Shallow Water Bathymetry Derived from Green Wavelength Terrestrial Laser Scanner     

Theodore Panagou  Emmanouil Oikonomou  Adonis F. Velegrakis 《Marine Geodesy》2020,43(5):472-492

Abstract

Shallow water bathymetry has proved to be a challenging task for remote sensing applications. In this work, Green-Wavelength Terrestrial Laser Scanning (GWTLS) is employed to survey nearshore bathymetry under clear atmospheric and water conditions. First, the obtained seabed points were corrected for refraction and then geo-registration, and filtering processes were exerted to obtain an accurate bathymetric surface. Terrain analysis was performed with respect to a reference surface derived from classical surveying techniques. The overall analysis has shown that the best results stem from 35° to 50° incident angles, whereas for angles higher than 65° measurements are not acceptable, although for the same angle in front and close to the instrument accuracy is considered acceptable due to the high laser power. Also, high resolution micro-topography, shallower than 1?m water depth, was managed to be captured. Systematic experimental approaches are expected to improve the GWTLS technique to detect bathymetry, which is anticipated to assist in mapping very shallow foreshore, tidal, and deltaic environments, to contribute conceptual into developing hybrid observation systems for coastal monitoring, and also to be applied in various maritime applications.  相似文献   

Measurements of magnetic fluxes and field strengths in the photospheric network     

Theodore D. Tarbell  Alan M. Title 《Solar physics》1977,52(1):13-25

We present digital pictures of an active region network cell in five quantities, measured simultaneously: continuum intensity, line-center intensity, equivalent width, magnetogram signal, and magnetic field strength. These maps are derived from computer analysis of circularly polarized line profiles of FeI 5250.2; spectral and spatial resolution are 1/40 Å and 1.5, respectively. Measured Zeeman splittings show the existence of strong magnetic fields (1000–1800 G) at nearly all points with a magnetogram signal exceeding 125 G. The mean and rms deviation of the field strengths change by less than 20% over a factor-of-four range of fluxes. From the significant disparity between measured fluxes and field strengths, we conclude that large flux patches (up to 4 across) consist of closely-packed unresolved filaments. The smallest filaments must be less than 0.7 in diameter. We also observe the dark component of the photospheric network, which appears to contain sizable transverse fields.  相似文献   

The Svecofennian gabbro-hosted Koivusaarenneva magmatic ilmenite deposit,Kälviä, Finland     

Niilo K. Kärkkäinen  Theodore J. Bornhorst 《Mineralium Deposita》2003,38(2):169-184

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Contrasting stable isotope behavior between calcite and dolomite marbles,Lone Mountain,Nevada     

I. J. Richards  Theodore C. Labotka  Robert T. Gregory 《Contributions to Mineralogy and Petrology》1996,123(2):202-221

 Late Proterozoic to Cambrian carbonate rocks from Lone Mountain, west central Nevada, record multiple post-depositional events including: (1) diagenesis, (2) Mesozoic regional metamorphism, (3) Late Cretaceous contact metamorphism, related to the emplacement of the Lone Mountain granitic pluton and (4) Tertiary hydrothermal alteration associated with extension, uplift and intrusion of silicic porphyry and lamprophyre dikes. Essentially pure calcite and dolomite marbles have stable isotopic compositions that can be divided into two groups, one with positive δ¹³C values from+3.1 to +1.4 ‰ (PDB) and high δ¹⁸O values from +21.5 to +15.8 ‰ (SMOW), and the other with negative δ¹³C values from –3.3 to –3.6‰ and low δ¹⁸O values from +16.9 to +11.1‰. Marbles also contain minor amounts of quartz, muscovite and phlogopite. Brown and blue luminescent, clear, smooth textured quartz grains from orange luminescent calcite marbles have high δ¹⁸O values from +23.9 to +18.1‰, while brown luminescent, opaque, rough textured quartz grains from red luminescent dolomite marbles typically have low δ¹⁸O values from +2.0 to +9.3‰. The δ¹⁸O values of muscovite and phlogopite from marbles are typical of micas in metamorphic rocks, with values between +10.4 and +14.4‰, whereas mica δD values are very depleted, varying from −102 to −156‰. No significant lowering of the δ¹⁸O values of Lone Mountain carbonates is inferred to have occurred during metamorphism as a result of devolatilization reactions because of the essentially pure nature of the marbles. Bright luminescence along the edges of fractures, quartz cements and quartz overgrowths in dolomite marbles, low δD values of micas, negative δ¹³C values and low δ¹⁸O values of calcite and dolomite, and depleted δ¹⁸O values of quartz from dolomite marbles all indicate that meteoric fluids interacted with Lone Mountain marbles during the Tertiary. Partial oxygen isotopic exchange between calcite and low ¹⁸O meteoric fluids lowered the δ¹⁸O values of calcite, resulting in uniform quartz-calcite fractionations that define an apparent pseudoisotherm. These quartz-calcite fractionations significantly underestimate both the temperature of metamorphism and the temperature of post-metamorphic alteration. Partial oxygen isotopic exchange between quartz and meteoric fluids also resulted in ¹⁸O depletion of quartz from dolomite marbles. This partial exchange was facilitated by an increase in the surface area of the quartz as a result of its dissolution by meteoric fluids. The negative δ¹³C values in carbonates result from the oxidation of organic material by meteoric fluids following metamorphism. Stable isotopic data from Lone Mountain marbles are consistent with the extensive circulation of meteoric hydrothermal fluids throughout western Nevada in Tertiary time. Received: 1 February 1994/Accepted: 12 September 1995  相似文献   

High-Altitude CUSP: The Extremely Dynamic Region in Geospace     

Jiasheng Chen  Theodore A. Fritz 《Surveys in Geophysics》2005,26(1-3):71-93

The high-altitude dayside cusps (both northern and southern) are extremely dynamic regions in geospace. Large diamagnetic cavities with significant fluctuations of the local magnetic field strength have been observed there. These cusp diamagnetic cavities are always there day after day and are as large as 6 R_E Associated with these cavities are charged particles with energies from 20 keV up to 10 MeV. The intensities of the cusp energetic ions have been observed to increase by as much as four orders of the magnitude when compared with regions adjacent to the cusp which includes the magnetosheath. Their seed populations are a mixture of ionospheric and solar wind particles. The measured energetic ion fluxes in the high-altitude cusp are higher than that in both the regions upstream and downstream from the bow shock. Turbulent electric fields with an amplitude of about 10 mV/m are also present in the cusp, and a cusp resonant acceleration mechanism is suggested. The observations indicate that the dayside high-altitude cusp is a key region for transferring the solar wind mass, momentum, and energy into the Earth’s magnetosphere.  相似文献   

Land classification of part of Thrace (East Rhodope) by visual interpretation of MSS images of first and second generation landsat images     

Theodore Astaras Dr.  Nikolaos Lambrinos 《GeoJournal》1988,17(3):357-363

The aim of this investigation was the classification of East Rhodope mountain ridge area and the surrounding hills and plains into mapping units by visual interpretation of 1:500,000 paper print enlargements of MSS false colour composites (bands 1, 2 and 4) of LANDSAT-4 and MSS (band 7) of LANDSAT-1, supported by limited field observation and background information available from earlier surveys and maps. The basic mapping units used in the present study was the land systems (developed by CSIRO in Australia) because they are easily recognizable on LANDSAT images by their destinctive combination of physiography, soils and vegetation.The twenty various land systems occurring in the study area, such as high/low mountains with smooth/sharp summits, nearly flat/undulated plains, slightly/strongly dissected hilles etc., were defined and mapped on small scale of 1:500,000. They are of considerable interest because they provide the framework for production of the same scale geological and geo-morphological maps, erosion studies, soil, vegetation and other thematic mapping for natural resources surveys, because LANDSAT images reveal details of terrain and microrelief that can never be reproduced on a topographic map. Also this land system map may modify or add to earlier small scale thematic maps (geology, soils and vegetation/forestry maps) produced in the past by other techniques.  相似文献   

Nutrient pore water chemistry,Great Bay,New Hampshire: Benthic fluxes     

William Berry Lyons  Theodore C. Loder  Susan M. Murray 《Estuaries and Coasts》1982,5(3):230-233

Benthic fluxes of C, N, P and Si have been measured at two sites in Great Bay Estuary, New Hampshire. Higher fluxes of reactive phosphate, nitrate and reactive silicate were observed at the site where bioturbation is known to occur and the fluxes of NH₄ ⁺, PO₄ ^?3 and reactive silicate at this location were from 3 to 6 times higher than that calculated by simple pore water diffusion models. *** DIRECT SUPPORT *** A01BY019 00010  相似文献   

Ultraviolet spectroscopy of the outer layers of stars     

Theodore P. Snow Jr.  Jeffrey L. Linsky 《Astrophysics and Space Science》1980,67(2):285-307

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Measurements of solar magnetic fields by Fourier transform techniques     

Theodore D. Tarbell  Alan M. Title 《Solar physics》1976,47(2):563-573

The Fourier techniques of Paper I have been exhaustively calibrated using Unno's results for the absorption profile of a simple Zeeman triplet. If a simple transformation is applied to the normalized line depths, then magnetic field strengths and inclination angles can be measured very accurately from noisy, saturated line profiles. Systematic errors caused by saturation effects can be estimated and reduced by varying one parameter. When a significant fraction of the line profile is unsplit and unpolarized, large errors may be made in measurements of low fields, unless the line is sufficiently weak. For a weak line, a vertical field of 1600 gauss can be measured to 10% accuracy even when 70% of the line profile is stray light. These stray light errors are troublesome in measuring fields of gaps and pores but not sunspots. Numerical results of our error analysis are presented graphically.  相似文献   

THE LEONARD MEDAL     

Theodore E. Bunch 《Meteoritics & planetary science》1973,8(3):291-291

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