Optimizing the Number of Double-Differenced Observations for GPS Networks in Support of Deformation Monitoring Applications

Deformation monitoring using GPS is usually carried out by installing and operating a local network of GPS receivers mounted on the deforming body, e. g., the flanks of a volcano. For continuous monitoring applications a near-real-time, epoch-by-epoch solution obtained from multi-baseline processing is desired in order to take into account between-baseline correlations and to detect movements over as short a period of time as possible. In the case of the volcano monitoring application, the sides of the volcano will block out part of the sky, hence the receivers are not likely to track a lot of satellites that are visible from all receiver stations at the same time. If the usual base-station/base-satellite approach is used in the baseline processing, only the common satellites are considered, resulting in the number of possible double-differenced observables being comparatively low; hence a ot of valuable information may be lost. The proposed method, based on the work by Saalfeld (1999), considers satellites that are visible from a small number of network stations only. Thus the number of independent double-differenced observables can be maximized in order to obtain a better solution. A numerical example is given that verifies the improved solutions that can be obtained using this data processing approach. ? 2001 John Wiley & Sons, Inc.     

Early Cretaceous (late Berriasian to early Aptian) palaeoceanographic change along the northwestern Tethyan margin (Vocontian Trough,southeastern France): δ13C, δ18O and Sr-isotope belemnite and whole-rock records

Stable carbon, oxygen, and strontium isotope records were obtained from uppermost Hauterivian to lowermost Aptian belemnite rostra, which were collected in well-dated sections from the Vocontian Trough (southeastern France). This data set complements previously published belemnite-isotope records from the uppermost Berriasian-Hauterivian interval from the same basin. The belemnite carbon and oxygen isotope record is compared to the carbonate bulk-rock isotope record from the same sections, and from additional Italian sections. With regards to their long-term trends, both belemnite and whole-rock δ¹⁸O records are well correlated, except for the uppermost Hauterivian-lower Barremian interval, within which they deviate. This discrepancy is interpreted to be linked to the latest Hauterivian Faraoni oceanic anoxic event and its early Barremian aftermath. The Faraoni level is characterized by enhanced sea-water stratification, probably induced by the onset of a warmer and more humid climate along the northern Tethyan margin. The early Barremian was characterized by stronger vertical sea-water mixing reflected by a decrease in density contrast between sea-surface and deeper waters. The belemnite oxygen isotope record shows a more stable evolution with smaller fluctuations than its bulk-rock counterpart, which indicates that deeper water masses were not as much subjected to density fluctuations as sea-surface water. The comparison of belemnite and bulk-rock carbon isotope records allows observing the impact of regional influence exerted by platform carbonate ooze shedding on the carbon cycle. Discrepancies in the two records are observed during time of photozoan carbonate platform growth. The strontium isotopic record shows a gradual increase from the uppermost Berriasian to the uppermost lower Barremian followed by a rapid decrease until the uppermost Barremian and a renewed small increase within the lowermost Aptian. The major inflection point in the uppermost lower Barremian appears to predate the onset in the formation of the Ontong-Java volcanic plateau.     

Research impact within the international arid literature: An Australian perspective based on network theory

While research-article impact is routinely judged by citation counts, there is recognition that a much broader view is needed to better judge the true value of citations. This paper applies a developing framework based on the application of network theory, where the network consists of journal articles on arid-systems research which are listed on ISI Web-of-Science. Keywords were used to identify articles related to arid-systems research. Linkages between articles were defined by citations, and we bound our analysis by focusing on how the Australian subsample contributes to the international arid-systems literature. The analysis showed that impact based on how articles contribute structurally to the flow of knowledge within the literature offers an alternative metric to citation counts. The analysis also presented a partitioned view of the Australian arid literature. This showed that there exists some citation-based structure within the literature, and we showed this structure better describes the literature than a partition based on which journal articles are published in.     

Modelling the effect of time‐dependent river dune evolution on bed roughness and stage

This paper presents an approach to incorporate time‐dependent dune evolution in the determination of bed roughness coefficients applied in hydraulic models. Dune roughness is calculated by using the process‐based dune evolution model of Paarlberg et al. ( 2009 ) and the empirical dune roughness predictor of Van Rijn ( 1984 ). The approach is illustrated by applying it to a river of simple geometry in the 1‐D hydraulic model SOBEK for two different flood wave shapes. Calculated dune heights clearly show a dependency on rate of change in discharge with time: dunes grow to larger heights for a flood wave with a smaller rate of change. Bed roughness coefficients computed using the new approach can be up to 10% higher than roughness coefficients based on calibration, with the largest differences at low flows. As a result of this larger bed roughness, computed water depths can be up to 15% larger at low flow. The new approach helps to reduce uncertainties in bed roughness coefficients of flow models, especially for river systems with strong variations in discharge with time. Copyright © 2010 John Wiley & Sons, Ltd.     

The microwave absorption of SO2 in the Venus atmosphere

Sulfur dioxide has a strong and complex rotational spectrum in the microwave and far infrared regions. The microwave absorption due to SO₂ in a CO₂ mixture is calculated for conditions applicable to the Venus atmosphere. It is shown that at the concentrations detected by Pioneer-Venus in situ measurements, SO₂ may be expected to contribute significantly to the microwave opacity of the Venus atmosphere. In particular, SO₂ might provide the major source of opacity in the atmospheric region immediately below the main sulfuric acid cloud deck. The spectrum is largely nonresonant at the pressures where SO₂ is expected to occur, however.     

Speckle spectro‐polarimetry of magnetic structures

Two‐dimensional spectrograms were obtained with the Vacuum Tower Telescope, Tenerife, in order to study small‐scale structures and faculae on the Sun. Using the speckle reconstruction method, we obtain high‐resolution images and wavelength scans. Magnetic fields can be studied from Stokes V profiles, and velocity maps are gained by the Doppler shift of the center of gravity of Stokes I. Here some results about small‐scale structures and their magnetic fields are shown.     

The sulfur species in hot rocky exoplanet atmospheres

The first JWST observations of hot Jupiters showed an unexpected detection of SO ${}_2$ in their hydrogen-rich atmospheres. We investigate how much sulfur can be expected in the atmospheres of rocky exoplanets and which sulfur molecules can be expected to be most abundant and detectable by transmission spectroscopy. We run thermochemical equilibrium models at the crust–atmosphere interface, considering surface temperatures 500–5000 K, surface pressures 1–100 bar, and various sets of element abundances based on common rock compositions. Between 1000 and 2000 K, we find gaseous sulfur concentrations of up to 25% above the rock in our models. SO ${}_2$, SO, H ${}_2$S, and S ${}_2$ are by far the most abundant sulfur molecules. SO ${}_2$ shows potentially detectable features in transmission spectra at about 4 $\mu$m, between 7 and 8 $\mu$m, and beyond 15 $\mu$m. In contrast, the sometimes abundant H ${}_2$S molecule is difficult to detect in these spectra, which are mostly dominated by H ${}_2$O and CO ${}_2$. Although the molecule PS only occurs with concentrations ppm, it can cause a strong absorption feature between 0.3 and 0.65 $\mu$m in some of our models for high surface pressures. The detection of sulfur molecules would enable a better characterization of the planetary surface.