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41.
Using the Global Positioning System (GPS) for geodetic positioning   总被引:1,自引:0,他引:1  
The development of relatively inexpensive satellite receivers in the early 1970's has resulted in cost-effective applications of satellites for a variety of geodetic surveying needs. Currently achievable accuracies range from 10 to 20 centimeters. The NAVSTAR Global Positioning System, now under development by the Department of Defense, incorporates advanced technology which has the potential capability of revolutionizing satellite geodesy. Several concepts for utilizing GPS signals are briefly reviewed, and another concept, called the reconstructed carrier phase method, is described in some detail. This concept is being pursued by the Defense Mapping Agency, National Oceanic and Atmospheric Administration, and the U.S. Geological Survey. These agencies have numerous requirements for accurate positioning. Several prototype receivers are planned to be available for testing in mid-1982. These receivers should be highly portable, consume little power, and obtain base line accuracies of several centimeters in several hours of observation time. However, water vapor radiometers will be needed in order to achieve the full accuracy. Initial simulation results utilizing the reconstructed carrier phase method are included.  相似文献   
42.
A relatively low-cost system for determining both the vertical and horizontal coordinates of several dozen points per year with an accuracy of about 2 cm appears feasible. One approach considered is to use a subnanosecond pulse length laser with a few millijoules per pulse output energy and to employ single photoelectron detection of the returned signal. The single photoelectron approach has been thoroughly tested in the Lunar Laser Ranging Experiment. With a laser average power of about 50 mW, a 30-cm diameter transmit-receive aperture, 10 arc sec pointing accuracy and a beam divergence of 20 arc sec, the expected returned signal level is about 70 pulses in a 3-min interval. If the differences between the observed ranges and those calculated from a reasonably good LAGEOS ephemeris over a 3-min interval are considered, the expected standard deviation of the mean is < 0.7 cm.The calibration procedure used in lunar ranging appears capable of reducing any bias due to the photomultiplier or timing system to 0.5 cm. The other main error source we have considered for the measured optical transit time is a possible difference in arrival time in different parts of the far field pattern because of laser mode structure. This effect needs to be checked experimentally, but we expect it to be 0.5 cm or less for a laser pulse length of about 200 psec. Based on these error estimates, simulations for one week of observations from the high-mobility station have been carried out for us at the National Geodetic Survey. When a refraction model error of 0.15% was used, the uncertainty of the high-mobility station position with respect to a reference station 500 km away was found to be 2.4 cm or less in each coordinate. After the gravity-field uncertainties have been reduced, the station location accuracy will be improved further and the limitation of measuring with respect to a regional reference station can be relaxed.  相似文献   
43.
Granodiorite and diorite plutons of the Rosetown complex, N.Y., which are associated with the nearby Cortlandt complex, have chemical and textural characteristics indicating that large-scale liquid immiscibility played a major role in their petrogenesis. Rare earth element, zirconium, niobium and phosphorus abundances are much greater in the diorite precluding the possibility that the Rosetown diorite and granodiorite are related by fractional crystallization. The trace element data also eliminate the possibility that the granodiorite represents: (1) a partial melt of crustal rocks including basalt; (2) a granitic cumulate; or (3) a residue from an aqueous fluid derived either from a silicate melt or crustal rocks. Liquid immiscibility appears to be viable model for the origin of the Rosetown granodiorite and iron-rich diorite. This model is supported by the following: (1) the major element compositions occur in a two-liquid field on a Greig diagram; (2) both bodies have similar Sr isotope compositions; (3) common phases in the two rock types have overlapping compositions; (4) the major and trace element data of the diorite and granodiorite are similar to the experimentally determined partition data of immiscible liquid pairs; and (5) possible ocelli of iron-rich diorite are found in the granodiorite.  相似文献   
44.
45.
Recent collecting in exposures of the lowermost Burgersdorp Formation (Beaufort Group), of the Karoo Basin of South Africa, has revealed a previously unknown fish fauna from the Early Triassic (Scythian), lowermost Cynognathus Assemblage Zone (CAZ), which forms an important component of the total vertebrate assemblage. The newly discovered fish material includes lungfish, saurichthyids, and a large microfauna that includes numerous isolated chondrichthyan teeth, two fin spine fragments, and actinopterygian scales and teeth. The latest fish finds, together with the lowermost Cynognathus Assemblage Zone vertebrate faunas, make this Karoo Basin Assemblage Zone one of the most diverse Early Triassic faunal assemblages, comparable in faunal diversity to those from the Czatkowice Formation (Poland) and the Arcadia Formation (Australia). The presence of the lungfish Ptychoceratodus phillipsi in the early Middle Triassic Cynognathus Assemblage Zone (Subzone B), and in the underlying latest Early Triassic Cynognathus Assemblage Zone (Subzone A), indicates that these lungfish could serve as range index fossils within the CAZ, and thus are potentially useful biostratigraphic markers across the Early-Middle Triassic boundary. Furthermore the ‘new’ fish fauna provides a vital marine realm link in particular with the faunas of Madagascar and Australia, that is unavailable using the tetrapod faunal elements of the lower CAZ.  相似文献   
46.
We investigate the effect of broken clouds on the satellite-based retrieval of columnar water vapor using a near-infrared radiance ratio technique. A typical difference between the retrieval using only pixels directly illuminated by the Sun and pixels with mixed illumination containing direct sunlight as well as cloud shadows is found to be within 3%.  相似文献   
47.
The present groundwater monitoring network in Bavaria consists mostly of wells and only a small number of natural groundwater springs, all of which are analyzed for mainly the common physical and chemical constituents in groundwater. In order to develop a long-term groundwater management plan for all the groundwater resources of Bavaria, the Bavarian State Office for Water Management intends to establish a separate spring-monitoring network throughout the 11 groundwater provinces of the state. As a first step, significant physicochemical parameters that show considerable annual fluctuation (after monitoring 1–3 years) were determined at 21 springs or spring systems to create a basic data set to guide future monitoring. A selection procedure was developed around four parameters: (1) geological units, which includes the principal aquifers; (2) rate of spring discharge; (3) land utilization within a catchment; and (4) approximate size of the subterranean catchment. However, in the initial phase of the study, only the first three parameters were investigated. These parameters established a matrix for evaluating each groundwater region of Bavaria to aid in the selection of additional springs for the proposed monitoring network. Electronic Publication  相似文献   
48.
The rates of organic carbon oxidation by O2, NO3?, MnO2, Fe2O3 and SO4? have been calculated for five pelagic Pacific and Atlantic sites using simple diffusion-reaction models. O2 everywhere oxidizes > 90% of the raining Corg; the fraction oxidized by the secondary oxidants decreases as the rain rate of organic C to the seafloor decreases. A large fraction of the Corg escaping oxidation by O2 is oxidized by the secondary oxidants. Hence while these oxidants play a small role in remineralization, they are important in regulating the burial of organic matter and the consequent removal from the oceans of reduced carbon and nutrients.  相似文献   
49.
Pore water profiles of total-CO2, pH, PO3?4, NO?3 plus NO?2, SO2?4, S2?, Fe2+ and Mn2+ have been obtained in cores from pelagic sediments of the eastern equatorial Atlantic under waters of moderate to high productivity. These profiles reveal that oxidants are consumed in order of decreasing energy production per mole of organic carbon oxidized (O2 > manganese oxides ~ nitrate > iron oxides > sulfate). Total CO2 concentrations reflect organic regeneration and calcite dissolution. Phosphate profiles are consistent with organic regeneration and with the effects of release and uptake during inorganic reactions. Nitrate profiles reflect organic regeneration and nitrate reduction, while dissolved iron and manganese profiles suggest reduction of the solid oxide phases, upward fluxes of dissolved metals and subsequent entrapment in the sediment column. Sulfate values are constant and sulfide is absent, reflecting the absence of strongly anoxic conditions.  相似文献   
50.
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