Improved Velocity Estimation Method for Doppler Sonar Based on Accuracy Evaluation and Selection

The matched filtering method and the waveform-tracking method cannot maintain optimal velocity estimation performance all of the time. In order to solve this problem, this paper proposes an improved velocity estimation method for Doppler sonar, based on accuracy evaluation and selection. The echo of Doppler sonar is divided into several segments with the same width as the transmitted pulse, and each segment is regarded as the echo of the corresponding water layer. According to our study’s results, the velocity estimation accuracy of each segment is positively correlated with the ratio of its autocorrelation modulus to its power. Based on this conclusion, a velocity accuracy criterion with high accuracy and low complexity is designed in order to select the optimal velocity estimation for water layers or bottoms. The proposed accuracy selection method flexibly selects the echo interval to be processed according to the accuracy criterion, so as to maintain the optimal estimation of the current’s or bottom’s velocity. Water tank and field experiments using a prototype Doppler sonar device demonstrates that, compared with the matched filtering method and the waveform-tracking method, the average velocity estimation accuracy and bias of the proposed method are superior.

Velocity Measurement of Coherent Doppler Sonar Assisted by Frequency Shift, Kalman Filter and Linear Prediction

Velocity is vital information for navigation and oceanic engineering. Coherent Doppler sonar is an accurate tool for velocity measurement, but its use is limited due to velocity ambiguity. Velocity measured by frequency shift has no velocity ambiguity, yet its measurement error is larger than that of coherent Doppler sonar. Therefore, coherent Doppler sonar assisted by frequency shift is used to accurately measure velocity without velocity ambiguity. However, the velocity measured by coherent Doppler sonar assisted by frequency shift is affected by impulsive noise. To decrease the impulsive noise, Kalman filter and linear prediction are proposed to improve the velocity sensing accuracy. In this method, the Kalman filter is used to decrease measurement error of velocity measured by frequency shift, and linear prediction is used to remove the impulsive noise generated by a wrong estimate of the integer ambiguity. Lab-based experiments were carried, and the results have shown that coherent Doppler sonar assisted by frequency shift, Kalman filter and linear prediction can provide accurate and precise velocity with short time delay in a large range of signal to noise ratio.

Acoustic analysis of swallowing sounds in tracheostomized patients affected by traumatic brain injury

ABSTRACT Purpose: to demonstrate the feasibility of using the acoustic analysis of swallowing sounds as a combined method in the clinical assessment of tracheostomized patients affected by traumatic brain injury. Methods: an observational, cross-sectional study. A total of 10 adult patients, in the mean age of 43.6 years, participated. They were hospitalized in wards, semi-intensive, or intensive care units, from May to July 2016. The inclusion criterion involved being affected by traumatic brain injury, confirmed with a CT scan. The Speech Therapy Tracheal Decannulation Protocol was used in the clinical assessment, as well as the cervical auscultation with the Doppler sonar. Fisher’s test was used, resulting in no significant relationship (p > 0.05) between the variables analyzed in the two consistencies and decannulation. Results: the presence of an acoustic signal of laryngeal elevation was observed, as well as noise between the swallowings, and acoustic signal suggestive of residue in 50% of the patients for the consistencies tested. When the peak frequency, mean wave time, presence of residue in between swallowings, and acoustic signal suggestive of residues were correlated with decannulation (Table 5), no significant correlation was verified (p > 0.05) between the variables analyzed in the two consistencies and the decannulation. Conclusion: the study suggests that it is feasible to use the Doppler sonar as a combined method in the clinical assessment of dysphagia for the decannulation of patients affected by traumatic brain injury.

SwathDop: Multibeam Pulse-Coherent Doppler Sonar for Scanning 2D Velocity Sections near the Sediment–Water Interface

This paper considers the problem of accurately measuring the sediment transport over bedforms where flow evolves continuously both in time and space. For this purpose, we have developed a pulse-to-pulse coherent Doppler sonar system designed in bistatic geometry with two fan-beam transmitters symmetrically positioned on each side of a multielement receive array. The system resolves 2D velocity components within a ±20° (~0.5 m by ~0.5 m) swath. The software-defined radio data acquisition and control system limited us at present to eight independent receiver channels, and consequently the azimuthal resolution of the system is 4°. As a preliminary test of the sonar system, the system operation was simulated using a model developed to predict coherent sonar performance. The uncertainties with respect to the prescribed values and mean measurements in the model results were confined to 0.35 and 0.23 cm s−1, respectively, in the presence of strong shear (~150 s−1) and 50 cm s−1 horizontal flow. An important thing is that the model allowed us to test and develop the signal processing algorithms necessary to invert the multibeam sonar data. Using sand of 0.4-mm median diameter, the laboratory trials were carried out in active sediment transport conditions over dunes with 2-m wavelength and ~0.90 m s−1 unidirectional flow velocities. The results presented here focus mainly on 2D velocity field and indicate an average 4% deviation from the wake law and 8% from independent observations made with the wide-band multifrequency coherent Doppler profiler (MFDop) instrument under similar flow conditions.