Postprocessing and corrections of bathymetry derived from sidescansonar systems: application with SeaMARC II

A procedure for postprocessing bathymetry data provided by a phase-measuring sidescan sonar system is presented. The data were collected with the SeaMARC II system, and are generally characterized by a high level of noise and uneven spatial sampling. Before any spatial filtering is applied, data are selected to remove most of the obvious artifacts and to retain instantaneous depth profiles whose slant ranges increase monotonically from a central location to the edges of the swath. An extrapolation scheme, patterned after a potential field, is proposed to fill gaps in the coverage or to extend the bathymetric swath to that of the corresponding sidescan image when regridding the data to a rectangular frame. To fill the near nadir gap typically found in these data, a specific interpolation methodology is developed that takes into account the slant range of the first bottom return as received by the sidescan sonar itself or by a shipboard echo-sounder. Spatial low-pass filtering is applied through convolutions with parabolic windows whose width is proportional to the footprint of the acoustic beam along track and roughly 1/8 of the swath width across track. Mismatches of contour lines between adjacent tracks are reduced through a statistical method design to correct systematic profile errors     

超短基线声学定位原理及其应用

声学定位系统（Acoustic Positioning System)的技术研究和应用开发在现代海洋科学调查中起着重要作用。以挪威Simrad公司的HPR410P超短基线定位系统为例，从几方面讨论了超短基线（Ultrashort Baseline)声学定位系统的原理、应用范围、定位误差来源及其相应的修正方法；通过最大程度地减少误差来提高系统的定位精度，从而获取高质量的海洋科研调查资料。     

EM1002型多波束测深系统及参数校正

多波束测深系统采用条带测量方式,可对水底进行全覆盖无遗漏测量,具有高精度、高效率、高质量等优点。本文概述了EM1002型多波束测深系统的技术性能,详细介绍了运用Calibrate多参数校准软件对其内部参数的校正。     

A generic swath‐mapping data format

There is a pressing need for standardization of data derived from bathy‐metric swath‐mapping systems. Currently several dozen multibeam and sidescan sonar data formats exist within the oceanographic community, and more can be expected as new systems are developed. Without some standardization of swath‐mapping data formats, the capability for use and integration of data from different systems will be severely compromised.

This paper presents a strategy for organizing swath bathymetry data in a logical modular fashion that will allow data from all current swath bathymetric sonar systems to be stored and accessed in a common fashion. We have chosen the approach of defining compact efficient modules for each logically independent portion of a data record and storing it in a manner that is portable between diverse computer architectures and operating systems. This approach is extensible to accommodate new types of data. Although specifically developed for swath bathymetry, this format is also capable of supporting digital sidescan data and other types of swath data.     

Feasibility of interferometric swath bathymetry using GLORIA, along-range sidescan

The feasibility of adding an interferometric swath bathymetric system to GLORIA, a 6.6 kHz long-range sidescan sonar, is discussed. The size of GLORIA's low-frequency transducer arrays and towfish precludes significant modifications, but even without such changes bathymetric errors could be several tens of metres over a usable swath somewhat smaller than the normal GLORIA swath. A swath bathymetry based on GLORIA will have random errors depending strongly on wind speed, water depth, and swath width. Within the range of these parameters, root-mean-square bathymetry errors in the range of 1-100 m can be expected     

Enabling technologies for REMUS docking: an integral component ofan autonomous ocean-sampling network

A dock for an autonomous underwater vehicle (AUV) allows the vehicle to be left on station ready for deployment. However, it represents a significant engineering challenge, as docking requires an accurate navigation system so that the vehicle can find the dock, and complex mechanics to make the required underwater power and data connections. This paper describes the docking system built for the REMUS AUV. It outlines the basis for the design decisions, the as-built configuration, and its performance once deployed. It also delineates the lessons learned from the deployments, and the refinements in the vehicle that have been made since that time, that will improve the system's utility and reliability     

Basement imaging with Side-Looking Seismics

The multistreamer Side-Looking Seismic system presented in this paper makes a sonograph of uncovered or buried crustal topography, thus revealing the structural fabric of the oceanic basement, even when this is covered with a sedimentary layer. Major elements of the system are an airgun as a sound source, five single-channel parallel streamers and two minicomputers for signal capture and processing.The system is used simultaneously for enhanced single-channel seismic profiling and for side-looking seismics. A vertical section with an improved signal-to-noise ratio and a suppression of side-echoes is produced on a digital seismic recorder. Primary side-looking seismic output in the form of 5 profiles with different angles of incidence is obtained within 10 seconds. This part of the processing can be done in real time.In sediment-covered areas the low frequencies used cause the slanted profiles (the side beams in the primary output) to be side-looking sonar images of buried topography. The projection process yielding final side-looking output corrects for slant range deformation caused by the water column and, if necessary, for deformation caused by refraction within the sedimentary column. The result approaches a conformal map of the structure of the traversed basement. Swath width is mainly determined by water depth and refraction effects in the sediment. In Madeira abyssal plain a swath width of 8000 m was attained in a water depth of 5000 m.Within the swath, oceanic basement structures are recognized in the form of elongate more or less parallel reflectors. They are interpreted as buried spreading topography. The lack of side-echoes within fracture zones combined with typical wall signatures can be used to trace fracture zones. These features are demonstrated for an area in Madeira abyssal plain.     

Analysis of swath bathymetry sonar accuracy

The practical limitations of many bottom mapping sonars lie in their ability to accurately estimate the angle of arrival. This paper addresses the accuracy of angle estimation when employed to determine the location of an extended target such as the bottom. A Gaussian model is assumed for the bottom backscatter and the corresponding Cramer-Rao lower bound for the variance of the angle estimate is determined for multi-element linear arrays. The paper focuses on determining the performance of high-resolution swath bathymetry sonars and, therefore, concentrates on the ability to determine bottom location with short pulses. Two error mechanisms, footprint shift and uncorrelated noise, are identified as important contributors to measurement errors. The two-element interferometric sonar configuration is investigated in detail. It is shown through the use of probability distributions, the Cramer-Rao bound, and simulation that it is difficult to get a good estimate of performance through simulation alone. Performance enhancement through pre-estimation and post-estimation averaging of multiple snapshots and changes in performance with pulse length and pulse rise time are also considered. Bottom estimation performance employing multi-element arrays is compared and contrasted with that of the two-element interferometric array. It is determined that there is little benefit associated with the multi-element array in terms of angle estimation performance alone. However, when other considerations such as angle ambiguities, multiple angles of arrival, and physical shortcomings associated with practical arrays are taken into account, the multi-element array is favored.     

Morpho-tectonic analysis of the Azores Volcanic Plateau from a new bathymetric compilation of the area

The existing studies of the Azores triple junction, although based on specific geological or geophysical data, largely rely upon morphological considerations. However, there is no systematic bathymetric coverage of this area, and the quality of the available bathymetric charts does not allow consistent morpho-structural analysis.In this work we present a new bathymetric grid elaborated with all the available data sources in an area comprised between 24° W to 32° W and 36° N to 41° N. The basic data set corresponds to the merge of NGDC data with new swath profiles. This new map, included as an Appendix, combined with other results from seismology and neotectonics, is the basis for the study of the morpho-structural pattern of the Azores area, the present day stress field and its implications on the current view of the Azores geodynamics.As a major result, we conclude that the Azores region is controlled by two sets of conjugated faults with 120° and 150° strikes that establish the framework for the onset of volcanism, expressing as linear volcanic ridges or as point source volcanism. This interaction develops what can be considered as the morphological signature of the Azores Spreading axis segmentation. We argue that the Azores domain, presently in a broad transtensional regime, is acting simultaneously as a ultra slow spreading centre and as a transfer zone between the MAR and the dextral Gloria Fault, as it accommodates the differential shear movement between the Eurasian and African plates.     

Stochastic modeling of seafloor morphology; Resolution oftopographic parameters by sea beam data

The authors explore the resolving power of an inversion algorithm which estimates five parameters of the seafloor covariance function from a single swath of multibeam echosounding data. The resolving power is evaluated as a function of the swath length, the orientation of ship track with respect to topographic grain, and the response width of the sounding system. The analysis is conducted by inverting sets of synthetic data with known statistics. The mean and standard deviation of the inverted parameters can be directly compared with the input parameters and the standard errors output from the inversion. Experiments show that resolution of the covariance parameters is strongly dependent on the number of characteristic lengths which are sampled. Root-mean-square seafloor height can be estimated to within ~15%, and anisotropic orientation to within ~5% (for a strong lineation), using track lengths as short as three characteristic lengths     

Multibeam bathymetric sonar: Sea beam and hydro chart

Abstract

In May, 1977, the first non‐military version of a multi‐beam, wide swath, deep ocean, bathymetric sonar was placed in service. Called SEA BEAM, this equipment provides high resolution bathymetric data across a swath width approximately equal to 78% of the depth. Angu ar resolution is 2.7° with a maximum operating depth of 11,000 m. Real time displays include a CRT presentation of the thwartship profile and a continuous strip chart of bottom contours. All sounding data are recorded on digital magnetic tape for final processing and merging with corrected navigation data. More recently, a companion system called HYDRO CHART has gone into operation for continental shelf surveys.     

Central swath mapping by a future satellite-borne fan-beam microwave scatterometer for inferring global ocean wind fields

The SeaSat-A satellite scatterometer is a microwave sensor designed to provide a capability for mapping the global ocean surface wind speed and direction. Four fan beams whose major axes are oriented atpm45andpm135degto the flight vector cover a swath width of 1900 km, but a central region remains that is inadequately mapped. In this paper, two additional fan beams are suggested for a future scatterometer that provide a more complete coverage of the central region.     

面向地形匹配的多波束测深数据抽稀方法研究

基于多波束测深的地形定位是水下潜器导航技术研究和发展的重点,多波束测深数据的高精度快速重采样是水下地形匹配定位的前提。传统的实时抽稀方法因对多波束测深数据模型的过分简化而效果欠佳。参考Douglas-Peucker算法和点云数据抽稀方法,采用角度-弦高联合准则对多波束每ping数据进行抽稀处理,参考导航地形图对抽稀后的多ping数据基于点云离散度进行二次抽稀处理,从而实现多波束测深数据的高精度快速抽稀处理。典型的数学仿真地形和实测多波束条带数据实验表明:文中提出的抽稀方法数据抽稀率仿真地形在85%以上,实测地形在90%以上,数据抽稀前后点云构成的曲面DEM误差在3%以内,并且算法实时性较好。     

Signal processing strategies for a bathymetric sidescan sonar

A dominant source of errors in swath bathymetry is acoustic interference. In 1989 the author published an analysis of these errors and predicted depth accuracies for a system which reduced their effect by averaging. This present paper shows how a considerable improvement in performance may be obtained by a variety of signal processing strategies that include the use of several widely spaced receivers and the elimination of the most unsatisfactory measurements before averaging. Simulations show how impressive sea bed profiles can be produced with a single ping, even at low signal-to-interference ratios     

Automatic indexing of underwater survey video: algorithm and benchmarking method

It is often the case that only a few sparse sequences of long videos from scientific underwater surveys actually contain important information for the expert. Locating such sequences is time consuming and tedious. A system that automatically detects those critical parts, online or during post-mission tape analysis, would alleviate the expert workload and improve data exploitation. In this paper, a methodology for evaluating the performance of such a system on real data is presented. Interesting sequences are started by changes of visual context. An algorithm to detect significant context changes in benthic videos in real time has been presented by Lebart et al. in 2000. It is used as an illustration for this methodology - its performance is studied and benchmarked on real underwater data, ground truthed by an expert biologist. Various issues relating to the complexity of the problems of automatically analyzing underwater video are also discussed.     

多波束与单波束测深数据融合处理方法

受声线弯曲的影响,多波束测深的边缘波束的数据质量较低,而单波束测深受声线弯曲的影响比较小。结合多波束覆盖面大和声速剖面误差对单波束影响相对较小的特点,研究了多波束和单波束的测深数据融合方法,利用同一位置单波束和多波束测深数据的差值,拟合一个与坐标位置相关的误差模型,并利用该误差曲面对多波束测深数据进行综合改正,从而提高多波束测深的数据质量。     

The SeaSat-A satellite scatterometer

This paper describes the methods used to develop performance requirements and design characteristics for the microwave scatterometer (SASS) ocean-surface wind sensor on the NASA SeaSat-A satellite. Wind vector measurement requirements from the SeaSat user community such as wind speed and direction accuracy, resolution cell size, grid spacing, and swath width formed the basis for defining instrument characteristics. The resulting scatterometer is designed for 14.6 GHz using four fan beam antennas to measure wind speed and direction over a 1000-km swath width with a resolution cell size50 times 50km. Results presented show scatterometer accuracy satisfies user requirements for wind speed from 4 m/s to greater than 24 m/s for the nominal SeaSat-A orbit of 790 km altitude,108deginclination, and 0.001 eccentricity.     

基于换位原理的对手建模模型

对抗性多机器人系统是 1个典型的多智能体系统 (MAS)。在 MAS中 ,建立对手模型 ,并进行意图和规划识别是对抗活动的基本前提。BDI是描述思维的有效手段 ,可用来建立通用的对手思维状态模型。本文在 BDI模型的基础上结合换位原理 ,提出了 1种对抗性多机器人系统中的对手建模模型 ,并将此方法应用到足球机器人系统 ,获得了较好的效果。     

OSCR wave measurements-some preliminary results

OSCR is an HF radar system that has been developed for high spatial resolution coastal surface current measurement. This paper describes preliminary results that demonstrate that wave measurement can be successfully obtained from suitably processed OSCR data. Comparisons with data from a WAVEC directional buoy are presented and show encouraging agreement. Some of the limitations to the measurement process are discussed and indicate a maximum range of about 20 km. Surface current variability on short time scales presents the most serious obstacle to wave measurement. This appears to be more of a problem when the mean currents are large, in that in these circumstances the data fail initial quality control criteria. However, in lower mean currents, the effect is often still present and leads to errors in long wave measurement     

Three-dimensional hydrodynamic-eutrophication model (HEM-3D): application to Kwang-Yang Bay, Korea

The purpose of this paper is twofold: to describe the water quality model of Three-Dimensional Hydrodynamic-Eutrophication Model (HEM-3D) and to present an application of HEM-3D to a coastal system in Korea. HEM-3D, listed as a tool for the development of Total Maximum Daily Load by US Environmental Protection Agency, is a general-purpose modeling package for simulation of the flow field, transport, and eutrophication processes throughout the water column and of diagenetic processes in the benthic sediment. This paper describes the water quality model of HEM-3D with emphasis on its unique features. Excessive loadings of organic wastes have significantly deteriorated water quality conditions of Korean coastal waters. This paper presents an application of HEM-3D to Kwang-Yang Bay, a coastal system in Korea, which is one of the first water quality modeling efforts for Korean coastal waters accompanied by a relatively comprehensive field program. The current status of data availability for water quality modeling in Korea is discussed.