Laser ranging error budget for the TOPEX/POSEIDON satellite.
A laser ranging error budget is detailed, and a specific error budget is derived for the TOPEX/POSEIDON satellite. A ranging uncertainty of 0.76 cm is predicted for TOPEX/POSEIDON at 20 degrees elevation using the presently designed laser retroreflector array and only modest improvements in present system operations. Atmospheric refraction and satellite attitude effects cause the predicted range error to vary with satellite elevation angle from 0.71 cm at zenith to 0.76 cm at 20 degrees elevation. This a priori error budget compares well with the ~1.2-cm rms a posteriori polynomial orbital fit using existing data taken for an extant satellite of similar size and orbit.
Time, frequency and space geodesy: impact on the study of climate and global change
The authors discuss the development of space geodetic systems-important tools in an attempt to understand the evolution of the atmosphere and oceans-particularly as they pertain to the problem of global warming. The science of time and frequency metrology has made possible the development of space geodetic systems that are being applied to the high accuracy tracking of new space-based instruments. These new instrument sets and methodologies have been designed to be appropriate for many years to decades of operation in order to measure the open ocean circulation and sea level as an indicator of global warming and will be a vital means for assessing the effectiveness of future remedial actions. The issues of time and frequency are tied into all of these space geodetic techniques, from the cesium and rubidium oscillators aboard global positioning system (GPS) satellites, to the epoch time and time interval measurements of satellite laser ranging (SLR) and hydrogen maser references used in very long baseline interferometry (VLBI). >
Chapter 6 Rift Basins of the Sudan
Abstract The Sudanese rift structures form intracontinental basins, bordered on all sides by anorogenic terrain. These basins are seen as the result of a multistructural system of rifts which appear to have been activated several times since the Palaeozoic. Improved methods of dating and extensive geophysical surveys have led to a better understanding of the mobile belts and the Basement rocks in the general environs of the basins, and of the elevated blocks and highs surrounding the sedimentary basins. Detailed mapping and extensive drilling in the sedimentary basins led to a better understanding of the Phanerozoic. The rapid rate of uplift and subsidence have assisted in the rapid accumulation and filling of the basins with unconsolidated sediments, ranging from a few hundred metres to some thousand metres. The rift structures contain sediments of several age groups, origin and mode of deposition. Some of them are as old as the Palaeozoic passing through to Mesozoic, Tertiary and Quaternary (Bahr El Arab rift and Blue Nile rift). The thickness of the Tertiary sediments exceeds 15 km in Bahr El Arab rift. Palaeozoic sediments were found to occupy NE-SW grabens. Jurassic? and Cretaceous sediments were deposited in NW-SE troughs. Tertiary sediments filled grabens that range in thicknesses up to 15 km. Highly saline ground-water bodies which coincide with hydrogeologically closed basins occupy the flowing end of each of the rift basins. These saline bodies have been interpreted as buried saline lakes, sabkhas or playas. Alternating wet and dry periods eventually filled up the basins with intercalating layers of fresh and saline layers. The filling up of the basins led to the interconnection of the hydrological regime and the development of the integrated River Nile. Rift structures in Sudan form the major ground-water basins, outside these basins ground water is found only in small quantities and is of poor quality. The rift basins also act as reservoirs for hydrocarbon accumulation; all the known oil fields of inland Sudan are located in these basins.