Doppler Frequency Measurements Research Articles

Sequential Multi-Sensor JPDA for Target Tracking in Passive Multi-Static Radar With Range and Doppler Measurements

Target tracking in passive multi-static radar (PMSR) with bistatic range and Doppler frequency measurements from multiple transmit–receive pairs is gaining increasing interest. For the data association problem in this scenario, the parallel architecture of a multi-sensor joint probabilistic data association (P-MSJPDA) filter has been significantly investigated. As an alternative architecture, the sequential MSJPDA (S-MSJPDA) is rarely discussed in PMSR. In this paper, we evaluate the behaviors of S-MSJPDA in PMSR target tracking with bistatic range and Doppler frequency measurements. A comprehensive comparison between the S-MSJPDA and the P-MSJPDA in PMSR is provided. It can be found from the analysis that S-MSJPDA outperforms its parallel counterpart in terms of computational efficiency, given an acceptable degradation in position accuracy. The S-MSJPDA is further applied to an experimental passive multi-static radar for aircrafts tracking. The real data results obtained are rather close to the true trajectories of the targets. This demonstrates that the S-MSJPDA has great potentials in PMSR target tracking.

Observations and Modeling of Traveling Ionospheric Disturbance Signatures From an Australian Network of Oblique Angle‐of‐Arrival Sounders

AbstractA network of oblique angle‐of‐arrival (AoA) ionosondes was installed as part of the Elevation‐scanned Oblique Incidence Sounder Experiment (ELOISE) in September 2015. The ELOISE experimental campaign was designed to study the spatial and temporal structure of ionospheric variability at midlatitudes, of which traveling ionospheric disturbances are a key component. The new AoA sounder makes use of Defence Science and Technology Group's direct‐digital high‐frequency transmitter and receiver technology, to enable multichannel collection of both ionograms and channel scattering functions (Doppler spectra) on a common 2‐D array. In this paper, the array design and onboard signal processing for the AoA sounder is described, along with a sample of results showing typical disturbance signatures across the delay, Doppler frequency, bearing, and elevation measurements. Realistic parameterized models of electron density perturbations, along with geometric ray tracing, were used to synthesize the effects of medium‐ to large‐scale traveling ionospheric disturbances on the sounder observables and aid in interpreting the measured signatures.

Position Determination for Moving Transmitter Using Single Station

A common case in location problem is that the terminal is unstable or moving. The classical methods construct equations related to the measurements observed at the individual receivers first, and then solves the problem to localize the source. In this paper, we focus on the moving transmitter localization problem using only one station. The thinking of inverse synthesis aperture is implied, which takes advantage of the motion model to increase the equivalent aperture for higher accuracy. The proposed method formulates the problem through the angle of arrival and Doppler frequency measurements that are obtained from independent observations. After pseudo linearization by ignoring higher order noise terms, the estimator of position and velocity is easily solved through weighted least squares method. The bias reduction (BR) is utilized for lower bias and better root-mean-square error (RMSE). Using the result of BR as an initial solution, the maximum likelihood estimator (MLE) is realized through Gauss–Newton iteration. Theoretical analysis verifies that the BR estimator is efficient, which has Cramer-Rao Lower Bound (CRLB) accuracy if the noise level is mild. While MLE attends CRLB in higher noise situation albeit the possible divergence problem. Simulations indicate the feasibility and validate the advocated performance. The RMSE and bias match the theory very well.

Simultaneous Echo Power and Doppler Frequency Measurement System Based on Microwave Photonics Technology

A Doppler shift measurement system based on four-wave mixing effect in a highly nonlinear fiber is demonstrated practically. The system exhibits two low-frequency voltages, which are functions of the Doppler shift, and therefore, low-cost low-frequency photodetectors can be employed in the system. No sophisticated electrical instrument is required to perform the measurement. The scheme is able to simultaneously and independently measure the Doppler frequency of a radar echo and its power level with carrier frequency up to 40 GHz. The system is suitable to be employed in any microwave photonics (MWP) radar system with broad frequency agility characteristics or the other MWP systems operating based on frequency hopping technique.

Improved Sensitivity RF Photonics Doppler Frequency Measurement System

An improved sensitivity Doppler frequency measurement system based on microwave photonics technology was demonstrated practically. The system employs a four-wave mixing effect to achieve broad radio-frequency (RF) frequency measurement. In addition, a lock-in amplification technique was utilized to achieve high-measurement sensitivity. The system is, thus, capable of Doppler frequency estimation of radar echoes with a carrier frequency up to 40 GHz and a power level as low as $-$ 35 dBm.

Phase tracking for pulsar navigation with Doppler frequency

Doppler frequency in pulsar navigation is an effect caused by spacecraft and pulsar motion, which would worsen the pulsar navigation accuracy. To describe this influence, we establish the Doppler frequency measurement model based on pulsar timing. With this model, we describe the relationship between the phase estimation performance and the observation time when Doppler frequency exists. To reduce the pulsar navigation error due to the Doppler frequency, we designed the phase tracking loop for the pulsar navigation. The pulsar frequency can be modified before the phase estimation. As a result, the impact of the Doppler frequency could be lessened, and the observation interval lengths can be lengthened to improve the phase estimation performance.

Doppler Effect-Based Optical Fiber Vibration Sensor Using Frequency-Shifted Interferometry Demodulation

A novel optic-fiber vibration sensing system based on frequency-shifted interferometry (FSI) is proposed and demonstrated in this paper. The sensor is based on the phenomenon that the light frequency transmitted through a segment of bent fiber can be Doppler shifted by vibration. The Doppler frequency shift is measured using FSI demodulation. Compared to traditional fiber Bragg grating vibration sensor, the proposed sensor is easy to fabricate, of low cost and without directional dependency. The application of FSI demodulation allows for custom tailoring of measurement sensitivity, and has superior signal stability due to its same-path interference nature. The measured Doppler frequency shift using the FSI system agrees well with the calculated one, derived from strain measurements. The results show that the system has a high sensitivity and wide frequency range, limited only by the excitation apparatus used in the experiment.

Group Sparsity Based Multi-Target Tracking in Passive Multi-Static Radar Systems Using Doppler-Only Measurements

In this paper, we consider the problem of tracking multiple targets in a passive multi-static radar system using Doppler-only measurements. The number of targets is assumed unknown and time-varying. The Doppler measurements are subject to additive noise, clutter, and missed detections. Doppler-only measurements from a single sensor provide incomplete information about the target state, commonly referred to as single-sensor unobservability. In a passive multi-static radar system, the availability of multiple bistatic links naturally lends itself to the fusion of measurements from spatially distributed sensors. However, data fusion emerges as a computationally intensive problem in multi-sensor multi-target tracking algorithms. We propose a two-step sequential approach to solve the underlying problem. We first cast the underlying problem as a group sparse problem in a discretized position-velocity space. A group sparsity based algorithm is applied to simultaneously exploit the multi-static Doppler frequency measurements to directly obtain the instantaneous target state estimates in the Cartesian coordinate system. These estimates are then fed as inputs to the linear Gaussian mixture probability hypothesis density (GMPHD) filter, which removes the false measurements, compensates for missed detections and reduces the localization error. The optimal sub-pattern assignment metric, which jointly comprises a weighted contribution of cardinality error and localization error, is used to evaluate the performance of the proposed method. Simulation results show that the proposed method successfully handles the multi-target tracking problem and outperforms the existing random receiver selection based multi-sensor implementation of the GMPHD filter.

Standalone Microwave Photonics Doppler Shift Estimation System

A standalone microwave photonics system for Doppler frequency measurement purposes is conceived and demonstrated practically. The system exhibits a maximum of 1.61% relative error in Doppler frequency estimation at the worst case. Utilization of all optical mixing has enabled RF frequency independent operation. The system is thus capable of operating at any radar carrier frequency up to 40 GHz. This makes it a perfect candidate for various types of photonic-based radars and frequency agility systems.

Current Developments on Optical Feedback Interferometry as an All-Optical Sensor for Biomedical Applications.

Optical feedback interferometry (OFI) sensors are experiencing a consistent increase in their applications to biosensing due to their contactless nature, low cost and compactness, features that fit very well with current biophotonics research and market trends. The present paper is a review of the work in progress at UPC-CD6 and LAAS-CNRS related to the application of OFI to different aspects of biosensing, both in vivo and ex vivo. This work is intended to present the variety of opportunities and potential applications related to OFI that are available in the field. The activities presented are divided into two main sensing strategies: The measurement of optical path changes and the monitoring of flows, which correspond to sensing strategies linked to the reconstruction of changes of amplitude from the interferometric signal, and to classical Doppler frequency measurements, respectively. For optical path change measurements, measurements of transient pulses, usual in biosensing, together with the measurement of large displacements applied to designing palliative care instrumentation for Parkinson disease are discussed. Regarding the Doppler-based approach, progress in flow-related signal processing and applications in real-time monitoring of non-steady flows, human blood flow monitoring and OFI pressure myograph sensing will be presented. In all cases, experimental setups are discussed and results presented, showing the versatility of the technique. The described applications show the wide capabilities in biosensing of the OFI sensor, showing it as an enabler of low-cost, all-optical, high accuracy biomedical applications.

Influence of speckle effect on doppler velocity measurement

In a coherent Lidar system, velocity measurement of a target is achieved by measuring Doppler frequency shift between the echo and local oscillator (LO) signals. The measurement accuracy is proportional to the spectrum width of Doppler signal. Actually, the speckle effect caused by the scattering of laser from a target will broaden the Doppler signal's spectrum and bring uncertainty to the velocity measurement. In this paper, a theoretical model is proposed to predict the broadening of Doppler spectrum with respect to different target's surface and motion parameters. The velocity measurement uncertainty caused by the broadening of spectrum is analyzed. Based on the analysis, we design a coherent Lidar system to measure the velocity of the targets with different surface roughness and transverse velocities. The experimental results are in good agreement with theoretical analysis. It is found that the target's surface roughness and transverse velocity can significantly affect the spectrum width of Doppler signal. With the increase of surface roughness and transverse velocity, the measurement accuracy becomes worse. However, the influence of surface roughness becomes weaker when the spot size of laser beam on the target is smaller.

Target coordinate determination based on the Doppler frequency and angular rate in the forward-scattering radar system

The target coordinates are determined from Doppler frequency measurements performed in the diversed receivers of a forward-scattering radar system. Before solving the given problem, the system’s angular rate is estimated using a difference in frequency of two receivers. The suitable-for-use formulas whereby target coordinates are related to the Doppler frequency and the angular rate are derived.

Emulating Sentinel-1 Doppler Radial Ice Drift Measurements Using Envisat ASAR Data

Using data from the Envisat Advanced Synthetic Aperture Radar (ASAR) instrument, this paper demonstrates how the high-precision radial surface velocity product, which will become available with the European Space Agency's Sentinel-1 satellite, can complement the analysis of sea ice motion. High-resolution Doppler frequency measurements are used to estimate the subsecond line-of-sight motion of drifting sea ice in Fram Strait. We compare the method with buoy measurements and a recent cross-correlation algorithm for tracking ice between pairs of images. Maximum speeds measured from the time series were on the order of 20 cm/s. Using our method, we measured instantaneous speeds reaching 40–60 cm/s.

一种基于脉冲相位和多普勒频率联合观测量的 X 射线脉冲星导航方法

In order to eliminate the impact of the Doppler effects caused by the motion of the spacecraft on the X-ray pulsar-based navigation, an innovative navigation method using the pulse phase and Doppler frequency measurements of the X-ray pulsars is proposed. Given the initial estimate of the spacecraft’s state, the real-time photon arrival model is established at the spacecraft with respect to the spacecraft’s position and velocity predicted by the orbit dynamic model and their estimation errors. On this basis, a maximum likelihood estimation algorithm directly using the observed photon event timestamps is developed to extract a single pair of pulse phase and Doppler frequency measurements caused by the spacecraft’s state estimation error. Since the phase estimation error increases as the observation time increases, we propose a new measurement updating scheme of referring the measurements to the middle time of an observation interval. By using the ground-based simulation system of X-ray pulsar signals, a series of photon-level simulations are performed. The results testify to the feasibility and real-timeliness of the proposed navigation method, and show that the incorporation of the Doppler measurement as well as the pulse phase into the navigation filter can improve the navigation accuracy.

Multi‐PLL with two‐stage fusion to mitigate ionospheric scintillation effects on GPS receivers

AbstractIonospheric scintillation poses a great threat to the reliability and accuracy of Global Positioning System (GPS) in various applications. It can increase tracking errors of the phase‐locked loop (PLL) in a GPS receiver and even cause the PLL loss of lock under severe scintillations. To mitigate the effect of scintillation on GPS receivers, especially to reduce the occurrence of loss of lock, a multi‐PLL with two‐stage fusion (i.e., tracking fusion and output fusion) is proposed in this paper. This algorithm integrates several parallel sub‐PLLs with different loop parameters into one channel to track one GPS satellite's signal. Every sub‐PLL has its own discriminator, loop filter, carrier numerical controlled oscillator, and a tracking fusion (i.e., the first stage fusion). The tracking fusion of each sub‐PLL integrates the Doppler frequency measurements from all other sub‐PLLs to detect the state of its own sub‐PLL and feeds back reliable Doppler frequency measurements. Simultaneously, the tracking fusion outputs the Doppler frequency measurements to the second stage fusion (i.e., output fusion), which integrates the outputs from all tracking fusions to provide continuous and accurate Doppler frequency measurements for the following positioning/navigation estimator. Performances of the proposed algorithm are tested using real‐world GPS data with different levels of scintillations and compared with results from single‐PLLs. For three real‐world scintillation cases (S4 = 0.26–1.1, σϕ = 0.05–1.49 rad, and average C/N0 = 41.2–45.7 dB Hz), the multi‐PLL algorithm performs more robustly than the single‐PLLs and is able to keep tracking in all scintillation cases.

Cramér‐Rao lower bound with P d < 1 for target localisation accuracy in multistatic passive radar

By exploiting the sources of opportunity not designed for radar applications, the passive radar system often operates with a P d in the range from 60 to 85% for acceptable false alarm rates. Multistatic radar networks can be used to both increase detection capability and localisation accuracy. The standard Cramer-Rao lower bound (CRLB) cannot be used for a realistic assessment of the target localisation accuracy in a surveillance area since it provides optimistic predictions. In this study, the authors derive the CRLB with missing observations, namely for P d < 1, for the multisensory case. The results are illustrated for the case study of a multistatic passive radar exploiting FM radio transmissions where each bistatic pair within the network is assigned with a detection probability for each target position in the surveillance area. The obtained CRLB with P d < 1 is then employed to compare the localisation performance achievable by a multistatic passive radar when using different sets of measurements: (A) only range measurements, (B) range and Doppler frequency measurements and (C) Doppler frequency measurements only. The reported results show that the proposed CRLB with P d < 1 yields a more reliable prediction of the achievable performance thus allowing a fair comparison of the above different strategies for target localisation.

Target Tracking Using Extended Kalman Filter with Bearing and Doppler Measurements

Electronic support measure (ESM) can detect the bearings and Doppler frequencies simultaneously. A target tracking algorithm is proposed which uses ESM’s Doppler frequency and bearing measurements using extended Kalman filter (EKF). Compared with traditional bearings-only target tracking methods, our algorithm increases the Doppler frequency measurements and introduces the second-order EKF which can preferably handle the nonlinear tracking problem. Finally the simulation results show that the method improves the accuracy of target state estimation as well as the filtering stability. The maneuvers of sensor platform also can be avoided. Monte-Carlo runs with result analysis further illustrate the effectiveness of the algorithm.

Pulse phase and doppler frequency estimation of X-ray pulsars under conditions of spacecraft and binary motion and its application in navigation

The pulse phase and doppler frequency estimation of X-ray pulsars in dynamic situations and its application in navigation is a problem that has not been fully investigated. In this paper, solutions are proposed to solve this problem under conditions of spacecraft and binary motion. A high-precision doppler frequency (velocity) measurement model as well as a phase (range) measurement model is established. The averaged maximum-likelihood estimator is developed for the dynamic pulse phase estimation. The pulse phase tracking technique is used in the doppler frequency determination. The tracking filter is redesigned and compared with the existing algorithms. The comparison verifies the advantage of the filter algorithm presented in this paper. Unlike traditional views, it is found that in dynamic situations, shorter observation interval lengths will result in higher-accuracy phase and frequency estimates as the tracking filter outputs. A photon-level integrated numerical simulation is performed. Simulation results testify to the validity of the proposed phase and doppler frequency estimation scheme, and show that incorporation of velocity measurements as well as the range ones into the navigation estimator will improve the navigation steady-state performance.

Real-Time Measurement Method of Doppler Based on GPS Carrier Signals

According to Doppler effect of satellite on the time synchronization technology between satellite and the ground station, a real-time measurement method of Doppler is proposed based on GPS carrier signals. Using Doppler observations from GPS receiver, the method can real-timely measure Doppler frequency shift of GPS including dynamic Doppler and media Doppler whose error can be timely modified in the receiver end. Simulation results show that the frequency shift caused by dynamic Doppler, a main influencing factor in the course of transmission of time-frequency signal by GPS satellite, is between plus or minus several thousands Hz. Comparing to traditional measurement method of Doppler, the method makes it possible to fast track phase of signal in large dynamic range in synchronous technology.

NRT-Monitoring am Vulkanausbruch Eyjafjallajokull (Island) mit TerraSAR-X

NRT-Monitoring of the Eyjafjallajo kull volcanic eruption (Iceland) with TerraSAR-X. Natural disaster monitoring in Iceland, based on remote sensing data is performed by the group of geological remote sensing at the University of Munich for the space agencies ESA, NASDA/JAXA and CSA since 1992. This will be an important contribution by remote sensing techniques for the early warning and monitoring of natural disasters. The recent volcanic eruptions of the Fimmvo rduha ls (20.3.- 12.4.2010) and beneath Eyjafjallajo kull (since 14.4.2010) were the motivation for acquiring a series of TerraSAR-X scenes covering the volcanoes. This new satellite generation with its different beam modes and the additional option of rotation of the satellite from right looking to left looking mode allows an almost daily coverage of the active region in Iceland. This high frequent time series allowed a detailed investigation of the impact of the volcanic activities on the ice cover. For the rst time, also a glacier outburst ood (jokulhlaup: massive ood originating from melted glacier ice) could be covered by the image (15.4.2010). The ow velocities of this ood have been determined by Doppler-frequency measurements. Our study shows that the very fast data availability from TerraSAR-X enables an NRT-monitoring for observing natural processes.