This study describes the floristic composition and structure of a woody stand in the Senegalese Sahel, paying particular attention to the edaphic factors of its floristic composition. A stratified inventory considerin...This study describes the floristic composition and structure of a woody stand in the Senegalese Sahel, paying particular attention to the edaphic factors of its floristic composition. A stratified inventory considering the different relief units was adopted. Woody vegetation was surveyed using a dendrometric approach. The results obtained show that the flora is dominated by a few species adapted to drought, such as Balanites aegyptiaca (L.) Del., Calotropis procera Ait. and Boscia senegalensis (Pers.). The distribution of this flora and the structure of the ligneous plants are linked to the topography. In the lowlands, the flora is more diversified and the ligneous plants reach their optimum level of development compared with the higher relief areas. In the lowlands, there are a few woody species which, in the past, were indicative of better climatic conditions. These are Anogeissus leiocarpus (DC.), Commiphora africana (A. Rich.), Feretia apodanthera Del., Loeseneriella africana (A. Smith), Mitragyna inermis (Willd.) and Sclerocarya birrea (A. Rich). It is important that their reintroduction into reforestation projects takes account of their edaphic preference.展开更多
Seafloor topography plays an important role in the evolution of submarine lobes.However,it is still not so clear how the shape of slope affects the three-dimensional(3-D)architecture of submarine lobes.In this study,w...Seafloor topography plays an important role in the evolution of submarine lobes.However,it is still not so clear how the shape of slope affects the three-dimensional(3-D)architecture of submarine lobes.In this study,we analyze the effect of topography factors on different hierarchical lobe architectures that formed during Pliocene to Quaternary in the Rovuma Basin offshore East Africa.We characterize the shape,size and growth pattern of different hierarchical lobe architectures using 3-D seismic data.We find that the relief of the topographic slope determines the location of preferential deposition of lobe complexes and single lobes.When the topography is irregular and presents topographic lows,lobe complexes first infill these depressions.Single lobes are deposited preferentially at positions with higher longitudinal(i.e.across-slope)slope gradients.As the longitudinal slope becomes higher,the aspect ratio of the single lobes increases.Lateral(i.e.along-slope)topography does not seem to have a strong influence on the shape of single lobe,but it seems to affect the overlap of single lobes.When the lateral slope gradient is relatively high,the single lobes tend to have a larger overlap surface.Furthermore,as the average of lateral slope and longitudinal slope gets greater,the width/thickness ratio of the single lobe is smaller,i.e.sediments tend to accumulate vertically.The results demonstrate that the shape of slopes more comprehensively influences the 3-D architecture of lobes in natural deep-sea systems than previously other lobe deposits and analogue experiments,which helps us better understand the development and evolution of the distal parts of turbidite systems.展开更多
We derive the potential energy of gravity waves(GWs)in the upper troposphere and stratosphere at 45°S-45°N from December 2019 to November 2022 by using temperature profiles retrieved from the Constellation O...We derive the potential energy of gravity waves(GWs)in the upper troposphere and stratosphere at 45°S-45°N from December 2019 to November 2022 by using temperature profiles retrieved from the Constellation Observing System for Meteorology,Ionosphere,and Climate-2(COSMIC-2)satellite.Owing to the dense sampling of COSMIC-2,in addition to the strong peaks of gravity wave potential energy(GWPE)above the Andes and Tibetan Plateau,we found weak peaks above the Rocky,Atlas,Caucasus,and Tianshan Mountains.The land-sea contrast is responsible for the longitudinal variations of the GWPE in the lower and upper stratosphere.At 40°N/S,the peaks were mainly above the topographic regions during the winter.At 20°N/S,the peaks were a slight distance away from the topographic regions and might be the combined effect of nontopographic GWs and mountain waves.Near the Equator,the peaks were mainly above the regions with the lowest sea level altitude and may have resulted from convection.Our results indicate that even above the local regions with lower sea level altitudes compared with the Andes and Tibetan Plateau,the GWPE also exhibits fine structures in geographic distributions.We found that dissipation layers above the tropopause jet provide the body force to generate secondary waves in the upper stratosphere,especially during the winter months of each hemisphere and at latitudes of greater than 20°N/S.展开更多
New information and communication technologies have led to the emergence of new techniques in our daily lives. Indeed, in topography, a lightning development of new techniques and new devices has been noticed. This de...New information and communication technologies have led to the emergence of new techniques in our daily lives. Indeed, in topography, a lightning development of new techniques and new devices has been noticed. This development has given rise to a multitude of choices of devices and various classes of precision. This implies that the decision-makers have to study the adequate equipment and the appropriate technique according to the topographic task to be realized. The objective is not to compare GNSS and topographic techniques, but to point out the contribution of the Global Navigation Satelite System (GNSS) techniques of topographic work. Thus, a theoretical study with a critical eye on the scientific principle of calculating the third topographic dimension followed by a leveling campaign, Real Time Kinematic (RTK) surveys will be used in order to be able to compare and interpret the result from these campaigns. The study of the difference resulting from the practical campaigns will allow us to identify the contribution of GNSS technology.展开更多
Forest canopy in a deciduous forest has significant sheltering effects on the sub-canopy solar radiation,significantly influencing the energy balance of snow and permafrost beneath the forest and their spatial distrib...Forest canopy in a deciduous forest has significant sheltering effects on the sub-canopy solar radiation,significantly influencing the energy balance of snow and permafrost beneath the forest and their spatial distribution.This study employs a digital camera mounted with a fisheye lens to acquire photographs at various times in a growth cycle of the forest canopy at three selected sites in a deciduous forest near the Greater Khingan Mountains Forest Ecological Station,Northeast China.The vegetation types and conditions at the selected sites include P1 in Ledum-Claopodium-L.dahurica,P2 in Carex tato-L.dahurica,and P3 in Betula fruticosa-L.dahurica.After necessary image processing,these photographs were used to identify the canopy structure and its impacts on the sub-canopy solar radiation.Results show that fisheye photographs can successfully capture the forest canopy structure and are useful in estimating the sub-canopy solar radiation.The order of sheltering effects from the largest to the smallest on sub-canopy solar radiation at three selected sites is P3,P1,and P2,highly depending on the canopy density.Then sub-canopy solar radiation was calculated using fisheye photographs and an algorithm validated by in-situ observed solar radiation beneath the canopy at P1 and P3.The results are reasonable,although the accuracy seems compromised due to the mismatch of conditions for calculation and observation.Results also show that the mean annual solar radiation above the canopy was about 148.3 W/m2 in 2018,and the mean annual solar radiation values beneath the canopy were about 90.0,123.8,and 61.0 W/m2 at P1,P2,and P3,with only 60%,84%,and 42%of the total solar radiation penetrating through the canopy,respectively.Even in winter,when the trees are leafless,the canopy sheltering effects cannot be ignored in dense forests.Despite the limitations,fisheye photographs and related algorithms are useful in investigating the forest canopy structure and its impacts on sub-canopy solar radiation.展开更多
Compared to single-polarization synthetic aperture radar(SAR)data,fully polarimetric SAR data can provide more detailed information of the sea surface,which is important for applications such as shallow sea topography...Compared to single-polarization synthetic aperture radar(SAR)data,fully polarimetric SAR data can provide more detailed information of the sea surface,which is important for applications such as shallow sea topography detection.The Gaofen-3 satellite provides abundant polarimetric SAR data for ocean research.In this paper,a shallow sea topography detection method was proposed based on fully polarimetric Gaofen-3 SAR data.This method considers swell patterns and only requires SAR data and little prior knowledge of the water depth to detect shallow sea topography.Wave tracking was performed based on preprocessed fully polarimetric SAR data,and the water depth was then calculated considering the wave parameters and the linear dispersion relationships.In this paper,four study areas were selected for experiments,and the experimental results indicated that the polarimetric scattering parameterαhad higher detection accuracy than quad-polarization images.The mean relative errors were 14.52%,10.30%,12.56%,and 12.90%,respectively,in the four study areas.In addition,this paper also analyzed the detection ability of this model for different topographies,and the experiments revealed that the topography could be well recognized when the topography gradient is small,the topography gradient direction is close to the wave propagation direction,and the isobath line is regular.展开更多
The typical location and number of anemometer towers in the assessed area are the key to the accuracy of wind resource assessment in complex topography.As calculation examples,this paper used two typical complex topog...The typical location and number of anemometer towers in the assessed area are the key to the accuracy of wind resource assessment in complex topography.As calculation examples,this paper used two typical complex topography wind farms in Guangxi,Yunnan province in China.Firstly,we simulated the wind resource status of the anemometer tower in the Meteodyn WT software.Secondly,we compared the simulated wind resource with the actual measured data by the anemometer tower in the same situation.Thirdly,we analyzed the influence of anemometer tower location and quantity in the accuracy of wind resource assessment through the comparison results.The results showed that the range which the anemometer tower can represent is limited(<5 kilometers),and the prediction error more than 5%.Besides,the anemometer towers in special terrain areas(such as wind acceleration areas)cannot be used as a representative choice.The relative error of the simulated average annual wind speed by choose different number of anemometer towers is about 4%,and the grid-connected power generation more than 6%.The representative effect of anemometer towers is of crucial for improving the accuracy of wind resource assessment in engineering applications.展开更多
文摘This study describes the floristic composition and structure of a woody stand in the Senegalese Sahel, paying particular attention to the edaphic factors of its floristic composition. A stratified inventory considering the different relief units was adopted. Woody vegetation was surveyed using a dendrometric approach. The results obtained show that the flora is dominated by a few species adapted to drought, such as Balanites aegyptiaca (L.) Del., Calotropis procera Ait. and Boscia senegalensis (Pers.). The distribution of this flora and the structure of the ligneous plants are linked to the topography. In the lowlands, the flora is more diversified and the ligneous plants reach their optimum level of development compared with the higher relief areas. In the lowlands, there are a few woody species which, in the past, were indicative of better climatic conditions. These are Anogeissus leiocarpus (DC.), Commiphora africana (A. Rich.), Feretia apodanthera Del., Loeseneriella africana (A. Smith), Mitragyna inermis (Willd.) and Sclerocarya birrea (A. Rich). It is important that their reintroduction into reforestation projects takes account of their edaphic preference.
基金The study is funded by the Cooperation Project of China National Petroleum Company(CNPC)and China University of Petroleum-Beijing(CUPB)(No.RIPED-2021-JS-552)the National Natural Science Foundation of China(Nos.42002112,42272110)+2 种基金the Strategic Cooperation Technology Projects of CNPC and CUPB(No.ZLZX2020-02)the Science Foundation for Youth Scholars of CUPB(No.24620222BJRC006)We thank the China Scholarship Council(CSC)(No.202106440048)for having funded the research stay of Mei Chen at MARUM,University of Bremen.We thank Elda Miramontes for her constructive comments and suggestions that helped us improve our manuscript.
文摘Seafloor topography plays an important role in the evolution of submarine lobes.However,it is still not so clear how the shape of slope affects the three-dimensional(3-D)architecture of submarine lobes.In this study,we analyze the effect of topography factors on different hierarchical lobe architectures that formed during Pliocene to Quaternary in the Rovuma Basin offshore East Africa.We characterize the shape,size and growth pattern of different hierarchical lobe architectures using 3-D seismic data.We find that the relief of the topographic slope determines the location of preferential deposition of lobe complexes and single lobes.When the topography is irregular and presents topographic lows,lobe complexes first infill these depressions.Single lobes are deposited preferentially at positions with higher longitudinal(i.e.across-slope)slope gradients.As the longitudinal slope becomes higher,the aspect ratio of the single lobes increases.Lateral(i.e.along-slope)topography does not seem to have a strong influence on the shape of single lobe,but it seems to affect the overlap of single lobes.When the lateral slope gradient is relatively high,the single lobes tend to have a larger overlap surface.Furthermore,as the average of lateral slope and longitudinal slope gets greater,the width/thickness ratio of the single lobe is smaller,i.e.sediments tend to accumulate vertically.The results demonstrate that the shape of slopes more comprehensively influences the 3-D architecture of lobes in natural deep-sea systems than previously other lobe deposits and analogue experiments,which helps us better understand the development and evolution of the distal parts of turbidite systems.
基金the National Natural Science Foundation of China(Grant Nos.41831073,42174196,and 42374205)the Project of Stable Support for Youth Team in Basic Research Field,Chinese Academy of Sciences(CAS+4 种基金Grant No.YSBR-018)the Informatization Plan of CAS(Grant No.CAS-WX2021PY-0101)the Youth Cross Team Scientific Research project of the Chinese Academy of Sciences(Grant No.JCTD-2021-10)the Open Research Project of Large Research Infrastructures of CAS titled“Study on the Interaction Between Low-/Mid-Latitude Atmosphere and Ionosphere Based on the Chinese Meridian Project.”This work was also supported in part by the Specialized Research Fund and the Open Research Program of the State Key Laboratory of Space Weather.
文摘We derive the potential energy of gravity waves(GWs)in the upper troposphere and stratosphere at 45°S-45°N from December 2019 to November 2022 by using temperature profiles retrieved from the Constellation Observing System for Meteorology,Ionosphere,and Climate-2(COSMIC-2)satellite.Owing to the dense sampling of COSMIC-2,in addition to the strong peaks of gravity wave potential energy(GWPE)above the Andes and Tibetan Plateau,we found weak peaks above the Rocky,Atlas,Caucasus,and Tianshan Mountains.The land-sea contrast is responsible for the longitudinal variations of the GWPE in the lower and upper stratosphere.At 40°N/S,the peaks were mainly above the topographic regions during the winter.At 20°N/S,the peaks were a slight distance away from the topographic regions and might be the combined effect of nontopographic GWs and mountain waves.Near the Equator,the peaks were mainly above the regions with the lowest sea level altitude and may have resulted from convection.Our results indicate that even above the local regions with lower sea level altitudes compared with the Andes and Tibetan Plateau,the GWPE also exhibits fine structures in geographic distributions.We found that dissipation layers above the tropopause jet provide the body force to generate secondary waves in the upper stratosphere,especially during the winter months of each hemisphere and at latitudes of greater than 20°N/S.
文摘New information and communication technologies have led to the emergence of new techniques in our daily lives. Indeed, in topography, a lightning development of new techniques and new devices has been noticed. This development has given rise to a multitude of choices of devices and various classes of precision. This implies that the decision-makers have to study the adequate equipment and the appropriate technique according to the topographic task to be realized. The objective is not to compare GNSS and topographic techniques, but to point out the contribution of the Global Navigation Satelite System (GNSS) techniques of topographic work. Thus, a theoretical study with a critical eye on the scientific principle of calculating the third topographic dimension followed by a leveling campaign, Real Time Kinematic (RTK) surveys will be used in order to be able to compare and interpret the result from these campaigns. The study of the difference resulting from the practical campaigns will allow us to identify the contribution of GNSS technology.
基金the National Natural Science Foundation of China(Grant Nos.41971079 and 41671059,41975081).
文摘Forest canopy in a deciduous forest has significant sheltering effects on the sub-canopy solar radiation,significantly influencing the energy balance of snow and permafrost beneath the forest and their spatial distribution.This study employs a digital camera mounted with a fisheye lens to acquire photographs at various times in a growth cycle of the forest canopy at three selected sites in a deciduous forest near the Greater Khingan Mountains Forest Ecological Station,Northeast China.The vegetation types and conditions at the selected sites include P1 in Ledum-Claopodium-L.dahurica,P2 in Carex tato-L.dahurica,and P3 in Betula fruticosa-L.dahurica.After necessary image processing,these photographs were used to identify the canopy structure and its impacts on the sub-canopy solar radiation.Results show that fisheye photographs can successfully capture the forest canopy structure and are useful in estimating the sub-canopy solar radiation.The order of sheltering effects from the largest to the smallest on sub-canopy solar radiation at three selected sites is P3,P1,and P2,highly depending on the canopy density.Then sub-canopy solar radiation was calculated using fisheye photographs and an algorithm validated by in-situ observed solar radiation beneath the canopy at P1 and P3.The results are reasonable,although the accuracy seems compromised due to the mismatch of conditions for calculation and observation.Results also show that the mean annual solar radiation above the canopy was about 148.3 W/m2 in 2018,and the mean annual solar radiation values beneath the canopy were about 90.0,123.8,and 61.0 W/m2 at P1,P2,and P3,with only 60%,84%,and 42%of the total solar radiation penetrating through the canopy,respectively.Even in winter,when the trees are leafless,the canopy sheltering effects cannot be ignored in dense forests.Despite the limitations,fisheye photographs and related algorithms are useful in investigating the forest canopy structure and its impacts on sub-canopy solar radiation.
基金The National Natural Science Foundation of China under contract Nos 51839002 and U2006207.
文摘Compared to single-polarization synthetic aperture radar(SAR)data,fully polarimetric SAR data can provide more detailed information of the sea surface,which is important for applications such as shallow sea topography detection.The Gaofen-3 satellite provides abundant polarimetric SAR data for ocean research.In this paper,a shallow sea topography detection method was proposed based on fully polarimetric Gaofen-3 SAR data.This method considers swell patterns and only requires SAR data and little prior knowledge of the water depth to detect shallow sea topography.Wave tracking was performed based on preprocessed fully polarimetric SAR data,and the water depth was then calculated considering the wave parameters and the linear dispersion relationships.In this paper,four study areas were selected for experiments,and the experimental results indicated that the polarimetric scattering parameterαhad higher detection accuracy than quad-polarization images.The mean relative errors were 14.52%,10.30%,12.56%,and 12.90%,respectively,in the four study areas.In addition,this paper also analyzed the detection ability of this model for different topographies,and the experiments revealed that the topography could be well recognized when the topography gradient is small,the topography gradient direction is close to the wave propagation direction,and the isobath line is regular.
基金the financial support by the National Natural Science Foundation of China(No.52176212).
文摘The typical location and number of anemometer towers in the assessed area are the key to the accuracy of wind resource assessment in complex topography.As calculation examples,this paper used two typical complex topography wind farms in Guangxi,Yunnan province in China.Firstly,we simulated the wind resource status of the anemometer tower in the Meteodyn WT software.Secondly,we compared the simulated wind resource with the actual measured data by the anemometer tower in the same situation.Thirdly,we analyzed the influence of anemometer tower location and quantity in the accuracy of wind resource assessment through the comparison results.The results showed that the range which the anemometer tower can represent is limited(<5 kilometers),and the prediction error more than 5%.Besides,the anemometer towers in special terrain areas(such as wind acceleration areas)cannot be used as a representative choice.The relative error of the simulated average annual wind speed by choose different number of anemometer towers is about 4%,and the grid-connected power generation more than 6%.The representative effect of anemometer towers is of crucial for improving the accuracy of wind resource assessment in engineering applications.
