最新刊期
卷 25 ， 期 10 ， 2021
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摘要：Geo-spatial cognition is an important method for humans to acquire geospatial knowledge and recognize geographical environment. For a long time, people carried out geo-spatial cognition based on maps and GIS, but it has been proven difficult due to the disadvantages of maps and GIS on geospatial expression, understanding of geographical process, and human-computer interaction. With the development of Virtual Geographic Environments (VGEs), people realize that VGEs have become important new tools for geo-spatial cognition because they are in accordance with the cognition habits in actual living. As an important new direction of geographic information science, VGE-based geo-spatial cognition has been extensively studied in recent years. However, in general, existing studies are still at the primary stage; they mostly focus on the concept, cognitive characteristics, and the preliminary framework. However, studies on the connotation and relevant technical methods are few.In accordance with the solution of the six classical geographical questions, the basic contents of VGE-based geo-spatial cognition from the three levels of geographical ontology cognition, geographical process cognition, and geographical behavior cognition are elaborated. Among them, the geographical ontology cognition solves the questions of “what, where, when, and their relationship.” Geographical process cognition solves the questions of “why is it there, how does it form, and how will it develops.” Geographic behavioral cognition solves the questions of “what’s the effect, what role does it play, and how it can be used.” Then, the relevant technical methods are discussed to realize VGE-based geo-spatial cognition, including urban spatial representation and urban computing, multimode human–computer interaction, geographical knowledge graph and spatial reasoning, geographical process simulation, geographical behavior pattern recognition, and emotional computing. Finally, a case study of Chongqing based on the overall framework and technical system is conducted.On the basis of “Chongqing 3D Space Digital Platform,” the corresponding practical results are presented from three levels of geographical ontology cognition, geographical process cognition, and geographical behavior cognition, displaying the use of relevant technical methods to recognize geographical environment and geospatial objects. Most existing studies focus on preliminary stages, such as the concept, research framework, expression of spatial objects, and geographical knowledge in the virtual environment. On the contrary, further exploration is conducted, thereby obtaining the actual cognitive results through the application of relevant technologies.Under the support of overall framework and technical system, the realization approach and the practice results of geographical ontology cognition, geographical process cognition, and geographical behavior cognition are presented. This approach provides new ideas and solution for in-depth development and technical implementation of VGE- based geo-spatial cognition, and transforms the research from the conceptual discussion stage to the technical practice stage.关键词：virtual geographic environments;geo-spatial cognition;cognition contents;cognition techniques;structured semantic modeling;urban computing;geographic knowledge graph;behavior pattern recognition- 1359
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发布时间：2021-10-21
Review
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摘要：Onboard the Chinese GF-5 satellite, Environmental trace gas Monitoring Instrument (EMI) is a nadir-viewing wide-field spectrometer that measures solar back-scattered earthshine radiances in the ultraviolet and visible spectra range. It was launched on 9 May 2018, and aims to quantify the global distribution of tropospheric and stratospheric trace gases. Meanwhile, formaldehyde (HCHO) is an intermediate oxidation reaction of various Volatile Organic Compounds (VOC) in the atmosphere, which is important for the formation of tropospheric ozone and secondary organic aerosols. Previous studies have proven that HCHO can be used as a tracer for VOCs in the absence of other VOC observations. Therefore, the monitoring of HCHO is essential for air quality. The spectral range of EMI covers HCHO absorption signature at 320—360 nm, with the potential for HCHO detection.We have evaluated the requirements and feasibility for HCHO retrieval based on simulation. We find that the irradiance of EMI is effectively calibrated with smaller wavelength shift. However, compared with OMI and TROPOMI, the FWHM and wavelength shifts of EMI are highly dependent on the cross-track positions. On the basis of the EMI Level 1 spectral quality evaluation, the Differential Optical Absorption Spectrometry (DOAS) method is used for HCHO retrieval. HCHO Slant Column Densities (SCDs) are initially obtained by spectral fitting, and then the SCDs are converted to Vertical Column Densities (VCDs) using Air–Mass Factors (AMFs) at 340 nm. We perform a wavelength adjustment procedure by using the solar Fraunhofer lines from a highly accurate reference solar atlas prior to the spectral fitting procedure to account for the influence of pixel-dependent wavelength shifts on HCHO SCDs. In the EMI HCHO spectral fitting procedure, the fitting interval is set to 328.5—346 nm with a fifth-order polynomial. The absorption cross-section of HCHO and the interfering species O3, NO2, BrO, O4, and the ring cross section calculated by the QDOAS Ring tool are included in the fitting process. All absorption cross-sections are convoluted with the EMI FWHM, according to the corresponding cross-track position.Simulation results demonstrate that HCHO retrieval is prone to noise, and the nominal SNR of EMI UV2 band is lower, leading to larger random error in the HCHO SCD retrieval as well as the fit residual. The SCD uncertainty of EMI HCHO is 1.2×1016 molec./cm2. The preliminary results of formaldehyde retrieval derived from EMI show that EMI can captures the spatial distribution of HCHO. The comparison of EMI and TROPOMI and EMI and OMI shows consistency in spatial, with the correlation coefficient larger than 0.8. However, EMI HCHO is generally higher than OMI and TROPOMI over east China, probably resulting from the imperfect wavelength calibration and the contamination of the remaining cloud after cloud screening. The results demonstrated the potential of EMI for HCHO retrieval in summer.关键词：remote sensing;GF-5;EMI;HCHO;DOAS;air quality- 1085
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发布时间：2021-10-21 -
摘要：Clouds cover 50 to 70 percent of the earth’s surface and are an important factor in the balance of atmospheric radiation and climate change. The Directional Polarimetric Camera (DPC) carried by the GaoFen-5 satellite can continuously observe the earth in multiple bands, multiple angles, and high spatial resolution. Its data are useful for studying global atmospheric cloud distribution, and cloud radiation feedback provides a new perspective.This study uses the French multiangle polarization load polarization and directionality of the earth’s reflectance (POLDER) cloud recognition algorithm as a reference, and combines DPC multiband reflectivity, polarization reflectivity, apparent pressure, and other information to develop a cloud detection algorithm suitable for DPC. The algorithm is mainly divided into three parts. First, the threshold method is used to detect cloud pixels, and the apparent pressure is introduced to further restrict the conditions of clouds (such as cirrus and stratocumulus) at different heights. Then, the 865 nm band polarization reflectance is used to identify the solar flare area reflected by the sea surface, and the solar flare interference is amended when the reflectance threshold is used to identify cloud pixels.The MOD06 cloud mask product of MODIS on October 1, 2018 was compared with the results of the proposed cloud recognition algorithm to verify the accuracy of the algorithm. The cloud recognition results were in good agreement with the MOD06 products. The CALIPSO-VFM data from October 01 to 04, 2018, the cloud detection results, and the MYDO6 cloud mask product were selected to calculate the cloud/clear pixels hit rate and false alarm rate to further quantitatively verify the accuracy of the cloud detection algorithm.The calculation results show that the average cloud hit rate of the algorithm is 13.501% higher than that of the MYD06 cloud mask product. The cloud error prediction rate is only 3.561% higher than that of the MYD06 cloud mask products, thereby indicating cloud detection effect. The proposed cloud detection algorithm can provide important data support for subsequent DPC research on cloud parameters, water vapor, and aerosols.关键词：atmospheric remote sensing;cloud detection;apparent pressure;multi-angular polarization;GF-5;DPC- 1094
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发布时间：2021-10-21
Atmospheric Remote Sensing
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摘要：Optical satellite is an important means to obtain remote sensing data by earth observation, and radiation calibration is an important guarantee for quantitative remote sensing. As the satellite sensor is subject to mechanical vibration and acceleration shock during transportation and launch, also taking into account of the aging of optoelectronic devices during long-term on-orbit operation, the radiation performance of the sensor is inevitably affected. As such, the on-orbit radiation calibration is needed to correct the sensor radiation performance. On-orbit calibration is a very important on-orbit calibration method that uses on-satellite calibration devices to measure the radiometric calibration data after the satellite launch. The on-satellite calibrators include calibration lamps, Solar Diffusers (SD) and lunar calibrators, etc. The relative radiometric calibration is used to reduce or eliminate the image high frequency vertical fringe and stripe noise, which are caused by the response difference between detection elements. This process is the premise and foundation of the quantitative application of remote sensing image. In the background of the national major project of global cartography, in order to explore the application potential of relative radiometric calibration for the deployable solar diffuse reflector similar to the Jilin-1 GP satellite, a relative radiometric calibration method based on the solar diffuser is proposed in this paper, which is in order to solve the shortcomings of conventional relative radiometric calibration methods. The method overcomes the dependence of relative radiometric calibration on the accumulation and the uniform consistency of features in the data by imaging through the closing process of the solar diffuse reflector. The solar diffuser is driven by the satellite mechanical structure to close up and adjusts the solar incident energy at the entrance pupil of sensor, by this way acquiring the onboard calibration image. The calibration image covers the whole gray dynamic range of the sensor. Then, the relative radiation calibration coefficients are solved by histogram matching algorithm. In order to verify the method proposed in this paper, the calibration experiment is carried out with the sensor of multispectral spectrometer on JL-1 GP satellite. The correction effect of calibration coefficients on original images are tested and the accuracy of relative radiation calibration is quantitatively analyzed by using non-uniformity. The experimental results show that the calibration coefficients could effectively eliminate the vertical high-frequency fringe and strip noise of the panchromatic and multispectral original image of the ground object. The results of quantitative analysis show that the method proposed in this paper could achieve a good correction effect in the whole dynamic range of sensor’s grayscale, and the relative radiometric calibration accuracy of each band is better than 2%, which fulfills the demand for high-quality remote sensing image applications. On-orbit experiments fully demonstrate that the radiometric calibration method proposed in this paper can complete the calibration task using one solar diffuse reflector closing action, and the proposed method could effectively overcome the dependence of relative radiometric calibration on data accumulation and the uniform consistency of features in the data, which provides a reliable guarantee for quantitative remote sensing applications during the satellite’s on-orbit operation.关键词：deployable solar diffuser;onboard relative radiation calibration;histogram matching;multispectral spectrometer;JL-1 satellite- 851
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发布时间：2021-10-21 -
摘要：The Microwave Radiation Imager (MWRI) is a main payload of the second-generation Chinese polar-orbiting meteorological satellite Fengyun-3. The MWRI observes the Earth radiation at 10.65 GHz, 18.7 GHz, 23.8 GHz, 36.5 GHz, and 89 GHz with dual polarization. Sensitivity is the minimum transformation amount of the brightness temperature that can be detected by the radiometer, that is, the equivalent noise temperature of the radiometer system; it is expressed as the Root Mean Square (RMS) standard deviation of the output temperatures when the radiometer observes a target with a fixed bright temperature. Therefore, sensitivity is a key parameter for evaluating the performance of the MWRI, and the long-term stability of this parameter could directly affect the application of remote sensing data. At present, the brightness temperature data of the hot load (black body) equipped on the MWRI are used to evaluate the on-orbit sensitivity of the instrument. However, when the spaceborne microwave imager is in flight, the hot load measurements could be affected by environmental noise, such as receiver temperature and ground Radio Frequency Interference (RFI), resulting in errors in the on-orbit sensitivity obtained by the RMS method. The validity of the Allan standard deviation method is studied to calculate the sensitivity and accurately evaluate the on-orbit sensitivity of the spaceborne microwave imager, and then the Allan method is used to evaluate the long-term stability of the on-orbit sensitivity of the MWRIs on board FY-3 B, C, and D satellites.Combining the ground and on-orbit observations of the MWRI, two methods of root mean square standard deviation and Allan standard deviation were used to calculate the sensitivities of the imager. The comparison found that: (1) The deviation between the results obtained by Allan method and the ground test is less than 0.03 K, indicating that under the vacuum calibration test, the Allan method can effectively calculate the sensitivity parameters of the radiometers. (2) When the observation area of the space-borne microwave imager is different, the on-orbit sensitivity obtained by Allan method is unchanged, indicating that the Allan method can eliminate the interference of RFI. (3) The on-orbit sensitivity obtained by Allan standard deviation is unaffected by the receiver’s ambient temperature change. Therefore, the Allan method could be used to calculate the on-orbit sensitivity of a space-borne microwave imager.The Allan method was used to analyze the long-term stability of the on-orbit sensitivity of MWRIs on board FY-3B, C, and D satellites, and concluded that: (1) The on-orbit sensitivities of the three microwave imagers were stable, and the stability of FY-3C and FY-3D MWRIs is better than that of FY-3B MWRI. The standard deviation of the on-orbit sensitivity of the FY-3B MWRI is ≤ 0.015 K, and the standard deviation of the on-orbit sensitivity of the FY-3C and FY-3D MWRIs is ≤ 0.01 K. (2) FY-3C and FY-3D MWRI sensitivities are the same, and the sensitivities of the 89 GHz receiving channels of the FY-3C and FY-3D MWRIs are significantly better than that of the FY-3B MWRI. The sensitivity of each receiving channel of the FY-3C and FY-3D MWRIs is better than 0.5 K, and that of the FY-3B MWRI is better than 0.6 K.The comparison of the ground test data and on-orbit observations confirmed that the Allan method can effectively calculate the sensitivity of the spaceborne radiometers. In addition, the calculation results of the FY-3 MWRIs show that the on-orbit sensitivity of the MWRIs is good, and the long-term on-orbit working state is stable.关键词：FY-3 MWRI;Sensitivity;RMS method;Allan method;long-term stability- 689
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发布时间：2021-10-21 -
摘要：Permanent Scatterer (PS) identification is a key step in the PS-InSAR technology, which is mainly used for obtaining ground subsidence data. The density and accuracy of the PS points are determined by setting the optimal threshold of PS identification. Receiver Operating Characteristic (ROC) curve is used to quantitatively analyze and determine the optimal threshold for PS identification.The ROC curve is drawn with some thresholds of every PS identification algorithm. According to the ROC curve, the larger area under the ROC curve indicates that the PS recognition method is more reliable. When the area under the ROC curve is sufficiently large, the optimal threshold of PS identification, which is the closest to the upper left of the ROC curve, is determined quantitatively according to the maximum sum of the sensitivity and specificity of the ROC curve. The positive ratio of PS points is sufficiently high, the false positive ratio of PS points is sufficiently low, and the density of the PS point is sufficient, using the optimal threshold.The PS points are identified with 60 X-band TerraSAR-X images (2010—2017) by three algorithms as amplitude dispersion (TD), correlation coefficient (Tγ), and dual-threshold (TD, Tγ) with amplitude dispersion index (ADI) and correlation coefficient index (CCI). The experimental area is approximately Beijing Longtan Park. First, three ROC curves are drawn separately with the algorithms ADI, CCI, and dual-threshold. Second, the optimal thresholds of every algorithm have been calculated according to the maximum sum of the sensitivity and specificity of ROC curve. Research found that: (1) the optimal threshold of ADI is TD=0.45; the optimal threshold of CCI is Tγ=0.45; the optimal threshold of dual-threshold of ADI and CCI is (TD, Tγ) = (0.50, 0.50). (2) The area under the ROC curve of dual threshold is AUC=0.762, which is higher than the AUC of the single threshold algorithm, such as ADI and CCI. Evidently the dual-threshold algorithm is much better than the single threshold of ADI or CCI to identify the PS points.Result of this research shows that the ROC curve can not only quantitatively determine the optimal threshold of PS identification, but can also be further applied for the quantitative selection of the thresholds during GIS spatial analysis and remote sensing image interpretation.关键词：remote sensing;ROC (Receiver Operating Characteristic) curve;Permanent scatterers;coherence coefficient;amplitude dispersion;dual-threshold;ground subsidence- 1315
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发布时间：2021-10-21 -
摘要：Wild fires, especially large-scale wild fires, in forests, grasslands and farmlands have a significant influence on crop productivity, atmospheric pollution, biodiversity, climate change and public health. In recent years, the increasing events of forest fires in China, US, Australia, and Amazon Rain Forests and grassland fires in Mongolia have caused a large number of causality. Due to its great influences, growing emphasis has been placed on the monitoring of wild fires based on remote sensing products, such as using MODIS, NOAA and other polar orbit meteorological satellites. With the launch of a new generation of geostationary meteorological satellites, the characteristics of high frequency and real-time observation have obvious advantages for fire spot detection. Based on the high frequency observation characteristics of Himawari-8 that a new generation geostationary meteorological satellite, the objectives of this paper proposes a temporal sequence detection method to extract the initial fire spot of fire behavior. This method of geostationary meteorological satellite will greatly improve the method of fire identification, give full play to the advantage of temporal sequential, and realize the early detection of fire by remote sensing.The method of study for identifying fire points is based on the pixel temperature brightness difference in observation times and its rate, which is different from the conventional contextual method used in remote sensing fire monitoring of polar orbit meteorological satellites. According to the brightness temperature change value of detected pixel at the same position and different time, when the brightness temperature change value of the current and subsequent times exceeds the threshold, the pixel can be identified as a fire point. The change of observation methods has brought about a great improvement in monitoring sensitivity and timeliness in fire monitor.The results showed that under the condition of cloud-free and no abnormal heat source, the mid-infrared bright temperature have little difference between the adjacent times. Generally, the brightness temperature change of minute interval is less than 0.5 K. When the bright temperature rate between the current time and later time reaches 3K, the fire spot can be identified, while the threshold of contextual method is above 6 K. Compared with the contextual method, the temporal sequential method reduces the threshold of recognition by half and increases the sensitivity by more than twice. The fire spot detection threshold of the temporal sequential method is significantly lower than that of the contextual method.This paper introduces the method of temporal sequence for fire spot detection, and verifies it with the satellite and ground synchronous observation experiment in huachuan county, heilongjiang province. The conclusion demonstrated that this method is benefit to find early fire spot. If the threshold of contextual method is used alone, the early fire is difficult to be obtained, but the method of temporal sequence can make up for this defect. Temporal sequence method is used in the early stage of fire identification, context method is used in the middle stage, The combination of the temporal sequence method and the fluctuation of contextual can improve the meteorological satellite monitoring ability of fire development process.关键词：remote sensing;Himawari-8;geostationary meteorological satellite;Temporal sequence method;Fire detection- 1207
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发布时间：2021-10-21 -
摘要：The structural characteristics of forest canopy directly affect the radiation interception of forest, which in turn affect the energy exchange between the canopy and the external environment. As an important part of forest canopy structure, crown shape is greatly important for calculating the gap fraction and clumping index. Researchers have calculated gap fraction and clumping index by simulating crown shape as basic geometry, such as cone, cylinder, and cone + cylinder. However, the growth of the crown is influenced by factors, such as external environment and internal apical dominance, resulting in the semiellipsoid shape of the crown. The semiellipsoid is more consistent with the natural growth low of the crowns than these crown shapes. In fact, the semiellipsoid is a very common crown shape, which is significantly different from other crown shapes with an important influence on the calculation of canopy structure parameters, such as the gap fraction of canopies and clumping index. The main objective is to exhibit the influence of the semiellipsoid-shaped crown on the gap fraction and clumping index of forest canopies.First, assuming that the crown is an opaque geometric entity with the Poisson distribution in space, the gap fraction on crown scale was calculated. Second, considering that gaps exist in an individual crown, the formula for calculating the gap fraction of an individual crown was introduced. Then, crowns with semiellipsoid and double semiellipsoid shapes were applied to the formula of gap fraction of canopies and clumping index. Meanwhile, considering the semiellipsoid-shaped crown as the calculation criterion, we analyzed the relative differences of gap fraction of canopies and clumping index with different crown shapes. The main input parameters included crown density, crown height, crown radius and leaf area index. Finally, the results were verified by virtual scenes.The results indicated that: (1) the gap fraction of canopies between the semiellipsoid-shaped crown and crowns with other shapes was relatively different. With the increment of view zenith angle, the relative differences of gap fraction between the semiellipsoid-shaped crown and crowns with other shapes increased. When the view zenith angle was 70°, the relative difference of gap fraction between the cone-shaped crown and the semiellipsoid-shaped crown was close to 100%. (2) The crown shape also had a significant influence on the clumping index. In extreme cases, the relative differences of clumping index between the cone-shaped crown and the semiellipsoid-shaped crown reached up to 30%. In addition, different crown densities had an important effect on the clumping index of different crown shapes. With the decrease in crown density, the relative difference in the clumping index of the semiellipsoid-shaped crown and crowns with other shapes showed an increasing trend. (3) When calculating the expectation value of the clumping index in the hemisphere space, the value of the cylinder-shaped crown was approximately 13% higher than the value of the semiellipsoid-shaped crown, and the value of the semiellipsoid-shaped crown was approximately 22% higher than that of cone-shaped crown. The value of the semiellipsoid-shaped crown and double semiellipsoid-shaped crown was close to each other, and the mixture of two crown shapes slightly influenced the results.Therefore, the semiellipsoid-shaped crown should be considered when studying the structural characteristics of forest canopy, such as gap fraction and clumping index.关键词：remote sensing;crown shape;semi-ellipsoid-shaped crown;double semi-ellipsoid-shaped crown;gap fraction;clumping index- 741
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发布时间：2021-10-21
Technologies and Methodologies
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摘要：Accurate quantification of surface solar radiation is the basis of remote sensing inversion of reflectivity, and a research on urban surface radiation is important. The sky view factor is selected to characterize the morphological characteristics of the underlying surface of the urban area, and the Urban Surface Solar Radiation Model (USSR) is constructed. This model has distinguished the different effects of direct solar radiation, diffuse sky radiation, and environmental radiation on ground objects. The remote sensing data of Landsat 8 visible and near-infrared bands are considered the examples, and the application prospect of the USSR model for the quantification of urban surface solar radiation is analyzed. The research conclusions are as follows: (1) The USSR clearly quantifies the radiation components of urban surface based on the sky view factor (V), which can effectively solve the simulation of solar radiation transfer process of urban surface and better express the influence of the morphological structure of urban underlying surface on the incident radiation. (2) When USSR is applied to the estimates of solar radiation in the visible and near-infrared bands of Landsat 8 remote sensing data, compared with the estimated values without considering the influence of the morphological characteristics of the underlying surface, the urban surface solar radiation values estimated based on the USSR model can better express the “interception” effect of urban underlying surfaces on the incident radiation. (3) Compared with the TEB model, the USSR model estimates have high correlation, which indirectly verifies the availability of the USSR model. (4) According to the sensitivity analysis of V and reflectivity of the underneath surface, the results show an increasing trend as the V value of the underlying surface increased. In general, the parameter setting value is weak and insensitive compared with the parameter V. The proposed USSR model can amend the estimation results of urban surface solar radiation and improve the reliability of estimation results, thereby expanding the application depth and breadth of urban remote sensing.关键词：solar radiation;urban surface;morphological characteristics;sky view factor;underlying surface reflectance- 1461
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发布时间：2021-10-21 -
摘要：Synthetic Aperture Radar (SAR) is an indispensable data source for the dynamic monitoring of flood events due to the capacity for all-weather and all-time sensing. At present, flooding mapping and damaging assessment are developed rapidly towards dynamic monitoring and large scale, owing to the emergence of cloud computing platforms, such as Google Earth Engine (GEE) and accessibility of short-revisit Sentinel-1A radar data. A novel method is proposed for detecting flood events and continuous monitoring of the inundated areas at a large scale based on the time-series processing and analysis from Sentinel-1A images, considering the complexity of land cover changes within the flooded areas and the temporal uncertainty of flood events. First, the binary segmentation threshold for the water extraction was determined by the maximum interclass variance algorithm, and accordingly, the coarse maps of spatiotemporal distribution of water body were generated from Sentinel-1A time series. Second, the frequency of candidate water pixels was computed through these coarse maps. The initial fine water map in the temporal sequence was refined by the water map retrieved by the NDWI from the Sentinel-2 optical image. In view of the distinctive inundation characteristics of different frequency areas, a differentiated sequential anomaly detection strategy was proposed to identify the flooded areas and the seasonal water areas. The change feature maps of backscattering coefficient were established by the Sentinel-1A time series. Euclidean distance was used to detect the sequential breakpoint in low-frequency water-covered area, which is regarded as the flooding disaster area with high disturbance intensity and short flooding time. Temporal Z-score was introduced to detect the breakpoint in high-frequency water-covered area, which is considered the continuous inundating area.Result We automatically, rapidly, and effectively detected the flood events in the middle and lower reaches of the Yangtze River Region between May and October in 2020 and monitored the inundated area change during flooding, using the proposed method deployed on the GEE. The results exhibited that the flooding areas, such as the middle reaches of the Huaihe River, the lower reaches of the Xinyi River, and the Chaohu Lake Basin, and displayed the max extents of seasonal water, such as Poyang Lake, Dongting Lake, and Shijiu Lake during extreme weather with serious precipitation. The storage, diversion, and release of the flood water in the Yangtze River Plain demonstrated a lower loss manner due to the function of the free Yangtze-linking lakes, such as Poyang Lake and Dongting Lake. In the Huaihe River Basin, the extreme rainy weather is more likely to result in flood disasters and causes public damage. The flood processing in the rainy season was described in a spatial fashion, and the regional differentiation of inundation patterns was revealed through the spatiotemporal information of the middle and lower reaches of the Yangtze River Region. The proposed rapid and robust flood monitoring method is greatly practical and important to the dynamic monitoring of flood situation, quantitative assessment of flood disaster, and rapid early warning response.关键词：flooding monitoring;water mapping;SAR time series;Google Earth Engine;Middle and Lower Reaches of the Yangtze River Region;Sentinel-1A- 1720
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发布时间：2021-10-21 -
摘要：River networks play an important role in the terrestrial water. They have become a hotspot in river remotely sensed studies on using remotely sensed imagery to monitor river dynamic changes. Recent development of CubeSat satellite, such as PlanetScope, allows monitoring of river networks at high spatial and high temporal resolution by providing near-daily revisit time imagery at 3 m spatial resolution. We selected the Yangtze headwaters (Tongtian river basin, ~227 km²) located in Tibetan Plateau as the study area. Five CubeSat images from May to October in 2017 were selected to extract river networks at 3 m resolution by enhancing the river cross sectional and longitudinal features, in order to monitor dynamic changes of in river networks at high-spatial resolution. In addition, we compared the 3 m CubeSat river networks with 30 m Landsat 8 and 10 m Sentinel-2 river networks, and the five existing hydrography data products including GRWL, GSW, FROM-GLC, OpenStreetMap, and HydroSHEDS. We concluded that: (1) Rivers in the study area begin to develop in May with drainage density of 0.38 km-1. July and August are the wet seasons, and the drainage density reaches the peak (0.61 km-1). In September, rivers reach the mean discharge with drainage density of 0.53 km-1, and then the rivers degrade gradually with drainage density of 0.37 km-1 and begin to freeze in October. (2) The high spatial resolution CubeSat river networks include more small rivers (3—30 m wide), and the CubeSat river length is 1.6 and 1.3 times larger than Landsat 8 and Sentinel-2 river networks, respectively. (3) The drainage density of CubeSat river networks is 2.9 to 12.4 times larger than existing hydrography data products, thereby compensating for any lack in the spatial and temporal resolution of the existing river network products.关键词：river network;remote sensing information extraction;dynamic monitoring;CubeSat;Tibetan Plateau- 953
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发布时间：2021-10-21
Remote Sensing Applications
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