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961.
Oil exploration and production (E&P) activities in remote regions are often considered a catalyst for landscape change through the direct alterations created by infrastructure features, as well as through the accessibility provided by roads. The construction, expansion and improvement of transportation routes in isolated areas can attract newcomers and resource users who engage in illegal logging, poaching, commercial agriculture, as well as planned and spontaneous colonization. These actions can lead to larger-scale surface disturbances that may also affect indigenous territories and natural preserves. However, do these parallel activities and outcomes always accompany E&P development, or can controlled access minimize changes? To answer this question we utilized an “accounting from above” approach that uses remote sensing and GIS techniques to analyze surface disturbance patterns linked to infrastructure features for both E&P and parallel activities. Our study area included four neighboring oil blocks in eastern Ecuador’s tropical forest, displaying three types of E&P development: public-access, controlled-access and roadless. The first objective was to determine the spatial relationship between infrastructure pattern, disturbance regimes and the type of road access for the year 2000 using land-use land-cover maps, soils data, protected areas and colonization zones. The second objective was to examine the statistical relationships between agricultural conversion and the above factors. Spatial analysis findings suggest that areas of overlap where colonization zones, public-access roads and fertile soils meet are most prone to deforestation. Statistical findings from a linear regression model suggest that the presence of public-access non-oil roads are significant at explaining the conversion of natural vegetation (forest) to agriculture, while the presence of protected areas helps explain the conservation of forested land. 相似文献
962.
Shoshana Z. Weider Bruce M. Swinyard Barry J. Kellett Chris J. Howe Katherine H. Joy Ian A. Crawford Jason Gow David R. Smith 《Planetary and Space Science》2011,59(13):1393-1407
We have conducted laboratory experiments as an analogue to planetary XRF (X-ray fluorescence) missions in order to investigate the role of changing incidence (and phase) angle geometry and sample grain-size on the intensity of XRF from regolith-like samples. Our data provide evidence of a grain-size effect, where XRF line intensity decreases with increasing sample grain-size, as well as an almost ubiquitous increase in XRF line intensity above incidence angles of ∼60°. Data from a lunar regolith simulant are also used to test the accuracy of an XRF abundance algorithm developed at the Rutherford Appleton Laboratory (RAL), which is used to estimate the major element abundance of the lunar surface from Chandrayaan-1 X-ray Spectrometer (C1XS) XRF data. In ideal situations (i.e., when the input spectrum is well defined and the XRF spectrum has a sufficient signal to noise ratio) the algorithm can recover a known rock composition to within 1.0 elemental wt% (1σ). 相似文献
963.
A fast-wave pulse in a simple, cold, inhomogeneous MHD model plasma is constructed by Fourier superposition over frequency
of harmonic waves that are singular at their respective Alfvén resonances. The pulse partially reflects before reaching the
resonance layer, but also partially tunnels through to it to convert to an Alfvén wave. The exact absorption/conversion coefficient
for the pulse is shown to be given precisely by a function of transverse wavenumber tabulated in Paper I of this sequence,
and to be independent of frequency and pulse width. 相似文献
964.
Rainfall over eastern Africa (10°S–10°N; 35°E–50°E) is bimodal, with seasonal maxima during the "long rains" of March–April–May (MAM) and the "short rains" of October–November–December (OND). Below average precipitation during consecutive long and short rains seasons over eastern Africa can have devastating long-term impacts on water availability and agriculture. Here, we examine the forcing of drought during consecutive long and short rains seasons over eastern Africa by Indo-Pacific sea surface temperatures (SSTs). The forcing of eastern Africa precipitation and circulation by SSTs is tested using ten ensemble simulations of a global weather forecast model forced by 1950–2010 observed global SSTs. Since the 1980s, Indo-Pacific SSTs have forced more frequent droughts spanning consecutive long and short rains seasons over eastern Africa. The increased frequency of dry conditions is linked to warming SSTs over the Indo-west Pacific and to a lesser degree to Pacific Decadal Variability. During MAM, long-term warming of tropical west Pacific SSTs from 1950–2010 has forced statistically significant precipitation reductions over eastern Africa. The warming west Pacific SSTs have forced changes in the regional lower tropospheric circulation by weakening the Somali Jet, which has reduced moisture and rainfall over the Horn of Africa. During OND, reductions in precipitation over recent decades are oftentimes overshadowed by strong year-to-year precipitation variability forced by the Indian Ocean Dipole and the El Niño–Southern Oscillation. 相似文献
965.
Pepijn de Vries Jacqueline E. Tamis Edwin M. Foekema Chris Klok Albertinka J. Murk 《Marine pollution bulletin》2013
The environmental impact of elevated carbon dioxide (CO2) levels has become of more interest in recent years. This, in relation to globally rising CO2 levels and related considerations of geological CO2 storage as a mitigating measure. In the present study effect data from literature were collected in order to conduct a marine ecological risk assessment of elevated CO2 levels, using a Species Sensitivity Distribution (SSD). It became evident that information currently available from the literature is mostly insufficient for such a quantitative approach. Most studies focus on effects of expected future CO2 levels, testing only one or two elevated concentrations. A full dose-response relationship, a uniform measure of exposure, and standardized test protocols are essential for conducting a proper quantitative risk assessment of elevated CO2 levels. Improvements are proposed to make future tests more valuable and usable for quantitative risk assessment. 相似文献
966.
Currently, the GNSS computing modes are of two classes: network-based data processing and user receiver-based processing. A GNSS reference receiver station essentially contributes raw measurement data in either the RINEX file format or as real-time data streams in the RTCM format. Very little computation is carried out by the reference station. The existing network-based processing modes, regardless of whether they are executed in real-time or post-processed modes, are centralised or sequential. This paper describes a distributed GNSS computing framework that incorporates three GNSS modes: reference station-based, user receiver-based and network-based data processing. Raw data streams from each GNSS reference receiver station are processed in a distributed manner, i.e., either at the station itself or at a hosting data server/processor, to generate station-based solutions, or reference receiver-specific parameters. These may include precise receiver clock, zenith tropospheric delay, differential code biases, ambiguity parameters, ionospheric delays, as well as line-of-sight information such as azimuth and elevation angles. Covariance information for estimated parameters may also be optionally provided. In such a mode the nearby precise point positioning (PPP) or real-time kinematic (RTK) users can directly use the corrections from all or some of the stations for real-time precise positioning via a data server. At the user receiver, PPP and RTK techniques are unified under the same observation models, and the distinction is how the user receiver software deals with corrections from the reference station solutions and the ambiguity estimation in the observation equations. Numerical tests demonstrate good convergence behaviour for differential code bias and ambiguity estimates derived individually with single reference stations. With station-based solutions from three reference stations within distances of 22–103 km the user receiver positioning results, with various schemes, show an accuracy improvement of the proposed station-augmented PPP and ambiguity-fixed PPP solutions with respect to the standard float PPP solutions without station augmentation and ambiguity resolutions. Overall, the proposed reference station-based GNSS computing mode can support PPP and RTK positioning services as a simpler alternative to the existing network-based RTK or regionally augmented PPP systems. 相似文献
967.
Due to the different signal frequencies for the GLONASS satellites, the commonly-used double-differencing procedure for carrier phase data processing can not be implemented in its straightforward form, as in the case of GPS. In this paper a novel data processing strategy, involving a three-step procedure, for integrated GPS/GLONASS positioning is proposed. The first is pseudo-range-based positioning, that uses double-differenced (DD) GPS pseudo-range and single-differenced (SD) GLONASS pseudo-range measurements to derive the initial position and receiver clock bias. The second is forming DD measurements (expressed in cycles) in order to estimate the ambiguities, by using the receiver clock bias estimated in the above step. The third is to form DD measurements (expressed in metric units) with the unknown SD integer ambiguity for the GLONASS reference satellite as the only parameter (which is constant before a cycle slip occurs for this satellite). A real-time stochastic model estimated by residual series over previous epochs is proposed for integrated GPS/GLONASS carrier phase and pseudo-range data processing. Other associated issues, such as cycle slip detection, validation criteria and adaptive procedure(s) for ambiguity resolution, is also discussed. The performance of this data processing strategy will be demonstrated through case study examples of rapid static positioning and kinematic positioning. From four experiments carried out to date, the results indicate that rapid static positioning requires 1 minute of single frequency GPS/GLONASS data for 100% positioning success rate. The single epoch positioning solution for kinematic positioning can achieve 94.6% success rate over short baselines (<6 km). 相似文献
968.
Jing Li Claire H. Jarvis Chris Brunsdon 《International journal of geographical information science》2013,27(4):591-605
Dilution of precision (DOP) is a fundamental concept in satellite navigation and surveying. A deeper understanding of this concept can be achieved through the means of 3D immersive visualisation. In this article, we present a method for visualising and exploring the spatial variation of DOP and discuss its presentation within an immersive virtual environment. The work demonstrates a real-time simulation of global positioning system (GPS) satellite geometry, modelled and visualised within a virtual representation of the university campus. The number of satellites visible to the receiver is modelled in real time as a user walks through the university campus. During this process, the changing satellite geometry is visualised in both 3D and aerial views. Various DOP values update to the screen against a pseudo-realistic building backdrop as the user travels. Both the aerial views and the changing volumes of the tetrahedra drawn in 3D provide an effective way of interpreting why exceptionally large or small horizontal DOP and vertical DOP values can occur in an urban context. Because the factors affecting DOPs are inherently 3D, communicating the spatial uncertainty of global positioning system coordinates within an immersive stereo environment has been viewed as a particularly powerful communication tool by both undergraduate and postgraduate students studying GI Science. 相似文献
969.
Abstract A modelling experiment is used to examine different land-use scenarios ranging from extreme deforestation (31% forest cover) to pristine (95% forest cover) conditions and related Payment for Ecosystem Services (PES) schemes to assess whether a change in streamflow dynamics, discharge extremes and mean annual water balance of a 73.4-km2 tropical headwater catchment in Costa Rica could be detected. A semi-distributed, conceptual rainfall–runoff model was adapted to conceptualize the empirically-based, dominant hydrological processes of the study area and was multi-criteria calibrated using different objective functions and empirical constraints on model simulations in a Monte Carlo framework to account for parameter uncertainty. The results suggest that land-use change had relatively little effect on the overall mean annual water yield (<3%). However, streamflow dynamics proved to be sensitive in terms of frequency, timing and magnitude of discharge extremes. For low flows and peak discharges of return periods greater than one year, land use had a minor influence on the runoff response. Below these thresholds (<1-year return period), forest cover potentially decreased runoff peaks and low flows by as much as 10%, and non-forest cover increased runoff peaks and low flows by up to 15%. The study demonstrated the potential for using hydrological modelling to help identify the impact of protection and reforestation efforts on ecosystem services. Editor Z.W. Kundzewicz Citation Birkel, C., Soulsby, C., and Tetzlaff, D., 2012. Modelling the impacts of land-cover change on streamflow dynamics of a tropical rainforest headwater catchment. Hydrological Sciences Journal, 57 (8), 1543–1561. 相似文献
970.
Emanuele Perinati Chris Tenzer Andrea Santangelo Konrad Dennerl Michael Freyberg Peter Predehl 《Experimental Astronomy》2012,33(1):39-53
The pn-CCD cameras at the focal plane of the eROSITA space observatory will be the first X-ray (0.2?C12?keV) detector to operate in a L-2 orbit. Therefore, no direct information of instrumental non X-ray background (NXB) is available to make predictions for eROSITA. Since, in general, the instrumental NXB experienced in orbit has a major impact on the overall sensitivity of the cameras, we investigated and modeled the L-2 radiation environment and its interaction with the eROSITA mass distribution and cameras, in order to quantify the expected pn-CCD NXB level. We obtain an average value of NXB ??25% lower than that observed by the pn-CCDs on-board the XMM-Newton satellite, which is placed in a Highly Elliptical Orbit (HEO). We discuss this result in light of the differences between the L-2 and HEO space environments. 相似文献