool for the flow velocity measurement based on the Doppler shift of the absorption line. Dual-comb absorption spectroscopy (DCAS), as a state-of-the-art Fourier-transform broadband spectroscopic technique, not only can detect multiple trace molecules in parallel but also can extract Doppler shifts to derive the flow velocity through the analysis of dozens of molecular absorption lines simultaneously with high precision. Here, we report a proof-of-principle demonstration of the velocity measurements of acetylene at various flow velocities by means of a high-resolution and broadband DCAS. Mode-resolved Doppler-shifted rotational-vibrational lines in the P branch of acetylene molecules are obtained. A model for multiline Doppler frequency determination is investigated and experimentally verified. The flow velocity measurements with a measuring uncertainty down to the submeter per second over the range from 8.7 m/s to 44.8 m/s at an effective time resolution of 1 s and a measuring uncertainty of 1.97 m/s at 0.1 s are demonstrated. With broadband mid-infrared frequency combs covering atmospheric transmission windows, the open-path measurement for monitoring diffusion of the weak pollutant source would be realized.

Recent progress in bistatic radar techniques can be used to improve performances of classical monostatic radar. A prominent limitation of coherent radar is its inability to measure the complete velocity vector (magnitude and direction) of a detected target. A single coherent detection can provide range-rate only. At least two detections, separated in time, are needed to estimate the target's velocity vector. This study discusses how the velocity vector can be determined by two simultaneous detections spaced in distance. The second detection is obtained by an auxiliary distant bistatic coherent receiver; an approach proposed in the 1990s to enhance meteorological radar. Being a very simple case of a distributed radar system allows for a simple demonstration of how to calculate the target's position and velocity vector and how to analyse the estimation accuracy, including geometric dilution of precision plots of the velocity error. Also discussed are two methods to identify correct data association when more than one target is detected.