最新刊期
卷 17 ， 期 1 ， 2013
- 摘要：We reviewed and analyzed the monitoring methods,the validation methods and the error sources of remote sensing phenology.First,the monitoring methods,including the threshold-based,delayed-moving-average and curve-fitting methods,etc.,were introduced and inter-compared.Second,the primary validation methods were analyzed,including sensor-network-monitoring,simulation model,etc.The error sources of remote sensing phenology products were further analyzed from the monitoring methods and the remote sensing data.At last,we made prospects for the future development of vegetation phenology monitoring by remote sensing:（1） To develop the new monitoring methodology by coupling the physiological and ecological respond mechanisms of vegetation phenology with the spectral response of remote sensing data.（2） To establish the standardized validation dataset for remote sensing phenology.（3） To improve the temporal resolution and the accuracy of remote sensing data for phenology monitoring by multi-satellite data.关键词：vegetation phenology;remote sensing phenology;remote sensing monitoring;growing season;phonological model
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发布时间：2021-06-10 - 摘要：In many studies about land surface parameters inversion using the zeroth order model,the equivalent scattering albedo are usually set to a small value（0.05—0.1） or to zero,which lacks of experimental data support.In this study,the equivalent scattering albedo for cotton and soybean in different growing stages are estimated based on the observations from the Truck-mounted Multi-frequency Microwave Radiometer using the least squares technique.Further investigations are also made to investigate the variation of equivalent scattering albedo versus frequency,observation angle and the crop phenology.The result can provide some theoretical reference for determining the equivalent scattering albedo of vegetation using the zeroth order model to inverse land surface parameters.关键词：passive microwave;remote sensing;crop;equivalent scattering albedo;radiometer;the zeroth order model
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发布时间：2021-06-10 - 摘要：The existing underwater topography SAR detection models did not consider polarization information of SAR.In this paper,the SAR polarization information is used for underwater topography detection,which is based on radar cross section（RCS） expression from Valenzuela,high frequency spectra expression of ocean waves and Polarization Whitening Filter（PWF）.Taiwan Shoal of China is taken as an example and its underwater topography is detected using single-polarization and full-polarization image of Radarsat-2.The results show that detection accuracy of full-polarization is better than that of single-polarization and illustrate that polarization information can effectively improve the accuracy of detection.关键词：polarization;underwater topography;SAR;Taiwan Shoal of China
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发布时间：2021-06-10 - 摘要：The use of Visual Odometry（VO） for planetary rover localization has been extensively researched.Traditionally,motion estimation is resolved only between adjacent frames;this neglected stronger geometric constraints possible from processing multiple consecutive frames.This paper presents a new visual odometry method based on bundle adjustment of an image network formed by feature tracking among multiple consecutive frames.In the feature-tracking process,outliers are detected based on the consistency of Euclidean distances in different stereo frames;geometric key frames are selected adaptively.Additionally,analysis of VO accuracy with respect to the geometric configuration of stereo camera is performed using Monte Carlo simulation.Results of field experiments demonstrate the effectiveness of the proposed method in improving localization accuracy.关键词：planetary rover;visual odometry;bundle adjustment;feature tracking;geometric key frame
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发布时间：2021-06-10 - 摘要：A model is implemented to simulate the Directional Brightness Temperature（DBT） of three dimensional urban targets based on the computer graphics and the environment simulation algorithm.Using urban three dimensional scene,the model is able to calculate the surface cells seen by the sensor in a given Field of View（FOV） and the sunlit and shade patterns created by three dimensional urban surface structures.The DBT over urban areas is accurately simulated in the Instantaneous Field of View（IFOV）.Model validation is conducted by comparing the simulated DBT with observed DBT,which demonstrates that the model has a high accuracy with the（Root Mean Square Error） RMSE of 0.7 K.The model can be used to describe the thermal anisotropy of urban targets at the micro-scale.The simulated results of DBT for scale model of urban targets reveal significant DBT variations for complex urban surfaces.The hot spot effect appears obviously in the upper hemispheric plot of DBT.关键词：thermal infrared remote sensing;simulation model;urban targets;three dimensional simulation scenarios;thermal anisotropy
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发布时间：2021-06-10 - 摘要：Multiple Instance Learning Via Embedded Instance Selection（MILES） has shown good performance in dealing with noisy training samples,but its bag prediction rule may introduce new uncertainty into the remote sensing image classification results.In order to overcome this limitation,two popular ensemble learning strategies,Bagging and AdaBoost are integrated with MILES.Two methods are proposed to constrain the uncertainty in remote sensing image classification:re-classification of coarse bags,and integration of MILES with diverse density and maximum likelihood classifier.The experimental results show that the uncertainty of remote sensing image classification can be obviously reduced by the integration of multiple instance learning with ensemble learning.关键词：multiple instance learning;multiple instance learning via embedded instance selection（miles）;ensemble learning;classifier;uncertainty
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发布时间：2021-06-10 - 摘要：The effects of rainfall backscattering on space-borne rotating fan-beam scatterometer measurements at Ku-band were investigated in this study.A new scattering model based on Integral Equation Method（IEM） for sea surface with precipitation that accounts for the effects of rain column was presented.The relation between rain scattering and incidence was analyzed,and hence the rain effects on a rotating fan-beam scatterometer are obtained.The rain column is modeled as sublayers with different physical characteristics determined by the vertical profile of rainfall.Each sublayer is assumed to be statistically homogeneous,and the gamma distribution is used to model the drop size distribution within each sublayer.Sea surface is modeled as a rough surface,and its backscattering is calculated using the IEM model.Multiple scattering within and interactions between the rain layers and sea surface are accounted for in the matrix doubling formulation.The presented model is validated using published TRMM PR measurements.Results from model analyses show that rain effects are incident angle dependent,which can lead to non-uniform impacts within the footprint of a fan-beam scatterometer;these effects are strongly related to rain column vertical profile and rain rate,as different rain rate corresponds to different physical parameters.关键词：scatterometer;rainfall;multiple scattering;vertical profile;fan-beam
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发布时间：2021-06-10 - 摘要：We propose a new sampling strategy based on Normalized Difference Vegetation Index（NDVI） prior knowledge for Leaf Area Index（LAI） ground measurements of non-homogeneous pixels.The method accuracy and stability have been analyzed in cases of different vegetation types and different pixel heterogeneity.The analysis results show that the proposed method is capable of properly dividing the non-homogeneous area into zones with different vegetation cover levels.It performed more accurate and robust than random sampling,systematic sampling and sampling based on classification in grassland and forest areas.The good performance indicates that this new sampling strategy for the LAI ground measurements may be used to remote sensing product validation for the heterogeneous pixels.关键词：Leaf Area Index（LAI）;sampling strategy;NDVI;prior knowledge;heterogeneous pixel;validation
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发布时间：2021-06-10 - 摘要：N-FINDR algorithm were employed for endmember extraction for decomposing the mixed pixels,which searches for each pixel from the dimension reduced feature space induced using principal component transformation or maximum noise factor transformation method.Due to the large search range for the endmembers,the efficiency of the N-FINDR algorithm is low.In this paper,we proposed the improved fast N-FINDR algorithm aiming to decrease the computation cost by providing a relative smaller search range,i.e.the candidate endmember set which was only a subset of the entire feature space.N-FINDR algorithm assumed that all the endmembers located at the vertexes of the simplex,which means that these pixels should be far away from the central part of all the pixels.Therefore,the percentile of chi-square distribution can be used to segment out these possible endmembers into a candidate set,which has much smaller size.The performance of the proposed algorithm has been verified using both synthetic and real hyperspectral data.Under the same endmember extraction precision,the modified N-FINDR algorithm has faster computation velocity and a higher overall efficiency.关键词：endmember spectra;hyperspectral image;N-FINDR;chi-square distribution;mixed pixel
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发布时间：2021-06-10 - 摘要：A parameter optimization method with adjustment of integration time is proposed with analysis of the imaging process and the affecting factors.An imaging parameter setting model is brought up.The model parameter calculation and selection are discussed.Specific post-processing of the images acquired with the proposed method is analyzed.Experiment is carried out with Beijing-1 small satellite data for optimized imaging and comparison.Results show that images acquired with the optimized method have wider dynamic range and higher radiometric resolution,and with advanced information entropy and signal noise ratio.关键词：integration time;imaging control;imaging parameter optimization;dynamic range;radiometric resolution
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发布时间：2021-06-10 - 摘要：Compared to moderate/low resolution satellite sensors for aerosol detection,the high spatial resolution of HJ-1 CCD camera（30 m） provides an opportunity to easily find spectrally pure pixels（SPP） over urban areas.In this study,we developed an SPP algorithm for urban Aerosol Optical Depth（AOD） retrieval using HJ-1 CCD data.Pixel Purity Index（PPI） is used to identify the pure pixels in the image.The surface reflectances of the pure pixels were estimated from the multi-temporal CCD measurements of HJ-1A and HJ-1B based on the surface Bi-directional Reflectance Distribution Function（BRDF） model.Then the AOD can be retrieved from satellite measurements.The comparison with ground-based AErosol RObotic NETwork AERONET AOD measurements shows good performance of our algorithm.A significant correlation coefficient with R=0.83 was obtained with a linear regression slope close to 1 and a intercept of 0.053.With the retrieved AOD as an input,HJ-1CCD data over urban areas was significantly improved after the atmospheric correction.关键词：aerosol optical depth;aerosol retrieval;HJ-1 CCD;atmospheric correction;pure pixel
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发布时间：2021-06-10 - 摘要：Accurate estimates of forest aboveground biomass（AGB） could reduce uncertainties in the characterization of terrestrial carbon fluxes.Light Detection and Ranging（LiDAR） provides an accurate measure of canopy height and vertical structure and information for the estimation of aboveground biomass of vegetation.Spaceborne large footprint LiDAR（ICESat GLAS） acquires over 250 million observations over forest regions globally and has been used successfully for forest height and biomass estimation in various sites.In this paper,airborne LiDAR and ICESat GLAS data were used to estimate aboveground biomass of forest at footprint level in Yunnan,China.Vegetation products from EOS MODIS and ENVISAT MERIS were used to expand these discrete estimations from GLAS data to a wall-to-wall map.The R2 between ICESat GLAS waveform parameters and airborne LiDAR estimated forest AGB is 0.52 after training with 260 footprints.Results showed that the total forest AGB in Yunnan Province was 1272 million ton and the average was 94 Mg/ha.The amount and distribution of predicted aboveground biomass were in good agreement with the reference data.The results showed that the predict model using GLAS data could be used to estimate regional forest aboveground biomass successfully.关键词：aboveground biomass estimation;lidar;ICESat GLAS;optical data
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发布时间：2021-06-10 -
Soil surface roughness estimation using multiangular remote sensing observations:a preliminary study
摘要：As a primary factor determining microwave radiative emission and scattering properties,soil surface roughness plays an important role in microwave remote sensing studies.Since microwave backscatter is also influenced by dielectric property and penetration depth,retrieval of soil roughness using solely microwave remote sensing data faces great difficulties.In this study,soil surface roughness is estimated using multiangular optical remote sensing data in order to provide useful information to microwave remote sensing studies.First,a geometric-optical model is established to simulate bidirectional reflectance for bare soil surface under different roughness conditions.The model assumes that soil aggregates or clods are semi-ellipsoids with circular bottom,and a number of aggregates of clods distribute randomly within a pixel.Then the model is inverted using multiangular reflectance to retrieve structural parameters of each soil pixel.After that,root-mean-square height,as an indicator of soil surface roughness,can be estimated from structural parameters of the model.This method is validated using in situ multiangular reflectance observations.Results demonstrate that estimation of soil surface roughness using multi angular remote sensing data is an effective approach.关键词：soil surface roughness;geometric-optical model;inversion;multi-angular- 144
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发布时间：2021-06-10 - 摘要：Taiwan is located in a subtropical region and issusceptible to typhoons and torrential rains during the summer seasons.Taiwan is also located on actively shifting tectonic plates that can cause dramatic terrain changes.Taiwan’s river terrain frequently sustains substantial changes,especially after typhoons and torrential rains.Presently,digital terrain maps or models made by airborne LiDAR technology are reliable,have sufficient resolutions,are accurate,convenient,and can filter out buildings or tree cover to restore the original ground topography.This type of map or model can meet the requirements of geological and topographical analysis studies.In 2008,the Lanyang River region experienced four major typhoon events:Kalmaegi,Fung-Wong,Sinlaku,and Jangmi.These typhoons changed the riverbed terrain dramatically.Therefore,we used two occasions of digital terrain data measured using the airborne LiDAR system to conduct analytical comparisons of the riverbed terrain and river sediment transportation changes before and after typhoon events.The study is the first of its kind to demonstrate the excellent applications of the airborne LiDAR system for measuring river terrains in a large watershed area;digital terrain data were produced for periods before and after a typhoon season.We used the elevation difference topography measurement method to calculate river terrain changes before and after a typhoon season.This study’s results showed that the airborne LiDAR high resolution digital terrain model data produced excellent results when used to calculate river terrain and sediment volume changes or change amounts.关键词：Lanyang river;typhoon torrential rain events;geomorphological features;airborne LiDAR;digital terrain model
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发布时间：2021-06-10 - 摘要：Vegetation Indices（VIs） derived from remotely sensed data have been developed to monitor the Earth’s vegetation cover.However,the topographic influence on VIs is an inevitable issue and is usually neglected in their large scale applications.In this study,the topographic effects on four commonly used vegetation indices,including Simple Ratio（SR）,Normalized Difference Vegetation Index（NDVI）,Reduced Simple Ratio（RSR）,and Modified Normalized Difference Vegetation Index（MNDVI）,derived from Landsat TM data over a mountainous forest area are evaluated.Two simple methods,the cosine correction and C-correction models,with different treatments of the influence of the diffused irradiance on reflectance,are used to remove the topographic effects on selected VIs.The results indicate that the reflectance in the Near Infrared（NIR） and Short Wave Infrared（SWIR） bands are more sensitive to topographical variations than that in the red band.Diffused radiance from the sky in the red band can moderate the variations of red band reflectance with topography,while this moderation is weak in the NIR and SWIR bands.The topography affects strongly vegetation indices which are not expressed as band ratios,such as RSR and MNDVI,resulting in negative biases on Sun-facing slopes and positive biases on Sun-backing slopes.As the slope increases,these biases increase rapidly.Therefore,the topographic effects should be carefully removed before using these non-band-ratio vegetation indices for vegetation parameter retrieval.Vegetation indices which are expressed as band ratios,such as SR,NDVI,can greatly reduce the noise caused by topographical variations.However,these indices still include significant topographic effects on steep slopes.SR is more sensitive to topographical variations on steep slopes than NDVI.The C-correction model is much better than the cosine correction model in removing topographic effects on VIs,especially on steep slopes.关键词：vegetation index;topographic effect;topographic correction;band ratio
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发布时间：2021-06-10
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