A practical algorithm of atmospheric correction for turbid coastal and inland waters is provided. The presentalgorithm uses the property that the water-leaving radiance at 412 nm increases very little with the increas...A practical algorithm of atmospheric correction for turbid coastal and inland waters is provided. The presentalgorithm uses the property that the water-leaving radiance at 412 nm increases very little with the increasing of waterturbidity. Thus, in very turbid coastal and inland waters, the radiance at 412 nm can be used to estimate the aerosolscattering radiance at 865 nm. The performance of the new algorithm is validated with simulation for several cases. Itis found that the retrieved remotely sensed reflectance is usually with error less than 10% for the first six bands ofSeaWiFS. This new algorithm is also tested under various atmospheric conditions in the Changjiang River Estuaryand the Hangzhou Bay where the sediment concentration is very high and the standard SeaWiFS atmosphericcorrection algorithm creates a mask due to atmospheric correction failure. The result proves the efficiency of thissimple algorithm in reducing the errors of the water-leaving radiance retrieving using SeaWiFS satellite data.展开更多
The space satellite programs, such as CZCS/Nimbus - 7, VHRSR/FY - 1, OCFS/ ADEOS and SeaWiFS/SeaStar, have demonstrated and proven that remote sensing is a powerful tool for understanding the spatial and temporal ocea...The space satellite programs, such as CZCS/Nimbus - 7, VHRSR/FY - 1, OCFS/ ADEOS and SeaWiFS/SeaStar, have demonstrated and proven that remote sensing is a powerful tool for understanding the spatial and temporal ocean color distribution. In general, there are two main techni-cal keys in the processing ocean color satellite data. They are the atmospheric correction and the inver-sion of water-leaving radiance into water constituents (such as chlorophyll, suspended material and yel low substance) quantitatively. The SeaWiFS (sea-viewing wide field-of-view sensor) atmospheric correc-tion algorithm for China's coastal waters is discussed. First, the major advantages of SeaWiFS are introduced. Second, in view of the problems of the SeaDAS algorithm applying in China' s coastal waters, the local atmospheric correction algorithms are discussed and developed. Finally, the advantages of the local algorithms are presented by the compari-son of the results from two different algorithms.展开更多
The data of SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), installed on SeaStar, has been used to generate SSC (suspended sediment concentration) of complex and turbid coastal waters in China. In view of the problem...The data of SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), installed on SeaStar, has been used to generate SSC (suspended sediment concentration) of complex and turbid coastal waters in China. In view of the problems of the SeaDAS (SeaWiFS Data Analysis System) algorithm applied to China coastal waters, a new atmospheric correction algorithm is discussed, developed, and used for the SSC of East China coastal waters. The advantages of the new algorithm are described through the comparison of the results from different algorithms.展开更多
In this paper, an atmospheric correction method to TM image is presented, which can simulate the atmospheric correction parameters, such as optical depth, sky radiance and path radiance at the time the satellite passe...In this paper, an atmospheric correction method to TM image is presented, which can simulate the atmospheric correction parameters, such as optical depth, sky radiance and path radiance at the time the satellite passes,by using interpolation among local meteorological records, parameterization models and dark pixels. The TM image of the Nanjing area in China was corrected by this method. For analyzing the accuracy of this method, the calculated reflectance, apparent reflectance and ground measured reflectance were compared. NDVI before and after atmospheric cor- rection were also compared. The results show that the method is applicable and efficient in the visible to near infrared band of TM image. In order to improve the accuracy of the method, the infrared spectrum measured data for the two other bands of TM image are required in future field investigations. The method is suitable to many other satellite optical remote sensing images with the same or similar spectral characteristics of TM images.展开更多
This paper demonstrates an atmospheric correction method to process MODIS/Aqua (Moderate-resolution Imaging Spectroradiometer) ocean color imagery over turbid coastal waters with the aid of concurrent CALIOP (Cloud-Ae...This paper demonstrates an atmospheric correction method to process MODIS/Aqua (Moderate-resolution Imaging Spectroradiometer) ocean color imagery over turbid coastal waters with the aid of concurrent CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) aerosol data, assuming that there exists "nonturbid" water in the study area where MODIS aerosol optical properties can be retrieved accurately. Aerosol properties from CALIOP measurements were obtained and related to those from MODIS. This relationship, combined with CALIOP aerosol data, was extended to turbid water to derive MODIS aerosol properties, where atmospheric correction using MODIS data alone often fails. By combining MODIS and CALIOP data, aerosol signals were separated from the total signals at the satellite level, and water-leaving radiances in turbid waters were subsequently derived. This method was tested on several MODIS/Aqua ocean color images over South China turbid waters. Comparison with field data shows that this method was effective in reducing the errors in the retrieved water-leaving radiance values to some extent. In the Zhujiang (Pearl) River Estuary, this method did not overestimate the aerosol effects as severely, and provided far fewer negative water-leaving radiance values than the NASA (National Aeronautics and Space Administration) default methods that used MODIS data alone.展开更多
High-resolution spectral radiance measurements were taken by a spectral radiometer on board a heli- copter over the US Oklahoma Southern Great Plain near the Atmospheric Radiation Measurements (ARM) site during August...High-resolution spectral radiance measurements were taken by a spectral radiometer on board a heli- copter over the US Oklahoma Southern Great Plain near the Atmospheric Radiation Measurements (ARM) site during August 1998. The radiometer has a spectral range from 350 nm to 2500 nm at 1 nm resolution The measurements covered several grass and cropland scene types at multiple solar zenith angles. Detailed atmospheric corrections using the Moderate Resolution Transmittance (MODTRAN) radiation model and in-situ sounding and aerosol measurements have been applied to the helicopter measurements in order to re- trieve the surface and top of atmosphere (TOA) Bidirectional Reflectance Distribution Function (BRDF) characteristics. The atmospheric corrections are most significant in the visible wavelengths and in the strong water vapor absorption wavelengths in the near infrared region Adjusting the BRDF to TOA requires a larger correction in the visible channels since Rayleigh scattenng contributes significantly to the TOA reflectance. The opposite corrections to the visible and near infrarred wavelengths can alter the radiance dif- ference and ratio that many remote sensing techniques are based on, such as the normalixed difference vege- tation index (NDVI). The data show that surface BRDFs and spectral albedos are highly sensitive to the veg- etation type and soldr zenith angle while BRDF at TOA depends more on atmospheric conditions and the vi ewing geometry. Comparison with the Clouds and the Earth's Radiant Energy System (CERES) derived clear sky Angular Distribution Model (ADM) for crop and grass scene type shows a standard deviation of 0.08 in broadband anisotropic function at 25°solar zenith angle and 0.15 at 50° solar zenith angle, respectively.展开更多
Hyperspectral images have wide applications in the fields of geology,mineral exploration,agriculture,forestry and environmental studies etc.due to their narrow band width with numerous channels.However,these images co...Hyperspectral images have wide applications in the fields of geology,mineral exploration,agriculture,forestry and environmental studies etc.due to their narrow band width with numerous channels.However,these images commonly suffer from atmospheric effects,thereby limiting their use.In such a situation,atmospheric correction becomes a necessary pre-requisite for any further processing and accurate interpretation of spectra of different surface materials/objects.In the present study,two very advance atmospheric approaches i.e.QUAC and FLAASH have been applied on the hyperspectral remote sensing imagery.The spectra of vegetation,man-made structure and different minerals from the Gadag area of Karnataka,were extracted from the raw image and also from the QUAC and FLAASH corrected images.These spectra were compared among themselves and also with the existing USGS and JHU spectral library.FLAASH is rigorous atmospheric algorithm and requires various parameters to perform but it has capability to compensate the effects of atmospheric absorption.These absorption curves in any spectra play an important role in identification of the compositions.Therefore,the presence of unwanted absorption features can lead to wrong interpretation and identification of mineral composition.FLAASH also has an advantage of spectral polishing which provides smooth spectral curves which helps in accurate identification of composition of minerals.Therefore,this study recommends that FLAASH is better than QUAC for atmospheric correction and correct interpretation and identification of composition of any object or minerals.展开更多
The tremendous development of Synthetic Aperture Radar(SAR)missions in recent years facilitates the study of smaller amplitude ground deformation over greater spatial scales using longer time series.However,this poses...The tremendous development of Synthetic Aperture Radar(SAR)missions in recent years facilitates the study of smaller amplitude ground deformation over greater spatial scales using longer time series.However,this poses greater challenges for correcting atmospheric effects due to the wider coverage of SAR imagery than ever.Previous attempts have used observations from Global Positioning System(GPS)and Numerical Weather Models(NWMs)to separate atmospheric delays,but they are limited by(1)The availability(and distribution)of GPS stations;(2)The low spatial resolution of NWM;And(3)The difficulties in quantifying their performance.To overcome these limitations,we have developed the Generic Atmospheric Correction Online Service for InSAR(GACOS)which utilizes the high-resolution European Centre for Medium-Range Weather Forecasts(ECMWF)products using an Iterative Tropospheric Decomposition(ITD)model.This enables the reduction of the coupling effects of the troposphere turbulence and stratification and hence achieves equivalent performances over flat and mountainous terrains.GACOS comprises a range of notable features:(1)Global coverage;(2)All-weather,all-time usability;(3)Available with a maximum of two-day latency;And(4)Indicators available to assess the model’s performance and feasibility.In this paper,we demonstrate some successful applications of the GACOS online service to a variety of geophysical studies.展开更多
To acquire high-quality operational data products for Chinese in-orbit and scheduled ocean color sensors, the performances of two operational atmospheric correction(AC) algorithms(ESA MEGS 7.4.1 and NASA Sea DAS 6.1) ...To acquire high-quality operational data products for Chinese in-orbit and scheduled ocean color sensors, the performances of two operational atmospheric correction(AC) algorithms(ESA MEGS 7.4.1 and NASA Sea DAS 6.1) were evaluated over the East China Seas(ECS) using MERIS data. The spectral remote sensing reflectance R_(rs)(λ), aerosol optical thickness(AOT), and ?ngstr?m exponent(α) retrieved using the two algorithms were validated using in situ measurements obtained between May 2002 and October 2009. Match-ups of R_(rs), AOT, and α between the in situ and MERIS data were obtained through strict exclusion criteria. Statistical analysis of R_(rs)(λ) showed a mean percentage difference(MPD) of 9%–13% in the 490–560 nm spectral range, and significant overestimation was observed at 413 nm(MPD>72%). The AOTs were overestimated(MPD>32%), and although the ESA algorithm outperformed the NASA algorithm in the blue-green bands, the situation was reversed in the red-near-infrared bands. The value of α was obviously underestimated by the ESA algorithm(MPD=41%) but not by the NASA algorithm(MPD=35%). To clarify why the NASA algorithm performed better in the retrieval of α, scatter plots of the α single scattering albedo(SSA) density were prepared. These α-SSA density scatter plots showed that the applicability of the aerosol models used by the NASA algorithm over the ECS is better than that used by the ESA algorithm, although neither aerosol model is suitable for the ECS region. The results of this study provide a reference to both data users and data agencies regarding the use of operational data products and the investigation into the improvement of current AC schemes over the ECS.展开更多
Atmospheric correction is one of the major challenges in ocean color remote sensing,thus threatening comprehensive evaluation of water quality within aquatic environments.In this study,five state-of-the-art atmospheri...Atmospheric correction is one of the major challenges in ocean color remote sensing,thus threatening comprehensive evaluation of water quality within aquatic environments.In this study,five state-of-the-art atmospheric correction(AC)processors(i.e.Acolite,C2RCC,iCOR,L2gen,and Polymer)were applied to Operational Land Imager(OLI)Landsat-8 scenes and evaluated against in situ measurements across various types of waters worldwide.A total of 262 matchups between in situ measured and satellite-derived remote sensing reflectance(R_(rs))at 20 sites were obtained between August 2013 and August 2021.Classification of optical water types(OWTs)was carried out using in situ measurements with matched satellite observations.OWT-specific analysis demonstrated that L2gen produced the most accurate Rrs with R^(2)≥0.74 and root mean squared error(RMSE)≤0.0018 sr^(–1) for the four visible bands of OLI,followed by Polymer,C2RCC,iCOR,and Acolite.In terms of R_(rs) spectral similarity,C2RCC yielded the lowest spectral angle(SA)of 8.55°,followed by L2gen(SA=9.20°).The advantage and disadvantage of each AC scheme were discussed.Recommendations to improve the accuracy for atmospheric correction were made,such as polarization observations and concurrent aerosol and ocean color measurements.展开更多
China Brazil Earth Resource Satellite(CBERS)CCD images have much potential for inland water environmental monitoring.However,their atmospheric accuracy correction can affect their quantitative applications.This paper ...China Brazil Earth Resource Satellite(CBERS)CCD images have much potential for inland water environmental monitoring.However,their atmospheric accuracy correction can affect their quantitative applications.This paper contains an atmospheric correction algorithm for CBERS CCD images with MODIS data from the same day,the use of which improves the atmospheric correction algorithm of ocean color remote sensing developed by Gordon(1993,1994)and makes it applicable to inland waters.The improved algorithm retrieves atmospheric parameters from MODIS data and uses them to perform the atmospheric correction of CBERS CCD images.Experimental results show that the atmospheric correction algorithm of CBERS CCD images assisted by MODIS data is reliable.Furthermore,MODIS data can be freely obtained on a daily basis,making the algorithm developed in this paper useful for environmental monitoring of inland waters.展开更多
Due to the atmosphere effect,the qualities of images decrease conspicuously,practically in the visible bands,in the processing of earth observation by the satellite-borne sensors.Thus,removing the atmosphere effects h...Due to the atmosphere effect,the qualities of images decrease conspicuously,practically in the visible bands,in the processing of earth observation by the satellite-borne sensors.Thus,removing the atmosphere effects has become a key step to improve the qualities of images and to retrieve the actual reflectivity of surface features.An atmospheric correction approach,called ACVSS(Atmospheric Correction based Vector Space of Spectrum),is proposed here based on the vector space of the features' spectrum.The reflectance image of each band is retrieved first according to the radiative transfer equation,then the spectrum's vector space is constructed using the infrared bands,and finally the residual errors of the reflectance images in the visible bands are corrected based on the pixel position in the spectrum's vector space.The proposed methodology is verified through atmospheric correction on Landsat-7 ETM+ imagery.The experimental results show that our method is more accurate and the corrected image is more distinct,compared with those offered by current popular atmospheric correction software.展开更多
With a spatial resolution of 50 m,a revisit time of three days,and a swath of 950 km,the coastal zone imager(CZI)offers great potential in monitoring coastal zone dynamics.Accurate atmo-spheric correction(AC)is needed...With a spatial resolution of 50 m,a revisit time of three days,and a swath of 950 km,the coastal zone imager(CZI)offers great potential in monitoring coastal zone dynamics.Accurate atmo-spheric correction(AC)is needed to exploit the potential of quantitative ocean color inversion.However,due to the band setting of CZI,the AC over coastal waters in the western Pacific region with complex optical properties cannot be realized easily.This research introduces a novel neural network(NN)AC algorithm for CZI data over coastal waters.Total 100,000 match-ups of HY-1 C CZI-observed reflectance at the top-of-atmosphere and Operational Land Imager(OLI)-retrieved high-quality remote sensing reflectance(Rrs)at the CZI bands are built to train the NN model.These reflectance data are obtained from the standard AC algorithm in the SeaDAS.Results indicate that the distributions of the CZI retrieved Rrs were consistent with the quasi-synchronous OLI data,but the spatial information from the CZI is more detailed.Then,the accuracy of the CZI data for AC is evaluated using the multi-source in-situ data.Results further show that the NN-AC can successfully retrieve Rrs for CZI and the coefficients of determination in the blue,green,red,and near-infrared bands were 0.70,0.77,0.76,and 0.67,respectively.The NN algorithm does not depend on shortwave-infrared bands and runs very fast once properly trained.展开更多
Passive microwave(PMW)observations from the Advanced Microwave Scanning Radiometer 2 provide a way to obtain cloudy land surface temperatures(LSTs).However,atmospheric corrections must be performed on cloudy LSTs due ...Passive microwave(PMW)observations from the Advanced Microwave Scanning Radiometer 2 provide a way to obtain cloudy land surface temperatures(LSTs).However,atmospheric corrections must be performed on cloudy LSTs due to the cloud effect at higher frequencies.In this paper,six reanalyzed profiles,including the fifth-generation European Centre for Medium-range Weather Forecasts Reanalysis(ERA5),Interim Reanalysis(ERA-Interim),Japanese 55-year Reanalysis Data(JRA-55),Modern-Era Retrospective analysis for Research and Application V2(MERRA2),National Centers for Environmental Prediction(NCEP)/Final Operational Global Analysis(FNL),and NCEP/Global Forecasting System(GFS),were compared with 2829 radiosonde profiles derived from the University of Wyoming.Then,their performances in correcting the atmospheric effects of LSTs at cloudy skies were investigated.Results showed that the ERA5 had the best accuracy in revealing the actual atmospheric conditions,and the RMSEs of transmittance,downward radiance,and upward radiance were about 0.007,2.01,and 1.89 K,respectively.The RMSEs between the estimated LSTs and referenced LSTs varied from 3.15 K of the ERA5 to 6.12 K of the NCEP/FNL,indicating the ERA5 can be recommended for the atmospheric correction of PMW-based LST retrievals.Additionally,transmittance accuracy plays an essential role in impacting the LST retrievals in any weather.展开更多
This paper proposed a method to retrieve the land surface reflectance from the HJ-1A/B CCD data. The aerosol optical depth（AOD）, the most important factor affecting the atmospheric correction of CCD images at all ba...This paper proposed a method to retrieve the land surface reflectance from the HJ-1A/B CCD data. The aerosol optical depth（AOD）, the most important factor affecting the atmospheric correction of CCD images at all bands, is proposed to retrieve from the CCD imagery by the approach of dense dark vegetation（DDV） method. A look-up table in terms of the transmittances, the path radiances and the atmospheric spherical albedo as functions of the AOD was established for a variety of sun-sensor geometry and aerosol loadings. The atmospheric correction is then achieved with the look-up table and the MODIS surface reflectance output（MOD09） as the priori datasets. Based on the retrieved AOD and the look-up table of atmospheric correction coefficients, the land surface reflectance was retrieved for the HJ-1A/B data according to the atmospheric radiative transfer equation. Some in-situ measurement Data for Yanzhou of Shandong province in East China and MODIS land surface reflectance products MOD09 are used to preliminarily validate the proposed method. The results show that the proposed method can remove effectively the atmospheric contributions, and the overall accuracy of the retrieval land surface reflectance can be improved substantially.展开更多
The radiance leaving the earth-atmosphere system which can be sensed by a satellite borne radiometer is the sum of radiation emission from the earth surface and each atmospheric level that are transmitted to the top o...The radiance leaving the earth-atmosphere system which can be sensed by a satellite borne radiometer is the sum of radiation emission from the earth surface and each atmospheric level that are transmitted to the top of the atmosphere. The radiation emission from the earth surface and the radiance of each atmospheric level can be separated from the radiance at the top the atmospheric level measured by a satellite borne radiometer. However, it is very difficult to measure the atmospheric radiance, especially the synchronous measurement with the satellite. Thus some atmospheric radiative transfer models have been developed to provide many options for modeling atmospheric radiation transport, such as LOWTRAN, MODTRAN, 6S, FASCODE, LBLRTM, SHARC, and SAMM. Meanwhile, these models can support the detailed detector system design, the optimization and evaluation of satellite mission parameters, and the data processing procedures. As an example, the newly atmospheric radiative transfer models, MODTRAN will be compared with other models after the atmospheric radiative transfer is described. And the atmospheric radiative transfer simulation procedures and their applications to atmospheric transmittance, retrieval of atmospheric elements, and surface parameters, will also be presented.展开更多
Rapidly monitoring regional water quality and the changing trend is of great practical and scientific significance,especially for the Beijing-Tianjin-Hebei(BTH)region of China where water resources are relatively scar...Rapidly monitoring regional water quality and the changing trend is of great practical and scientific significance,especially for the Beijing-Tianjin-Hebei(BTH)region of China where water resources are relatively scarce and inland water bodies are generally small.The remote sensing data of the GF 1 satellite launched in 2013 have characteristics of high spatial and temporal resolution,which can be used for the dynamic monitoring of the water environment in small lakes and reservoirs.However,the water quality remote sensing monitoring model based on the GF 1 satellite data for lakes and reservoirs in BTH is still lacking because of the considerable differences in the optical characteristics of the lakes and reservoirs.In this paper,the typical reservoirs in BTH-Guanting Reservoir,Yuqiao Reservoir,Panjiakou Reservoir,and Daheiting Reservoir are taken as the study areas.In the atmospheric correction of GF 1-WFV,the relative radiation normalized atmospheric correction was adopted after comparing it with other methods,such as 6 S and FLAASH.In the water clarity retrieval,a water color hue angle based model was proposed and outperformed other available published models,with the R 2 of 0.74 and MRE of 31.7%.The clarity products of the four typical reservoirs in the BTH region in 2013-2019 were produced using the GF 1-WFV data.Based on the products,temporal and spatial changes in clarity were analyzed,and the main influencing factors for each water body were discussed.It was found that the clarity of Guanting,Daheiting,and Panjiakou reservoirs showed an upward trend during this period,while that of Yuqiao Reservoir showed a downward trend.In the influencing factors,the water level of the water bodies can be an important factor related to the water clarity changes in this region.展开更多
Wet path delay caused by tropospheric water vapor must be considered before altimeter data are used in oceanic application. This paper analyzed several methods of atmosphere water range correction (AWRC) using Seasat,...Wet path delay caused by tropospheric water vapor must be considered before altimeter data are used in oceanic application. This paper analyzed several methods of atmosphere water range correction (AWRC) using Seasat, Geosat, TOPEX and ERS-1 data, especially the calculated delay path using brightness temperature of TMR on TOPEX and EMR on ERS-1; and discussed some other problems of AWRC.展开更多
Since the reform and opening-up in 1978, the urbanization level of our country has been continuously improved and the urban development has made great progress. However, with the rapid expansion of urban construction ...Since the reform and opening-up in 1978, the urbanization level of our country has been continuously improved and the urban development has made great progress. However, with the rapid expansion of urban construction land, the population density and building density have been greatly increased, resulting in the urban heat island effect, which has negative impact on the urban thermal environment and restricts the high-quality development of urbanization. This paper focuses on how the urban surface thermal environment of Hangzhou changes in 20 years. In this paper, the characteristics of land surface temperature (LST) in Hangzhou urban area from 2000 to 2020 were studied by using Landsat images. The radiative transfer equation method is used to retrieve the land surface temperature, and the retrieval results are analyzed. The results show that: 1) the land surface temperature in Hangzhou city area has a slight upward trend in the past 20 years;2) the area of high temperature area is expanding;3) the land surface temperature in the city center area has decreased significantly in the past 20 years, while the ground temperature in other areas around the city center has increased significantly.展开更多
For the reduction of atmospheric effects,observed gravity has initially been corrected by using the computed barometric admittance k of the in situ measured pressure,expressed in nms-2/hPa units and estimated by least...For the reduction of atmospheric effects,observed gravity has initially been corrected by using the computed barometric admittance k of the in situ measured pressure,expressed in nms-2/hPa units and estimated by least squares method.However,the local pressure changes alone cannot account for the atmospheric mass attraction and loading when the coherent pressure field exceeds a specific size,i.e.,with increasing periodicities.To overcome this difficulty,it is necessary to compute the total atmospheric effect at each station using the global pressure field.However,the direct subtraction of the total gravity effect,provided by the models of pressure correction,is not yet satisfactory for S2 and other tidal components,such as K2 and P1,which include solar heating pressure tides.This paper identifies the origin of the problem and presents strategies to obtain a satisfactory solution.First,we set up a difference vector between the tidal factors of M2 and S2 after correction of the pressure and ocean tides effects.This vector,hereafter denoted as RES,presents the advantage of being practically insensitive to calibration errors.The minimum discrepancy between the tidal parameters of M2 and S2 corresponds to the minimum of the RES vector norm d.Secondly we adopt the hybrid pressure correction method,separating the local and the global pressure contribution of the models and replacing the local contribution by the pressure measured at the station multiplied by an admittance kATM.We tested this procedure on 8 stations from the IGETS superconducting gravimeters network(former GGP network).For stations at an altitude lower than 1000 m,the value of dopt is always smaller than0.0005.The discrepancy between the tidal parameters of the M2 and S2 waves is always lower than0.05% on the amplitude factors and 0.025° on the phases.For these stations,a correlation exists between the altitude and the value kopt.The results at the three Central European stations Conrad,Pecny and Vienna are in excellent agreement(0.05%) with the DDW99NH model for all the main tidal waves.展开更多
基金This study was supported by the National“863”Project of China under contract No.2002AA639490 and No.2002AA639220.
文摘A practical algorithm of atmospheric correction for turbid coastal and inland waters is provided. The presentalgorithm uses the property that the water-leaving radiance at 412 nm increases very little with the increasing of waterturbidity. Thus, in very turbid coastal and inland waters, the radiance at 412 nm can be used to estimate the aerosolscattering radiance at 865 nm. The performance of the new algorithm is validated with simulation for several cases. Itis found that the retrieved remotely sensed reflectance is usually with error less than 10% for the first six bands ofSeaWiFS. This new algorithm is also tested under various atmospheric conditions in the Changjiang River Estuaryand the Hangzhou Bay where the sediment concentration is very high and the standard SeaWiFS atmosphericcorrection algorithm creates a mask due to atmospheric correction failure. The result proves the efficiency of thissimple algorithm in reducing the errors of the water-leaving radiance retrieving using SeaWiFS satellite data.
文摘The space satellite programs, such as CZCS/Nimbus - 7, VHRSR/FY - 1, OCFS/ ADEOS and SeaWiFS/SeaStar, have demonstrated and proven that remote sensing is a powerful tool for understanding the spatial and temporal ocean color distribution. In general, there are two main techni-cal keys in the processing ocean color satellite data. They are the atmospheric correction and the inver-sion of water-leaving radiance into water constituents (such as chlorophyll, suspended material and yel low substance) quantitatively. The SeaWiFS (sea-viewing wide field-of-view sensor) atmospheric correc-tion algorithm for China's coastal waters is discussed. First, the major advantages of SeaWiFS are introduced. Second, in view of the problems of the SeaDAS algorithm applying in China' s coastal waters, the local atmospheric correction algorithms are discussed and developed. Finally, the advantages of the local algorithms are presented by the compari-son of the results from two different algorithms.
文摘The data of SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), installed on SeaStar, has been used to generate SSC (suspended sediment concentration) of complex and turbid coastal waters in China. In view of the problems of the SeaDAS (SeaWiFS Data Analysis System) algorithm applied to China coastal waters, a new atmospheric correction algorithm is discussed, developed, and used for the SSC of East China coastal waters. The advantages of the new algorithm are described through the comparison of the results from different algorithms.
基金Project 2003DKA1T007 supported by the National Facility Information Infrastructure (China-NFII) Foundation of the Ministry of Science and Technology
文摘In this paper, an atmospheric correction method to TM image is presented, which can simulate the atmospheric correction parameters, such as optical depth, sky radiance and path radiance at the time the satellite passes,by using interpolation among local meteorological records, parameterization models and dark pixels. The TM image of the Nanjing area in China was corrected by this method. For analyzing the accuracy of this method, the calculated reflectance, apparent reflectance and ground measured reflectance were compared. NDVI before and after atmospheric cor- rection were also compared. The results show that the method is applicable and efficient in the visible to near infrared band of TM image. In order to improve the accuracy of the method, the infrared spectrum measured data for the two other bands of TM image are required in future field investigations. The method is suitable to many other satellite optical remote sensing images with the same or similar spectral characteristics of TM images.
基金Supported by the National Basic Research Program of China (973 Program, Nos. 2009CB723905, 2006CB701300)the National High Technology Research and Development Program of China (863 Program, No. 2007AA12Z161)+3 种基金the NSFC (Nos. 40676094, 40721001, 40706060)MOST, China (No. 2007BAC23B05)Open Fund of Nanchang University (No. Z03975)the Open Fund of Ocean University of China for visiting Ph. D students.
文摘This paper demonstrates an atmospheric correction method to process MODIS/Aqua (Moderate-resolution Imaging Spectroradiometer) ocean color imagery over turbid coastal waters with the aid of concurrent CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) aerosol data, assuming that there exists "nonturbid" water in the study area where MODIS aerosol optical properties can be retrieved accurately. Aerosol properties from CALIOP measurements were obtained and related to those from MODIS. This relationship, combined with CALIOP aerosol data, was extended to turbid water to derive MODIS aerosol properties, where atmospheric correction using MODIS data alone often fails. By combining MODIS and CALIOP data, aerosol signals were separated from the total signals at the satellite level, and water-leaving radiances in turbid waters were subsequently derived. This method was tested on several MODIS/Aqua ocean color images over South China turbid waters. Comparison with field data shows that this method was effective in reducing the errors in the retrieved water-leaving radiance values to some extent. In the Zhujiang (Pearl) River Estuary, this method did not overestimate the aerosol effects as severely, and provided far fewer negative water-leaving radiance values than the NASA (National Aeronautics and Space Administration) default methods that used MODIS data alone.
文摘High-resolution spectral radiance measurements were taken by a spectral radiometer on board a heli- copter over the US Oklahoma Southern Great Plain near the Atmospheric Radiation Measurements (ARM) site during August 1998. The radiometer has a spectral range from 350 nm to 2500 nm at 1 nm resolution The measurements covered several grass and cropland scene types at multiple solar zenith angles. Detailed atmospheric corrections using the Moderate Resolution Transmittance (MODTRAN) radiation model and in-situ sounding and aerosol measurements have been applied to the helicopter measurements in order to re- trieve the surface and top of atmosphere (TOA) Bidirectional Reflectance Distribution Function (BRDF) characteristics. The atmospheric corrections are most significant in the visible wavelengths and in the strong water vapor absorption wavelengths in the near infrared region Adjusting the BRDF to TOA requires a larger correction in the visible channels since Rayleigh scattenng contributes significantly to the TOA reflectance. The opposite corrections to the visible and near infrarred wavelengths can alter the radiance dif- ference and ratio that many remote sensing techniques are based on, such as the normalixed difference vege- tation index (NDVI). The data show that surface BRDFs and spectral albedos are highly sensitive to the veg- etation type and soldr zenith angle while BRDF at TOA depends more on atmospheric conditions and the vi ewing geometry. Comparison with the Clouds and the Earth's Radiant Energy System (CERES) derived clear sky Angular Distribution Model (ADM) for crop and grass scene type shows a standard deviation of 0.08 in broadband anisotropic function at 25°solar zenith angle and 0.15 at 50° solar zenith angle, respectively.
文摘Hyperspectral images have wide applications in the fields of geology,mineral exploration,agriculture,forestry and environmental studies etc.due to their narrow band width with numerous channels.However,these images commonly suffer from atmospheric effects,thereby limiting their use.In such a situation,atmospheric correction becomes a necessary pre-requisite for any further processing and accurate interpretation of spectra of different surface materials/objects.In the present study,two very advance atmospheric approaches i.e.QUAC and FLAASH have been applied on the hyperspectral remote sensing imagery.The spectra of vegetation,man-made structure and different minerals from the Gadag area of Karnataka,were extracted from the raw image and also from the QUAC and FLAASH corrected images.These spectra were compared among themselves and also with the existing USGS and JHU spectral library.FLAASH is rigorous atmospheric algorithm and requires various parameters to perform but it has capability to compensate the effects of atmospheric absorption.These absorption curves in any spectra play an important role in identification of the compositions.Therefore,the presence of unwanted absorption features can lead to wrong interpretation and identification of mineral composition.FLAASH also has an advantage of spectral polishing which provides smooth spectral curves which helps in accurate identification of composition of minerals.Therefore,this study recommends that FLAASH is better than QUAC for atmospheric correction and correct interpretation and identification of composition of any object or minerals.
基金National Natural Science Foundation of China(No.41941019)Fundamental Research Funds for the Central Universities(Nos.300102260301/087,300102260404/087)。
文摘The tremendous development of Synthetic Aperture Radar(SAR)missions in recent years facilitates the study of smaller amplitude ground deformation over greater spatial scales using longer time series.However,this poses greater challenges for correcting atmospheric effects due to the wider coverage of SAR imagery than ever.Previous attempts have used observations from Global Positioning System(GPS)and Numerical Weather Models(NWMs)to separate atmospheric delays,but they are limited by(1)The availability(and distribution)of GPS stations;(2)The low spatial resolution of NWM;And(3)The difficulties in quantifying their performance.To overcome these limitations,we have developed the Generic Atmospheric Correction Online Service for InSAR(GACOS)which utilizes the high-resolution European Centre for Medium-Range Weather Forecasts(ECMWF)products using an Iterative Tropospheric Decomposition(ITD)model.This enables the reduction of the coupling effects of the troposphere turbulence and stratification and hence achieves equivalent performances over flat and mountainous terrains.GACOS comprises a range of notable features:(1)Global coverage;(2)All-weather,all-time usability;(3)Available with a maximum of two-day latency;And(4)Indicators available to assess the model’s performance and feasibility.In this paper,we demonstrate some successful applications of the GACOS online service to a variety of geophysical studies.
基金Supported by the State Key Program of National Natural Science Foundation of China(No.60638020)the State Scholarship Fund of the China Scholarship Council(CSC)+1 种基金the National Natural Science Foundation of China(Nos.41321004,41276028,41206006,41306192,41306035)the Natural Science Foundation of Zhejiang Province(No.LY15D060001)
文摘To acquire high-quality operational data products for Chinese in-orbit and scheduled ocean color sensors, the performances of two operational atmospheric correction(AC) algorithms(ESA MEGS 7.4.1 and NASA Sea DAS 6.1) were evaluated over the East China Seas(ECS) using MERIS data. The spectral remote sensing reflectance R_(rs)(λ), aerosol optical thickness(AOT), and ?ngstr?m exponent(α) retrieved using the two algorithms were validated using in situ measurements obtained between May 2002 and October 2009. Match-ups of R_(rs), AOT, and α between the in situ and MERIS data were obtained through strict exclusion criteria. Statistical analysis of R_(rs)(λ) showed a mean percentage difference(MPD) of 9%–13% in the 490–560 nm spectral range, and significant overestimation was observed at 413 nm(MPD>72%). The AOTs were overestimated(MPD>32%), and although the ESA algorithm outperformed the NASA algorithm in the blue-green bands, the situation was reversed in the red-near-infrared bands. The value of α was obviously underestimated by the ESA algorithm(MPD=41%) but not by the NASA algorithm(MPD=35%). To clarify why the NASA algorithm performed better in the retrieval of α, scatter plots of the α single scattering albedo(SSA) density were prepared. These α-SSA density scatter plots showed that the applicability of the aerosol models used by the NASA algorithm over the ECS is better than that used by the ESA algorithm, although neither aerosol model is suitable for the ECS region. The results of this study provide a reference to both data users and data agencies regarding the use of operational data products and the investigation into the improvement of current AC schemes over the ECS.
基金support for this study is provided by the National Natural Science Foundation of China[grant number 42176173]the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhu-hai)[grant number 311020004]+1 种基金Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)[grant number SML2021SP308]Guangdong Geographical Science Data Center[grant number 2021B1212100003].
文摘Atmospheric correction is one of the major challenges in ocean color remote sensing,thus threatening comprehensive evaluation of water quality within aquatic environments.In this study,five state-of-the-art atmospheric correction(AC)processors(i.e.Acolite,C2RCC,iCOR,L2gen,and Polymer)were applied to Operational Land Imager(OLI)Landsat-8 scenes and evaluated against in situ measurements across various types of waters worldwide.A total of 262 matchups between in situ measured and satellite-derived remote sensing reflectance(R_(rs))at 20 sites were obtained between August 2013 and August 2021.Classification of optical water types(OWTs)was carried out using in situ measurements with matched satellite observations.OWT-specific analysis demonstrated that L2gen produced the most accurate Rrs with R^(2)≥0.74 and root mean squared error(RMSE)≤0.0018 sr^(–1) for the four visible bands of OLI,followed by Polymer,C2RCC,iCOR,and Acolite.In terms of R_(rs) spectral similarity,C2RCC yielded the lowest spectral angle(SA)of 8.55°,followed by L2gen(SA=9.20°).The advantage and disadvantage of each AC scheme were discussed.Recommendations to improve the accuracy for atmospheric correction were made,such as polarization observations and concurrent aerosol and ocean color measurements.
基金This work was supported by the Key Project of the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.KZCX3-SW-350).
文摘China Brazil Earth Resource Satellite(CBERS)CCD images have much potential for inland water environmental monitoring.However,their atmospheric accuracy correction can affect their quantitative applications.This paper contains an atmospheric correction algorithm for CBERS CCD images with MODIS data from the same day,the use of which improves the atmospheric correction algorithm of ocean color remote sensing developed by Gordon(1993,1994)and makes it applicable to inland waters.The improved algorithm retrieves atmospheric parameters from MODIS data and uses them to perform the atmospheric correction of CBERS CCD images.Experimental results show that the atmospheric correction algorithm of CBERS CCD images assisted by MODIS data is reliable.Furthermore,MODIS data can be freely obtained on a daily basis,making the algorithm developed in this paper useful for environmental monitoring of inland waters.
基金supported by National High-tech R&D Program (Grant Nos.2011AA120300,2011AA120302)Foster-ing Program of Science and Technology Innovative Platform,Northeast Normal University (Grant No.106111065202)
文摘Due to the atmosphere effect,the qualities of images decrease conspicuously,practically in the visible bands,in the processing of earth observation by the satellite-borne sensors.Thus,removing the atmosphere effects has become a key step to improve the qualities of images and to retrieve the actual reflectivity of surface features.An atmospheric correction approach,called ACVSS(Atmospheric Correction based Vector Space of Spectrum),is proposed here based on the vector space of the features' spectrum.The reflectance image of each band is retrieved first according to the radiative transfer equation,then the spectrum's vector space is constructed using the infrared bands,and finally the residual errors of the reflectance images in the visible bands are corrected based on the pixel position in the spectrum's vector space.The proposed methodology is verified through atmospheric correction on Landsat-7 ETM+ imagery.The experimental results show that our method is more accurate and the corrected image is more distinct,compared with those offered by current popular atmospheric correction software.
基金the National Key R&D Program of China[grant numbers 2018YFB0504900 and 2018YFB0504904]the National Natural Science Foundation of China[grant numbers 42071325 and 42176183]+1 种基金LIESMARS Special Research Fundingthe“985 Project”of Wuhan University,and Special funds of State Key Laboratory for equipment.
文摘With a spatial resolution of 50 m,a revisit time of three days,and a swath of 950 km,the coastal zone imager(CZI)offers great potential in monitoring coastal zone dynamics.Accurate atmo-spheric correction(AC)is needed to exploit the potential of quantitative ocean color inversion.However,due to the band setting of CZI,the AC over coastal waters in the western Pacific region with complex optical properties cannot be realized easily.This research introduces a novel neural network(NN)AC algorithm for CZI data over coastal waters.Total 100,000 match-ups of HY-1 C CZI-observed reflectance at the top-of-atmosphere and Operational Land Imager(OLI)-retrieved high-quality remote sensing reflectance(Rrs)at the CZI bands are built to train the NN model.These reflectance data are obtained from the standard AC algorithm in the SeaDAS.Results indicate that the distributions of the CZI retrieved Rrs were consistent with the quasi-synchronous OLI data,but the spatial information from the CZI is more detailed.Then,the accuracy of the CZI data for AC is evaluated using the multi-source in-situ data.Results further show that the NN-AC can successfully retrieve Rrs for CZI and the coefficients of determination in the blue,green,red,and near-infrared bands were 0.70,0.77,0.76,and 0.67,respectively.The NN algorithm does not depend on shortwave-infrared bands and runs very fast once properly trained.
基金supported by National Natural Science Foundation of China:[Grant Number 41871242,42001309].
文摘Passive microwave(PMW)observations from the Advanced Microwave Scanning Radiometer 2 provide a way to obtain cloudy land surface temperatures(LSTs).However,atmospheric corrections must be performed on cloudy LSTs due to the cloud effect at higher frequencies.In this paper,six reanalyzed profiles,including the fifth-generation European Centre for Medium-range Weather Forecasts Reanalysis(ERA5),Interim Reanalysis(ERA-Interim),Japanese 55-year Reanalysis Data(JRA-55),Modern-Era Retrospective analysis for Research and Application V2(MERRA2),National Centers for Environmental Prediction(NCEP)/Final Operational Global Analysis(FNL),and NCEP/Global Forecasting System(GFS),were compared with 2829 radiosonde profiles derived from the University of Wyoming.Then,their performances in correcting the atmospheric effects of LSTs at cloudy skies were investigated.Results showed that the ERA5 had the best accuracy in revealing the actual atmospheric conditions,and the RMSEs of transmittance,downward radiance,and upward radiance were about 0.007,2.01,and 1.89 K,respectively.The RMSEs between the estimated LSTs and referenced LSTs varied from 3.15 K of the ERA5 to 6.12 K of the NCEP/FNL,indicating the ERA5 can be recommended for the atmospheric correction of PMW-based LST retrievals.Additionally,transmittance accuracy plays an essential role in impacting the LST retrievals in any weather.
基金National High Technology Research and Development Program of China,No.2012AA12A302
文摘This paper proposed a method to retrieve the land surface reflectance from the HJ-1A/B CCD data. The aerosol optical depth（AOD）, the most important factor affecting the atmospheric correction of CCD images at all bands, is proposed to retrieve from the CCD imagery by the approach of dense dark vegetation（DDV） method. A look-up table in terms of the transmittances, the path radiances and the atmospheric spherical albedo as functions of the AOD was established for a variety of sun-sensor geometry and aerosol loadings. The atmospheric correction is then achieved with the look-up table and the MODIS surface reflectance output（MOD09） as the priori datasets. Based on the retrieved AOD and the look-up table of atmospheric correction coefficients, the land surface reflectance was retrieved for the HJ-1A/B data according to the atmospheric radiative transfer equation. Some in-situ measurement Data for Yanzhou of Shandong province in East China and MODIS land surface reflectance products MOD09 are used to preliminarily validate the proposed method. The results show that the proposed method can remove effectively the atmospheric contributions, and the overall accuracy of the retrieval land surface reflectance can be improved substantially.
文摘The radiance leaving the earth-atmosphere system which can be sensed by a satellite borne radiometer is the sum of radiation emission from the earth surface and each atmospheric level that are transmitted to the top of the atmosphere. The radiation emission from the earth surface and the radiance of each atmospheric level can be separated from the radiance at the top the atmospheric level measured by a satellite borne radiometer. However, it is very difficult to measure the atmospheric radiance, especially the synchronous measurement with the satellite. Thus some atmospheric radiative transfer models have been developed to provide many options for modeling atmospheric radiation transport, such as LOWTRAN, MODTRAN, 6S, FASCODE, LBLRTM, SHARC, and SAMM. Meanwhile, these models can support the detailed detector system design, the optimization and evaluation of satellite mission parameters, and the data processing procedures. As an example, the newly atmospheric radiative transfer models, MODTRAN will be compared with other models after the atmospheric radiative transfer is described. And the atmospheric radiative transfer simulation procedures and their applications to atmospheric transmittance, retrieval of atmospheric elements, and surface parameters, will also be presented.
基金Supported by the International Partnership Program of Chinese Academy of Sciences(No.313GJHZ2022085 FN)the Dragon 5 Cooperation(No.59193)。
文摘Rapidly monitoring regional water quality and the changing trend is of great practical and scientific significance,especially for the Beijing-Tianjin-Hebei(BTH)region of China where water resources are relatively scarce and inland water bodies are generally small.The remote sensing data of the GF 1 satellite launched in 2013 have characteristics of high spatial and temporal resolution,which can be used for the dynamic monitoring of the water environment in small lakes and reservoirs.However,the water quality remote sensing monitoring model based on the GF 1 satellite data for lakes and reservoirs in BTH is still lacking because of the considerable differences in the optical characteristics of the lakes and reservoirs.In this paper,the typical reservoirs in BTH-Guanting Reservoir,Yuqiao Reservoir,Panjiakou Reservoir,and Daheiting Reservoir are taken as the study areas.In the atmospheric correction of GF 1-WFV,the relative radiation normalized atmospheric correction was adopted after comparing it with other methods,such as 6 S and FLAASH.In the water clarity retrieval,a water color hue angle based model was proposed and outperformed other available published models,with the R 2 of 0.74 and MRE of 31.7%.The clarity products of the four typical reservoirs in the BTH region in 2013-2019 were produced using the GF 1-WFV data.Based on the products,temporal and spatial changes in clarity were analyzed,and the main influencing factors for each water body were discussed.It was found that the clarity of Guanting,Daheiting,and Panjiakou reservoirs showed an upward trend during this period,while that of Yuqiao Reservoir showed a downward trend.In the influencing factors,the water level of the water bodies can be an important factor related to the water clarity changes in this region.
基金KeyBasicResearchandDevelopmentProgramofChinaOceancirculationunderlyingdatabaseandoceanicdynamicin formationsystem (No .G19990 43 80 1)
文摘Wet path delay caused by tropospheric water vapor must be considered before altimeter data are used in oceanic application. This paper analyzed several methods of atmosphere water range correction (AWRC) using Seasat, Geosat, TOPEX and ERS-1 data, especially the calculated delay path using brightness temperature of TMR on TOPEX and EMR on ERS-1; and discussed some other problems of AWRC.
文摘Since the reform and opening-up in 1978, the urbanization level of our country has been continuously improved and the urban development has made great progress. However, with the rapid expansion of urban construction land, the population density and building density have been greatly increased, resulting in the urban heat island effect, which has negative impact on the urban thermal environment and restricts the high-quality development of urbanization. This paper focuses on how the urban surface thermal environment of Hangzhou changes in 20 years. In this paper, the characteristics of land surface temperature (LST) in Hangzhou urban area from 2000 to 2020 were studied by using Landsat images. The radiative transfer equation method is used to retrieve the land surface temperature, and the retrieval results are analyzed. The results show that: 1) the land surface temperature in Hangzhou city area has a slight upward trend in the past 20 years;2) the area of high temperature area is expanding;3) the land surface temperature in the city center area has decreased significantly in the past 20 years, while the ground temperature in other areas around the city center has increased significantly.
基金supported by Major Program of the National Natural Science Foundation of China (42192535)。
文摘For the reduction of atmospheric effects,observed gravity has initially been corrected by using the computed barometric admittance k of the in situ measured pressure,expressed in nms-2/hPa units and estimated by least squares method.However,the local pressure changes alone cannot account for the atmospheric mass attraction and loading when the coherent pressure field exceeds a specific size,i.e.,with increasing periodicities.To overcome this difficulty,it is necessary to compute the total atmospheric effect at each station using the global pressure field.However,the direct subtraction of the total gravity effect,provided by the models of pressure correction,is not yet satisfactory for S2 and other tidal components,such as K2 and P1,which include solar heating pressure tides.This paper identifies the origin of the problem and presents strategies to obtain a satisfactory solution.First,we set up a difference vector between the tidal factors of M2 and S2 after correction of the pressure and ocean tides effects.This vector,hereafter denoted as RES,presents the advantage of being practically insensitive to calibration errors.The minimum discrepancy between the tidal parameters of M2 and S2 corresponds to the minimum of the RES vector norm d.Secondly we adopt the hybrid pressure correction method,separating the local and the global pressure contribution of the models and replacing the local contribution by the pressure measured at the station multiplied by an admittance kATM.We tested this procedure on 8 stations from the IGETS superconducting gravimeters network(former GGP network).For stations at an altitude lower than 1000 m,the value of dopt is always smaller than0.0005.The discrepancy between the tidal parameters of the M2 and S2 waves is always lower than0.05% on the amplitude factors and 0.025° on the phases.For these stations,a correlation exists between the altitude and the value kopt.The results at the three Central European stations Conrad,Pecny and Vienna are in excellent agreement(0.05%) with the DDW99NH model for all the main tidal waves.
