Sonar Measurements Research Articles

3D Sonar Measurements in Wakes of Ships of Opportunity

Abstract The aim of this work is to test the potential capabilities of 3D sonar technology for studying small-scale processes in the near-surface layer of the ocean, using the centerline wake of ships of opportunity as the object of study. The first tests conducted in Tampa Bay, Florida, with the 3D sonar have demonstrated the ability of this technology to observe the shape of the centerline wake in great detail starting from centimeter scale, using air bubbles as a proxy. An advantage of the 3D sonar technology is that it allows quantitative estimates of the ship wake geometry, which presents new opportunities for validation of hydrodynamic models of the ship wake. Three-dimensional sonar is also a potentially useful tool for studies of air-bubble dynamics and turbulence in breaking surface waves.

Novel Sonar Salient Feature Structure for Extended Kalman Filter-Based Simultaneous Localization and Mapping of Mobile Robots

Not all line or point features capable of being extracted by sonar sensors from a cluttered home environment are useful for simultaneous localization and mapping (SLAM) of a mobile robot. This is due to unfavorable conditions such as environmental ambiguity and sonar measurement uncertainty. We present a novel sonar feature structure suitable for a cluttered environment and the extended Kalman filter (EKF)-based SLAM scheme. The key concept is to extract circle feature clouds on salient convex objects by sonar data association called convex saliency circling. The centroid of each circle cloud, called a sonar salient feature, is used as a natural landmark for EKF-based SLAM. By investigating the environmental inherent feature locality, cylindrical objects are augmented conveniently at the weak SLAM-able area as a natural supplementary saliency to achieve consistent SLAM performance. Experimental results demonstrate the validity and robustness of the proposed sonar salient feature structure for EKF-based SLAM.

Supervisory Recurrent Fuzzy Neural Network Guidance Law Design for Autonomous Underwater Vehicle

A guidance law, based on supervisory recurrent fuzzy neural network control (SRFNNC), is proposed for the autonomous underwater vehicle (AUV) guidance systems. This SRFNNC system is comprised of a recurrent fuzzy neural network (RFNN) controller and a supervisory controller. The RFNN controller is used to mimic an ideal controller and the supervisory controller is designed to compensate for the approximation error between the RFNN controller and the ideal controller. The proposed design method is applied to investigate the active acoustic homing guidance of an AUV, which is affected by sonar propagation time-delay and measurement noise. A comparison is made for the proposed SRFNNC, a proportional navigation (PN) and a sliding-mode control (SMC) guidance laws. Simulation results show that the proposed SRFNNC guidance law is more robust and can obtain smaller miss distance than the PN and SMC guidance laws.

21st World Congress on Ultrasound in Obstetrics and Gynecology, 18-22 September 2011, Los Angeles, USA: presentations and awards

21st World Congress on Ultrasound in Obstetrics and Gynecology, 18-22 September 2011, Los Angeles, USA: presentations and awards

초음파 데이터의 신뢰도 모델 기반 지도 작성

This paper proposes a novel approach to building an occupancy grid map using sonar data. It is very important for a mobile robot to recognize and construct its surrounding environments for navigation. However, the grid map constructed by ultrasonic sensors cannot represent a realistic shape of given environments due to incorrect sonar measurements caused by specular reflection. To overcome this problem, we propose an advanced sonar sensor model which consists of distance and shape factors used to determine the reliability of sensor data. Through this sensor model, a robot can build a high-quality grid map. The proposed method was verified by various experiments and showed that the robot could build an accurate map with sonar data in various indoor environments.

Variability and changes of Arctic sea ice draft distribution – submarine sonar measurements revisited

Abstract. Changes in the mean sea ice thickness and concentration in the Arctic are well known. However, quantitative information about changes in the ice thickness distribution and the composition of the pack ice is lacking. In this paper we determine the ice draft distributions, mean and modal thicknesses, and their regional and seasonal variability in the Arctic for the time period 1975–2000. We compare characteristics of the Arctic pack ice for the years 1975–1987 and 1988–2000. These periods represent different large-scale atmospheric circulation modes and sea ice circulation patterns, most evident in clearly weaker Beaufort Gyre and stronger as well as westward shifted Transpolar Drift during the later period. The comparison of these two periods reveals that the peak of sea ice draft distributions has narrowed and shifted toward thinner ice, with reductions in both mean and modal ice draft. These noticeable changes are attributed to the loss of thick, mostly deformed ice. Springtime, loss of ice volume with draft greater than 5 m exceeds 35 % in all regions except the Nansen Basin, with as much as 45 % or more at the North Pole and in the Eastern Arctic. Autumn volume reduction, mostly of deformed ice, exceeds 40 % in the Canada Basin only, but is above 30 % also in the Beaufort and Chukchi Seas. During the later period, the volume of ice category consisting thin, mostly level first-year ice, is clearly larger than during the former period, especially in the spring. In the Beaufort Sea region, changes in the composition of ice cover have resulted in a shift of modal draft from level multiyear ice draft range to values of level first-year ice. The regional and seasonal variability of sea ice draft has decreased, since the thinning has been most pronounced in regions with the thickest pack ice (the Western Arctic), and during the spring (0.6–0.8 m per decade).

Modeling backscatter from a series of sediment rough interfaces and mud inclusions by a normal incident chirp sonar

A chirp sonar measures reflection and backscatter of normal incident sound from sediment interfaces and volume heterogeneity. Motivated by using such chirp sonar data to invert for goeacoustic parameters, a forward model has been developed and reported that uses an exact method on which practical models can be based. Further development of the model is presented to (1) investigate spatial resolution of rough interface scatter for given bandwidth and (2) to include the scattering from volume heterogeneity such as mud inclusions.

Laboratory calibration of upward looking sonars for measuring suspended frazil ice concentration

Abstract This paper describes a series of laboratory experiments conducted at the University of Alberta Cold Room Facility, investigating the use of upward looking sonars to measure frazil ice concentration. Two upward looking sonars, one high (546 kHz) frequency and one low (235 kHz) frequency were deployed on the bottom of a custom built frazil ice tank located in the cold room. A step by step procedure is provided for processing the raw sonar signal to compute the volume backscatter strength. A sieving technique was used to make direct measurements of frazil ice concentrations in the tank and sieved frazil ice particles were examined under a microscope to determine their average shape and size. Measured mass concentrations ranged from 0.012% to 0.135% and the majority of observed frazil particles were disk shaped, varying in diameter from 0.25 to 4.25 mm. The sonar measurements showed that the high frequency model is more sensitive to the presence of suspended frazil particles than the low frequency model, especially at lower concentrations. The depth averaged volume backscatter strength, computed from both the high and low frequency data, was found to be correlated with the frazil ice concentration and the resulting regression equations are provided. These correlations need to be tested in the field prior to being used for quantitative measurements of frazil ice concentration in rivers. The applicability of simplified theoretical backscatter models to estimate frazil ice properties is also discussed.

Asymptotic Properties of an Autocorrelation Coefficient for Coherent Doppler Sonar

Abstract A new formula is derived for the asymptotic form of the magnitude of an autocorrelation coefficient for coherent Doppler sonar. The autocorrelation magnitude is shown to be a biased estimator in the limit of infinite ensemble length. Numerical simulation of a Gaussian random process is used to verify the asymptotic formula and to show that a bias persists for finite pulse-pair averages. Validity of the asymptotic formula is also confirmed using a high-fidelity coherent Doppler sonar simulation, and from sonar measurements in a towing tank. It is shown that the distribution of observed autocorrelation coefficients is well predicted by a Gaussian random process once the autocorrelation bias has been removed.

Autonomous loop exploration and SLAM with fusion of advanced sonar and laser polar scan matching

SUMMARYSLAM is a well-studied technique for robots to build a map of environments while at the same time keeping track of their pose (position and orientation). However, SLAM does not provide motion control approaches for how the robot explores the environment. This paper presents an integrated approach to create a fully autonomous exploring and mapping robot. An Extended Kalman Filter (EKF)-SLAM approach is used to fuse Advanced Sonar measurements and the results of Laser Polar Scan Matching. The inclusion of Advanced Sonar data tackles the problem of map drifts in environments where lasers do not supply sufficient information, such as along a corridor. In addition, the proposed exploration strategy takes advantage of the characteristic of the Voronoi graph to enable the robot to strategically explore the environment in a loop-closing fashion and a safe manner. By revisiting areas to close loops as early as possible, the robot builds a more stable map incrementally while still reliably tracking its pose. Experimental results of the integrated approach are shown to demonstrate the paper's approach that provides real-time exploration of a mobile robot in an initially unknown real environment. Experimental map quality comparisons using exploration strategies show the benefits of early local loop-closing.

Modeling backscatter from a series of sediment rough interfaces by a normal incident chirp sonar.

Chirp sonar is widely used as a survey tool in shallow water. A chirp sonar measures reflection and backscatter of normal incident sound from sediment interfaces and volume heterogeneity. Motivated by using such chirp sonar data to invert for goeacoustic parameters, a forward model is developed that uses an exact method on which practical models can be based. Here volume heterogeneity is ignored and only scattering by a set of rough interface is modeled. If these interfaces are flat, the received data will be a series of reflections from the interfaces. However, these interfaces are in general rough and a forward model should be able to quantitatively handle scattering from these rough interfaces, including full scattering from each interface and multiple scattering among the set of interfaces. A set of integral equations is derived, which provides the numerical mechanism to calculate the scattered field from the rough interfaces, and numerical examples are presented.

Multibeam sonar observations of hydrothermal flows at the Main Endeavour Field.

The Cabled Observatory Vent Imaging Sonar has been deployed at the Main Endeavour Node of the Canadian Neptune cabled observatory and has acquired data on plume and diffuse hydrothermal flows. Based on the Reson 7125 multibeam sonar and operating at 200 and 400 kHz, two‐dimensional and three‐dimensional time series are produced using plume backscattering, Doppler shift, and acoustic scintillation. Hydrothermal plumes and diffuse flow are important as agents of transfer of heat, chemicals, and biological material from the mantle and crust into the ocean in quantitatively significant amounts. High‐frequency sonar measurements offer the possibility of inversion to obtain fluxes of central importance in these processes. Long‐term time series, obtainable in cabled systems, allow observations of hydrothermal response to tidal, tectonic, and volcanic forcing. Examples will be given of plume bending due to currents, determination of entrainment of ambient water, time variation of diffuse flows, and Doppler determ...

A thermodynamic model for estimating sea and lake ice thickness with optical satellite data

Sea ice is a very important indicator and an effective modulator of regional and global climate change. Current remote sensing techniques provide an unprecedented opportunity to monitor the cryosphere routinely with relatively high spatial and temporal resolutions. In this paper, we introduce a thermodynamic model to estimate sea and lake ice thickness with optical (visible, near‐infrared, and infrared) satellite data. Comparisons of nighttime ice thickness retrievals to ice thickness measurements from upward looking submarine sonar show that this thermodynamic model is capable of retrieving ice thickness up to 2.8 m. The mean absolute error is 0.18 m for samples with a mean ice thickness of 1.62 m, i.e., an 11% mean absolute error. Comparisons with in situ Canadian stations and moored upward looking sonar measurements show similar results. Sensitivity studies indicate that the largest errors come from uncertainties in surface albedo and downward solar radiation flux estimates from satellite data, followed by uncertainties in snow depth and cloud fractional coverage. Due to the relatively large uncertainties in current satellite retrievals of surface albedo and surface downward shortwave radiation flux, the current model is not recommended for use with daytime data. For nighttime data, the model is capable of resolving regional and seasonal variations in ice thickness and is useful for climatological analysis.

Sonar detection and measurements of ice in a freezing river I: Methods and data characteristics

The basic concepts and operating principles of SWIPS (Shallow Water Ice Profiling Sonar) measurements in freezing rivers are outlined and described with reference to ongoing BC Hydro ice- and flow monitoring programs in the Peace River. Emphasis is given to identifying the nature of the measured quantities and their connections to the parameters conventionally used to describe and model rivers and their ice contents. Difficulties in deployment and data recovery, mostly associated with the growth of anchor ice, are described in terms of the evolution of successful approaches and the pitfalls encountered along the way. Distinctions are made among results obtained from targets at or inside floating surface ice and from particulate targets, suspended in the water column. Example results are presented in each case and put in the context of seasonal changes in the monitored quantities of interest. The usefulness of lower frequency measurements for ice cover studies is highlighted. Limited results from simultaneous multifrequency measurements on suspended particulate (frazil) targets are reviewed and analyzed to show the likely applicability of Rayleigh Law assumptions for observations made prior to ice cover stabilization and in, at least, the lower water column. This applicability is combined with estimates of absolute return strengths to make rough assessments of the ranges of particle sizes and concentration encountered in the Peace River studies.

Sonar Measurements in Ship Wakes Simultaneous With TerraSAR-X Overpasses

A pilot experiment was conducted in the period from April to June 2008 in the Straits of Florida near Port Everglades, Florida, in order to study the dynamics of far wakes of ships. In this experiment, a small boat with downward-looking sonar made ¿snakelike¿ sections through wakes of ships of opportunity during the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TerraSAR-X</i> overpasses. The ship and its parameters (length, speed, course, etc.) were identified utilizing an automated identification system. The sonar responded to the clouds of microbubbles generated in the ship wake by the propulsion system and ship-hull turbulence. The ship wakes were traced in the sonar signal typically from 10 to 30 min after the ship's passage. A preliminary analysis of the measurements suggests that the visibility of the centerline ship wake in synthetic aperture radar (SAR) images is correlated with the presence of microbubbles in the wake. This supports the hypothesis that natural surfactants scavenged and brought to the surface by rising bubbles play an important role in the wake visibility in SAR. The influence of the wind-wave field on the ship wake, as well as the effect of screening of the wind-wave field by the ship's hull, adds another level of complexity to wake patterns observed in SAR images.

Concurrent Map Building and Behavior Learning for Navigation in Unknown Environments

In this paper, we report a robust and low-cost navigation algorithm for an unknown environment based on integration of a grid-based map building algorithm with behavior learning. The study focuses on mobile robots that utilize ultrasonic sensors as their prime interface with the outside world. The proposed algorithm takes into account environmental information to augment the readings from the low angular accuracy sonar measurements for behavior learning. The environmental information is obtained by an online grid-based map learning design that is concurrently operating with the behavior learning algorithm. The proposed algorithm is implemented and tested on an in-house-built mobile robot, and its performance is verified through online navigation in an indoor environment.

Decline in Arctic sea ice thickness from submarine and ICESat records: 1958–2008

The decline of sea ice thickness in the Arctic Ocean from ICESat (2003–2008) is placed in the context of estimates from 42 years of submarine records (1958–2000) described by Rothrock et al. (1999, 2008). While the earlier 1999 work provides a longer historical record of the regional changes, the latter offers a more refined analysis, over a sizable portion of the Arctic Ocean supported by a much stronger and richer data set. Within the data release area (DRA) of declassified submarine sonar measurements (covering ∼38% of the Arctic Ocean), the overall mean winter thickness of 3.64 m in 1980 can be compared to a 1.89 m mean during the last winter of the ICESat record—an astonishing decrease of 1.75 m in thickness. Between 1975 and 2000, the steepest rate of decrease is −0.08 m/yr in 1990 compared to a slightly higher winter/summer rate of −0.10/−0.20 m/yr in the five‐year ICESat record (2003–2008). Prior to 1997, ice extent in the DRA was &gt;90% during the summer minimum. This can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to &lt;55% during the record setting minimum in 2007. This combined analysis shows a long‐term trend of sea ice thinning over submarine and ICESat records that span five decades.

Effective Maximum Likelihood Grid Map With Conflict Evaluation Filter Using Sonar Sensors

In this paper, we address the problem of building a grid map using cheap sonar sensors, i.e., the problem of using erroneous sensors when seeking to model an environment as accurately as possible. We rely on the inconsistency of information among sonar measurements and the sound pressure of the waves from the sonar sensors to develop a new method of detecting incorrect sonar readings, which is called the conflict evaluation with sound pressure (CEsp). To fuse the correct measurements into a map, we start with the maximum likelihood (ML) approach due to its ability to manage the angular uncertainty of sonar sensors. However, since this approach suffers from heavy computational complexity, we convert it to a light logic problem called the maximum approximated likelihood (MAL) approach. Integrating the MAL approach with the CEsp method results in the conflict evaluated maximum approximated likelihood (CEMAL) approach. The CEMAL approach generates a very accurate map that is close to the map that would be built by accurate laser sensors and does not require adjustment of parameters for various environments.

Enhanced wavelet-based methods for reducing complexity and calculation time in sonar measurements

We introduce two enhanced wavelet-based methods to improve accuracy and optimize calculation efficiency for sonar time delay estimation. Existing time delay estimations provide poor results because of many environmental effects such as noise, multipath, and crosstalk. While advanced digital signal processing (DSP) techniques have been proposed to overcome these problems, they entail increased complexity and calculation time. We use prediction in the methods we propose; the position where the reflected wave starts to occur is predicted by a recognition technique. The results are much better and the calculation time is shorter than other methods that use DSP techniques. In the first method, the optimization procedure is applied in the time domain, while in the second method, the optimization is calculated in the wavelet domain. Numerical comparisons and simulations using synthetic signals are provided to demonstrate the effectiveness of the proposed enhanced methods. We also demonstrate that our new algorithms are more stable than the existing ones and that the calculation time is reduced dramatically while maintaining increased accuracy, especially in a high-noise environment.

잘못된 초음파 센서 데이터를 여과하기 위한 음압 비교법

In this paper, we address the problem of detecting incorrect sonar measurements. We use ideas from the inconsistency of information among sonar measurements together with the sound pressure of the wave from the sonar sensor to develop a new method, called the comparison of the sound pressure (CSP), to detect incorrect sonar readings. The inconsistency of information in cells can be a clue that indicates candidates for incorrect measurements, and the sound pressure of the wave from the sonar sensor determines incorrect readings among the candidates. From various experiments, the proposed method is confirmed that it is better than existing method at deciding the state of sonar measurements.