Sloping Environment Research Articles

옥외용 이동로봇의 확장 칼만 필터 기반 3차원 위치평가 방법

This paper proposes a 3D localization method for an outdoor mobile robot. This method assesses the 3D position including the altitude information, which is impossible in the existing 2D localization method. In this method, the 3D position of the robot is predicted using an encoder and an inclination sensor. The predicted position is fused with the position information obtained from the DGPS and the digital compass using extended kalman filter to evaluate the 3D position of the robot. The experimental results showed that the proposed method can effectively evaluate the 3D position of the robot in a sloping environment. Moreover, this method was found to be more effective than the conventional 2D localization method even in the evaluation of the plane position where altitude information is unnecessary.

Sound propagation in deep water with a sloping bottom

Variation of bathymetry has a large effect on the sound propagation in deep water. An acoustic propagation experiment is carried out in the South China Sea. Some different propagation phenomena are observed for two different tracks in the flat bottom and the sloping bottom environments. Numerical analysis based on the parabolic equation model RAM (range-dependent acoustic model) is performed to explain the causes of the differences. The experimental and numerical results show that the transmission losses (TLs) decrease down to about 5 dB above the slope due to the reflection of the bottom, with a high-intensity region appearing below the sea surface. When a sea hill with a height of 320 m, which is less than 1/10 of water depth, exists in the incident range of sound beams on bottom first time, the sound beams are blocked due to the reflection of the sea hill. Then their propagating directions are changed, which makes an inverted-triangle shadow zone appearing in the reflection area of the sea hill. Compared with the TL results in the flat bottom environment, TLs increase up to about 8 dB in the corresponding area of the first shadow zone, and the abnormal TL effects can reach a maximal depth of 1500 m. Consequently, the shadow amplification effect caused by a small variation of bathymetry in deep water for long-range/large-depth sound propagation should receive enough attention. Furthermore, the convergence-zone structure in the sloping environment is different from that in deep water with flat bottom. The first convergence zone caused by refractions from the water above the axis of sound channel disappears. There are only the sound beams refracted back from water below the axis of sound channel. The numerical simulations show that the reflection-blockage of sound beams caused by the sloping bottom is significant. When the source is located somewhere above the slope, sound beams with large grazing angles can be reflected by the sloping bottom, and only some sound beams with small grazing angles can be refracted in the water without touching the slope and then come into the depth range of the vertical line array (VLA), forming the first part of the convergence zone refracted back from water. As the source moves farther from the VLA, the reflection-blockage of the sloping bottom becomes stronger. Sound beams are all reflected by the slope at a depth of about 3000 m, and they go through below the VLA, which leads to the absence of the first convergence zone caused by refractions from the water above the axis of sound channel. Therefore, the accuracy of bathymetry is meaningful for the sound propagation and target detection in deep water.

Flexible culverts in sloping terrain: Numerical simulation of soil loading effects

This paper investigates the performance of flexible culverts – often referred to as soil–steel composite bridges (SSCB) – when constructed in sloping topography. A number of 2D finite element models were created to simulate three case studies compromising two pipe arches and one high profile arch. The models were generated to investigate the effect of different surface slopes for different depths of soil cover. The aim was to understand and perceive the change of sectional forces in the structure with respect to slope increase under different soil covers. In addition, the effect of structure presence in the soil was also investigated in terms of soil stability. The results enable to realize the susceptibility of such structures to low heights of soil cover when built in sloping environment, which is seen in the incremental change in displacements and sectional forces, specially the bending moments. It is also found that the geometrical aspects of the profile shapes have more pronounced effect on their performance when introducing steeper slopes. The safety factor of soil stability is found to decrease when introducing such structures in the soil.

R/V Marcus G. Langseth seismic source: Modeling and calibration

This paper presents analyses of calibration data of the R/V Marcus G. Langseth seismic sources that were collected in 2007–2008. The analysis includes measurements of the levels and azimuthal directivity of the Langseth two‐string source, which is used for 3‐D seismic surveys and compares these data with multichannel seismic hydrophone array data in shallow water. The analysis also shows the important contribution of seafloor and subseafloor reflected and refracted arrivals and the associated effects of water depth and seafloor slope. As expected and predicted by modeling, azimuthal directivity depends greatly on the “footprint” dimensions of the seismic array. In shallow water, where the acoustic field is dominated by near‐vertically traveling reflected and refracted waves, data recorded using a towed MCS array are a useful proxy for single hydrophone calibration data. In deeper water, the easily modeled direct arrivals are exceeded in amplitude by seafloor reflected and subseafloor refracted energy at offsets which depend upon the water depth, limiting the applicability of a priori modeling that does not include these interactions. In addition, in a seafloor sloping environment, amplitudes depend greatly on whether the receivers are upslope or downslope from the source.

Particle filter source tracking in a changing geoacoustic environment.

This paper addresses the problem of tracking the acoustic source parameters such as the depth, range, and speed in evolving geoacoustic environments. It is well known that inaccurate knowledge about the environmental parameters such as the sound speed profile (SSP), water depth, sediment, and bottom parameters may result in significant errors in source parameters. To counter this, a particle filtering (PF) approach is adopted here where the geoacoustic parameters are tracked together with the source location and speed in a range-dependent environment. This allows accurate, real-time updating of the environment the ship is moving in and hence source can be located at any time accurately. As a sequential Monte Carlo technique that can operate on nonlinear systems with non-Gaussian probability densities, the PF is an ideal tracking algorithm to perform tracking of source and environmental parameters and their evolving probability distributions. The algorithm is tested on a sloping environment with the SSP, water depth, and sediment parameters evolving as the ship moves. The change in the water depth created the well-known “source mirage effect,” but the PF was still able to track the true source, geoacoustic parameters, and their evolving densities in this spatially varying environment. [Work supported by ONR.]

Modelling water erosion in the Sahel: application of a physically based soil erosion model in a gentle sloping environment

AbstractWater is a major limiting factor in arid and semi‐arid agriculture. In the Sahelian zone of Africa, it is not always the limited amount of annual rainfall that constrains crop production, but rather the proportion of rainfall that enters the root zone and becomes plant‐available soil moisture. Maximizing the rain‐use efficiency and therefore limiting overland flow is an important issue for farmers. The objectives of this research were to model the processes of infiltration, runoff and subsequent erosion in a Sahelian environment and to study the spatial distribution of overland flow and soil erosion.The wide variety of existing water erosion models are not developed for the Sahel and so do not include the unique Sahelian processes. The topography of the Sahelian agricultural lands in northern Burkina Faso is such that field slopes are generally low (0–5°) and overland flow mostly occurs in the form of sheet flow, which may transport large amounts of fine, nutrient‐rich particles despite its low sediment transport capacity. Furthermore, pool formation in a field limits overland flow and causes resettlement of sediment resulting in the development of a surface crust.The EUROSEM model was rewritten in the dynamic modelling code of PCRaster and extended to account for the pool formation and crust development. The modelling results were calibrated with field data from the 2001 rainy season in the Katacheri catchment in northern Burkina Faso. It is concluded that the modified version of EUROSEM for the Sahel is a fully dynamic erosion model, able to simulate infiltration, runoff routing, pool formation, sediment transport, and erosion and deposition by inter‐rill processes over the land surface in individual storms at the scale of both runoff plots and fields. A good agreement is obtained between simulated and measured amounts of runoff and sediment discharge. Incorporating crust development during the event may enhance model performance, since the process has a large influence on infiltration capacity and sediment detachment in the Sahel. Copyright © 2005 John Wiley & Sons, Ltd.

Broad-band Matched-Field Source Localization in the East China Sea

An incoherent broad-band frequency (100-200 Hz) domain Bartlett processor is applied to the wide-band source (WBS) signals for source localization. The coupled normal mode-parabolic equation theory based on the WKBZ approximation is used to calculate the replica fields in the sloping bottom environment. The experimental analysis shows that the accuracy of the source localization is largely improved with the consideration of the slope of bottom. The range estimates of the majority of signals by localized by matched-field processing in the range from 30.0 to 50.0 km are consistent with the global positioning system measured ranges.

Measurement of shallow-water reverberation characteristics

The frequency dependence and level of shallow-water (SW) reverberation, key parameters in sonar performance, represent the combined effect of scattering from the bottom, volume, and sea surface, and are a function of the transmission loss. SW, however, has the attribute of a seasonal dependence to the sound-speed structure, which can emphasize one of the above. A downward refracting profile in a gently sloping environment emphasizes the bottom and when the transmission is measured provides for a means of correcting for this loss and estimating the angle of incidence. This paper describes such measurements performed in several SW–sandy-bottom experiments with horizontal arrays, vertical arrays, and specially designed and calibrated sources. The scattering results are shown to be homogeneous and isotropic and to exhibit a frequency-dependent characteristic below 1 kHz with a minimum value apparently determined by the sediment layering. Numerical modeling suggests that scattering arises from the top several meters of sediment. The values determined here are consistent with previous measurements and the angular dependence determined by the use of vertical arrays and analytical calculations are consistent with Lambert’s Law. Limits on the values of this type of reverberation and performance differences with sonar operating frequency are discussed.

Quantitative studies on the smaller macrobenthos inhabiting various topographical environments around the Sagami bank in the deep-sea system of Sagami Bay

A survey was made in an area of complicated topography within the deep-sea system of Sagami Bay. Samples were obtained quantitatively with the Smith-McIntyre bottom-sampler of 1/10 m2 and were washed through a screen of 1.0 mm mesh. The biomass, the number of individuals and the number of species were studied at each station in relationship to submarine topography. All the items showed more or less parallel features in three topographical environments. High figures were found on the top of the bank and low ones in the canyon, while those values obtained in the sloping environment were intermediate and variable. The percent composition of the quantitatively important animal groups was rather constant throughout the top of the bank, and in this hahitat the faunal diversity was higher than in the others. From the distributional patterns of the species, and also from the species composition and dominancy at each station, the benthic communities of the bank-top and of the canyon were known to be distinct. In the sloping environment, however, the benthic assemblages at some stations were related to the bank-top community, either being its impoverished phase or with several elements peculiar to the slope, while at the remaining stations they were rather peculiar but related to the canyon community. All the aspects of the benthic ecology mentioned above were found to be closely related, both in their general and special features, to the nature of the sediments, in which three major types were recognized corresponding to the above three topographical environments. From the nature of the sediment, water movement, if any, can be expected on the top of the bank, and this is reflected in the preponderance of plankton- and/or ceston feeders making up this benthic community. Within the canyon, there were found the impoverishment of benthic community which is supposed to be due to the stagnant environment. The biomasses of the whole area were compared to those in other regions in the form of cumulative curves. In the deep-sea system of Sagami Bay which is well surrounded by land, the biomasses were only slightly lower than those of the shallow-sea system on the shelves in neighbouring regions, and those of a shallow enclosed bay were an order of magnitude higher than these figures. Those in the offshore parts of the continental shelf, remote from the coast, were nearly an order of magnitude lower.