The chlorophyll-a concentration data obtained through remote sensing are important for a wide range of scientific concerns. However, cloud cover and limitations of inversion algorithms of chlorophyll-a concentration lead to data loss, which critically limits studying the mechanism of spatial-temporal patterns of chlorophyll-a concentration in response to marine environment changes. If the commonly used operational chlorophyll-a concentration products can offer the best data coverage frequency, highest accuracy, best applicability, and greatest robustness at different scales remains debatable to date. Therefore, in the present study, four commonly used operational multi-sensor multi-algorithm fusion products were compared and subjected to validation based on statistical analysis using the available data measured at multiple spatial and temporal scales. The experimental results revealed that in terms of spatial distribution, the chlorophyll-a concentration products generated by averaging method (Chl1-AV/AVW) and GSM model (Chl1-GSM) presented a relatively high data coverage frequency in Case I water regions and extremely low or no data coverage frequency in the estuarine coastal zone regions and inland water regions, the chlorophyll-a concentration products generated by the Neural Network algorithm (Chl2) presented high data coverage frequency in the estuarine coastal zone Case 2 water regions. The chlorophyll-a concentration products generated by the OC5 algorithm (ChlOC5) presented high data coverage frequency in Case I water regions and the turbid Case II water regions. In terms of absolute precision, the Chl1-AV/AVW and Chl1-GSM chlorophyll-a concentration products performed better in Class I water regions, and the Chl2 product performed well only in Case II estuarine coastal zones, while presenting large errors in absolute precision in the Case I water regions. The ChlOC5 product presented a higher precision in Case I and Case II water regions, with a better and more stable performance in both regions compared to the other products.
Deltaic sedimentary systems form the most favorable hydrocarbon reservoirs in continental faulted lacustrine basins, and their types and controlling factors directly affect the distribution of hydrocarbons. The systematic study of typical modern delta deposition provides significant guidance regarding the distribution of oil and gas reservoirs in the subsurface. For this reason, the Heima River delta in Qinghai Lake, which features multiple sediment sources and clear sedimentary evolution stages, was selected for this research. A detailed study of the sedimentology and architectural characteristics of the Heimahe delta in Qinghai Lake was conducted. A total of 4 types of gravel facies, 4 types of sand facies, and 2 types of mud facies were identified. This study also focuses on recognizing the architectural elements within channels and bars. The delta plain features debris-flow, switched, and migrated channels and vertical and bilateral aggradation bars. The delta front features migrated and filled channels and bilateral and lateral aggradation bars. Twenty-two representative outcrop sections were selected. Detailed observation and analysis of these sections revealed three stages: the progradation to aggradation (PA) stage, in which the deposits show evidence of sigmoid-type and coarse-grained sedimentation; the retrogradation (R) stage, which is characterized by imbricated regression; and the aggradation to progradation and degradation (APD) stage, which is characterized by a terraced-stepping, progression stacking pattern. Based on the integrated analysis of the sedimentary environment, outcrop lithofacies associations, architecture stacking patterns, fossils and bioclasts, we identified diverse depositional associations and constructed a sedimentary evolution model of the depositional system in this area. We suggest that the depositional system transitioned from an early single-provenance gravel-rich fan delta to a multi-provenance mud-rich delta and that two factors mainly controlled the transition: the southern boundary fault activity and lake level variations. The contemporaneous activity of the fault increased the accommodation in the low-stand systems tract, which resulted in continuous coarse-sediment deposition.
A new digital elevation model (DEM) upscaling method based on high accuracy surface modeling (HASM) is proposed by combining the elevation information of DEM and the valley lines extracted from DEM with different flow accumulation thresholds. The proposed method has several advantages over traditional DEM upscaling methods. First, the HASM ensures the smoothness of the upscaled DEM. Secondly, several DEMs with different topographic details can be obtained using the same DEM grid size by incorporating the valley lines with different flow accumulation thresholds. The Jiuyuangou watershed in China’s Loess Plateau was used as a case study. A DEM with a grid size of 5 m obtained from the local surveying and mapping department was used to verify the proposed DEM upscaling method. We established the surface complexity index to describe the complexity of the topographic surface and quantified the differences in the topographic features obtained from different upscaling results. The results show that topography becomes more generalized as grid size and flow accumulation threshold increase. At a large DEM grid size, an increase in the flow accumulation threshold increases the difference in elevation values in different grids, increasing the surface complexity index. This study provides a new DEM upscaling method suitable for quantifying topography.
The Permian Lucaogou Formation represents one of the most important hydrocarbon source rock intervals in the Junggar Basin, although the sedimentary paleoenvironment and organic matter enrichment mechanism of the Lucaogou Formation remain controversial. We studied the temporal evolution of the sedimentary paleoenvironment in the Lucaogou Formation by analyzing the elemental composition and total organic carbon content of 27 hydrocarbon source rock samples from the J305 well in the Jimsar Sag. Using these data, we found that the Lucaogou Formation overall was deposited in a semisaline to saline, reducing lake basin under an arid climate. We identified five organic matter-enriched intervals, which can be correlated with the parameters that indicate a wetter climate and a more anoxic lake environment. To compare sedimentary environments spatially, we compiled environmental indicators from 10 cores and outcrops in three sags around the Bogda Mountains. The compilation shows that the organic matter-enriched Jimsar Sag experienced a more arid climate and a more saline and anoxic lake environment during the deposition of the Lucaogou Formation, which was possibly controlled by the paleogeographic position. We conclude that the spatially arid climate and anoxic environment induced organic matter burial in the Jimsar Sag, while temporal events of a more humid climate and more anoxic environment triggered the enrichment of organic matter in some intervals of the Lucaogou Formation.
Remote sensing image scene classification and remote sensing technology applications are hot research topics. Although CNN-based models have reached high average accuracy, some classes are still misclassified, such as “freeway,” “spare residential,” and “commercial_area.” These classes contain typical decisive features, spatial-relation features, and mixed decisive and spatial-relation features, which limit high-quality image scene classification. To address this issue, this paper proposes a Grad-CAM and capsule network hybrid method for image scene classification. The Grad-CAM and capsule network structures have the potential to recognize decisive features and spatial-relation features, respectively. By using a pre-trained model, hybrid structure, and structure adjustment, the proposed model can recognize both decisive and spatial-relation features. A group of experiments is designed on three popular data sets with increasing classification difficulties. In the most advanced experiment, 92.67% average accuracy is achieved. Specifically, 83%, 75%, and 86% accuracies are obtained in the classes of “church,” “palace,” and “commercial_area,” respectively. This research demonstrates that the hybrid structure can effectively improve performance by considering both decisive and spatial-relation features. Therefore, Grad-CAM-CapsNet is a promising and powerful structure for image scene classification.
Turkey is located in the Alpine-Himalayan seismic zone. The Anatolian plate has witnessed very severe and destructive earthquakes both in the past and today. In this study, statistical analyses of earthquakes that occurred between 1914 and 2019 along the Fethiye-Burdur fault zone, which is an active line, were conducted using geographic information systems. Analyses of standard distance, standard deviational eclipse, mean center, and median center were conducted to determine the geographic distributions of epicenters with a magnitude value of 3.5 and above. Quadrat and Average Nearest Neighbor analyses were used to reveal the spatial pattern. Anselin Local Moran I and Getis Ord Gi* method were used to determining where the earthquake epicenters are clustered locally. Kernel Density analyses were conducted to measure earthquake epicenters’ density. Quadrat analysis, Average Nearest Neighbor, Global Moran’s I, and Getis - Ord General G indices demonstrated that earthquakes are clustered in certain regions and are related to each other positionally. Anselin Moran’s I regional analyses revealed that high values were clustered in the West of Burdur city center and the district of Yeşilova, and similar results were obtained in the Getis Ord Gi* method.
After the construction of cascade reservoirs in the upper reaches of the Three Gorges Reservoir (TGR), the sediment load outflow of the upper Yangtze River Basin (YRB) has been significantly altered, decreasing from 491.8 Mt/yr (1956–2002) to 36.1 Mt/yr (2003–2017) at Yichang station. This has widely affected river hydrology, suspended sediment grain size distribution, and channel morphology. This study analyzed hydrological variations in water discharge and sediment load of the upper YRB over the past 62 years (1956–2017) by employing a double mass curve. The variations in the source areas of sediment yielding for the upper YRB were quantified, and field measurement data of the cross-channel profile were collected to investigate the sedimentation process in the TGR from 2003 to 2017. More than 90% of the sediment load reduction in the upper YRB may be explained by human activities. The Jinshajiang River was no longer the largest sediment source area for the Zhutuo station (accounting for 5.23%) in the 2013–2017 time span, and the sediment rating rates for the inflow and outflow of the TGR shifted to negatively correlated. A longitudinal fining trend was revealed in the suspended sediment size. Still, the mean median grain size of suspended sediment in the TGR had an increasing trend in the 2013–2017 period. This result may be closely related to sediment regulation in reservoirs and incoming sediment load reduction. Sedimentation in the TGR decreased sharply from 299.8 Mt/yr in 2003–2012 to 47.2 Mt/yr in 2013–2017, but the sedimentation rate of the TGR remained at > 80% annually. Moreover, some cross sections in the fluctuating backwater zone experienced scouring.
This study aims to propose an empirical prediction model of hydraulic aperture of 2D rough fractures through numerical simulations by considering the influences of fracture length, average mechanical aperture, minimum mechanical aperture, joint roughness coefficient (JRC) and hydraulic gradient. We generate 600 numerical models using successive random additions (SRA) algorithm and for each model, seven hydraulic gradients spanning from 2.5 × 10−7 to 1 are considered to fully cover both linear and nonlinear flow regimes. As a result, a total of 4200 fluid flow cases are simulated, which can provide sufficient data for the prediction of hydraulic aperture. The results show that as the ratio of average mechanical aperture to fracture length increases from 0.01 to 0.2, the hydraulic aperture increases following logarithm functions. As the hydraulic gradient increases from 2.5 × 10−7 to 1, the hydraulic aperture decreases following logarithm functions. When a relatively low hydraulic gradient (i.e., 5 × 10−7) is applied between the inlet and the outlet boundaries, the streamlines are of parallel distribution within the fractures. However, when a relatively large hydraulic gradient (i.e., 0.5) is applied between the inlet and the outlet boundaries, the streamlines are disturbed and a number of eddies are formed. The hydraulic aperture predicted using the proposed empirical functions agree well with the calculated results and is more reliable than those available in the preceding literature. In practice, the hydraulic aperture can be calculated as a first-order estimation using the proposed prediction model when the associated parameters are given.
Soil organic carbon (SOC) is a critical variable used to determine the carbon balance. However, large uncertainties arise when predicting the SOC stock in soil profiles in Chinese grasslands, especially on desert rangelands. Recent studies have shown that desert ecosystems may be potential carbon sinks under global climate change. Because of the high spatial heterogeneity, time-consuming sampling methods, and difficult acquisition process, the relationships the SOC storage and distribution have with driving factors in desert rangelands remain poorly understood. Here, we investigated and developed an SOC database from 3162 soil samples (collected at depths of 0−10 cm and 10−20 cm) across 527 sites, as well as the climate conditions, vegetation types, and edaphic factors associated with the sampling sites in the desert rangelands of northern Xinjiang, north-west China. This study aims to determine the SOC magnitude and drivers in desert rangelands. Our findings demonstrate that the SOC and SOC density (SOCD) were 0.05−37.13 g·kg−1 and 19.23−9740.62 g·m−2, respectively, with average values of 6.81 ± 5.31 g·kg−1 and 1670.38 ± 1202.52 g·m−2, respectively. The spatial distributions of SOC and SOCD all showed gradually decreasing trends from south-west to north-east. High-SOC areas were mainly distributed in the piedmont lowlands of the Ili valley, while low-SOC regions were mainly concentrated in the north-west area of Altay. The redundancy analysis results revealed that all environmental factors accounted for approximately 37.6% of the spatial variability in SOC; climate factors, vegetation factors, and soil properties explained 15.0%, 1.7%, and 12.3%, respectively. The structural equation model (SEM) further indicated that evapotranspiration, average annual precipitation, and the SWC were the dominant factors affecting SOC accumulation, mainly through direct effects, although indirect effects were also delivered by the vegetation factors. Taken together, the results obtained herein updated the SOC data pool available for desert rangelands and clarified the main driving factors of SOC variations. This study provided supporting data for the sustainable use and management of desert rangelands and the global ecosystem carbon budget.
The identification of superimposed gas-bearing systems in coal measures is the basis for expediting the optimization of coal measure gas co-production. Through the analysis of drill cores and log data of Upper Carboniferous Benxi Formation to the member 8 of Middle Permian Lower Shihezi Formation in Daning-Jixian block, eastern margin of Ordos Basin, four distinct superimposed coal measure gas-bearing systems were identified, and their formation mechanism was discussed from the sequence stratigraphic perspective. Type I system mainly contains multiple coal seams, shales and sandstone layers. Type II system is dominated by multiple coal seams and shales. Type III is characterized by multiple sandstone layers, and type IV system is dominated by limestones and mudstones. In general, the gas-bearing systems deposited in barrier-lagoon are type II, those deposited in carbonate tidal flats are type IV, and those deposited in the delta front are types I and III. The marine mudstone, acting as a key layer near the maximum flooding surface, exhibits very low permeability, which is the main factor contributing to the formation of superimposed gas-bearing systems. The sedimentary environment plays a significant role in controlling the distribution of gas-bearing systems. Notably, the vertical gas-bearing systems in the south-western region, where delta front and lagoon facies overlap, are more complex than those in the north-eastern delta front facies.
An improved evaluation method for estimating gas content during the inversion process of deep-burial coal was established based on the on-site natural desorption curves. The accuracy of the US Bureau of Mines (USBM), Polynomial fitting, Amoco, and the improved evaluation methods in the predicting of lost gas volume in deep seams in the Mabidong Block of the Qinshui Basin were then compared. Furthermore, the calculation errors of these different methods in simulating lost gas content based on coring time were compared. A newly established nonlinear equation was developed to estimate the minimum error value, by controlling the lost time within 16 min, the related errors can be reduced. The improved evaluation was shown to accurately and rapidly predict the gas content in deep seams. The results show that the deep coal bed methane accumulation is influenced by various factors, including geological structure, hydrodynamic conditions, roof lithology, and coalification. Reverse faults and weak groundwater runoff can hinder the escape of methane, and these factors should be considered in the future exploration and development of coalbed methane.
It is crucial to investigate the characteristics of fire danger in the areas around Beijing to increase the accuracy of fire danger monitoring, forecasting, and management. Using meteorological data from 17 national meteorological stations in the areas around Beijing from 1981−2021, this study calculated the fire weather index (FWI) and analyzed its spatiotemporal characteristics. It was found that the high and low fire danger periods were in April−May and July−August, with spatial patterns of “decrease in the northwest−increase in the southeast” and a significant increase throughout the areas around Beijing, respectively. Next, the contributions of different meteorological factors were quantified by the multiple regression method. We found that during the high fire danger period, the northern and southern parts were affected by precipitation and minimum relative humidity, respectively. However, most areas were influenced by wind speed during the low fire danger period. Finally, comparing with the FWI characteristics under different SSP scenarios, we found that the FWI decreased during high fire danger period and increased during low fire danger period under different SSP scenarios (i.e., SSP245, SSP585) for periods of 2021−2050, 2071−2100, 2021−2100, except for SSP245 in 2071−2100 with an increasing trend both in high and low fire danger periods. This study implies that there is a higher probability of FWI in the low fire danger period, threatening the ecological environment and human health. Therefore, it is necessary to enhance research on fire danger during the low fire danger period to improve the ability to predict summer fire danger.
The major controlling factors of organic matter and its enrichment model of the black shale from the Wufeng-Longmaxi Formation were explored by investigating the vertical variation characteristics, as well as major element and trace element abundances in the Wuxi Bailu section. The results show that the sedimentary tectonic setting of the Wufeng-Longmaxi Formation in the north-east margin of the upper Yangtze platform is located on the active continental margin, which is a passive continental margin and continental island arc. The parent rock in the source area is mainly felsic volcanic rocks mixed with small amounts of sedimentary recycling materials. Due to increased plate activity and a drop in sea levels, terrigenous pyroclastic input increased. The palaeoclimate was semi-humid, and a robust dysoxic-reduction environment and a high level of palaeoproductivity, causing the formation of the organic-rich shale in the Wufeng Formation. At the base of the Longmaxi Formation, the sedimentary water body was affected by global transgression, showing a strong anoxic-reductive environment, and the paleoclimate was a warm and humid condition. The palaeoproductivity level was high, resulting in the formation of organic shale. Due to the sea level drop at the top of the Longmaxi Formation, the sedimentary water was in an oxic-reduced environment, but the input of terrigenous pyroclastic matter increased. Because the paleoclimate was warm and humid and the palaeoproductivity level was high, organic-rich shale was formed. The findings demonstrate that terrigenous clastic input circumstances, palaeoproductivity conditions, and paleo-redox conditions had the greatest influence on the enrichment of organic matter in the Wufeng-Longmaxi Formation. Thus, organic matter enrichment was controlled by multiple paleoenvironmental factors.
A sandy, braided river is a typical type of river that exists in ancient and modern alluvial plains and is inherent with significant seasonal water discharge variations. The variations play an important role in the depositional process and the formation of the sedimentary architecture of braided rivers. In this paper, a braided river outcrop along the Yellow River in Fugu is used to describe the effects of seasonal hydrodynamic variations on braided river sedimentary architecture. The results show that the braided channel network exhibits two different patterns during flood period and normal period. During flood periods, the main braided channels surrounding channel bars and the secondary braided channels distributed on the top of the channel bars coexist, forming a highly braided channel network. Migration of the main braided channels control the formation of middle channel bars and side bars. The generation and evolution of the secondary braided channels reformed the upper part of preexisting channel bars and produced affiliated bars along their flow path. During the normal period, water levels decrease, causing the secondary river channels to be abandoned and forming abandoned channels, and only the main braided channels stay active. In the long term sedimentation process, strong water flow during the flood period continuously erodes pre-existing sediments and forms new sediments, while weak water flow during the normal period can only reform the main braided channels and their adjacent channel bar sediments. Based on differences in sedimentary processes and associated hydrodynamic conditions, braided river sediments are divided into two combinations. The strong hydrodynamic combination includes main braided channels, middle channel bar, and side bar, while the weak hydrodynamic combination includes secondary braided channels, abandoned channels, and affiliated bars. The proportion of strong hydrodynamic combinations is much larger than that of weak hydrodynamic combinations. Based on this, we construct a braided river sedimentary architecture model that is helpful for the fine characterization of subsurface oil and gas reservoirs.
