Seabed geoacoustic characterization and classification by multisonar fusion

International audienceThis paper deals with potentialities of improvement of seabed geoacoustic properties characterization and classification by multisensor fusion. The aim of this work is to improve the performance prediction of low frequencies sonar (Anti Submarine Warfare). Geoacoustic and scattering properties estimation by inversion of received acoustic signals remains very difficult and strongly dependent on the system of measurement. Indeed the interaction between an acoustic wave and the sediment is heavily dependent on frequency, measurement angle and micro roughness of seafloor. The fusion of geoacoustic models inverted from different sonar systems with wide diversity of insonification angles and frequencies (single beam echosounder, multibeam echosounder, sidescan sonar and subbottom profiler) allow an extended description of the acoustic properties of the seafloor and the first sediment layers. A characterization method based on the Dempster Shafer theory of evidence is used to fuse geoacoustic models in order to classify the seafloor in three homogeneous acoustic zones (scattered solid, reflective fluid and absorbent fluid). Then, estimation of the geoacoustic parameters is conducted on each zone

Bottom and Suspended Sediment Backscatter Measurements in a Flume—Towards Quantitative Bed and Water Column Properties

For health and impact studies of water systems, monitoring underwater environments is essential, for which multi-frequency single- and multibeam echosounders are commonly used state-of-the-art technologies. However, the current scarcity of sediment reference datasets of both bottom backscatter angular response and water column scattering hampers empirical data interpretation. Comprehensive reference data derived from measurements in a controlled environment should optimize the use of empirical backscatter data. To prepare for such innovative experiments, we conducted a feasibility experiment in the Delta Flume (Deltares, The Netherlands). Several configurations of sonar data were recorded of the flume floor and suspended sediment plumes. The results revealed that flume reverberation was sufficiently low and that the differential settling of fine-sand plumes in the water column was clearly detected. Following this successful feasibility test, future comprehensive experiments will feature multi-frequency multi-angle measurements on a variety of sediment types, additional scatterers and sediment plumes, resulting in reference datasets for an improved interpretation of underwater backscatter measurements for scientific observation and sustainable management

Analysis of calibrated seafloor backscatter for habitat classification methodology and case study of 158 spots in the Bay of Biscay and Celtic Sea

An automated signal-based method was developed in order to analyse the seafloor backscatter data logged by calibrated multibeam echosounder. The processing consists first in the clustering of each survey sub-area into a small number of homogeneous sediment types, based on the backscatter average level at one or several incidence angles. Second, it uses their local average angular response to extract discriminant descriptors, obtained by fitting the field data to the Generic Seafloor Acoustic Backscatter parametric model. Third, the descriptors are used for seafloor type classification. The method was tested on the multi-year data recorded by a calibrated 90-kHz Simrad ME70 multibeam sonar operated in the Bay of Biscay, France and Celtic Sea, Ireland. It was applied for seafloor-type classification into 12 classes, to a dataset of 158 spots surveyed for demersal and benthic fauna study and monitoring. Qualitative analyses and classified clusters using extracted parameters show a good discriminatory potential, indicating the robustness of this approach

AUV swath bathymetric sensor data fusion for Rapid Environment Assessment

International audienceNowadays, Autonomous Underwater Vehicles (AUVs) become significant contributors to Rapid Environment Assessment (REA). Indeed, a variety of acoustic sensors can be mounted on AUVs allowing a complete seafloor representation (images, 3d data, video, sub-bottom layers, etc.). The AUV DAURADE platform is a new generation of AUVs. It can acquire bathymetry simultaneously with two acoustic sensors: a multibeam echo sounder (MBES) and an interferometric sidescan sonar (ISSS).In this paper, we propose a framework to fuse the bathymetric data coming from the two swath bathymetric sensors using the theory of belief functions. Here in after, obtained results on actual data are discussed

A statistical approach for analyzing and modeling multibeam echosounder backscatter, including the influence of high-amplitude scatterers

The statistical analysis of acoustic backscatter samples recorded by multibeam echosounders can be a valuable tool for remote seafloor characterization and interpretation. The present paper aims at analyzing the statistics of backscatter data values, both in “raw” status and after various averaging operations, using field data. It is shown that the statistics of the data can be adequately described by a Weibull distribution parametrized by the incidence angle and the level of applied processing: the distribution of the averaged backscatter amplitude, processed according to various schemes, varies from a Rayleigh law for raw data to lognormal and finally to Gaussian distribution after successive averaging operations. Based on these results, some recommendations for the calculation of the mean backscatter strength are presented. Finally, the influence of high-amplitude scatterers in the backscatter probability density function is addressed; a scheme is suggested to separate the contributions of the substrate from the contributions of the scatterers on the statistical distribution of sonar data sample

The fusion of digital terrain models measured from multiple acoustic sensors – Application to the DAURADE autonomous underwater vehicle

International audienceBuilding an accurate digital terrain model (DTM) of the seabed is a key issue for various military and civilian hydrographers applications.In the past decades, the emergence of autonomous underwater vehicles (AUV) offers new methodologies to collect the bathymetric data used in the estimation of the DTM. In our study, we use the DAURADE AUV platform which is capable of acquiring bathymetry with two acoustic sensors: A multibeam echo sounder (MBES) and an interferometric sidescan sonar (ISSS). The two sensors (MBES and ISSS) are synchronized to operate concurrently. In fact, the final DTM can be improved by performing a fusion of the data; the two systems acquire the bathymetry with different resolutions, geometries and error models; these parameters are introduced in the fusion process to improve the estimation of the DTM and to increase its accuracy.The aim of this paper is to describe the fusion method and discuss our simulated results. First, the modeling of two acoustic sensors (MBES and ISSS) will be briefly described. The input data sets are simulated by applying the sensor models on simplified seabed models. The use of seabed models provides ground truth and, therefore, allows for quantifying the accuracy of the fusion process

Fusion of Swath Bathymetric Data: Application to AUV Rapid Environment Assessment

International audienceBuilding an accurate and large digital terrain model (DTM) of the seabed is a key issue in various applications, especially for covert rapid environment assessment using autonomous underwater vehicles (AUVs). New AUV generations are capable of acquiring bathymetry with multiple acoustic sensors: single-beam echosounder, Doppler velocity log, multibeam echosounder (MBES), interferometric sidescan sonar (ISSS), etc. As these sensors acquire the seabed with different geometries, they can be combined to produce a DTM in shorter time. For example, ISSS can reach a wide swath in shallow water but it shows an information gap at nadir, which is usually covered by completing an additional track. Simultaneously using the MBES to acquire the nadir removes the need for this additional track and reduces the energy consumption of the whole survey. This paper focuses on fusion algorithms to extract best information of the two sensors (MBES and ISSS) to feed DTM production software with optimal bathymetric information. This problem may be solved by taking into account the average information of the two sensors. However, the sensors do not always give accurate information and the average information therefore becomes biased. Another way to tackle the problem is to select a priori information given by the better of the two sensors based on a given geometric parameter (e.g., grazing angle). In this case, when the assumed best sensor fails, the information produced by the second sensor cannot be used to compensate for the erroneous information. Our approach consists in using all the available information and fuses it ahead of producing the DTM. Based on the theory of belief functions, this paper presents a framework to fuse the information coming from the two swath bathymetric sensors (MBES and ISSS). The belief theory, applied successfully to other fields, has been extended to handle the bathymetric information. The reliability and the uncertainty of each sonar are introduced in the fusion process to improve the estimation and the accuracy of the final terrain model. First, simulated sonar data, with perfectly known ground truth, are used to quantitatively assess the performance of the fusion process by comparing DTM obtained with and without fusion. Then, the experimental validation is conducted on actual data, acquired simultaneously by the two sonars systems (Klein K5000 ISSS, Reson 8125 MBES) mounted on the DAURADE AUV. Our evaluation of the fusion method shows significant quantitative and qualitative improvement in the production of the final DTM

Swath bathymetric data fusion Application to autonomous underwater vehicles

International audienceThe autonomous underwater vehicle (AUV) DAURADEplatform can acquire bathymetry with two acoustic sensors:a multibeam echo sounder (MBES) and an interferometricsidescan sonar (ISSS). The two sensors (MBES and ISSS) aresynchronized and they can simultaneously operate and acquirethe bathymetry with different resolutions, geometries and errormodels. This complementarily allows us to improve the accuracyand the coverage of the collected bathymetric data by fusing bothof them. We applied the fusion process on actual data from thetwo bathymetric sensors of DAURADE (Reson 7125 MBES andKlein 5000 Interferometric); the obtained results are presentedand discussed

Multispectral and multiangle measurements of acoustic seabed backscatter acquired with a tilted calibrated echosounder

A multispectral and multiangle analysis of seabed backscatter intensity has been conducted using data from a calibrated single-beam echosounder (SBES) with five frequency channels deployed over four homogeneous areas with different sediment types in the Bay of Brest (France). The SBES transducers were tilted at incidence angles from 0 degrees to 70 degrees to record the seafloor backscatter angular response at discrete frequencies ranging from 35 to 450 kHz. The recorded backscatter levels were analyzed for their angular dependence (average backscatter strength versus frequency and angle) as well as for their sample statistical distribution. The angle and frequency dependence of the seafloor backscatter obtained using a calibrated SBES can potentially be used to calibrate multibeam systems, and it can also help in elucidating the physical processes of backscatter controlled by the interaction between the acoustic wave characteristics and the sediment properties. Backscatter measurements for each area showed a consistent frequency dependence with little variation between the four sediment types