共查询到20条相似文献，搜索用时 312 毫秒
1.
Robert T. Bird Roger C. Searle Valerie Paskevich David C. Twichell 《Marine Geophysical Researches》1996,18(6):651-661
We have replaced the usual band of poor-quality data in the near-nadir region of our GLORIA long-range sidescan-sonar imagery with a shaded-relief image constructed from swath bathymetry data (collected simultaneously with GLORIA) which completely cover the nadir area. We have developed a technique to enhance these pseudo-sidescan images in order to mimic the neighbouring GLORIA backscatter intensities. As a result, the enhanced images greatly facilitate the geologic interpretation of the adjacent GLORIA data, and geologic features evident in the GLORIA data may be correlated with greater confidence across track. Features interpreted from the pseudo-sidescan may be extrapolated from the near-nadir region out into the GLORIA range where they may nt have been recognized otherwise, and therefore the pseudo-sidescan can be used to ground-truth GLORIA interpretations. Creation of digital sidescan mosaics utilized an approach not previously used for GLORIA data. Pixels were correctly placed in cartographic space and the time required to complete a final mosaic was significantly reduced. Computer software for digital mapping and mosaic creation is incorporated into the newly-developed Woods Hole Image Processing System (WHIPS) which can process both low- and high-frequency sidescan, and can interchange data with the Mini Image Processing System (MIPS) most commonly used for GLORIA processing. These techniques are tested by creating digital mosaics of merged GLORIA sidescan and Hydrosweep pseudo-sidescan data from the vicinity of the Juan Fernandez microplate along the East Pacific Rise (EPR). 相似文献
2.
This paper reports a comparative study of digital enhancement techniques using spatial filtering to improve the geologic interpretation of side-scan sonar GLORIA images. Seven algorithms for speckle reduction with window sizes of 3×3-7×7 pixel and various numbers of iterations were tested for cosmetic purposes, and also to improve subsequent image processing. The filtered images were evaluated using both quantitative and qualitative techniques. It was determined that a normalized inverse gradient weighted smoothing scheme, with a 3×3 pixel filter and five iterations, allows a significant speckle reduction without blurring the edges in the GLORIA image which correspond to geological structures. Three local contrast enhancement techniques were also tested and evaluated to increase the perception of these geologic structures. Subtracting the gradient magnitude twice, calculated with spatial filters of a 5×5 pixel on smoothed images, was found to enhance most GLORIA images. Texture analysis methods developed for GLORIA images of mid-oceanic ridges and based on edge detection and orientation determination by spatial filtering are also presented. It enables the GLORIA mosaic of the Rodriguez triple junction (Indian Ocean) to be partitioned into regions of preferred orientation corresponding to the different seafloor fabrics generated at each arm of the triple junction 相似文献
3.
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 相似文献
4.
Le Bas T.P. Somers M.L. Campbell J.M. Beale R. 《Oceanic Engineering, IEEE Journal of》1996,21(4):545-553
For many years, GLORIA has been producing sonar images of the deep ocean floor. In the mid-1980's, the SeaMARC II system came to prominence producing depth values as well as sonar images. The basic method compares the phases of the signals returning from the seafloor to two rows of transducers. The phase differences are converted into angles of arrival and together with the arrival times converted into range and depth values. This capability has now been added to the GLORIA system. The fact that GLORIA uses a 2s FM pulse means the backscattered reverberation can come from a strip of seafloor up to 1.5 km wide. To accommodate this, overlapping complex FFT's are used to produce a time-frequency matrix for the returning signals. In this matrix, a constant range feature appears as a diagonal. Phases are then calculated using a least-mean-squares estimate along diagonals. The main source of error and bias is due to surface reflection, and this is taken into account. The GLORIA swath bathymetry system was tested on two cruises and it was possible to produce depth contours with a good level of confidence. The total swath width was over eight water depths and would have been greater with a more favorable velocity profile. Comparison with other bathymetry data (such as multibeam systems) showed excellent correlation, having a standard deviation of only 4% of total water depth 相似文献
5.
Q. J. Huggett A. K. Cooper M. L. Somers A. R. Stubbs 《Marine Geophysical Researches》1992,14(1):47-63
GLORIA side-scan sonographs from the Bering Sea Basin show a complex pattern of interference fringes sub-parallel to the ship's track. Surveys along the same trackline made in 1986 and 1987 show nearly identical patterns. It is concluded from this that the interference patterns are caused by features in the shallow subsurface rather than in the water column. The fringes are interpreted as a thin-layer interference effect that occurs when some of the sound reaching the seafloor passes through it and is reflected off a subsurface layer. The backscattered sound interferes (constructively or desctructively) with the reflected sound. Constructive/destructive interference occurs when the difference in the length of the two soundpaths is a whole/half multiple of GLORIA's 25 cm wavelength. Thus as range from the ship increases, sound moves in and out of phase causing bands of greater and lesser intensity on the GLORIA sonograph. Fluctuations (or wiggles) of the fringes on the GLORIA sonographs relate to changes in layer thickness. In principle, a simple three dimensional image of the subsurface layer may be obtained using GLORIA and bathymetric data from adjacent (parallel) ship's tracks. These patterns have also been identified in images from two other systems; SeaMARC II (12 kHz) long-range sonar, and TOBI (30 kHz) deep-towed sonar. In these, and other cases world-wide, the fringes do not appear with the same persistence as those seen in the Bering Sea. 相似文献
6.
Kathryn M. Scanlon 《Geo-Marine Letters》1984,4(1):1-4
The first continuous overview of a large segment of the continental slope and rise off the northeastern United States has been obtained using the GLORIA II long-range sidescan-sonar system. Extensive dissection by canyon and gully systems and evidence of possible large-scale sediment sliding are seen on the slope. The style and degree of incision, as well as the numbers and locations of canyons, have been found to differ significantly from previously published maps. It is suggested that the slope is a significant source of the sediment that has been deposited on the rise, and that some abrupt changes in the courses of canyons may be the result of local structural control. 相似文献
7.
GLORIA and SeaMARC II sea-floor images of offshore Western Samoa reveal large-scale mass movements, volcanism, and structural modification. These processes are driven by hot-spot mantle diapirism and nearby plate subduction. Debris avalanche deposits extend from the island slope onto the adjacent abyssal plains, covering at least 20,000 km2. Sediment flows occur in sheets up to 30 km wide; slump structures are common on steep slopes. Volcanic cones and lava sheets are evident on lower slopes and abyssal plains. Major volcanic rift zones on the island of Savaii continue offshore. Subduction-induced flexure has produced intense tensional fracturing on the outer wall of the Tonga Trench. 相似文献
8.
It is shown that useful relative backscatter strengths can be calculated from GLORIA long-range side-scan sonar data using a simple acoustic model. The calculation was performed on GLORIA side-scan sonar data collected during 1987 in the southern Indian Ocean. GEOSECS hydrographic information was used to access the effects of refraction (ray bending and aspherical spreading signal losses). Sea Beam bathymetry was used to correct the effective insonified area and compute the grazing angle. A major difficulty in performing this calculation over the terrain chosen (mid-ocean ridge topography) was one of adjusting navigation so that small features in Sea Beam and GLORIA data matched. Preliminary results show a 10-dB falloff in backscatter strength with decreasing grazing angle (10°-40°) at 6.5 kHz over what must presumably be a rough surface (extruded basalts and breccias) 相似文献
9.
Morphological features on the Mississippi Fan in the eastern Gulf of Mexico were mapped using GLORIA II, a long-range side-scan
sonar system. Prominent is a sinuous channel flanked by well-developed levees and occasional crevasse splays. The channel
follows the axis and thickest part of the youngest fan lobe; seismic-reflection profiles offer evidence that its course has
remained essentially constant throughout lobe development. Local modification and possible erosion of levees by currents indicates
a present state of inactivity. Superficial sliding has affected part of the fan lobe, but does not appear to have been a factor
in lobe construction. 相似文献
10.
R. C. Searle T. P. Le Bas N. C. Mitchell M. L. Somers L. M. Parson PH. Patriat 《Marine Geophysical Researches》1990,12(1-2):21-39
This chapter presents a summary of the image-processing techniques being used at present in the Institute of Oceanographic Sciences Deacon Laboratory's GLORIA long-range sidescan sonar system. It begins with a brief review of the development of GLORIA, and then describes in outline the present shipboard data acquisition, recording and replay system, including simple image-processing techniques that can be used on-board ship. Next, a detailed form of the sonar equation is developed, and this is evaluated factor-by-factor, to demonstrate the effects of beam directivity, refraction and water depth on the form of intensity variation to be expected in the final image. Finally, we discuss recent developments in shore-based image-processing. These include the development of improved radiometric corrections to normalize range-dependent intensity variations, recovery of true backscattering levels and estimation of backscattering coefficients, and combination of GLORIA with other data sets into single, colour digital images. As an example of the last process we show a digital mosaic of sonar data from the Southwest Indian Ridge, coloured as a function of depth derived from Sea Beam data in the same area. 相似文献
11.
In side-scan sonars such as GLORIA, along-track resolution is usually much worse than across-track resolution. This paper shows how along-track resolution may be improved by the application of an image restoration (deblurring) technique known as the Jansson-van Cittert method. Employing a model of the image formation process, this involves iterated convolution of the estimated deblurred image radiances with the theoretical alongtrack point spread function. The method and its implementation for GLORIA images are described. Smoothing of high frequency noise prior to restoration has been found to lead to an improved end-product. The restored images exhibit sharper edges and a greater clarity much appreciated by the interpreter. This visual impression is borne out by quantitative measurement. The technique is shown to be a useful adjunct to the battery of digital preprocessing techniques which can be applied to the sonar image prior to the information extraction stage. 相似文献
12.
Denis Mougenot Robert B. Kidd Alain Mauffret Hervé Regnauld R. Guy Rothwell Jean-René Vanney 《Marine Geophysical Researches》1984,6(4):329-363
Long-range sidescan sonar (GLORIA) data over Porto and Vigo Seamounts collected in 1978 has been re-interpreted in the light of SEABEAM bathymetric surveys conducted in 1982. The application of quantitative bathymetric information enables the interpreter to allow for artefacts inherent in the GLORIA data and to separate topography-related primary backscattering variations on the sonographs from more subtle changes that result from textural, slope and outcrop effects. The distinctions are made easier when slant-range corrected GLORIA data are available.Use of the combined survey data to precisely locate seismic profiling tracks and to identify likely areas of outcrop has allowed refined geological maps of the seamounts to be drawn and regional fault trends detected. The overall outline of the seamounts appears strongly fault-controlled.Porto and Vigo Seamounts are made up of the same geological formations and have had a similar structural history since their uplift as continental fault blocks in the Late Cretaceous to Middle Eocene period. Ravines that dissect the presumably lithified scarps bounding the seamounts may be relict features but still appear to control sediment input to gulley and channel systems in the surrounding topography. Sedimentary ridges associated with the seamounts represent anomalously thick sequences of post-Eocene material and probably result from interaction of downslope sedimentary processes and contour-following boundary currents.Contribution No. 274 from the Groupe d'Etude de la Marge Continentale (ERA 605). 相似文献
13.
The I.O.S. long range side-scan sonar GLORIA has been widely used over a variety of seabed types, but until recently had not been used over an independently authenticated field of manganese nodules. In the Eastern Atlantic Ocean at approximately 31°25 N 25°15 W, a field of nodules approximately 3–6 cm in diameter covering up to 18% of the seafloor was observed using an underwater camera. The nodule field occurred over approximately 2.8 km of the 8.3 km camera run. The corresponding GLORIA image shows an area of medium intensity backscattering, approximately 3.7 km in diameter. Considering the likely contrast in acoustic reflectivity between manganese nodules and deep sea sediments, we propose a correlation between the nodules observed in the photographs and the medium intensity echo target revealed by the GLORIA system. 相似文献
14.
Neil H. Kenyon 《Geo-Marine Letters》1992,12(1):24-32
Published analyses of 61 piston cores, bottom photographs, and dredge samples provide ground truth for 6.5 kHz GLORIA side-scan sonar records of the Mississippi and De Soto fans. GLORIA sound appears to have penetrated through up to 4 m of foraminiferal ooze and terrigenous mud to reach sandy sediments. Possible primary geological causes of high backscatter include slump structures at various scales (1->1,000 cm), possible debris flow fabrics (roughness 1–100 cm) in sandy (5–21%) sediments, and thin ironstone crusts with a roughness of tens of centimeters. 相似文献
15.
D. L. Tiffin 《Geo-Marine Letters》1993,13(2):126-131
The SOPAC GLORIA survey covered principally an east—west region of the southwest Pacific approximately along latitude 16°S between longitudes 167°E and 171°W. Although a main objective was to determine the potential for seabed resources, the survey covered parts of the boundary between the Pacific and Indo-Australian plates and therefore addresses fundamental tectonic processes in these areas. The boundary is complicated and in some regions is not completely known. It is made more complicated by being unstable in places, making its history unclear. This paper brings together the general results of the survey as discussed by other contributions in this special issue to provide an overall interpretation, particularly as it relates to the major plate boundary through the region. 相似文献
16.
A new bathymetry processing software package has been developed to postprocess new GLORI-B swath bathymetry data using preexisting techniques. GLORI-B bathymetry is calculated using an interferometry (phase delay) method using the modified GLORIA towfish which has parallel rows of transducers on both sides. We describe four types of artifacts observed during the first use of this new system during Legs 5 and 6 of the Gloria Expedition which surveyed the fastest spreading segment of the global seafloor spreading system and the broad chain of volcanoes near Easter Island. These artifacts include cross-track bias, along-track bias, a 'dropped edge' effect, and random noise. We describe and illustrate how we minimize these artifacts. We merge the SeaBeam 2000 bathymetry data with the GLORI-B bathymetry data to produce a final bathymetric mosaic which covers about 243,400 km2 and shows a different style of diffuse widely spread volcanism not previously observed along hotspot chains. The data are used in several studies describing seamount morphology, elastic thickness of the lithosphere, tectonic and geochemical evolution of the area, and mantle flow from a hotspot to a superfast seafloor spreading center. 相似文献
17.
The EM12 multibeam echosounder can record acoustic backscatter information as well as high resolution bathymetry. The dataset presented, from the axis of the Mid-Atlantic Ridge at 45° N, was the first EM12 survey of a mid-ocean ridge. This paper presents methods for utilising the backscatter information. Data processing enables the production of a mosaic of acoustic backscatter, and visualisation techniques are investigated to provide initial qualitative views of the combined backscatter and bathymetry datasets. The co-registration of the backscatter and bathymetry data enables quantitative analysis of their relationships. Various sites of different geological type have been selected and their angular acoustic backscattering relationships estimated, including the effect on backscatter of incidence angle, its regional variability with bottom type and the influence of bottom slope. Incidence angles and bottom type are shown to affect backscatter to a similar degree, while slopes appear to contribute little. The geometry of hull-mounted systems, such as the EM12, is significantly different from that of conventional sidescan sonars, such as GLORIA, and the backscatter images from the two types differ in various respects. Because of the wide variations in incidence angle that are common with hull-mounted systems, and the importance of incidence angle in determining backscatter strength, it is vital to consider the effect of incidence angle during interpretation. 相似文献
18.
Lindsay M. Parson Philippe Patriat Roger C. Searle Anne R. Briais 《Marine Geophysical Researches》1993,15(4):265-282
The present morphology and tectonic evolution of more than 1500 kilometres of the Central Indian Ridge are described and discussed following the integration of GLORIA side-scan sonographs with conventional geophysical datasets. Segmentation of the ridge occurs by a series of ridge axis discontinuities ranging in periodicity along strike from 275 km to less than 30 km. These segment boundaries we have classified into two types: first order fracture zones of offsets greater than 50 km which bound five major (mega-) segments, and smaller scale structures of a variety of offset styles and amplitudes which cut four of these segments. We refer to these as ridge-axis discontinuities. The frequent opposite sense of offset identified between the first order structures and the subordinate discontinuities between these major structures is interpreted as resulting from the adjustment to new kinematic parameters after magnetic anomaly 20. As far as our data allows us to determine, the central major segment is not subdivided by minor ridge axis discontinuities, which we suggest is a result of its proximity to the Rodriguez hotspot. 相似文献
19.
Michele Rebesco Robert D. Larter Angelo Camerlenghi Peter F. Barker 《Geo-Marine Letters》1996,16(2):65-75
Multichannel seismic reflection profiles from the continental rise west of the Antarctic Peninsula between 63° and 69°S show the growth of eight very large mound-shaped sedimentary bodies. MCS profiles and long-range side-scan sonar (GLORIA) images show the sea floor between mounds is traversed by channels originating in a dendritic pattern near the base of the continental slope. The mounds are interpreted as sediment drifts, constructed mainly from the fine-grained components of turbidity currents originating on the continental slope, entrained in a nepheloid layer within the ambient southwesterly bottom currents and redeposited downcurrent. 相似文献
20.
Debris flow deposits of large aerial extent have been detected on the lower continental rise off northwest Africa using GLORIA long-range dual sidescan sonar. A preliminary interpretation of the sonographs with high-resolution (3.5 kHz) seismic profiles and gravity cores illustrates the potential for spatial mapping of these deposits. The transport directions indicated on the sonographs show that these sediments, emplaced by mass transport, are the downslope continuation of the Saharan Sediment Slide. The distance from an observed “toe” of a debris flow lobe to the most southerly slide scar is of the order of 1,000 km. 相似文献