最新刊期
卷 19 ， 期 3 ， 2015
- 摘要：Land surface albedo is a critical physical variable that affects the energy budget in land-atmosphere interactions. Precise retrieval of albedo must consider the reflectance anisotropy,which is the general characteristic of surface reflectance. Six spectral Bidirectional Reflectance Distribution Function（ BRDF） archetypes have been previously distilled from a single year of the Moderate Resolution Imaging Spectroradiometer（ MODIS） operational BRDF / albedo V005 product（ MCD43） over global Earth Observing System Land Validation Core Sites. This study attempted to analyze the distribution of MODIS BRDF anisotropy with the aid of MODIS AFX and BRDF archetypes. A method that attempts to convert surface directional reflectance to albedo with primary BRDF archetypes,which were obtained statistically from concurrent MODIS BRDF product,was introduced. Results were compared with routine MODIS BRD / albedo product and ground observations. The semiempirical kernel-driven BRDF model was used in this study.Six spectral BRDF archetypes,which were taken as prior knowledge of the reflectance anisotropy,were used to fit directional observation to adjust the magnitude of reflectance and to convert directional reflectance into albedo. First,multiangular ground and MODIS reflectance were used to evaluate the precision and applicability of MODIS BRDF archetype in different spatial scales.Second,the distribution characteristics of BRDFs were analyzed with the assistance of the BRDF archetype. The dominant BRDF archetype that can represent the reflectance anisotropy of most pixels over the study surface can be extracted from a concurrent MODIS BRDF product through statistic method. Finally,the dominant BRDF archetype and HJ directional reflectance were combined to generate 30 m resolution land surface albedo. The retrievals were compared with ground observations. Results showed that MODIS BRDF archetypes represent the general variability of surface reflectance anisotropy that can be used to retrieve albedo at both tens of meters and MODIS scale. The distribution of BRDF is unequal,and the primary BRDF archetype that was obtained statistically can represent the reflectance anisotropy of 70% pixels. Albedos retrieved from the primary BRDF archetype and driectional reflectance meet the accuracy requirements in routine albedo retrievals. High consistency exists between ground observations and HJ albedos based on primary BRDF archetype,which was extracted from the MODIS BRDF product,whereas the albedos under the assumption of a Lambertian surface are greater than those from the ground observations. BRDF archetypes provide a standard to distinguish the characteristic of reflectance anisotropy and to provide a new way to evaluate the effect of reflectance anisotropy on albedo. The distribution of reflectance is unequal,and a dominant BRDF archetype that can represent most pixels over a study area exists. Given this characteristic of BRDF,BRDF archetypes may potentially be used for surface albedo retrievals from directional reflectance. The method employed in this paper considers the reflectance anisotropy properly and can obtain a high accuracy albedo from directional reflectance. The method can be performed conveniently and provide a key reference to retrieve national high and medial resolution albedos from directional satellites and / or airborne observations.关键词：HJ-1;MODIS;directional reflectance;albedo;Bidirectional Reflectance Distribution Function（BRDF）;AFX;BRDF archetype
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发布时间：2021-06-10 - 摘要：Analyzing the effect of vegetation biochemical and biophysical variables to canopy reflectance and defining the importance of variables are useful in constructing reasonable spectral indices and inverse vegetation biochemical and biophysical variables accurately. In this study,we qualitatively calculated the sensitivity of canopy reflectance to leaf biochemical variables（ chloro-phyll,carotenoid,water content,and dry matter）,canopy structure parameter（ Leaf Area Index（ LAI））,and the background of soil（ soil moisture）. Considering that canopy reflectance easily becomes saturated with the increase of LAI,the sensitivity change of those parameters in different canopy density scenes is analyzed. We also discussed the precision of a priori knowledge used in vegetation biophysical and biochemical parameter inversion.In this study,PROSAIL model（ coupled with PROSPECT-5 leaf optical model and 4SAIL canopy radiative transfer model）was used to obtain adequate data,including vegetation variables and the corresponding canopy reflectance spectrum,which are impossible to obtain with in-site measurement. The adopted sensitivity analysis method was the extended Fourier amplitude sensitivity test（ EFAST）. This method first defined a search curve to scan the multidimensional space of model input parameters,and then the samples of model input parameters were generated by searching each axis of the multidimensional space at different frequencies.These samples were entered into the models to obtain the model output value. Fourier decomposition was used to compute the firstorder and total-order index.The result shows that the sensitivity of canopy reflectance to vegetation parameters is strongly related to canopy density. For medium and high canopy density,the canopy reflectance of VIS is mainly affected by Cab,and Cmand Cwexplain the bulk variation of canopy reflectance in NIR and SWIR. The canopy reflectance is slightly responsive to the variation in LAI and soil moisture.Results indicate that the requirement for accurate estimation of LAI is particularly urgent for very thick vegetation. For low canopy density,LAI is the most important variable that influences the canopy reflectance in NIR and SWIR regions,and the contribution of Cmand Cwis covered by LAI. Results show that estimating equivalent water thickness and dry matter content is difficult when LAI is low. Given that the canopy is sparse,the background of soil has a significant effect on canopy reflectance.With regard to the accuracy requirement of priori knowledge,the result shows that the priori knowledge,which may be able to distinguish dry or wet condition of soil,is enough to obtain the valid inversion result of vegetation biochemical and biophysical variables for low canopy density.In this study,we quantitatively analyzed the effect of canopy density on the sensitivity of canopy reflectance on various vegetation and background parameters with PROSAIL radiative transfer model and EFAST global sensitivity analysis method. Results obtained in this study can be used to choose and improve the inverse methods according to the real condition of the study area. In addition,we discussed in general terms the accuracy requirement of priori knowledge only for the spare canopy region.关键词：canopy;reflectance;sensitivity analysis;PROSAIL;extended Fourier amplitude sensitivity test（EFAST）
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发布时间：2021-06-10 - 摘要：Polarimetric microwave radiometer can provide sea surface wind vector products; this ability is a new development in spaceborne passive sensing. Sensitivity analysis of polarimetric microwave radiometer brightness temperature observations with respect to environmental factors may indicate the effect of environmental factors on polarimetric microwave radiometer brightness temperature observations. This finding may provide theoretical support for channel selection in the retrieval of important physical factors.On the basis of the polarimetric microwave forward model,we adopted sensitivity analysis to analyze,calculate,and quantify the sensitivity of each channel from the polarimetric microwave radiometer with important environmental parameters,such as sea surface wind speed,sea surface wind direction,sea surface temperature,atmospheric water vapor content,and cloud liquid water content,under fixed background field conditions. We also analyzed the sensitivity of the brightness temperature,which is simulated by the forward model or measured by using spaceborne polarimetric microwave radiometer WindS at,with respect to important environment parameters under real background field conditions from WindS at environmental data record,NCEP analysis data field,and TAO / TRITON buoy data record.Results include:（ 1） The brightness temperature of 6. 8 GHz and 10. 7 GHz vertical and horizontal polarization channel has good linearity relative to sea surface temperature,which can be used for sea surface temperature inversion.（ 2） The changes in the brightness temperature of 23. 8 GHz vertical and horizontal polarization channel are the largest relative to the rate of atmospheric water vapor content changes,which is mainly used for atmospheric water vapor content retrieval.（ 3） Vertical and horizontal polarization channels at 37 GHz have relatively obvious characterization relative to cloud liquid water content,which could be used to cloud liquid water content inversion.（ 4） The brightness temperatures of vertical polarization and horizontal polarization channel have good linearity retrieval to wind speed at a low observation frequency,which is used for sea surface wind speed inversion.（ 5）When the wind direction changes,the brightness temperature channels of the third and fourth Stokes channels exhibit obvious inverted fluctuation characteristics,which can be used for sea surface wind direction inversion.（ 6） The fluctuation with wind direction is completely covered in the real background field at the vertical and horizontal polarization channels,but the third and fourth Stokes channel observations can still characterize wind direction changes.（ 7） The sensitivity of the third and fourth Stokes channels to other environmental parameters is much lower than the sensitivity to sea surface wind speed and wind direction,which cannot be used for inversion of other environmental parameters.（ 8） The third and fourth Stokes channels for sea surface wind speed are also highly sensitive. Under a high wind speed condition,the actual measured brightness temperature of the third and fourth Stokes channels is large,which indicates that the measurement includes strong wind vector signals. Sea surface wind retrieval accuracy is better under high wind conditions compared with that under low wind speed conditions.（ 9） In the 0° ± 30°,180° ±30° range,the brightness temperature measured value of the third and fourth Stokes channels is small,and the noise signal influence to wind is large. Thus,the retrieval accuracy of wind directions decreases in those ranges,and retrieval results appear fuzzy.（ 10） In the actual measurement,the wind direction signal from the third and fourth Stokes channels is subject to interference from other environmental factors to some extent,which makes retrieving the sea surface wind direction difficult.The conclusions from sensitivity analysis could provide support to the independent development of China to design a polarimetric microwave radiation channel,select an environmental parameter inversion channel,and propose an environmental parameter inversion algorithm. Moreover,this study establishes a foundation to improve the accuracy of surface wind vector retrieval by removing adverse effects caused by atmospheric water vapor content and cloud liquid water content.关键词：polarimetric microwave radiometer;polarization;sensitivity analysis method;sensitivity;sea surface wind;sea surface temperature
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发布时间：2021-06-10 - 摘要：Terrestrial Laser Scanner（ TLS） technology can quickly acquire three-dimensional information of targets with high precision. Given that TLS is a new data collection technique,it has been gradually applied to characterize the structural attributes of forest canopy. However,the inversion accuracy of Leaf Area Index（ LAI） is highly dependent on the intrinsic configuration of the sensor,such as beam size and echo detection energy. In this paper,a computer simulation model was proposed to simulate point clouds from TLS and to analyze quantitatively the influence of beam characteristic on LAI inverted from TLS data.A realistic tree was generated with Onyx TREE BROADLEAF software. Moreover,a computer model was proposed to simulate the interactions of lasers with a single tree and to acquire the point clouds from a TLS Riegl VZ-1000 based on the ray tracing algorithm. This model consisted of the ray intersection with triangular patches of photorealistic trees,the coordinate system conversion,and the acceleration of the algorithm. The beam size at exit,beam divergence,and echo detection algorithm were considered in the computer simulation method. One laser beam was divided into multiple bins,and each bin was treated as a separate pulse with its location,propagation direction,and an initial energy changing into a Gaussian shape. We inverted the crown-level Leaf Area Index（ LAI） by using gap fraction analysis with the simulated point clouds,and the influence of beam characteristics（ such as beam diameter and minimum echo detection intensity） on the LAI inversion was analyzed. Finally,we conducted the validation with the measured points of a birch tree located in Root River. We analyzed the influences of beam characteristics,such as beam size,beam divergence,and echo detection energy,on LAI inversion. The inversion results indicate that beam size and detection limit greatly influence LAI inversion. The points are increased with the decrease of the corresponding gap fraction because several points can be returned from one beam when the beam width and divergence were considered,particularly when significant differences are achieved at the edge of leaves. A larger beam size means that components in the edge portion are intercepted more easily. Thus,the deviation of LAI inversion would be greater. When the detection intensity threshold was small,echo information could be returned even if only part of the spot edge was intercepted. Thus,gap fraction is undervalued. However,when the energy threshold setting was large,the returned energy may be below the threshold value and cannot be recorded,thereby resulting in overestimation of the gap fraction and underestimation of LAI. Therefore,the points caused by beam size and echo detection must be filtered,and suitable points must be chosen before inverting LAI with the gap fraction model.The simulation model based on the ray tracing algorithm was presented to explore the laser beam interceptions with an individual tree generated by using Onyx Tree software. The LAI was retrieved via gap fraction analysis with zenith slicing method. The beam characteristics,such as beam size,echo detection energy,and beam divergence,were considered. The simulation model enables efficient and cost-effective research that can avoid environmental and instrumental error. This model contributes to an improved understanding of the intersections of laser beams with the tree crown well,and the LAI inversion of an individual tree is facilitated.关键词：terrestrial laser scanner;computer simulation;ray tracing;gap fraction;leaf area index
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发布时间：2021-06-10 - 摘要：Polarimetric Synthetic Aperture Radar（ SAR） data record an increased amount of scattering information of ground targets with fully polarimetric patterns. Thus,polarimetric SAR has become a key issue in development. Polarimetric SAR technologies have made significant progress in applications such as military and civil remote sensing. However,because of the limitation of coherent imaging,speckle in SAR and polarimetric SAR data seriously affects the relative information extraction. Therefore,speckle suppression is an important step in SAR and polarimetric SAR data processing. Subsequent applications with polarimetric SAR data could be supported. The Bilateral Filter（ BF） that combines spatial closeness and gray similarity to suppress speckle is an excellent edge preservation filtering algorithm. This paper proposes an Improved Cross Bilateral Filter（ ICBF） to resolve the deficiency of the BF in speckle suppression of polar metric SAR data. The reference image was imported to improve the gray similarity measurement accuracy of the original data,and a new strategy that sets two key parameters of bilateral filter based on the variance coefficient of filter window was presented to adapt to the change in the homogeneity degree of the filter window. The ICBF added scattering mechanism measurement to extend the original weight kernel,adjusted spatial closeness variance via the local coefficient of variation by using SPAN image,and measured the similarity of gray value and scattering mechanism by using a reference image.The experiment was conducted with AIRSAR polar metric data in the San Francisco region. The proposed filter algorithm was then compared with classic filter algorithms,such as Boxcar,IDAN,and Refined Lee,based on speckle suppression,detailed information preservation,scattering and polarization information preservation with the visual and index methods. The experimental results show that ICBF could improve the gray similarity measurement accuracy of the original data and that ICBF can suppress speckle and preserve detailed information,such as point targets and edges in the original data,better than the classic filter algorithms. By contrast,the measurement of scattering mechanism was combined in the kernel function of bilateral filter,the parameter of the space distance weight was obtained from SPAN image,and the weights of gray value and scattering mechanism were measured with the standard deviation of the corresponding data. Thus,the polarization information and scattering characteristics of the original data were preserved well. Compared with classic filtering algorithms,the ICBF can smooth noise and preserve detailed information better. Furthermore,polarization information and scattering characteristics of the original data are maintained to support subsequent application based on polarimetric SAR data.关键词：polarimetric synthetic aperture radar;cross bilateral filtering;despeckling;filtering
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发布时间：2021-06-10 - 摘要：The accepted Rational Function（ RF） model application for satellite images is limited to transformations between object and image space. However,the use of the third-order RF model and of the 80 Rational Polynomial Coefficients（ RPCs） in the Radarsat-2 metadata extends its application from optical images to Synthetic Aperture Radar（ SAR） images. We provide a brief overview of the generation process and properties of multiple SAR RPC products,with special emphasis on the processing chain of basic SAR products in combination with orbit model approximation. Finally,we validate new types of RPC geometric performance experimentally. We consider the different basic products of Terra SAR-X,the COSMO-Sky Med of the Guangzhou area（ in China）in stripmap mode as test data and demonstrated the effectiveness of the RF model for the geometric processing of SAR images.关键词：rational polynomial coefficient products;rational function model;spaceborne SAR;high resolution
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发布时间：2021-06-10 - 摘要：This paper presents our research on developing a dense image matching algorithm to generate a high-quality disparity map from airborne oblique stereo images. We conducted off-site measurements and analysis not on models but on the actual aerial photography of a site. The Oblique Photogrammetry System（ OPS） was influenced by and significantly affected photogrammetry.Oblique images released by OPS are becoming an indispensable tool for general use,such as tax assessment and building deviation,urban and infrastructural planning,management of military and security operations,and critical infrastructural protection. However,processing oblique images is quite challenging in terms of automation and accuracy. For example,oblique image stereo matching is subjected to various obstacles,such as obvious illumination differences,serious occlusions,discontinuous object boundaries,and low or repetitive textures. To address such problems,an image matching approach based on the integration of improved SGM and SIFT algorithm is proposed to generate a dense disparity map from an airborne oblique image pair,which establishes a basis for automatic photogrammetry Digital Surface Model（ DSM） generation or Computer Vision three dimensional visualization.The proposed approach is composed of two stages:（ 1） The first stage is sparse oblique image matching with improved SIFT algorithm,in which the affine invariance of the SIFT descriptor is enhanced by implementing local two-order moment transformation to feature neighbors detected by using Hessian-Gabor algorithm. Thus,robust matching results for various wide-baseline oblique image pairs are obtained and used to estimate epipolar geometry model or as path constraints incorporated into SGM in next stages.（ 2）The second stage is dense oblique image matching with constrained SGM algorithm,in which mutual information from matched features are used as an unchanged"anchor"to block the propagation of mistaken matching cost along some SGM paths and based on TPS transformation. Discrete parallax from matched features is used to generate a continuous disparity map for reliable SGMmutual information computation. In addition,to generate the epipolar image input into SGM,an ideal photogrammetry image leveling algorithm is extended to oblique image pairs with various wide-baseline conditions by globally rotating wide-aseline vector to be horizontal. Then,orientation parameters of oblique image pairs are estimated with a matched feature coordinate by using photogrammetry relative orientation process. Selected five airborne oblique images from OPS with cameras positioned in the configuration of a Maltese cross are tested by using the proposed approaches. Thus,a high-quality dense disparity map is obtained. The following results were obtained:（ 1） The incorporation of Hessian-Gabor feature detector and local two-order moment transformation into the SIFT algorithm greatly enhances its affine invariance. Thus,reliable and rich conjunctive pixels can be obtained in various widebaseline oblique image pairs,and these pixels are intended to be used as strong constraint for further dense matching.（ 2）Improved SGM could block the propagation of mistaken matching and accelerate path searching by means of mutual information and discrete parallax knowledge from known conjunctive pixels. Thus,a high-quality dense match result from oblique images can be obtained.关键词：dense matching;oblique photogrammetry;SGM;SIFT
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发布时间：2021-06-10 - 摘要：This study on the vector C-V model and hyperspectral remote sensing image aims is to segment a hyperspectral remote sensing image. A hyperspectral remote sensing image contains not only general two-dimensional image spatial information but also have one-dimensional spectrum information. Thus,traditional methods of two-dimensional image segmentation are unsuitable for hyperspectral remote sensing images. To solve this problem,we propose a hypespectral remote sensing image vector C-V model segmentation method based on band selection,which can deal with the multiband images at the same time. Method First,bands of goals and backgrounds contrast that exhibit a significant contrast were chosen based on the band correlation coefficient. Then,the greater relevance band-by-band correlation coefficient was removed,and a new band combination was formed. Finally,a hyperspectral remote sensing image vector matrix was built. On these basis,we can construct a vector C-V model that takes full advantage of this vector matrix while introducing a gradient-based edge guide function. Result Numerical experiments were conducted on HYPERION data,and these experiments were compared with the traditional C-V model and Wang & Jin method. The result shows that the proposed method can immediately segment a hyperspectal remote sensing image effectively,and it not only has a lower fasepositive ratio and false-negative ratio but also a smaller error ratio. These results prove that the segmentation of the proposed model is more effective than that of the traditional C-V model and Wang & Jin method. In sum,compared with the traditional C-V model and Wang & Jin method,the proposed model improved the segmentation speed and accuracy. Conclusion The proposed model does not retain the traits of conventional C-V model,which is based on the regional information. Rather,it increased the ability of capture the boundary of the target in heterogeneous regions and complex background by using image edge details. However,the method has some shortcomings. For instance,it uses only the gray level information without the spectral information of hyperstpectral remote image during the process of segmentation,which causes a small amount of error in its results. Using the combination of spatial information and spectral information effectively in the process of the segmentation is a problem that needs further research.关键词：hyperspectral image;image segmentation;vector C-V model;edge guide function
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发布时间：2021-06-10 - 摘要：Land Surface Temperature（ LST） plays an important role in energy exchange between the land surface and the atmosphere. LST is a key variable in many applications,such as land surface modeling. Many satellite-based algorithms have been proposed to retrieve LST,such as Split-Window（ SW）,dual-angle,and single-channel algorithms. In this study,four satellitebased LST retrieval algorithms,including two SW algorithms（ Juan C. Jiménez-Muoz and Offer Rozenstein SW algorithms） and two mono-window algorithms（ Juan C. Jiménez-Muoz and Qin Zhihao mono-window algorithms）,were compared with Landsat-8satellite data over the region around Wuxi City. The accuracy of the four algorithms was evaluated against the ground measurements from 16 floating stations over Lake Tai. The results showed that the performance of the two SW algorithms,which have an average error of 0. 7 K,was better than that of the SW algorithms,which have an average error of 1. 3—1. 4 K,when compared with ground measurements. The sensitivity analysis of these algorithms showed that the Juan C. Jiménez-Muoz SW algorithm was the least sensitive to key input parameters（ emissivity and water vapor）,whereas the Offer Rozenstein SW algorithm and the Qin Zhihao mono-window algorithm showed high sensitivity to input parameters. The limitations of these four LST retrieving algorithms were also discussed.关键词：land surface temperature;Landsat 8;split-window algorithm;mono-window algorithm;thermal infrared
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发布时间：2021-06-10 - 摘要：Radio-Frequency Interference（ RFI） is an increasingly severe problem for present and future microwave satellite missions. It causes serious problems to passive and active microwave sensing observations and to corresponding retrieval products.Detecting RFI signals is an important step before data can be used. The Microwave Radiation Image（ MWRI） on board the Feng Yun（ FY）-3B satellite can provide the brightness temperature data at 10. 65 GHz,18. 7 GHz,23. 8 GHz,36. 5 GHz,and89 GHz,each having dual channels at horizontal and vertical polarization states. RFI signals are present in MWRI data over land and ocean. RFI signals from data over ocean are more difficult to detect than those over land because of the low microwave emissivity of the sea surface. In general,RFI signals are detectable by using a multichannel regression method and retrieval chi-square probability. However,the two methods need auxiliary brightness temperature data within a certain period of time under conditions without ice and RFI,and located away from the coast. In this study,we use multichannel regression and Double Principal Component Analysis（ DPCA） to identify the RFI signals from MWRI data over ocean. DPCA takes advantage of the decorrelation for RFI signals and the correlation characteristics of radiation data in different channels for nature surface,including snow cover and synoptic process. This method does not need auxiliary brightness temperature data,and it can been used to offer a real-time RFI detection method before data are provided. Compared with the results of multichannel regression,the results of DPCA can be considered effective in detecting RFI signals from MWRI ocean brightness temperatures. Moreover,the results obtained from the water near North America in winter indicate that multichannel regression produces false results over sea ice. The false signals could be avoided effectively in DPCA. The consistent results from different methods show that the RFI signals detected are credible. The RFI signals of MWRI at 10. 65 GHz horizontal polarization over ocean are distributed widely over the ocean of Europe,and these signals are present at the offshore marine areas of East Asia and North America.关键词：microwave remote sensing;microwave radiation image;radio-frequency interference;double principal component analysis
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发布时间：2021-06-10 - 摘要：Urban thermal environment has had a far-reaching impact on local climates and on the quality of living environments.Distinct differences between urban areas and surrounding rural areas have been widely observed; this phenomenon is called the Urban Heat Island（ UHI） effect. The conditions in surrounding rural areas also affect the magnitude of UHI. UHI intensity was inversely correlated with rural Land Surface Temperature（ LST）. However,simply comparing the difference in LST between urban land and the surrounding rural area is not an effective method to quantify the intensity of UHI. Changes in urban construction land also varied in the rural area. Hence,the problem can be transformed into determining how areas affected by the UHI can be identified spatially.This paper researched the UHI effect during the period between 2001 and 2012 in the Beijing metropolitan area based on MODIS LST products obtained by using split-window algorithm. This paper presented the concepts of UHI footprint and capacity to spatially distinguish the areas affected by UHI. Then,the relationship between land use and UHI footprint was analyzed by using the radius method,and the influence mechanism of land use on UHI was discussed.UHI footprint and capacity differ significantly during daytime and nighttime. The area of urban island footprint in the daytime is 1. 5 times that in the nighttime in 2012. This finding is due to the comprehensive factor of differences in thermal characteristics of urban land and human activities. The high temperature zone spatially extended to the north and south during 2001—2012,and UHI footprint and capacity exhibited a periodical growth. The largest UHI footprint appeared in daytime in 2010,that is,the radius was 28 km,and the area of the UHI footprint was 2. 4 times that in 2001. UHI capacity is affected by the distribution and planning of urban green space and water function zone,even if UHI footprints are not different in two periods. The contributions of urban land and rural residential to UHI are significantly higher than the contributions of other land use types. When the area of construction land is more than 50%,the region produces obvious UHI.This paper presented improvement measures according to the spatiotemporal character of UHI footprint and capacity. Construction scale on the underlying surface is the critical mechanism of the urban thermal environment. This study can serve as a guide to plan and manage the urban thermal environment in cities,and it can help to control UHI effectively.关键词：MODIS;urban heat island footprint;urban heat island capacity;radius method;Beijing
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发布时间：2021-06-10 - 摘要：Rubber plantations are expanding rapidly in the tropical region of China because of their high profitability,while large areas of natural rainforests are deforested and replaced by artificial rubber trees. A series of ecological problems has occurred because of unreasonable and disordered plantation of rubber trees in some areas. Acquiring spatial distribution of rubber plantations rapidly and monitoring their dynamics can contribute to control and manage rubber plantations and to protect the local ecological environment. Remote sensing plays an important role in monitoring the dynamics of land use and cover. However,the high complexity of tropical ecosystems makes it difficult to extract information from a single-temporal image. This study aims to develop a method that extracts information about rubber plantations effectively and to improve classification accuracy of a tropical ecosystem with multi-temporal remote sensing images. Based on Moderate Resolution Imaging Spectroradiometer（ MODIS） Normalized Difference Vegetation Index（ NDVI） time series data and multi-temporal Landsat TM data,the seasonal characteristics and spectral characteristics of different objects,including rubber plantation,broadleaved evergreen forest,dry land,and paddy field in the study area,are analyzed and compared in this study. A decision tree model that integrates object-oriented technology is developed to extract rubber plantation in Hainan province. The model choose appropriate characteristic parameters and remote sensing data to separate rubber plantation and other land cover types. Rubber plantation demonstrates obvious seasonal characteristics according to time series data. During the dormant period of rubber trees,an obvious difference in spectral characteristics among different land covers is observed. NDVI and Land Surface Water Index（ LSWI） can be selected as the two main parameters to distinguish rubber plantation and other land covers in the study area. In addition,remote sensing data in winter are optimal for extracting rubber plantation. Rubber plantation and four other objects are extracted by using the five-level classification decision tree model based on LSWI,NDVI,MNDWI,and slope data. The total accuracy in the study area is 94. 5% according to the test result obtained with field observation data. Rubber plantation and broadleaved evergreen forest have a high classification accuracy,whereas dry land has a low classification accuracy. For the rubber plantation,the producer accuracy obtained with two-temporal TM images（ February and December） is 96. 2%,whereas the results obtained with a single-temporal image are 78. 1%（ December） and 86. 1%（ February）. Similarly,the user accuracy of rubber plantation obtained with two-temporal images is higher than that obtained with a single-temporal image. The presented decision tree model with multiple temporal images effectively integrates spectral and phonological information on vegetation,and some uncertainties of single temporal image are avoided. The use of this model ensures that rubber plantation can be extracted with high accuracy. The key and premise of this study are to identify the phonological and spectral characteristics of specific vegetation. Moreover,appropriate images that show specific characteristics of object must be available. Furthermore,if additional images in the key phonological phase of vegetation can be acquired,the classification accuracy can be improved further.关键词：rubber;multi-temporal images;decision tree;object-oriented;Land Surface Water Index（LSWI）;Normalized Difference Vegetation Index
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发布时间：2021-06-10 - 摘要：Focusing on the important role of ground-based sun radiation and aerosol observation in the fields of climate change,atmospheric environmental monitoring, and earth observation, we established a Sun-sky radiometer Observation NETwork（ SONET） in typical Chinese regions by applying multi-wavelength polarimetric observation techniques. We present the following in this paper:（ 1） the characteristics,measurement,principles,and functions of the multi-wavelength polarization radiometer and the establishment of SONET in typical Chinese regions with a brief introduction of the observation sites;（ 2） observation patterns of sun-sky radiation and polarization as well as measurement parameters under direct sun,solar principal plane,and almucantar geometries;（ 3） calibration of solar irradiance,sky radiance,and degree of linear polarization measurements and data processing methods for aerosol and water vapor,with illustrations of typical SONET observation under clear and hazy conditions;（ 4） establishment of urban,rural,and haze aerosol type models of the total column atmosphere based on long-term continuous remote sensing observation in typical sites in China. On the basis of extension of multi-wavelength polarization measurements,SONET was employed to develop operational techniques for the network of sun-sky radiometers,including automatic observation,fast data processing,and regular calibration and maintenance,which contribute to the construction of atmospheric aerosol type models,retrieval and validation of satellite aerosol products,and remote monitoring of the atmospheric environment.关键词：sun-sky radiometer observation network;polarization measurement;atmospheric aerosol;radiometric and polarimetric calibration;SON
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发布时间：2021-06-10 - 摘要：Rapid economic development along with urbanization and industrialization has exacerbated air pollution in China,particularly haze pollution,in recent years. The Beijing-Tianjin-Hebei area,the Yangtze River Delta,and the Pearl River Delta region are the three major focus areas of haze pollution in China.In January 2013,a high-intensity continuous atmospheric haze pollution swept across East Central China. According to the AirQuality Index,this phenomenon occurred five times in Beijing,and the score reached beyond 200（ severe pollution）,occurring on January 6—8,9—15,17—19,22—23,and 25—31. At present,studies on haze pollution focus on physical and optical properties,influencing factors,haze source apportionment,aerosol chemistry and other aspects. Few studies investigated the vertical properties of large-scale,high-intensity haze aerosols. Vertical distribution of aerosols is one of the most critical and uncertain factors of radiative forcing and climate impact.The vertical distribution of aerosol optical properties during haze days in North China Plain（ NCP） in January 2013 are analyzed by using Cloud-Aerosol LiD AR with Orthogonal Polarization（ CALIOP） data,Aerosol Robotic Network（ AERONET）data,ground meteorological observation data,and Hybrid Single-Particle Lagrangian Integrated Trajectory（ HYSPLIT） model.CALIOP laser radar provided the vertical distribution of aerosol and cloud features with high vertical resolution（ 30 m）. The Level1 B aerosol layer products of CALIOP that overpass NCP（ 34° N to 41° N,114° E to 120° E） in January 2013,including attenuated backscatter coefficient,volume depolarization ratio,and total attenuated color ratio,were used in the study. The AERONET Aerosol Optical Thickness（ AOT） at 500 nm and Angstrom exponent of 440—870 nm at the Beijing（ 39. 97° N,116. 38° E） and Xianghe（ 39. 75° N,116. 96° E） sites were used to investigate the aerosol properties in hazy days. In addition,HYSPLIT model was used to simulate the backward trajectory of heavy haze process of NCP（ 34° N to 41° N,114° E to 120° E） on January29,2013.Our results are listed as below:（ 1） The meteorological elements of three haze events（ January 9—15,22—23,and 25—31） in January 2013 were compared with the 30-year（ 1980—2010） mean of meteorological elements at the Beijing site. The results showed that the average relative humidity during the haze events is about 47% higher than the 30-year mean and that the average wind speed during the haze events is about 35% lower than the 30-year mean. These findings indicate that the increased relative humidity and decreased wind speed in January 2013 are unfavorable for cleaning aerosols,thereby resulting in severe haze.（ 2） The lowest troposphere（ < 2 km） was polluted most severely during the hazy days in NCP in January 2013. The total attenuated backscatter coefficient increased to 0. 0045 km- 1sr- 1,volume depolarization ratios were greater than 20%,and the maximum value of color ratio was greater than 0. 8. These findings suggest that aerosol particles aggregate in the lowest troposphere,and a large number of irregular coarse particles coexist during the haze events in NCP.（ 3） The color ratios below 2 km and 6—8 km heights increased during the severe haze on January 29. This finding indicates an increased proportion of large particles. The 6—8 km height may be affected by coarse particle aerosol delivery and cloud particles. The lower atmosphere below 2 km is influenced by local construction dust,which resulted in increased proportion of coarse particles.（ 4） AOT（ 500 nm） increased from 0. 2 to 2. 1,and the Angstrom index decreased from 1. 4 to 0. 9 during the severe haze on January 29,which indicated that the proportion of coarse particles mixed in the atmospheric aerosol increased. The simulation results of HYSPLIT backward trajectory showed that the airflow at heights of 500 m,1000 m,and 1500 m comes from Mongolia,Inner Mongolia,China,and Northwest China,and finally affects the NCP.Three severe haze events in NCP in January 2013 were analyzed by using CALIOP data,AERONET data,ground meteorological observation data,and HYSPLIT model. The three-dimensional structure of the haze is provided when the size distribution and possible sources of atmospheric aerosol during haze events are analyzed in depth. Results show that heavy haze pollution in NCP is not only composed of fine aerosol particles from human activities but also accompanied by coarse dust aerosols. Dust aerosols from remote region could affect the haze composition in NCP.关键词：haze;aerosols;Cloud-Aerosol LiD AR with Orthogonal Polarization;attenuated backscatter coefficient;vertical distribution;optical
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发布时间：2021-06-10 - 摘要：As a newly launched earth observing satellite of China,the GF-1 satellite is intended to be applied for land resource,agriculture,and environment protection. This satellite contains four wide field viewing cameras that have a spatial resolution of16 m at nadir. For the application of 16 m cameras,the aerosol monitoring research need to be processed as soon as possible. This study investigated the application of dark dense vegetation to the 16 m camera of GF-1.First,blue-only algorithm was compared with blue and red algorithm with simulation retrieval based on the ground-based measurements of the typical vegetation surface spectrum. A linear relationship exists between blue and red vegetation surfaces. Thus,compared with the blue-only algorithm,the blue and red algorithm can remove land surface influence better from the top of the atmosphere reflectance. During retrieval,atmosphere correction needs to be performed to remove false dark targets,which are caused by the decrease of Normalized Difference Vegetation Index with the increase of Aerosol Optical Depth（ AOD）.Tianjin,which is located in the north of China,was selected as the area of the retrieval experiment,which was conducted from August 2013 to October 2013. The result shows that aerosol distribution can be monitored efficiently by using GF-1 16 m cameras.However,the result is partly affected by cloud and haze,which restrict the capability of these cameras. The algorithm is validated by ground-based measurements of a handheld sun photometer in the west of Tianjin and the Beijing site of AERONET. Satelliteretrieved measurements demonstrate good agreement with ground-based measurements,and the correlation coefficient is greater than0. 8.Error analysis shows that:（ 1） If the viewing zenith angles of the entire image are set to the same value,the retrieved AOD error can be maximized to 0. 3;（ 2） Calibration accuracy influences retrieved accuracy,and when the calibration error is lower than 3%,the retrieved error is lower than 10%;（ 3） Urban aerosol can cause a large retrieval error.关键词：GF-1;remote sensing;dark dense vegetation;aerosol
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发布时间：2021-06-10
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