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Sounding Data (sounding + data)

Distribution by Scientific Domains

Earth and Environmental Science	100%

Selected Abstracts

Macro-scale bed roughness of the siple coast ice streams in West Antarctica

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2004
Martin J. Siegert
Abstract Subglacial bed conditions are key to understanding ice stream behaviour and evolution, with bed roughness re,ecting substrate composition and ,ow resistance. Here we present an analysis of bed roughness in the Siple Coast region of West Antarctica from airborne radio-echo sounding data. The ice streams are associated generally with low bed roughness values, which decrease downstream. The bed of the slow-,owing Ice Stream C (,10 000 km2) is also characterized by being smooth at all scales (wavelengths ranging from 5 km to in excess of 40 km). Furthermore, the bed is smooth either side of Ice Stream C. This suggests the location of the ice stream is controlled by internal ice sheet dynamics rather than by bed morphology. If the ice stream were encouraged to migrate laterally, when active, there would be little resistance offered by the subglacial morphology. Other inter-ice stream regions are rough, however, indicating a subglacial topographic in,uence on ice stream position. Bed roughness increases up-,ow of ice streams, which, unless the bed is modi,ed, may limit the inland migration of these systems. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Simple relative space,time scaling of electrical and electromagnetic depth sounding arrays: implications for electrical static shift removal and joint DC-TEM data inversion with the most-squares criterion

GEOPHYSICAL PROSPECTING, Issue 4 2005
Max A. Meju
ABSTRACT A simple scaling relationship is shown to facilitate comparison, correlation and integration of data recorded using the common experimental configurations in electrical and electromagnetic depth sounding. Applications of the scheme to field data from typical geological and landfill environments show that it is robust and, where transient electromagnetic (TEM) data are available, enables easy identification and quantification of electrical static shift (galvanic distortion) in magnetotelluric and direct current (DC) sounding curves. TEM-based procedures are suggested for both the direct removal of static shift in DC sounding curves and effective joint data inversion with the most-squares criterion in the presence of static shift. A case study of aquifer characterization using sounding data from borehole sites in the Vale of York in England shows that static shift is a common problem in this glacial-covered terrain and demonstrates the effectiveness of the proposed joint DC-TEM inversion strategy in handling distorted soundings. [source]

Use of VFSA for resolution, sensitivity and uncertainty analysis in 1D DC resistivity and IP inversion

GEOPHYSICAL PROSPECTING, Issue 5 2003
Bimalendu B. Bhattacharya
ABSTRACT We present results from the resolution and sensitivity analysis of 1D DC resistivity and IP sounding data using a non-linear inversion. The inversion scheme uses a theoretically correct Metropolis,Gibbs' sampling technique and an approximate method using numerous models sampled by a global optimization algorithm called very fast simulated annealing (VFSA). VFSA has recently been found to be computationally efficient in several geophysical parameter estimation problems. Unlike conventional simulated annealing (SA), in VFSA the perturbations are generated from the model parameters according to a Cauchy-like distribution whose shape changes with each iteration. This results in an algorithm that converges much faster than a standard SA. In the course of finding the optimal solution, VFSA samples several models from the search space. All these models can be used to obtain estimates of uncertainty in the derived solution. This method makes no assumptions about the shape of an a posteriori probability density function in the model space. Here, we carry out a VFSA-based sensitivity analysis with several synthetic and field sounding data sets for resistivity and IP. The resolution capability of the VFSA algorithm as seen from the sensitivity analysis is satisfactory. The interpretation of VES and IP sounding data by VFSA, incorporating resolution, sensitivity and uncertainty of layer parameters, would generally be more useful than the conventional best-fit techniques. [source]

A comparison of the impact of TOVS arid ATOVS satellite sounding data on the accuracy of numerical weather forecasts

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 569 2000
S. J. English
Abstract The Advanced TIROS Operational Vertical Sounder (ATOVS) was launched on the NOAA-15 satellite in May 1998. This provided a very significant improvement in the information available from meteorological polar-orbiting satellites compared with the previous TIROS Operational Vertical Sounder system, particularly for humidity and vertical resolution of temperature in cloudy areas. In preparation for assimilation of the observations into a three-dimensional analysis of atmospheric temperature and humidity, the observations have been compared with calculated top-of-atmosphere brightness temperatures computed from numerical weather prediction model profiles of temperature and humidity. Differences between observed and modelled brightness temperature are small. In some parts of the tropics and northern hemisphere the standard deviation of these differences for the tropospheric Advanced Microwave Sounding Unit sounding channels is only marginally higher than the radiometric noise of the observations. Early in 1999 a series of observation-system experiments were completed in which ATOVS observations were assimilated using a one-dimensional variational analysis. No use of the new humidity information could be made because of interference problems experienced by the microwave humidity sounder on ATOVS. Nonetheless, these experiments showed that the assimilation of the new temperature information provided by the radiance observations reduces forecast errors by as much as 20% in the southern hemisphere and 5% in the northern hemisphere. Further improvements have been found by assimilating more data over land. The major impact arises from the microwave channels. Whilst forward-model errors may be slightly lower for the microwave channels than the infrared channels the primary reason is the provision of sounding information in active weather systems, which are usually cloudy. [source]