Maintaining real-time precise point positioning during outages of orbit and clock corrections

The precise point positioning (PPP) is a popular positioning technique that is dependent on the use of precise orbits and clock corrections. One serious problem for real-time PPP applications such as natural hazard early warning systems and hydrographic surveying is when a sudden communication break takes place resulting in a discontinuity in receiving these orbit and clock corrections for a period that may extend from a few minutes to hours. A method is presented to maintain real-time PPP with 3D accuracy less than a decimeter when such a break takes place. We focus on the open-access International GNSS Service (IGS) real-time service (RTS) products and propose predicting the precise orbit and clock corrections as time series. For a short corrections outage of a few minutes, we predict the IGS-RTS orbits using a high-order polynomial, and for longer outages up to 3 h, the most recent IGS ultra-rapid orbits are used. The IGS-RTS clock corrections are predicted using a second-order polynomial and sinusoidal terms. The model parameters are estimated sequentially using a sliding time window such that they are available when needed. The prediction model of the clock correction is built based on the analysis of their properties, including their temporal behavior and stability. Evaluation of the proposed method in static and kinematic testing shows that positioning precision of less than 10 cm can be maintained for up to 2 h after the break. When PPP re-initialization is needed during the break, the solution convergence time increases; however, positioning precision remains less than a decimeter after convergence.     

A long-term trend in precipitation of different spatial regions of Bangladesh and its teleconnections with El Niño/Southern Oscillation and Indian Ocean Dipole

A long-term (1948 to 2012) trend of precipitation (annual, pre-monsoon, monsoon, and post-monsoon seasons) in Bangladesh was analyzed in different regions using both parametric and nonparametric approaches. Moreover, the possible teleconnections of precipitation (annual and monsoon) variability with El Niño/Southern Oscillation (ENSO) episode and Indian Ocean Dipole (IOD) were investigated using both average and individual (both positive and negative) values of ENSO index and IOD. Our findings suggested that for annual precipitation, a significant increasing monotonic trend was found in whole Bangladesh (4.87 mm/year), its western region (5.82 mm/year) including Rangpur (9.41 mm/year) and Khulna (4.95 mm/year), and Sylhet (10.12 mm/year) and Barisal (6.94 mm/year) from eastern region. In pre-monsoon, only Rangpur (2.88 mm/year) showed significant increasing trend, while in monsoon, whole Bangladesh (3.04 mm/year), Sylhet (7.17 mm/year), and Barisal (6.94 mm/year) showed similar trend. In post-monsoon, there was no significant trend. Our results also revealed that the precipitation (annual or monsoon) of whole Bangladesh and almost all of the spatial regions did not show any significant correlation with ENSO events, whereas the average IOD values showed significant correlation only in monsoon precipitation of western region. The individual positive IODs showed significant correlation in whole Bangladesh, western region, and its two divisions (Rajshahi and Khulna). So, in the context of Bangladesh climate, IOD has the more teleconnection to precipitation than that of ENSO. Our findings indicate that the co-occurrence of ENSO and IOD events may suppress their influence on each other.

     

A review of volunteered geographic information quality assessment methods

With the ubiquity of advanced web technologies and location-sensing hand held devices, citizens regardless of their knowledge or expertise, are able to produce spatial information. This phenomenon is known as volunteered geographic information (VGI). During the past decade VGI has been used as a data source supporting a wide range of services, such as environmental monitoring, events reporting, human movement analysis, disaster management, etc. However, these volunteer-contributed data also come with varying quality. Reasons for this are: data is produced by heterogeneous contributors, using various technologies and tools, having different level of details and precision, serving heterogeneous purposes, and a lack of gatekeepers. Crowd-sourcing, social, and geographic approaches have been proposed and later followed to develop appropriate methods to assess the quality measures and indicators of VGI. In this article, we review various quality measures and indicators for selected types of VGI and existing quality assessment methods. As an outcome, the article presents a classification of VGI with current methods utilized to assess the quality of selected types of VGI. Through these findings, we introduce data mining as an additional approach for quality handling in VGI.     

Effect of hot dry summer tropical climate on forage intake and milk yield in Holstein–Friesian and indigenous zebu cows in Sudan

The effects of dry summer ambient temperature on some physiological and productive responses were studied in an exotic European breed (Holstein–Friesian) and a local zebu breed (Butana ecotype) of cattle in Sudan. Rectal temperature and respiration rate were positively correlated, and dry matter intake and milk yield were negatively correlated with variation in ambient temperature. However, significant adverse effects on high ambient temperature were only observed in the exotic breed.     

Structures controlling U and Th mineralisation in the Gebel Felat area of the south Eastern Desert of Egypt

In the Eastern Desert of Egypt, younger granites host U and Th mineralisations which are concentrated along faults and joints. In particular, the Gebel Felat Pluton is characterised by a high level of radioactivity as shown by an aeroradiometric survey. The U content is 82 ppm and the Th content is 15 ppm in areas of high radioactivity. The rocks are cross-cut by two main sets of fractures trending east-west and northwest-southeast. The contour maps of these two trends can be correlated with the aeroradiometric map of the same area.     

Basement relief map of kalabsha and seiyal areas, northwest of Aswan lake, Egypt

The Bouguer anomaly map of the Kalabsha and Seiyal areas was analysed on the basis of the available data about the depth to the basement from three boreholes. The density contrast between the basement complex and the Nubia formation was estimated from the gravity values and basement depths. Applying the estimated value of the density contrast, a residual map representing the basement effect and a basement relief map were constructed. The basement depth in Kalabsha and Seiyal areas range from 150 to 500 m below mean sea level. Comparing the general characteristics of the Bouguer anomaly of the Kalabsha and Seiyal areas with the clusters of earthquakes in the area since 1982 till present reveals a gravity low coinciding with a deep focal area. The gravity values increase toward a shallow focal area.     

Effects of ground motion spatial variability on the response of cable-stayed bridges

In order to extend our knowledge of the performance of long-span bridges under earthquake loading the effects of spatial variability of ground motion on the structural response of cable-stayed bridges are studied; the result can be useful to practising bridge engineers. The multiple-support excitation analysis is described, and two three-dimensional models representing the modern and future trends in cable-stayed bridge design are utilized to shed some light on salient features of the seismic response characteristics of these modern bridges. In addition, models of steel- and concrete-design alternates of an existing bridge are considered. Differential ground motion records (obtained from dense instrument arrays) are used as synchronous and non-synchronous support motions; in addition, non-dispersive seismic waves travelling along the bridge are considered. The bridge response to non-uniform ground motion is compared to its response to uniform input. An overview of the unique dynamic characteristics of these cable-supported bridges is also presented. Finally, the study, which was used in the seismic design of several existing cable-stayed bridges in U.S. and Canada, indicates that the response quantities may increase substantially from the non-uniform input ground motion, especially for more rigid bridges and for bridges having different dynamic properties of the local soils at the supporting points, but the degree of increase depends upon the specific problem, in particular upon the aspects of span length, rigidity and structural redundancy. Thus, the response to non-uniform input ground motion should be examined for these bridges.     

Petrophysical parameters and modelling of the Eocene reservoirs in the Qadirpur area,Central Indus Basin,Pakistan: implications from well log analysis

The Eocene rock units of the Qadirpur field, Central Indus Basin (Pakistan), are investigated petrophysically for their detailed reservoir characterization. The different petrophysical parameters determined include the following: true resistivity, shale volume, total porosity, effective porosity, density and neutron porosity, water and hydrocarbon saturation, bulk volume of water, lithology, gas effect, P-wave velocity, movable hydrocarbon index and irreducible water saturation and integrated with different cross-plots. The Eocene reservoirs are excellent with high effective porosity (2–32 %) and hydrocarbon saturation (10–93 %). Among these, the Sui Upper Limestone is an overall a poor reservoir; however, it has some hydrocarbon-rich intervals with high effective porosity and better net pay. All the net pay zones identified show low and variable shale volume (5–30 %). The secondary porosity has added to the total and effective porosities in these reservoirs. The main contributors to the porosity are the chalky, intercrystalline and vuggy/fracture types. The thickness of the reservoirs zones ranges from 4.5 to 62 m. These reservoirs are gas-producing carbonates with almost irreducible water saturation (0.002–0.01) and are likely to produce water-free hydrocarbons. The lower values of moveable hydrocarbon index (0.07–0.9) show that the hydrocarbons are moveable spontaneously to the well bore. The proposed correlation model shows that the reservoirs have an inclined geometry and are a part of an anticlinal trap.     

Seismic spectrograms of an anelastic layer with different source-receivers configurations

Thin and relatively thin anelastic layers (compared to the signal wavelength) generally represent hydrocarbon reservoirs, where the rock is a sandstone or a source rock saturated with brine, oil and gas. The study of the seismic response of these layers is important to detect the hydrocarbons on the basis of the reflection and transmission coefficients and the wave velocity and attenuation properties. Different seismic experiments (source-receiver configurations) can provide useful information to characterise its properties. In this work, we consider varying thicknesses and Q values of the layer and analyse the reflection and transmission coefficients. Moreover, we obtain spectrograms of surface seismic profiles and vertical and horizontal well profiles (VSP and HSP, respectively) to analyse their frequency content with offset due to variations of the attenuation properties of the layer. In addition, we compare the effects due to NMO stretching and intrinsic attenuation related to the low-frequency shadows (LFS) observed in real data after stacking, since LFS can have several causes. Ambiguity is present in this case, indicating that non-stretch NMO is required, otherwise an offset mute of the data may remove useful information regarding the intrinsic (physical) loss.