Accurate estimation of forest terrain and canopy height is crucial for timely understanding of forest growth.Gao Fen-7(GF-7)Satellite is China’s first sub-meter-level three-dimensional(3D)mapping satellite for civili...Accurate estimation of forest terrain and canopy height is crucial for timely understanding of forest growth.Gao Fen-7(GF-7)Satellite is China’s first sub-meter-level three-dimensional(3D)mapping satellite for civilian use,which was equipped with a two-line-array stereo mapping camera and a laser altimeter system that can provide stereo images and full waveform LiDAR data simultaneously.Most of the existing studies have concentrated on evaluating the accuracy of GF-7 for topographic survey in bare land,but few have in-depth studied its ability to measure forest terrain elevation and canopy height.The purpose of this study is to evaluate the potential of GF-7 LiDAR and stereo image for forest terrain and height measurement.The Airborne Laser Scanning(ALS)data were utilized to generate reference terrain and forest vertical information.The validation test was conducted in Pu’er City,Yunnan Province of China,and encouraging results have obtained.The GF-7 LiDAR data obtained the accuracy of forest terrain elevation with RMSE of 8.01 m when 21 available laser footprints were used for results verification;meanwhile,when it was used to calculate the forest height,R^(2)of 0.84 and RMSE of 3.2 m were obtained although only seven effective footprints were used for result verification.The canopy height values obtained from GF-7 stereo images have also been proven to have high accuracy with the resolution of 20 m×20 m compared with ALS data(R2=0.88,RMSE=2.98 m).When the results were verified at the forest sub-compartment scale that taking into account the forest types,further higher accuracy(R^(2)=0.96,RMSE=1.23 m)was obtained.These results show that GF-7 has considerable application potential in forest resources monitoring.展开更多
Dual-frequency and multi-polarization spaceborne rain and cloud measuring radar is the inevitable trend of remote sensing techniques.Techniques of new generation dual-frequency and multi-polarization spaceborne rain a...Dual-frequency and multi-polarization spaceborne rain and cloud measuring radar is the inevitable trend of remote sensing techniques.Techniques of new generation dual-frequency and multi-polarization spaceborne rain and cloud measuring radar are studied systematically.Radar block diagram and main parameters are presented.Antenna subsystem scheme is analyzed and antenna parameters are proposed.Central electronic device subsystem scheme is given and data rate of spaceborne radar is calculated.This paper is a meaningful try for carrying out spaceborne rain and cloud measuring radar design,acting as a reference to Chinese spaceborne rain and cloud measuring radar design and production in future.展开更多
In determining the orbits of low Earth orbit （LEO） satellites using spaceborne GPS, the errors caused by receiver antenna phase center offset （PCO） and phase center variations （PCVs） are gradually becoming a maj...In determining the orbits of low Earth orbit （LEO） satellites using spaceborne GPS, the errors caused by receiver antenna phase center offset （PCO） and phase center variations （PCVs） are gradually becoming a major limiting factor for continued improvements to accuracy. Shiyan 3, a small satellite mission for space technology experimentation and climate exploration, was developed by China and launched on November 5, 2008. The dual-frequency GPS receiver payload delivers 1 Hz data and provides the basis for precise orbit determination within the range of a few centimeters. The antenna PCO and PCV error characteristics and the principles influencing orbit determination are analyzed. The feasibility of PCO and PCV estimation and compensation in different directions is demonstrated through simulation and in-flight tests. The values of receiver antenna PCO and PCVs for Gravity Recovery and Climate Experiment （GRACE） and Shiyan 3 satellites are estimated from one month of data. A large and stable antenna PCO error, reaching up to 10.34 cm in the z-direction, is found with the Shiyan 3 satellite. The PCVs on the Shiyan 3 satellite are estimated and reach up to 3.0 cm, which is slightly larger than that of GRACE satellites. Orbit validation clearly improved with independent k-band ranging （KBR） and satellite laser ranging （SLR） measurements. For GRACE satellites, the average root mean square （RMS） of KBR residuals improved from 1.01 cm to 0.88 cm. For the Shiyan 3 satellite, the average RMS of SLR residuals improved from 4.95 cm to 4.06 cm.展开更多
With the maturation of satellite technology,Hyperspectral Remote Sensing(HRS)platforms have developed from the initial ground-based and airborne platforms into spaceborne platforms,which greatly promotes the civil app...With the maturation of satellite technology,Hyperspectral Remote Sensing(HRS)platforms have developed from the initial ground-based and airborne platforms into spaceborne platforms,which greatly promotes the civil application of HRS imagery in the fields of agriculture,forestry,and environmental monitoring.China is playing an important role in this evolution,especially in recent years,with the successful launch and operation of a series of civil hyper-spectral spacecraft and satellites,including the Shenzhou-3 spacecraft,the Gaofen-5 satellite,the SPARK satellite,the Zhuhai-1 satellite network for environmental and resources monitoring,the FengYun series of satellites for meteorological observation,and the Chang’E series of spacecraft for planetary exploration.The Chinese spaceborne HRS platforms have various new characteristics,such as the wide swath width,high spatial resolution,wide spectral range,hyperspectral satellite networks,and microsatellites.This paper focuses on the recent progress in Chinese spaceborne HRS,from the aspects of the typical satellite systems,the data processing,and the applications.In addition,the future development trends of HRS in China are also discussed and analyzed.展开更多
Spaceborne synthetic remote sensing of atmospheric aerosol optical depth and vegetation reflectance is very significant, but it remains to be a question unresolved yet. Based on the property of vegetation reflectance ...Spaceborne synthetic remote sensing of atmospheric aerosol optical depth and vegetation reflectance is very significant, but it remains to be a question unresolved yet. Based on the property of vegetation reflectance spectra from near ultra violet to near infrared and the sensitivity of outgoing radiance to vegetation reflectance and atmospheric aerosol optical depth, a new method for spaceborne synthetic remote sensing of the reflectance and the depth is proposed, and an iteration correlation inversion algorithm is developed in this paper. According to numerical experiment, effects of radiance error, error in aerosol imaginary index and vegetation medium inhomogeneity on retrieved result are analyzed. Inversion results show that the effect of error in aerosol imaginary index is very important. As the error of aerosol imaginary index is within 0.01, standard errors of aerosol optical depth and vegetation reflectance solutions for 14 spectral channels from 410 nm to 900 nm are respectively less than 0.063 and 0.023. And as the radiance error is within 2%, the standard errors are less than 0.023 and 0.0056.展开更多
The purpose of this study is to evaluate the Spectral Angle Mapper （SAM） classification method for determining the optimum threshold （maximum spectral angle） to unveil the hydrothermal mineral assemblages related ...The purpose of this study is to evaluate the Spectral Angle Mapper （SAM） classification method for determining the optimum threshold （maximum spectral angle） to unveil the hydrothermal mineral assemblages related to mineral deposits. The study area indicates good potential for Cu-Au porphyry, epithermal gold deposits and hydrothermal alteration well developed in arid and semiarid climates, which makes this region significant for Advanced Spaceborne Thermal Emission and Reflection Radiometer （ASTER） image processing analysis. Given that achieving an acceptable mineral mapping requires knowing the alteration patterns, petrochemistry and petrogenesis of the igneous rocks while considering the effect of weathering, overprinting of supergene alteration, overprinting of hypogene alteration and host rock spectral mixing, SAM classification was implemented for argillic, sericitic, propylitic, alunitization, silicification and iron oxide zones of six previously known mineral deposits： Maherabad, a Cu-Au porphyry system; Sheikhabad, an upper part of Cu-Au porphyry system; Khoonik, an Intrusion related Au system; Barmazid, a low sulfidation epithermal system; Khopik, a Cu-Au porphyry system; and Hanish, an epithermal Au system. Thus, the investigation showed that although the whole alteration zones are affected by mixing, it is also possible to produce a favorable hydrothermal mineral map by such complementary data as petrology, petrochemistry and alteration patterns.展开更多
Doppler centroid frequency is an essential parameter in the imaging processing of the Scanning mode Synthetic Aperture Radar (ScanSAR). Inaccurate Doppler centroid frequency will result in ghost images in imaging resu...Doppler centroid frequency is an essential parameter in the imaging processing of the Scanning mode Synthetic Aperture Radar (ScanSAR). Inaccurate Doppler centroid frequency will result in ghost images in imaging result. In this letter, the principle and algorithms of Doppler centroid frequency estimation are introduced. Then the echo data of ScanSAR system is analyzed. Based on the algorithms of energy balancing and correlation Doppler estimator in the estimation of Doppler centroid frequency in strip mode SAR, an improved method for Doppler centroid frequency estimation in ScanSAR is proposed. The method has improved the accuracy of Doppler centroid frequency estimation in ScanSAR by zero padding between burst data. Finally, the proposed method is validated with the processing of ENVIronment SATellite Advanced Synthetic Aperture Radar (ENVISAT ASAR) wide swath raw data.展开更多
The spaceborne synthetic aperture radar(SAR)sparse flight 3-D imaging technology through multiple observations of the cross-track direction is designed to form the cross-track equivalent aperture,and achieve the third...The spaceborne synthetic aperture radar(SAR)sparse flight 3-D imaging technology through multiple observations of the cross-track direction is designed to form the cross-track equivalent aperture,and achieve the third dimensionality recognition.In this paper,combined with the actual triple star orbits,a sparse flight spaceborne SAR 3-D imaging method based on the sparse spectrum of interferometry and the principal component analysis(PCA)is presented.Firstly,interferometric processing is utilized to reach an effective sparse representation of radar images in the frequency domain.Secondly,as a method with simple principle and fast calculation,the PCA is introduced to extract the main features of the image spectrum according to its principal characteristics.Finally,the 3-D image can be obtained by inverse transformation of the reconstructed spectrum by the PCA.The simulation results of 4.84 km equivalent cross-track aperture and corresponding 1.78 m cross-track resolution verify the effective suppression of this method on high-frequency sidelobe noise introduced by sparse flight with a sparsity of 49%and random noise introduced by the receiver.Meanwhile,due to the influence of orbit distribution of the actual triple star orbits,the simulation results of the sparse flight with the 7-bit Barker code orbits are given as a comparison and reference to illuminate the significance of orbit distribution for this reconstruction results.This method has prospects for sparse flight 3-D imaging in high latitude areas for its short revisit period.展开更多
The principal purpose of this paper is to extract entire sea surface wind＇s information from spaceborne lidar, and particularly to utilize a appropriate algorithm for removing the interference information due to whit...The principal purpose of this paper is to extract entire sea surface wind＇s information from spaceborne lidar, and particularly to utilize a appropriate algorithm for removing the interference information due to white caps and subsurface water. Wind speeds are obtained through empirical relationship with sea surface mean square slopes. Wind directions are derived from relationship between wind speeds and wind directions im plied in CMOD5n geophysical models function （GMF）. Whitecaps backscattering signals were distinguished with the help of lidar depolarization ratio measurements and rectified by whitecaps coverage equation. Subsurface water backscattering signals were corrected by means of inverse distance weighted （IDW） from neighborhood non-singular data with optimal subsurface water backscattering calibration parameters. To verify the algorithm reliably, it selected NDBC＇s TAO buoy-laying area as survey region in camparison with buoys＇ wind field data and METOP satellite ASCAT of 25 km single orbit wind field data after temporal-spa tial matching. Validation results showed that the retrieval algorithm works well in terms of root mean square error （RMSE） less than 2m/s and wind direction＇s RMSE less than 21 degree.展开更多
With the increasing availability of precipitation radar data from space,enhancement of the resolution of spaceborne precipitation observations is important,particularly for hazard prediction and climate modeling at lo...With the increasing availability of precipitation radar data from space,enhancement of the resolution of spaceborne precipitation observations is important,particularly for hazard prediction and climate modeling at local scales relevant to extreme precipitation intensities and gradients.In this paper,the statistical characteristics of radar precipitation reflectivity data are studied and modeled using a hidden Markov tree(HMT)in the wavelet domain.Then,a high-resolution interpolation algorithm is proposed for spaceborne radar reflectivity using the HMT model as prior information.Owing to the small and transient storm elements embedded in the larger and slowly varying elements,the radar precipitation data exhibit distinct multiscale statistical properties,including a non-Gaussian structure and scale-to-scale dependency.An HMT model can capture well the statistical properties of radar precipitation,where the wavelet coefficients in each sub-band are characterized as a Gaussian mixture model(GMM),and the wavelet coefficients from the coarse scale to fine scale are described using a multiscale Markov process.The state probabilities of the GMM are determined using the expectation maximization method,and other parameters,for instance,the variance decay parameters in the HMT model are learned and estimated from high-resolution ground radar reflectivity images.Using the prior model,the wavelet coefficients at finer scales are estimated using local Wiener filtering.The interpolation algorithm is validated using data from the precipitation radar onboard the Tropical Rainfall Measurement Mission satellite,and the reconstructed results are found to be able to enhance the spatial resolution while optimally reproducing the local extremes and gradients.展开更多
Based on dual-frequencies dual-apertures spaceborne SAR （Synthetic Aperture Radar）, a new SAR system with four receiving channels and two operation modes is presented in this paper, SAR imaging and Moving Target Ind...Based on dual-frequencies dual-apertures spaceborne SAR （Synthetic Aperture Radar）, a new SAR system with four receiving channels and two operation modes is presented in this paper, SAR imaging and Moving Target Indication （MTI） are studied in this system. High resolution imaging with wide swath is implemented by the Mode Ⅰ, and MTI is completed by the Mode Ⅱ. High azimuth resolution is achieved by the Displaced Phase Center （DPC） multibeam technique. And the Coherent Accumulation （CA） method, which combines dual channels data of different carrier frequency, is used to enhance the range resolution. For the data of different carrier frequency, the two aperture interferometric processing is executed to implement clutter cancellation, respectively. And the couple of clutter suppressed data are employed to implement Dual Carrier Frequency Conjugate Processing （DCFCP）, then both slow and fast moving targets detection can be completed, followed by moving target imaging. The simulation results show the validity of the signal processing method of this new SAR system.展开更多
A new Chirp Scaling algorithm for spaceborne synthetic aperture radar(SAR) with large squint angle is presented and compared with the Range-Doppler algorithm and the algorithm in literatur [6] in the paper. The simula...A new Chirp Scaling algorithm for spaceborne synthetic aperture radar(SAR) with large squint angle is presented and compared with the Range-Doppler algorithm and the algorithm in literatur [6] in the paper. The simulation results of processing point target echocs show that the algorithm developed in this paper can give more accurate image especially in the case of large squint angle.展开更多
An increasing number of low,medium,and high resolution SAR satellites creates a demand for a generalized sensor model to replace the rigorous sensor model(RSM).The rational polynomial coefficient(RPC)model is a generi...An increasing number of low,medium,and high resolution SAR satellites creates a demand for a generalized sensor model to replace the rigorous sensor model(RSM).The rational polynomial coefficient(RPC)model is a generic sensor model which accurately fits the object-image geometry for various sensor systems with different coefficient values.It has been widely used as an alternative to RSM for photogrammetric processing of optical images,but its applications to SAR images are rarely discussed in publications.In this paper,the feasibility and practicability of the RPC model for SAR images are studied.The RPC model can not only be used to replace the RSM(range–Doppler model for SAR),but also applied to the processing chain for SAR data,thus facilitating the processing of SAR and InSAR data for end users.展开更多
The linear relationship between Doppler centroid and range walking in spaceborne SAR data is analyzed, and a new method to estimate Doppler centroid is proposed, which is so called amplitude correlation method. Compar...The linear relationship between Doppler centroid and range walking in spaceborne SAR data is analyzed, and a new method to estimate Doppler centroid is proposed, which is so called amplitude correlation method. Compared with clutter-lock method which is widely used now, the new method has much less computation burden and is able to give higher estimation accuracy for a quasi-homogeneous scene or a non-homogeneous scene. This is clearly verified by the experimental results of estimating Doppler centroid for SEASAT-A raw data.展开更多
The mathematical model of spaceborne SAR systems and its computer simulationsare described. Results of computer simulations about range migration, range migration correction,azimuth weighting and signal generation/pro...The mathematical model of spaceborne SAR systems and its computer simulationsare described. Results of computer simulations about range migration, range migration correction,azimuth weighting and signal generation/processing are given. This software can be used tosimulate the dynamic processes in spaceborne SAR systems, to develop new signal processingtechniques and to evaluate the performance of the designed system.展开更多
Synthetic aperture radar(SAR)three-dimensional(3D)imaging technology can reconstruct the complete structure of observed targets and has been a hot topic.Compared with tomographic SAR,array interferometric SAR,and circ...Synthetic aperture radar(SAR)three-dimensional(3D)imaging technology can reconstruct the complete structure of observed targets and has been a hot topic.Compared with tomographic SAR,array interferometric SAR,and circular SAR,curve SAR can use less data to achieve 3D positioning of targets.Most existing algorithms for estimating Doppler frequency modulation(FM)rate are based on sub aperture partitioning,resulting in low computational efficiency.To address this,this article establishes a target height estimation model,which reflects the relation-ship between the height and the residual Doppler FM rate for spaceborne curve SAR.Then,a fast SAR 3D localization processing flow based on fractional Fourier transform(FrFT)is proposed.Experimental verification demonstrates that this method can estimate the Doppler FM of the target column by column,and the 3D position error for non-overlapping targets is controlled within 1 m.For overlapping points with an intensity ratio greater than 1.5,the root mean square error(RMSE)of the estimation results is around 5 m.If the separation between overlapping points is greater than 35 m,the RMSE decreases to approximately 2 m.展开更多
Accurately and timely monitoring the spatial distribution and composition of mangrove species is critical for assessing mangroves’health,dynamics,and biodiversity,as well as mangroves’degradation and restoration.Rec...Accurately and timely monitoring the spatial distribution and composition of mangrove species is critical for assessing mangroves’health,dynamics,and biodiversity,as well as mangroves’degradation and restoration.Recent advances in machine learning algorithms,coupled with spaceborne remote sensing technique,offer an unprecedented opportunity to map mangroves at species level with high resolution over large extents.However,a single data source or data type is insufficient to capture the complex features of mangrove species and cannot satisfy the need for fine species classification.Moreover,identifying and selecting effective features derived from integrated multisource data are essential for integrating high-dimensional features for mangrove species discrimination.In this study,we developed a novel framework for mangrove species classification using spectral,texture,and polarization information derived from 3-source spaceborne imagery:WorldView-2(WV-2),OrbitaHyperSpectral(OHS),and Advanced Land Observing Satellite-2(ALOS-2).A total of 151 remote sensing features were first extracted,and 18 schemes were designed.Then,a wrapper method by combining extreme gradient boosting with recursive feature elimination(XGBoost-RFE)was conducted to select the sensitive variables and determine the optical subset size of all features.Finally,an ensemble learning algorithm of XGBoost was applied to classify 6 mangrove species in the Zhanjiang Mangrove National Nature Reserve,China.Our results showed that combining multispectral,hyperspectral,and L-band synthetic aperture radar features yielded the best mangrove species classification results,with an overall accuracy of 94.02%,a quantity disagreement of 4.44%,and an allocation disagreement of 1.54%.In addition,this study demonstrated important application potential of the XGBoost classifier.The proposed framework could provide fine-scale data and conduce to mangroves’conservation and restoration.展开更多
With the development of satellite miniaturization and remote sensing,the establishment of microsatellite constellations is an inevitable trend.Due to their limited size,weight,and power,spaceborne storage systems with...With the development of satellite miniaturization and remote sensing,the establishment of microsatellite constellations is an inevitable trend.Due to their limited size,weight,and power,spaceborne storage systems with excellent scalability,performance,and reliability are still one of the technical bottlenecks of remote sensing microsatellites.Based on the commercial off-the-shelf field-programmable gate array and memory devices,a spaceborne advanced storage system(SASS)is proposed in this paper.This work provides a dynamic programming,queue scheduling multiple-input multiple-output cache technique and a high-speed,high-reliability NAND flash controller for multiple microsatellite payload data.Experimental results show that SASS has outstanding scalability with a maximum write rate of 2429 Mb/s and preserves at least 78.53%of the performance when a single NAND flash fails.The scheduling technique effectively shortens the data scheduling time,and the data remapping method of the NAND flash controller can reduce the retention error by at least 50.73%and the program disturbance error by at least 37.80%.展开更多
Confirming tornado occurrence and estimating tornado intensity are quite challenging,especially for long-track tornadoes and tornado outbreaks,because of the inefficiency or absence of on-site damage surveys,especiall...Confirming tornado occurrence and estimating tornado intensity are quite challenging,especially for long-track tornadoes and tornado outbreaks,because of the inefficiency or absence of on-site damage surveys,especially in sparsely populated regions,which brings about large uncertainties in the tornado record.Some potential methods to alleviate this uncertainty in tornado records have been introduced,such as reports from tornado enthusiasts,trawling of social media sites,and spaceborne photography,which have been shown to be efficient in collecting damage information and depicting the damage swath and ascertaining tornado records.Unmanned aerial vehicles may help in effectively rating tornado intensities.Since 2021,some of these methods have been being tested or are under operation at the China Meteorological Administration Tornado Key Laboratory and the Foshan Tornado Research Center,and have proved to be effective.They have great potential in advancing tornado or downburst damage surveys nationally or worldwide,as well as assessing tornado climatologies,especially in sparsely populated regions such as Northeast China.展开更多
基金supported by the National Key Research and Development Program of China[grant numbers 2021YFE0117700 and 2022YFF1302100]the ESA-MOST China Dragon 5 Cooperation[grant number 59313]National Science and Technology Major Project of China's High Resolution Earth Observation System[grant numbers 30-Y30A02-9001-20/22-7 and 21-Y20B01-9001-19/22].
文摘Accurate estimation of forest terrain and canopy height is crucial for timely understanding of forest growth.Gao Fen-7(GF-7)Satellite is China’s first sub-meter-level three-dimensional(3D)mapping satellite for civilian use,which was equipped with a two-line-array stereo mapping camera and a laser altimeter system that can provide stereo images and full waveform LiDAR data simultaneously.Most of the existing studies have concentrated on evaluating the accuracy of GF-7 for topographic survey in bare land,but few have in-depth studied its ability to measure forest terrain elevation and canopy height.The purpose of this study is to evaluate the potential of GF-7 LiDAR and stereo image for forest terrain and height measurement.The Airborne Laser Scanning(ALS)data were utilized to generate reference terrain and forest vertical information.The validation test was conducted in Pu’er City,Yunnan Province of China,and encouraging results have obtained.The GF-7 LiDAR data obtained the accuracy of forest terrain elevation with RMSE of 8.01 m when 21 available laser footprints were used for results verification;meanwhile,when it was used to calculate the forest height,R^(2)of 0.84 and RMSE of 3.2 m were obtained although only seven effective footprints were used for result verification.The canopy height values obtained from GF-7 stereo images have also been proven to have high accuracy with the resolution of 20 m×20 m compared with ALS data(R2=0.88,RMSE=2.98 m).When the results were verified at the forest sub-compartment scale that taking into account the forest types,further higher accuracy(R^(2)=0.96,RMSE=1.23 m)was obtained.These results show that GF-7 has considerable application potential in forest resources monitoring.
基金Supported by Horizontal Program of Space Long March Rocket Technology Co. Ltd (500036)
文摘Dual-frequency and multi-polarization spaceborne rain and cloud measuring radar is the inevitable trend of remote sensing techniques.Techniques of new generation dual-frequency and multi-polarization spaceborne rain and cloud measuring radar are studied systematically.Radar block diagram and main parameters are presented.Antenna subsystem scheme is analyzed and antenna parameters are proposed.Central electronic device subsystem scheme is given and data rate of spaceborne radar is calculated.This paper is a meaningful try for carrying out spaceborne rain and cloud measuring radar design,acting as a reference to Chinese spaceborne rain and cloud measuring radar design and production in future.
基金co-supported by the National Natural Science Foundation of China (Nos.61370013 and 91438202)the High Resolution Earth Observation System Major Special Project Youth Innovation Foundation of China (No.GFZX04060103)
文摘In determining the orbits of low Earth orbit （LEO） satellites using spaceborne GPS, the errors caused by receiver antenna phase center offset （PCO） and phase center variations （PCVs） are gradually becoming a major limiting factor for continued improvements to accuracy. Shiyan 3, a small satellite mission for space technology experimentation and climate exploration, was developed by China and launched on November 5, 2008. The dual-frequency GPS receiver payload delivers 1 Hz data and provides the basis for precise orbit determination within the range of a few centimeters. The antenna PCO and PCV error characteristics and the principles influencing orbit determination are analyzed. The feasibility of PCO and PCV estimation and compensation in different directions is demonstrated through simulation and in-flight tests. The values of receiver antenna PCO and PCVs for Gravity Recovery and Climate Experiment （GRACE） and Shiyan 3 satellites are estimated from one month of data. A large and stable antenna PCO error, reaching up to 10.34 cm in the z-direction, is found with the Shiyan 3 satellite. The PCVs on the Shiyan 3 satellite are estimated and reach up to 3.0 cm, which is slightly larger than that of GRACE satellites. Orbit validation clearly improved with independent k-band ranging （KBR） and satellite laser ranging （SLR） measurements. For GRACE satellites, the average root mean square （RMS） of KBR residuals improved from 1.01 cm to 0.88 cm. For the Shiyan 3 satellite, the average RMS of SLR residuals improved from 4.95 cm to 4.06 cm.
基金This work was supported by National Natural Science Foundation of China under Grant Nos.42071350,41820104006,41771385 and 41622107supported by Postdoctoral Research Foundation of China.
文摘With the maturation of satellite technology,Hyperspectral Remote Sensing(HRS)platforms have developed from the initial ground-based and airborne platforms into spaceborne platforms,which greatly promotes the civil application of HRS imagery in the fields of agriculture,forestry,and environmental monitoring.China is playing an important role in this evolution,especially in recent years,with the successful launch and operation of a series of civil hyper-spectral spacecraft and satellites,including the Shenzhou-3 spacecraft,the Gaofen-5 satellite,the SPARK satellite,the Zhuhai-1 satellite network for environmental and resources monitoring,the FengYun series of satellites for meteorological observation,and the Chang’E series of spacecraft for planetary exploration.The Chinese spaceborne HRS platforms have various new characteristics,such as the wide swath width,high spatial resolution,wide spectral range,hyperspectral satellite networks,and microsatellites.This paper focuses on the recent progress in Chinese spaceborne HRS,from the aspects of the typical satellite systems,the data processing,and the applications.In addition,the future development trends of HRS in China are also discussed and analyzed.
文摘Spaceborne synthetic remote sensing of atmospheric aerosol optical depth and vegetation reflectance is very significant, but it remains to be a question unresolved yet. Based on the property of vegetation reflectance spectra from near ultra violet to near infrared and the sensitivity of outgoing radiance to vegetation reflectance and atmospheric aerosol optical depth, a new method for spaceborne synthetic remote sensing of the reflectance and the depth is proposed, and an iteration correlation inversion algorithm is developed in this paper. According to numerical experiment, effects of radiance error, error in aerosol imaginary index and vegetation medium inhomogeneity on retrieved result are analyzed. Inversion results show that the effect of error in aerosol imaginary index is very important. As the error of aerosol imaginary index is within 0.01, standard errors of aerosol optical depth and vegetation reflectance solutions for 14 spectral channels from 410 nm to 900 nm are respectively less than 0.063 and 0.023. And as the radiance error is within 2%, the standard errors are less than 0.023 and 0.0056.
基金supported by National Geoscience Database and Geological Survey of Iran
文摘The purpose of this study is to evaluate the Spectral Angle Mapper （SAM） classification method for determining the optimum threshold （maximum spectral angle） to unveil the hydrothermal mineral assemblages related to mineral deposits. The study area indicates good potential for Cu-Au porphyry, epithermal gold deposits and hydrothermal alteration well developed in arid and semiarid climates, which makes this region significant for Advanced Spaceborne Thermal Emission and Reflection Radiometer （ASTER） image processing analysis. Given that achieving an acceptable mineral mapping requires knowing the alteration patterns, petrochemistry and petrogenesis of the igneous rocks while considering the effect of weathering, overprinting of supergene alteration, overprinting of hypogene alteration and host rock spectral mixing, SAM classification was implemented for argillic, sericitic, propylitic, alunitization, silicification and iron oxide zones of six previously known mineral deposits： Maherabad, a Cu-Au porphyry system; Sheikhabad, an upper part of Cu-Au porphyry system; Khoonik, an Intrusion related Au system; Barmazid, a low sulfidation epithermal system; Khopik, a Cu-Au porphyry system; and Hanish, an epithermal Au system. Thus, the investigation showed that although the whole alteration zones are affected by mixing, it is also possible to produce a favorable hydrothermal mineral map by such complementary data as petrology, petrochemistry and alteration patterns.
文摘Doppler centroid frequency is an essential parameter in the imaging processing of the Scanning mode Synthetic Aperture Radar (ScanSAR). Inaccurate Doppler centroid frequency will result in ghost images in imaging result. In this letter, the principle and algorithms of Doppler centroid frequency estimation are introduced. Then the echo data of ScanSAR system is analyzed. Based on the algorithms of energy balancing and correlation Doppler estimator in the estimation of Doppler centroid frequency in strip mode SAR, an improved method for Doppler centroid frequency estimation in ScanSAR is proposed. The method has improved the accuracy of Doppler centroid frequency estimation in ScanSAR by zero padding between burst data. Finally, the proposed method is validated with the processing of ENVIronment SATellite Advanced Synthetic Aperture Radar (ENVISAT ASAR) wide swath raw data.
基金This work was supported by the General Design Department,China Academy of Space Technology(10377).
文摘The spaceborne synthetic aperture radar(SAR)sparse flight 3-D imaging technology through multiple observations of the cross-track direction is designed to form the cross-track equivalent aperture,and achieve the third dimensionality recognition.In this paper,combined with the actual triple star orbits,a sparse flight spaceborne SAR 3-D imaging method based on the sparse spectrum of interferometry and the principal component analysis(PCA)is presented.Firstly,interferometric processing is utilized to reach an effective sparse representation of radar images in the frequency domain.Secondly,as a method with simple principle and fast calculation,the PCA is introduced to extract the main features of the image spectrum according to its principal characteristics.Finally,the 3-D image can be obtained by inverse transformation of the reconstructed spectrum by the PCA.The simulation results of 4.84 km equivalent cross-track aperture and corresponding 1.78 m cross-track resolution verify the effective suppression of this method on high-frequency sidelobe noise introduced by sparse flight with a sparsity of 49%and random noise introduced by the receiver.Meanwhile,due to the influence of orbit distribution of the actual triple star orbits,the simulation results of the sparse flight with the 7-bit Barker code orbits are given as a comparison and reference to illuminate the significance of orbit distribution for this reconstruction results.This method has prospects for sparse flight 3-D imaging in high latitude areas for its short revisit period.
文摘The principal purpose of this paper is to extract entire sea surface wind＇s information from spaceborne lidar, and particularly to utilize a appropriate algorithm for removing the interference information due to white caps and subsurface water. Wind speeds are obtained through empirical relationship with sea surface mean square slopes. Wind directions are derived from relationship between wind speeds and wind directions im plied in CMOD5n geophysical models function （GMF）. Whitecaps backscattering signals were distinguished with the help of lidar depolarization ratio measurements and rectified by whitecaps coverage equation. Subsurface water backscattering signals were corrected by means of inverse distance weighted （IDW） from neighborhood non-singular data with optimal subsurface water backscattering calibration parameters. To verify the algorithm reliably, it selected NDBC＇s TAO buoy-laying area as survey region in camparison with buoys＇ wind field data and METOP satellite ASCAT of 25 km single orbit wind field data after temporal-spa tial matching. Validation results showed that the retrieval algorithm works well in terms of root mean square error （RMSE） less than 2m/s and wind direction＇s RMSE less than 21 degree.
基金This study was funded by the National Natural Science Foundation of China(Grant No.41975027)the Natural Science Foundation of Jiangsu Province(Grant No.BK20171457)the National Key R&D Program on Monitoring,Early Warning and Prevention of Major Natural Disasters(Grant No.2017YFC1501401).
文摘With the increasing availability of precipitation radar data from space,enhancement of the resolution of spaceborne precipitation observations is important,particularly for hazard prediction and climate modeling at local scales relevant to extreme precipitation intensities and gradients.In this paper,the statistical characteristics of radar precipitation reflectivity data are studied and modeled using a hidden Markov tree(HMT)in the wavelet domain.Then,a high-resolution interpolation algorithm is proposed for spaceborne radar reflectivity using the HMT model as prior information.Owing to the small and transient storm elements embedded in the larger and slowly varying elements,the radar precipitation data exhibit distinct multiscale statistical properties,including a non-Gaussian structure and scale-to-scale dependency.An HMT model can capture well the statistical properties of radar precipitation,where the wavelet coefficients in each sub-band are characterized as a Gaussian mixture model(GMM),and the wavelet coefficients from the coarse scale to fine scale are described using a multiscale Markov process.The state probabilities of the GMM are determined using the expectation maximization method,and other parameters,for instance,the variance decay parameters in the HMT model are learned and estimated from high-resolution ground radar reflectivity images.Using the prior model,the wavelet coefficients at finer scales are estimated using local Wiener filtering.The interpolation algorithm is validated using data from the precipitation radar onboard the Tropical Rainfall Measurement Mission satellite,and the reconstructed results are found to be able to enhance the spatial resolution while optimally reproducing the local extremes and gradients.
基金Supported by the National Natural Science Foundation of China (NSFC) (No.60772103)China National Key Laboratory of Microwave Imaging Technology Foundation (No.9140C1903050804)
文摘Based on dual-frequencies dual-apertures spaceborne SAR （Synthetic Aperture Radar）, a new SAR system with four receiving channels and two operation modes is presented in this paper, SAR imaging and Moving Target Indication （MTI） are studied in this system. High resolution imaging with wide swath is implemented by the Mode Ⅰ, and MTI is completed by the Mode Ⅱ. High azimuth resolution is achieved by the Displaced Phase Center （DPC） multibeam technique. And the Coherent Accumulation （CA） method, which combines dual channels data of different carrier frequency, is used to enhance the range resolution. For the data of different carrier frequency, the two aperture interferometric processing is executed to implement clutter cancellation, respectively. And the couple of clutter suppressed data are employed to implement Dual Carrier Frequency Conjugate Processing （DCFCP）, then both slow and fast moving targets detection can be completed, followed by moving target imaging. The simulation results show the validity of the signal processing method of this new SAR system.
文摘A new Chirp Scaling algorithm for spaceborne synthetic aperture radar(SAR) with large squint angle is presented and compared with the Range-Doppler algorithm and the algorithm in literatur [6] in the paper. The simulation results of processing point target echocs show that the algorithm developed in this paper can give more accurate image especially in the case of large squint angle.
基金Supported by National Technology Support Project(Nos.2011BAB01B01,2012BAH28B04)the National Natural Science Foundation of China(No.40930532)the National High Technology Research&Development Programme of China(No.2011AA120404).
文摘An increasing number of low,medium,and high resolution SAR satellites creates a demand for a generalized sensor model to replace the rigorous sensor model(RSM).The rational polynomial coefficient(RPC)model is a generic sensor model which accurately fits the object-image geometry for various sensor systems with different coefficient values.It has been widely used as an alternative to RSM for photogrammetric processing of optical images,but its applications to SAR images are rarely discussed in publications.In this paper,the feasibility and practicability of the RPC model for SAR images are studied.The RPC model can not only be used to replace the RSM(range–Doppler model for SAR),but also applied to the processing chain for SAR data,thus facilitating the processing of SAR and InSAR data for end users.
文摘The linear relationship between Doppler centroid and range walking in spaceborne SAR data is analyzed, and a new method to estimate Doppler centroid is proposed, which is so called amplitude correlation method. Compared with clutter-lock method which is widely used now, the new method has much less computation burden and is able to give higher estimation accuracy for a quasi-homogeneous scene or a non-homogeneous scene. This is clearly verified by the experimental results of estimating Doppler centroid for SEASAT-A raw data.
文摘The mathematical model of spaceborne SAR systems and its computer simulationsare described. Results of computer simulations about range migration, range migration correction,azimuth weighting and signal generation/processing are given. This software can be used tosimulate the dynamic processes in spaceborne SAR systems, to develop new signal processingtechniques and to evaluate the performance of the designed system.
基金supported in part by the National Key Research and Development Program of China(No.SQ2022YFB 3900055)in part by the National Natural Science Foundation of China(No.62101039)+1 种基金in part by the Shandong Excellent Young Scientists Fund Program(Overseas)in part by China Postdoctoral Science Foundation(No.2022M720443).
文摘Synthetic aperture radar(SAR)three-dimensional(3D)imaging technology can reconstruct the complete structure of observed targets and has been a hot topic.Compared with tomographic SAR,array interferometric SAR,and circular SAR,curve SAR can use less data to achieve 3D positioning of targets.Most existing algorithms for estimating Doppler frequency modulation(FM)rate are based on sub aperture partitioning,resulting in low computational efficiency.To address this,this article establishes a target height estimation model,which reflects the relation-ship between the height and the residual Doppler FM rate for spaceborne curve SAR.Then,a fast SAR 3D localization processing flow based on fractional Fourier transform(FrFT)is proposed.Experimental verification demonstrates that this method can estimate the Doppler FM of the target column by column,and the 3D position error for non-overlapping targets is controlled within 1 m.For overlapping points with an intensity ratio greater than 1.5,the root mean square error(RMSE)of the estimation results is around 5 m.If the separation between overlapping points is greater than 35 m,the RMSE decreases to approximately 2 m.
基金National Natural Science Foundation of China(42171379,42222103,42101379,and 42171372)Science and Technology Development Program of Jilin Province,China(20210101396JC)+2 种基金Youth Innovation Promotion Association of the Chinese Academy of Sciences(2017277 and 2021227)Young Scientist Group Project of Northeast Institute of Geography and Agroecology,Chinese Academy of Sciences(2022QNXZ03)Shenzhen Science and Technology Program(JCYJ20210324093210029).
文摘Accurately and timely monitoring the spatial distribution and composition of mangrove species is critical for assessing mangroves’health,dynamics,and biodiversity,as well as mangroves’degradation and restoration.Recent advances in machine learning algorithms,coupled with spaceborne remote sensing technique,offer an unprecedented opportunity to map mangroves at species level with high resolution over large extents.However,a single data source or data type is insufficient to capture the complex features of mangrove species and cannot satisfy the need for fine species classification.Moreover,identifying and selecting effective features derived from integrated multisource data are essential for integrating high-dimensional features for mangrove species discrimination.In this study,we developed a novel framework for mangrove species classification using spectral,texture,and polarization information derived from 3-source spaceborne imagery:WorldView-2(WV-2),OrbitaHyperSpectral(OHS),and Advanced Land Observing Satellite-2(ALOS-2).A total of 151 remote sensing features were first extracted,and 18 schemes were designed.Then,a wrapper method by combining extreme gradient boosting with recursive feature elimination(XGBoost-RFE)was conducted to select the sensitive variables and determine the optical subset size of all features.Finally,an ensemble learning algorithm of XGBoost was applied to classify 6 mangrove species in the Zhanjiang Mangrove National Nature Reserve,China.Our results showed that combining multispectral,hyperspectral,and L-band synthetic aperture radar features yielded the best mangrove species classification results,with an overall accuracy of 94.02%,a quantity disagreement of 4.44%,and an allocation disagreement of 1.54%.In addition,this study demonstrated important application potential of the XGBoost classifier.The proposed framework could provide fine-scale data and conduce to mangroves’conservation and restoration.
基金supported by the Fundamental Research Funds for the Zhejiang Provincial Universities,China(No.2021XZZX038)。
文摘With the development of satellite miniaturization and remote sensing,the establishment of microsatellite constellations is an inevitable trend.Due to their limited size,weight,and power,spaceborne storage systems with excellent scalability,performance,and reliability are still one of the technical bottlenecks of remote sensing microsatellites.Based on the commercial off-the-shelf field-programmable gate array and memory devices,a spaceborne advanced storage system(SASS)is proposed in this paper.This work provides a dynamic programming,queue scheduling multiple-input multiple-output cache technique and a high-speed,high-reliability NAND flash controller for multiple microsatellite payload data.Experimental results show that SASS has outstanding scalability with a maximum write rate of 2429 Mb/s and preserves at least 78.53%of the performance when a single NAND flash fails.The scheduling technique effectively shortens the data scheduling time,and the data remapping method of the NAND flash controller can reduce the retention error by at least 50.73%and the program disturbance error by at least 37.80%.
基金supported by the National Natural Science Foundation of China(Grant Nos.42275006 and 42030604)the Science and Technology Research Project in Social Field of Foshan(Grant No.2120001008761)。
文摘Confirming tornado occurrence and estimating tornado intensity are quite challenging,especially for long-track tornadoes and tornado outbreaks,because of the inefficiency or absence of on-site damage surveys,especially in sparsely populated regions,which brings about large uncertainties in the tornado record.Some potential methods to alleviate this uncertainty in tornado records have been introduced,such as reports from tornado enthusiasts,trawling of social media sites,and spaceborne photography,which have been shown to be efficient in collecting damage information and depicting the damage swath and ascertaining tornado records.Unmanned aerial vehicles may help in effectively rating tornado intensities.Since 2021,some of these methods have been being tested or are under operation at the China Meteorological Administration Tornado Key Laboratory and the Foshan Tornado Research Center,and have proved to be effective.They have great potential in advancing tornado or downburst damage surveys nationally or worldwide,as well as assessing tornado climatologies,especially in sparsely populated regions such as Northeast China.
