A generalised background correction algorithm for a Halo Doppler lidar and its application to data from Finland

Current commercially available Doppler lidars provide an economical and robust solution for measuring vertical and horizontal wind velocities, together with the ability to provide co- and cross-polarised backscatter profiles. The high temporal resolution of these instruments allows turbulent properties to be obtained from studying the variation in radial velocities. However, the instrument specifications mean that certain characteristics, especially the background noise behaviour, become a limiting factor for the instrument sensitivity in regions where the aerosol load is low. Turbulent calculations require an accurate estimate of the contribution from velocity uncertainty estimates, which are directly related to the signal-to-noise ratio. Any bias in the signal-to-noise ratio will propagate through as a bias in turbulent properties. In this paper we present a method to correct for artefacts in the background noise behaviour of commercially available Doppler lidars and reduce the signal-to-noise ratio threshold used to discriminate between noise, and cloud or aerosol signals. We show that, for Doppler lidars operating continuously at a number of locations in Finland, the data availability can be increased by as much as 50 % after performing this background correction and subsequent reduction in the threshold. The reduction in bias also greatly improves subsequent calculations of turbulent properties in weak signal regimes.

Statistical analysis of the Doppler broadening coincidence spectrum of electron-positron annihilation radiation in silicon

We report a statistical analysis of Doppler broadening coincidence data of electron-positron annihilation radiation in silicon using a (22)Na source. The Doppler broadening coincidence spectrum was fit using a model function that included positron annihilation at rest with 1s, 2s, 2p, and valence band electrons. In-flight positron annihilation was also fit. The response functions of the detectors accounted for backscattering, combinations of Compton effects, pileup, ballistic deficit, and pulse-shaping problems. The procedure allows the quantitative determination of positron annihilation with core and valence electron intensities as well as their standard deviations directly from the experimental spectrum. The results obtained for the core and valence band electron annihilation intensities were 2.56(9)% and 97.44(9)%, respectively. These intensities are consistent with published experimental data treated by conventional analysis methods. This new procedure has the advantage of allowing one to distinguish additional effects from those associated with the detection system response function. (C) 2009 Elsevier B.V. All rights reserved.

High reproducibility of patellar tendon vascularity assessed by colour doppler ultrasonography : a reliable measurement tool for quantifying tendon pathology

Background: This study examined whether patellar tendon vascularity could be quantified accurately in the clinical setting using colour Doppler ultrasonography.

Methods: A sonographer and two radiologists visually estimated tendon vascularity in millimetres in 74 tendons during ultrasound (US) examination and from hard copy films. These estimates were then compared to the length of vessels measured from the digital image in millimetres and the correlation between them was determined. A subset of 16 tendons was used to compare the estimates of vascularity by two examiners at US examination.

Results: The estimation of vascular length at US examination correlated highly with the measured vascular length (r = 0.92; 95% confidence interval (CI) 0.87 to 0.94), as did the length estimated from the films (r = 0.94; 95% CI 0.9 to 0.96). The correlation between examiners was 0.84 (95% CI 0.51 to 0.94) for the estimates made during US examination and 0.85 (95% CI 0.59 to 0.95) for the vessel lengths measured from the digital images.

Conclusions: These excellent correlations indicate that tendon vascularity can be reliably estimated using colour Doppler ultrasonography and tendon vascularity could therefore be used by clinicians to rate clinical change. This method of quantifying tendon vascularity could also be used in research to investigate the effects of tendon treatments on vascularity.

A wavelet-based ammunition doppler radar system

Today’s state-of-the-art ammunition Doppler radars use the Fourier spectrogram for the joint time-frequency analysis of ammunition Doppler signals. In this paper, we implement the joint time-frequency analysis of ammunition Doppler signals based on the theory of wavelet packets. The wavelet-based approach is demonstrated on Doppler signals for projectile velocity measurement, projectile inbore velocity measurement and on modulated Doppler signal for projectile spin rate measurement. The wavelet-based representation with its good resolution in time and frequency and reasonable computational complexity as compared to the Fourier spectrogram is a good alternative for the joint time-frequency analysis of ammunition Doppler signals.

A wavelet-based ammunition Doppler radar system

Current ammunition Doppler radar systems use Fourier spectrogram for the joint time-frequency analysis (JFTA) of the radar signals. Two wavelet-based systems are presented for the JFTA of the radar signals. This research concludes that the proposed wavelet-based implementations are able to overcome this resolution limitation of the Fourier spectrogram method.

Maximum likelihood approach for tracking multiple mobile agents with a moving doppler radar system

Tracking mobile agents with a Doppler radar system mounted on a moving vehicle is considered in this paper. Dopplers modulated from mobile agents on the single frequency continuous wave signals are analyzed in order to estimate the positions and velocities of multiple mobile agents. The measurement noise is assumed to be Gaussian and the maximum likelihood estimation is utilized to enhance the localization accuracy.

Further applications of doppler radar for non-contact respiratory assessment

This paper further investigates the use of Doppler radar for detecting and identifying certain human respiratory characteristics from observed frequency and phase modulations. Specifically, we show how breathing frequencies can be determined from the demodulated signal leading to identifying abnormalities of breathing patterns using signal derivatives, optimal filtering and standard statistical measures. Specifically, we report results on a robust method for distinguishing cessation of the normal breathing cycle. The proposed approach can have potential application in the management of sudden infant death syndrome(SIDS) and sleep apnea.

Doppler radar in respiratory monitoring : detection and analysis

This paper presents the preliminary results of our work in detecting respiration using Doppler Radar in the 2.7 GHz operating band. We demonstrate the capability of Doppler Radar in capturing breathing patterns under various breathing forms such as normal breathing, fast breathing, as well as different rate of inhale and exhale. From the captured signals, respiration rate was obtained using Fast Fourier Transform and validated. The proposed approach could potentially be used in number of applications involving breathing rate and breathing pattern analysis via non-contact methods.

Respiration rate and breathing patterns from doppler radar measurements

This paper presents an evaluation of microwave Doppler radar used for capturing different types of breathing patterns in addition to the respiration rate. Finding therespiration rate is equally important as identifying abnormal breathing patterns which it could be used to gain a better insight into respiratory disorders. Various known breathing disorders were role played and captured using a non-contactmicrowave Doppler radar which further supports the feasibility of Doppler radar in obtaining an accurate detection of different types of breathing patterns. The results obtained for all the experiments were compared with a standard measurementapparatus, respiration strap, yielding a good correlations with the Doppler radar signals. In a nutshell, Doppler radar can be potentially used as an alternative approach, not only for finding the respiration rates, but also for identifying respiration patterns replacing the conventional contact methods.

Monitoring and analysis of respiratory patterns using microwave doppler radar

 Noncontact detection characteristic of Doppler radar provides an unobtrusive means of respiration detection and monitoring. This avoids additional preparations, such as physical sensor attachment or special clothing, which can be useful for certain healthcare applications. Furthermore, robustness of Doppler radar against environmental factors, such as light, ambient temperature, interference from other signals occupying the same bandwidth, fading effects, reduce environmental constraints and strengthens the possibility of employing Doppler radar in long-term respiration detection, and monitoring applications such as sleep studies. This paper presents an evaluation in the of use of microwave Doppler radar for capturing different dynamics of breathing patterns in addition to the respiration rate. Although finding the respiration rate is essential, identifying abnormal breathing patterns in real-time could be used to gain further insights into respiratory disorders and refine diagnostic procedures. Several known breathing disorders were professionally role played and captured in a real-time laboratory environment using a noncontact Doppler radar to evaluate the feasibility of this noncontact form of measurement in capturing breathing patterns under different conditions associated with certain breathing disorders. In addition to that, inhalation and exhalation flow patterns under different breathing scenarios were investigated to further support the feasibility of Doppler radar to accurately estimate the tidal volume. The results obtained for both experiments were compared with the gold standard measurement schemes, such as respiration belt and spirometry readings, yielding significant correlations with the Doppler radar-based information. In summary, Doppler radar is highlighted as an alternative approach not only for determining respiration rates, but also for identifying breathing patterns and tidal volumes as a preferred nonwearable alternative to the conventional - ontact sensing methods.

Detection of respiratory paradoxical movement via doppler radar measurements

 This paper presents an evaluation of microwave Doppler radar in capturing the respiration signal from the chest and abdomen simultaneously using two radar systems. Two experiments were conducted to investigate the feasibility of using Doppler radar in measuring respiration from both chest and abdomen simultaneously. Results obtained indicate that the respiration patterns from the radar were highly correlated with the reference respiration strap readings for normal breathing scenarios and also sensitive enough in capturing the paradoxical movement between the chest and the abdomen in the professionally role played experiments.

Towards localisation with Doppler radar

In this thesis the author introduces a novel method for Geo Localisation via Doppler Radar. The area of research is in the three dimensional space using amplitude and magnitude measurements. Geo Localisation in mobile applications is a useful technology that enables monitoring and gathering information about objects of interest.

Noncontact detection and analysis of respiratory function using microwave Doppler Radar

Real-time respiratory measurement with Doppler Radar has an important advantage in the monitoring of certain conditions such as sleep apnoea, sudden infant death syndrome (SIDS), and many other general clinical uses requiring fast nonwearable and non-contact measurement of the respiratory function. In this paper, we demonstrate the feasibility of using Doppler Radar in measuring the basic respiratory frequencies (via fast Fourier transform) for four different types of breathing scenarios: normal breathing, rapid breathing, slow inhalation-fast exhalation, and fast inhalation-slow exhalation conducted in a laboratory environment. A high correlation factor was achieved between the Doppler Radar-based measurements and the conventional measurement device, a respiration strap. We also extended this work from basic signal acquisition to extracting detailed features of breathing function (I: E ratio). This facilitated additional insights into breathing activity and is likely to trigger a number of new applications in respiratory medicine.

Separation of Doppler radar-based respiratory signatures

Respiration detection using microwave Doppler radar has attracted significant interest primarily due to its unobtrusive form of measurement. With less preparation in comparison with attaching physical sensors on the body or wearing special clothing, Doppler radar for respiration detection and monitoring is particularly useful for long-term monitoring applications such as sleep studies (i.e. sleep apnoea, SIDS). However, motion artefacts and interference from multiple sources limit the widespread use and the scope of potential applications of this technique. Utilising the recent advances in independent component analysis (ICA) and multiple antenna configuration schemes, this work investigates the feasibility of decomposing respiratory signatures into each subject from the Doppler-based measurements. Experimental results demonstrated that FastICA is capable of separating two distinct respiratory signatures from two subjects adjacent to each other even in the presence of apnoea. In each test scenario, the separated respiratory patterns correlate closely to the reference respiration strap readings. The effectiveness of FastICA in dealing with the mixed Doppler radar respiration signals confirms its applicability in healthcare applications, especially in long-term home-based monitoring as it usually involves at least two people in the same environment (i.e. two people sleeping next to each other). Further, the use of FastICA to separate involuntary movements such as the arm swing from the respiratory signatures of a single subject was explored in a multiple antenna environment. The separated respiratory signal indeed demonstrated a high correlation with the measurements made by a respiratory strap used currently in clinical settings.