Agricultural greenhouse gas(GHG)emissions are influenced by a combination of climate,soil and agricultural management practices.Over the past 30 years,approximately 5% of China's cropland has shifted from the sout...Agricultural greenhouse gas(GHG)emissions are influenced by a combination of climate,soil and agricultural management practices.Over the past 30 years,approximately 5% of China's cropland has shifted from the south to the north.This shift has significantly altered the geographical environment,with potential substantial impacts on agricultural GHG emissions.This study used the DeNitrification DeComposition(DNDC)process-based model to simulate GHG emissions(CH_(4)and N_(2)O)from the production of China's 10 major food crops and explored changes in agricultural GHG emissions caused by the spatial shift of cropland in China.Results from the validated DNDC model indicate that total emissions from the major food crop production in China were approximately 343 Tg CO_(2)-eq yr^(-1)with CH_(4)emissions accounting for about 74%.Meanwhile,the spatial shift of cropland from 1990 to 2020 resulted in a 3% decrease in average CH_(4)emissions per unit cropland area and an 8% increase in average N_(2)O emissions per unit cropland area,respectively.The expansion of dryland in the Northwest Arid Region emitted less CH_(4)but significantly more N_(2)O,thereby driving changes in national GHG emissions.This study provides a scientific foundation for the sustainable use of cropland and the formulation of strategies to reduce agricultural GHG emissions.展开更多
Advent of High Resolution Satellite Data (HRSD) with development of high spatial resolution sensors have revolutionized the generation of large scale maps. Generation of large scale digital utility maps using HRSD inv...Advent of High Resolution Satellite Data (HRSD) with development of high spatial resolution sensors have revolutionized the generation of large scale maps. Generation of large scale digital utility maps using HRSD involves different methodologies and includes several steps wherein errors or spatial shift may be induced at any stage of data generation. It may be interesting to note that the characteristics of the spatial shift vary with methodologies adopted in its processing and has unique implications with respect to the data usage along with its application. Spatial shifts of points on a satellite data is result of unexpected translation and rotation of pixel with respect to the original location. Present study analyzes the spatial shift generated in satellite data with reference to the change in area and orientation of a group of pixels i.e. conformal and equal area properties of the rectified satellite data. This study aims to establish a relationship between the spatial resolutions of the satellite image used for digital map generation with the spatial accuracy achieved. In this study, Ground Control Points (GCP’s) identified on satellite data for a sample study area were validated using Differential Global Positioning System. Five different high resolution satellite images were analyzed to verify changes in area and shape with reference to the GCP’s. The results indicate that with improvement in the spatial resolution, higher precision in the digital maps is accomplished in terms of spatial shift of the points.展开更多
The spatial shift of the North Atlantic Oscillation (NAO) is analyzed by using the Twentieth Century Reanalysis version 2 dataset and identifying NAO action centers directly on winter mean sealevel pressure (SLP) anom...The spatial shift of the North Atlantic Oscillation (NAO) is analyzed by using the Twentieth Century Reanalysis version 2 dataset and identifying NAO action centers directly on winter mean sealevel pressure (SLP) anomaly maps. The spatial shift of the NAO is characterized by four NAO spatial shift indices: the zonal and meridional shifts of the NAO southern and northern action centers. It is found that the zonal and meridional shift trends of the NAO action centers move along a path of southwest-northwest direction. Spectral analysis shows that the four NAO spatial shift indices have periodicity of 2-6 years and the NAO index has periodicity of 2-3 years in terms of high-frequency variations. On a decadal time scale, the NAO spatial shift indices are closely (positively) related to the NAO index, which is in agreement with previous studies of the relationship between the NAO index and the spatial shift of the NAO pattern. However, there is no relationship between the NAO index and the meridional shift of the northern action center on an interannual time scale. The significant relationship between the NAO index and the interannual variability of NAO spatial shift indices is very likely to be associated with synopticscale Rossby wave breaking, which generates surface pressure anomalies and thus affects the phase and pattern of the NAO. The correlations of winter westerly winds over 90°W-0° and the NAO index and the NAO spatial shift indices have a '+ - + -' structure from the Equator to the North Pole. Although there is close correlation between the NAO spatial shift indices and the strength of the zonal winds in the North Atlantic region, the effect of the zonal winds on the NAO spatial shift differs at different latitudes. Hence, the role of the zonal winds is probably a result of the NAO spatial shifts.展开更多
We investigate the co-propagation of a strong pump beam and a weak signal beam in lead glass, and find that the large phase shift of the strongly nonlocal spatial optical soliton （SNSOS） can be realized via cross-ph...We investigate the co-propagation of a strong pump beam and a weak signal beam in lead glass, and find that the large phase shift of the strongly nonlocal spatial optical soliton （SNSOS） can be realized via cross-phase modulation. The theoretical study suggests a synchronous propagation of the pump SNSOS and the signal SNSOS under the required initial condition. A π-phase shift of the signal SNSOS is experimentally obtained by changing the power of the pump SNSOS by about 13 mW around the soliton critical power, which agrees qualitatively with our theoretical prediction. The ratio of the phase shift rate of the signal SNSOS to that of the pump SNSOS shows a close match to the reciprocal of the ratio between their wavelengths.展开更多
This paper presents a novel approach that can quickly and effectively partition images based on fully exploiting the spatially coherent property. We propose an algorithm named iterative loopy belief propagation（iLBP...This paper presents a novel approach that can quickly and effectively partition images based on fully exploiting the spatially coherent property. We propose an algorithm named iterative loopy belief propagation（iLBP） to integrate the homogenous regions and prove its convergence. The image is first segmented by mean shift（MS） algorithm to form over-segmented regions that preserve the desirable edges and spatially coherent parts. The segmented regions are then represented by region adjacent graph（RAG） . Motivated by k-means algorithm,the iLBP algorithm is applied to perform the minimization of the cost function to integrate the over-segmented parts to get the final segmentation result. The image clustering based on the segmented regions instead of the image pixels reduces the number of basic image entities and enhances the image segmentation quality. Comparing the segmentation result with some existing algorithms,the proposed algorithm shows a better performance based on the evaluation criteria of entropy especially on complex scene images.展开更多
Doppler asymmetric spatial heterodyne spectroscopy(DASH)technique has developed rapidly in passive Doppler-shift measurements of atmospheric emission lines over the last decade.With the advantages of high phase shift ...Doppler asymmetric spatial heterodyne spectroscopy(DASH)technique has developed rapidly in passive Doppler-shift measurements of atmospheric emission lines over the last decade.With the advantages of high phase shift sensitivity,compact,and rugged structure,DASH is proposed to be used for celestial autonomous navigation based on Doppler radial velocity measurement in this work.Unlike atmospheric emission lines,almost all targeted lines in the research field of deep-space exploration are the absorption lines of stars,so a mathematical model for the Doppler-shift measurements of absorption lines with a DASH interferometer is established.According to the analysis of the components of the interferogram received by the detector array,we find that the interferogram generated only by absorption lines in a passband can be extracted and processed by a method similar to the approach to studying the emission lines.In the end,numerical simulation experiments of Doppler-shift measurements of absorption lines are carried out.The simulation results show that the relative errors of the retrieved speeds are less than 0.7%under ideal conditions,proving the feasibility of measuring Doppler shifts of absorption lines by DASH instruments.展开更多
A phase-shifting digital holography scheme developed to investigate internal defects in artworks is described. Phase-shifting is utilized to obtain a clear reconstructed object wave from a rough surface texture. A rev...A phase-shifting digital holography scheme developed to investigate internal defects in artworks is described. Phase-shifting is utilized to obtain a clear reconstructed object wave from a rough surface texture. A reverse-transform algorithm is employed to reconstruct the object wave on its original position of unknown distance or the imaging position from the object wave information on the holographic plane. To get the clearest reconstruction the exact registration of the unknown distance is determined by applying the intensity sum as the auto-focusing function, The spatial resolution of the reconstruction image is also investigated for a variety of affecting factors. Laboratory results of reconstruction images under deformation are presented.展开更多
基金National Natural Science Foundation of China,No.42361144881,No.42201310The Third Xinjiang Scientific Expedition Program,No.2021xjkk0900。
文摘Agricultural greenhouse gas(GHG)emissions are influenced by a combination of climate,soil and agricultural management practices.Over the past 30 years,approximately 5% of China's cropland has shifted from the south to the north.This shift has significantly altered the geographical environment,with potential substantial impacts on agricultural GHG emissions.This study used the DeNitrification DeComposition(DNDC)process-based model to simulate GHG emissions(CH_(4)and N_(2)O)from the production of China's 10 major food crops and explored changes in agricultural GHG emissions caused by the spatial shift of cropland in China.Results from the validated DNDC model indicate that total emissions from the major food crop production in China were approximately 343 Tg CO_(2)-eq yr^(-1)with CH_(4)emissions accounting for about 74%.Meanwhile,the spatial shift of cropland from 1990 to 2020 resulted in a 3% decrease in average CH_(4)emissions per unit cropland area and an 8% increase in average N_(2)O emissions per unit cropland area,respectively.The expansion of dryland in the Northwest Arid Region emitted less CH_(4)but significantly more N_(2)O,thereby driving changes in national GHG emissions.This study provides a scientific foundation for the sustainable use of cropland and the formulation of strategies to reduce agricultural GHG emissions.
文摘Advent of High Resolution Satellite Data (HRSD) with development of high spatial resolution sensors have revolutionized the generation of large scale maps. Generation of large scale digital utility maps using HRSD involves different methodologies and includes several steps wherein errors or spatial shift may be induced at any stage of data generation. It may be interesting to note that the characteristics of the spatial shift vary with methodologies adopted in its processing and has unique implications with respect to the data usage along with its application. Spatial shifts of points on a satellite data is result of unexpected translation and rotation of pixel with respect to the original location. Present study analyzes the spatial shift generated in satellite data with reference to the change in area and orientation of a group of pixels i.e. conformal and equal area properties of the rectified satellite data. This study aims to establish a relationship between the spatial resolutions of the satellite image used for digital map generation with the spatial accuracy achieved. In this study, Ground Control Points (GCP’s) identified on satellite data for a sample study area were validated using Differential Global Positioning System. Five different high resolution satellite images were analyzed to verify changes in area and shape with reference to the GCP’s. The results indicate that with improvement in the spatial resolution, higher precision in the digital maps is accomplished in terms of spatial shift of the points.
基金supported by the National Basic Research Program of Chi-na (2010CB950204)the Innovation Team Project of the National Natural Science Foundation of China (40721061)the 111 Project (B06026)
文摘The spatial shift of the North Atlantic Oscillation (NAO) is analyzed by using the Twentieth Century Reanalysis version 2 dataset and identifying NAO action centers directly on winter mean sealevel pressure (SLP) anomaly maps. The spatial shift of the NAO is characterized by four NAO spatial shift indices: the zonal and meridional shifts of the NAO southern and northern action centers. It is found that the zonal and meridional shift trends of the NAO action centers move along a path of southwest-northwest direction. Spectral analysis shows that the four NAO spatial shift indices have periodicity of 2-6 years and the NAO index has periodicity of 2-3 years in terms of high-frequency variations. On a decadal time scale, the NAO spatial shift indices are closely (positively) related to the NAO index, which is in agreement with previous studies of the relationship between the NAO index and the spatial shift of the NAO pattern. However, there is no relationship between the NAO index and the meridional shift of the northern action center on an interannual time scale. The significant relationship between the NAO index and the interannual variability of NAO spatial shift indices is very likely to be associated with synopticscale Rossby wave breaking, which generates surface pressure anomalies and thus affects the phase and pattern of the NAO. The correlations of winter westerly winds over 90°W-0° and the NAO index and the NAO spatial shift indices have a '+ - + -' structure from the Equator to the North Pole. Although there is close correlation between the NAO spatial shift indices and the strength of the zonal winds in the North Atlantic region, the effect of the zonal winds on the NAO spatial shift differs at different latitudes. Hence, the role of the zonal winds is probably a result of the NAO spatial shifts.
基金Project supported by the National Natural Science Foundation of China(Grant No.11274125)
文摘We investigate the co-propagation of a strong pump beam and a weak signal beam in lead glass, and find that the large phase shift of the strongly nonlocal spatial optical soliton （SNSOS） can be realized via cross-phase modulation. The theoretical study suggests a synchronous propagation of the pump SNSOS and the signal SNSOS under the required initial condition. A π-phase shift of the signal SNSOS is experimentally obtained by changing the power of the pump SNSOS by about 13 mW around the soliton critical power, which agrees qualitatively with our theoretical prediction. The ratio of the phase shift rate of the signal SNSOS to that of the pump SNSOS shows a close match to the reciprocal of the ratio between their wavelengths.
基金Supported by the National Natural Science Foundation of China (60703107, 60703108)the National High Technology Research and Development Program of China (863 Program) (2006AA01Z107)+1 种基金the National Basic Research Program of China (973 Program) (2006CB705700)the Program for Changjiang Scholars and Innovative Research Team in University (IRT0645)
文摘This paper presents a novel approach that can quickly and effectively partition images based on fully exploiting the spatially coherent property. We propose an algorithm named iterative loopy belief propagation（iLBP） to integrate the homogenous regions and prove its convergence. The image is first segmented by mean shift（MS） algorithm to form over-segmented regions that preserve the desirable edges and spatially coherent parts. The segmented regions are then represented by region adjacent graph（RAG） . Motivated by k-means algorithm,the iLBP algorithm is applied to perform the minimization of the cost function to integrate the over-segmented parts to get the final segmentation result. The image clustering based on the segmented regions instead of the image pixels reduces the number of basic image entities and enhances the image segmentation quality. Comparing the segmentation result with some existing algorithms,the proposed algorithm shows a better performance based on the evaluation criteria of entropy especially on complex scene images.
基金Project supported by the National Basic Research Program of China(Grant No.2014CB744204).
文摘Doppler asymmetric spatial heterodyne spectroscopy(DASH)technique has developed rapidly in passive Doppler-shift measurements of atmospheric emission lines over the last decade.With the advantages of high phase shift sensitivity,compact,and rugged structure,DASH is proposed to be used for celestial autonomous navigation based on Doppler radial velocity measurement in this work.Unlike atmospheric emission lines,almost all targeted lines in the research field of deep-space exploration are the absorption lines of stars,so a mathematical model for the Doppler-shift measurements of absorption lines with a DASH interferometer is established.According to the analysis of the components of the interferogram received by the detector array,we find that the interferogram generated only by absorption lines in a passband can be extracted and processed by a method similar to the approach to studying the emission lines.In the end,numerical simulation experiments of Doppler-shift measurements of absorption lines are carried out.The simulation results show that the relative errors of the retrieved speeds are less than 0.7%under ideal conditions,proving the feasibility of measuring Doppler shifts of absorption lines by DASH instruments.
文摘A phase-shifting digital holography scheme developed to investigate internal defects in artworks is described. Phase-shifting is utilized to obtain a clear reconstructed object wave from a rough surface texture. A reverse-transform algorithm is employed to reconstruct the object wave on its original position of unknown distance or the imaging position from the object wave information on the holographic plane. To get the clearest reconstruction the exact registration of the unknown distance is determined by applying the intensity sum as the auto-focusing function, The spatial resolution of the reconstruction image is also investigated for a variety of affecting factors. Laboratory results of reconstruction images under deformation are presented.
