Adaptive Doppler Research Articles

Multichannel ATI-SAR with application to the adaptive Doppler filtering of ocean swell waves

Multichannel along track interferometric (MATI) SAR systems are discussed from the point of view of ocean remote sensing. It is shown that the signals scattered by range moving scatterers can be Doppler filtered using a MATI-SAR. Processing techniques are presented, including a phase screen method for the removal of phase errors (including systematic errors and also those resulting from platform motions). A particular radar system (the ESR, enhanced surveillance radar) is described; this has a 3 cm wavelength MATI with two, three or four beams. It is used for investigating and exploiting Doppler effects in ocean radar scattering. It is demonstrated that, by applying adaptive Doppler filtering techniques, the MATI-SAR can significantly increase the imaging sensitivity of ocean features with respect to a conventional SAR. Examples illustrate the use of the ESR MATI-SAR system for imaging ship generated swell waves. Using three beams, the visibility of the wave images is increased by 9.5 dB looking downwind and 5.0 dB looking upwind for horizontal polarisation at grazing angles of 39° and 32°, respectively. Associated Doppler filter responses are shown which show that the scatterers modulated by the swell wave are located in the neighbourhood of the wave crests.

Adaptive Compensation Method Using the Prediction Algorithm for the Doppler Frequency Shift in the LEO Orbit Mobile Satellite Communication System

In low earth orbit (LEO) satellite communication systems, more severe phase distortion due to Doppler shift is frequently detected in the received signal than in cases of geostationary earth orbit (GEO) satellite systems or terrestrial mobile systems. Therefore, an estimation of Doppler shift would be one of the most important factors to enhance performance of LEO satellite communication system. In this paper, a new adaptive Doppler compensation scheme using location information of a user terminal and satellite, as well as a weighting factor for the reduction of prediction error is proposed. The prediction performance of the proposed scheme is simulated in terms of the prediction accuracy and the cumulative density function of the prediction error, with considering the offset variation range of the initial input parameters in LEO satellite system. The simulation results showed that the proposed adaptive compensation algorithm has the better performance accuracy than Ali's method. From the simulation results, it is concluded the adaptive compensation algorithm is the most applicable method that can be applied to LEO satellite systems of a range of altitude between 1,000 km and 2,000 km for the general error tolerance level, M = 250 Hz.

Adaptive Doppler compensation for coherent acoustic communication

Doppler shift tracking and compensation based on block and adaptive estimation methods are presented. These methods enable robust high data-rate acoustic communication between moving platforms such as autonomous underwater vehicles. The proposed schemes are incorporated within a wideband beamforming array with decision feedback equalisation. The block-based Doppler compensator is used as a pre-processor to the beamforming structure, whereas the adaptive compensator and the beamforming structure are jointly updated. The two methods employ multirate sampling and linear interpolation to compensate for the Doppler shift. Simulation and experimental sea-trial results are reported for both block and adaptive methods, which demonstrate successful communication at 16 kbit/s with a transmitting platform moving at up to ±2.6 m/s.

Adaptive Doppler processing technique

Abstract In this paper we have investigated the possibility of realizing an adaptive signal Doppler processing in stationary clutter regions by using modern spectral analysis technique. Burg's algorithm is chosen to update the whitening filter weights of the lattice. The coherent integration is realized by FFT processor. The computer simulation results are shown.

On-Line Echocardiographic Assessment of Hemodynamic Indexes by an Adaptive Doppler Analysis Algorithm and Signal/Noise Ratio Calculation

On-Line Echocardiographic Assessment of Hemodynamic Indexes by an Adaptive Doppler Analysis Algorithm and Signal/Noise Ratio Calculation

On-line echocardiographic assessment of hemodynamic indexes by an adaptive Doppler analysis algorithm and signal/noise ratio calculation

Assessment of cardiac diseases commonly involves the use of spectral Doppler echocardiography. Its use, however, often requires manual digitization of various transvalvular flow profiles. A new approach has been developed for on-line analysis of Doppler data, which involves thresholding based on the signal/noise ratio, calculating instantaneous values, and plotting on the spectral display in real time. We examined the reliability of this new method in 32 patients with 59 various flow jets by comparing it with the data derived by manual analysis. Correlations between the algorithm analysis and manual analysis for peak velocity, peak gradient, velocity-time integral, and acceleration time were excellent. These indexes were obtained with the algorithm in a shorter time and with better reproducibility than with manual analysis. Thus this new adaptive Doppler analysis algorithm yields reliable on-line quantification of valuable hemodynamic variables and represents an advance in quantitative echocardiography.

Performance of adaptive optimal Doppler processors in heterogeneous clutter

The performance of adaptive Hsiao-optimal clutter-suppression filters operating in spatially varying clutter backgrounds is investigated. The case of practical adaptive estimation of the covariance matrix, and limiting cases where the estimate of the covariance matrix tends to the mean clutter covariance matrix, are considered. Three classes of nonhomogeneous clutter are studied: the amplitude and spectral width in each range bin are drawn from spatially invariant independent gamma distributed parent populations; clutter edges, in which the range profiles of the amplitude and/or spectrum exhibit a step change; and homogeneous clutter in which some range bins are corrupted by point-clutter sources or extraneous targets with significantly different amplitude and spectral characteristics. The use of prefilter MTI is investigated as a means of reducing losses in improvement factor (IF) in some classes of clutter nonhomogeneity. It is shown that adaptive filters suffer significant reductions in IF in nonhomogeneous clutter environments. These losses are generally greater than the benefit afforded by ideal adaptive processors over other conventional Doppler processors. The mean IF loss is an optimistic performance measure in adaptive Doppler processors.

An effect of range-heterogeneous clutter on adaptive Doppler filters

The practical implementation of adaptive Doppler filters requires estimates of clutter parameters to determine the adaptive weights. A method of deriving the estimate via the sample matrix inversion (SMI) algorithm using multiple data snapshots from adjacent range cells is presented. For homogeneous clutter environments, the results of this technique asymptotically approach the optimum (a priori known covariance matrix) as the number of snapshots approaches infinity; this asymptotic behavior does not occur for heterogeneous clutter environments. An equation for the decrease in improvement factor is derived. To promote understanding, the simplified special case of narrowband clutter is considered in detail. In almost all cases, the loss is small. >

Adaptive Pulse Doppler Ambiguity Resolution

This paper demonstrates and tests a new algorithm for extracting velocity information from a pulse Doppler radar signal. The system is adaptive and performs weil in the presence of target scintillation. This paper also shows a special steady-state version of the adaptive algorithm. lt is computationally attractive and produces near optimal velocity estimates.