Precise point positioning (PPP) has become a powerful tool for the scientific analysis of Global Positioning System (GPS)
measurements. Until recently, ambiguity resolution at a single station in PPP has been considered difficult, due to the receiver-
and satellite-dependent uncalibrated hardware delays (UHD). However, recent studies show that if these UHD can be determined
accurately in advance within a network of stations, then ambiguity resolution at a single station becomes possible. In this
study, the method proposed by Ge et al. J Geod 82(7):389–399, 2007 is adopted with a refinement in which only one single-difference narrow-lane UHD between a pair of satellites is determined
within each full pass over a regional network. This study uses the EUREF (European Reference Frame) Permanent Network (EPN)
to determine the UHD from Day 245 to 251 in 2007. Then 12 International GNSS Service stations inside the EPN and 15 outside
the EPN are used to conduct ambiguity resolution in hourly PPP. It is found that the mean positioning accuracy in all hourly
solutions for the stations inside the EPN is improved from (3.8, 1.5, 2.8) centimeters to (0.5, 0.5, 1.4) centimeters for
the East, North and Up components, respectively. For the stations outside the EPN, some of which are over 2,000 km away from
the nearest EPN stations, the mean positioning accuracy in the East, North and Up directions still achieves (0.6, 0.6, 2.0)
centimeters, respectively, when the EPN-based UHD are applied to these stations. These results demonstrate that ambiguity
resolution at a single station can significantly improve the positioning accuracy in hourly PPP. Particularly, UHD can be
even applied to a station which is up to thousands of kilometers from the UHD-determination network, potentially showing a
great advantage over current network-based GPS augmentation systems. Therefore, it is feasible and beneficial for the operators
of GPS regional networks and providers of PPP-based online services to provide these UHD estimates as an additional product. 相似文献
The Ordos Basin is a large cratonic basin with an area of 250,000 km2 in central China. Upper Paleozoic coals and shales serve as gas source rocks with peak generation and migration at the end of the early Cretaceous. Recent exploration has verified the huge gas potential in the “basin-centered gas accumulation system” (BCGAS). However, the mechanism for the gas accumulation is controversial. With an integrated approach of thin-section petrography, ultra-violet fluorescence microscopy, fluid inclusion microthermometry, Raman microspectrometry, scanning electron microscopy, and X-ray diffractometry, we identified diagenetic trapping and evaluated the diagenetic history of sandstone reservoirs in the Yulin Gas Field in the central area, where structural, stratigraphic and/or sedimentary lithologic traps have not been found. It was revealed that three phases of diagenesis and hydrocarbon charging occurred, respectively, in the late Triassic, late Jurassic and at the end of the early Cretaceous. In the first two phases, acidic water entered the reservoir and caused dissolution and cementation, resulting in porosity increase. However, further subsidence and diagenesis, including compaction and cementation, markedly reduced the pore space. At the end of the early Cretaceous, the bulk of the gas migrated into the tight reservoirs, and the BCGAS trap was formed. In the updip portion of this system, cementation continued to occur due to low gas saturation and has provided effective seals to retain gas for a longer period of time than water block in the BCGAS. The mechanism for the gas entrapment was changed from water block by capillary pressure in the BCGAS to diagenetic sealing. The diagenetic seals in the updip portion of the sand body were formed after gas charging, which indicates that there is a large hydrocarbon exploration potential at the basin-centered area. 相似文献
Ocean underwater exploration is a part of oceanography that investigates the physical and biological conditions for scientific and commercial purposes. And video technology plays an important role and is extensively applied for underwater environment observation. Different from the conventional methods, video technology explores the underwater ecosystem continuously and non-invasively. However, due to the scattering and attenuation of light transport in the water, complex noise distribution and lowlight condition cause challenges for underwater video applications including object detection and recognition. In this paper, we propose a new deep encoding-decoding convolutional architecture for underwater object recognition. It uses the deep encoding-decoding network for extracting the discriminative features from the noisy low-light underwater images. To create the deconvolutional layers for classification, we apply the deconvolution kernel with a matched feature map, instead of full connection, to solve the problem of dimension disaster and low accuracy. Moreover, we introduce data augmentation and transfer learning technologies to solve the problem of data starvation. For experiments, we investigated the public datasets with our proposed method and the state-of-the-art methods. The results show that our work achieves significant accuracy. This work provides new underwater technologies applied for ocean exploration. 相似文献
Sweet spots identification for unconventional shale reservoirs involves detection of organic-rich zones with abundant porosity. However, commonly used elastic attributes, such as P- and S-impedances, often show poor correlations with porosity and organic matter content separately and thus make the seismic characterization of sweet spots challenging. Based on an extensive analysis of worldwide laboratory database of core measurements, we find that P- and S-impedances exhibit much improved linear correlations with the sum of volume fraction of organic matter and porosity than the single parameter of organic matter volume fraction or porosity. Importantly, from the geological perspective, porosity in conjunction with organic matter content is also directly indicative of the total hydrocarbon content of shale resources plays. Consequently, we propose an effective reservoir parameter (ERP), the sum of volume fraction of organic matter and porosity, to bridge the gap between hydrocarbon accumulation and seismic measurements in organic shale reservoirs. ERP acts as the first-order factor in controlling the elastic properties as well as characterizing the hydrocarbon storage capacity of organic shale reservoirs. We also use rock physics modeling to demonstrate why there exists an improved linear correlation between elastic impedances and ERP. A case study in a shale gas reservoir illustrates that seismic-derived ERP can be effectively used to characterize the total gas content in place, which is also confirmed by the production well. 相似文献
Biological soil crusts (BSCs) are ubiquitous living covers that have been allowed to grow on abandoned farmlands over the Loess Plateau because the “Grain for Green” project was implemented in 1999 to control serious soil erosion. However, few studies have been conducted to quantify the effects of BSC coverage on soil hydraulic properties. This study was performed to assess the effects of BSC coverage on soil hydraulic properties, which are reflected by the soil sorptivity under an applied pressure of 0 (S 0 ) and ?3 (S 3 ) cm, saturated hydraulic conductivity (K s ), wetting front depth (WFD ), and mean pore radius (λ m ), for the Loess Plateau of China. Five classes of BSC coverage (i.e., 1–20%, 20–40%, 40–60%, 60–80%, and 80–100%) and a bare control were selected at both cyanobacteria‐ and moss‐covered sites to measure soil hydraulic properties using a disc infiltrometer under 2 consecutive pressure heads of 0 and ?3 cm, allowing the direct calculation of S 0 , S 3 , K s , and λ m . The WFD was measured onsite using a ruler immediately after the experiments of infiltration. The results indicated that both cyanobacteria and moss crusts were effective in changing the soil properties and impeding soil infiltration. The effects of moss were greater than those of cyanobacteria. Compared to those of the control, the S 0 , S 3 , K s , WFD , and λ m values of cyanobacteria‐covered soils were reduced by 13.7%, 11.0%, 13.3%, 10.6%, and 12.6% on average, and those of moss‐covered soils were reduced by 27.6%, 22.1%, 29.5%, 22.2%, and 25.9%, respectively. The relative soil sorptivity under pressures of 0 (RS 0 ) and ?3 (RS 3 ) cm, the relative saturated hydraulic conductivity (RK s ), the relative wetting front depth (RWFD ), and the relative mean pore radius (Rλ m ) decreased exponentially with coverage for both cyanobacteria‐ and moss‐covered soils. The rates of decrease in RS 0 , RS 3 , RK s , RWFD , and Rλ m of cyanobacteria were significantly slower than those of moss, especially for the coverage of 0–40%, with smaller ranges. The variations of soil hydraulic properties with BSC coverage were closely related to the change in soil clay content driven by the BSC coverage on the Loess Plateau. The results are useful for simulating the hydraulic parameters of BSC‐covered soils in arid and semiarid areas. 相似文献
Jiuzhaigou, located in the transitional area between the Qinghai–Tibet Plateau and the Sichuan Basin, is highly prone to geological hazards (e.g., rock fall, landslide, and debris flow). High-performance-based hazard prediction models, therefore, are urgently required to prevent related hazards and manage potential emergencies. Current researches mainly focus on susceptibility of single hazard but ignore that different types of geological hazards might occur simultaneously under a complex environment. Here, we firstly built a multi-geohazard inventory from 2000 to 2015 based on a geographical information system and used satellite data in Google earth and then chose twelve conditioning factors and three machine learning methods—random forest, support vector machine, and extreme gradient boosting (XGBoost)—to generate rock fall, landslide, and debris flow susceptibility maps. The results show that debris flow models presented the best prediction capabilities [area under the receiver operating characteristic curve (AUC 0.95)], followed by rock fall (AUC 0.94) and landslide (AUC 0.85). Additionally, XGBoost outperformed the other two methods with the highest AUC of 0.93. All three methods with AUC values larger than 0.84 suggest that these models have fairly good performance to assess geological hazards susceptibility. Finally, evolution index was constructed based on a joint probability of these three hazard models to predict the evolution tendency of 35 unstable slopes in Jiuzhaigou. The results show that these unstable slopes are likely to evolve into debris flows with a probability of 46%, followed by landslides (43%) and rock falls (29%). Higher susceptibility areas for geohazards were mainly located in the southeast and middle of Jiuzhaigou, implying geohazards prevention and mitigation measures should be taken there in near future.