最新刊期

    10 2023
    封面故事

      Common Technology of Historical data Re-Calibration of Domestic Remote Sensing Satellite

    • HU Xiuqing,WANG Ling,ZHANG Peng,XU Na,QI Chengli,XU Hanlie,HE Xingwei,HE Yuqing,CHEN Lin,SUN Ling,LU Naimeng
      Vol. 27, Issue 10, Pages: 2229-2251(2023) DOI: 10.11834/jrs.20233359
      Overview of historical data retrospective calibration for space-borne optical payloads
      摘要:After more than thirty years of effort, China’s meteorological, land, ocean, and environmental disaster reduction constellations have formed a systematic and operational development trend. Domestically developed multi-series remote sensing satellites have accumulated long-term continuous observation data, which provide possibilities for climate change research and environmental change detection.To unleash the enormous potential of satellite observation historical data in climate change research, it is necessary to address the high-precision radiometric calibration problem of remote sensing payloads between different satellites and throughout the entire lifespan of a single satellite. This requires the establishment of a unified historical radiometric reference and a refined recalibration model, ensuring the comparability of observation data from different instruments and different time periods.This article provides an overview of the methods and approaches for historical data recalibration of spaceborne optical remote sensing instruments. It includes the development of radiometric reference models based on Earth-stable targets and celestial bodies such as the Moon, as well as the reconstruction of fine algorithm models for recalibrating long sequences of historical data. The paper systematically introduces how to construct radiometric reference models using Earth-stable targets such as deserts, ice and snow, DCC, as well as typical reference instruments and benchmark data evaluation for cross-calibration and benchmark traceability.This article also reviews several key aspects that need to be considered when reconstructing recalibration models for optical payload historical data. This includes the influence mechanisms of stray light, ghosting, polarization, and other factors affecting radiometric calibration uncertainty. It discusses the establishment of short-period fluctuation correction models and long-period decay models for instrument response through full-link simulation of instrument calibration, fine reconstruction of key calibration parameters, and the construction of fine calibration mechanism models related to spatial, spectral, thermal, and orbital elements. The article explores multi-objective tracking of instrument response, calculation of long sequence wide dynamic range calibration coefficients, and the application of computational intelligence for relative calibration techniques. This allows for automatic recalibration and long-period decay correction of satellite historical data, as well as the establishment of radiation response and decay characteristic models within the lifespan of a single instrument.By providing the latest research progress on historical radiometric references, recalibration models, and analysis of calibration mechanisms, this article offers a systematic approach to the recalibration of China’s historical remote sensing data. It lays the methodological foundation for further improving the long-term calibration quality and reliability of remote sensing data.  
      关键词:retrospective calibration;radiometric reference;fine recalibration model;calibration mechanism model;instrumental degradation model   
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      发布时间:2023-12-05
    • GU Songyan,GOU Yang,XIE Xinxin,HE Jieying,DOU Fangli,WU Qiong,WANG Zhenzhan,ZHANG Shengwei,AN Dawei,WU Shengli,ZHANG Peng
      Vol. 27, Issue 10, Pages: 2252-2269(2023) DOI: 10.11834/jrs.20221436
      Recalibration of the FY-3 microwave payload historical data records
      摘要:This study focuses on the latest recalibration results of the historical data of domestic satellite microwave payload, which is a national key research and development plan, to apply the long-time passive microwave historical data from Chinese satellites to the study of climate and climate change. Chinese Feng Yun 3 series satellites (FY-3) have accumulated historical microwave remote sensing data of microwave radiometer imager (MWRI), microwave temperature sounder (MWTS), and microwave humidity sounder (MWHS) for more than 13 years from May 27, 2008. We have also completed the launch and operation of four satellites in two batches. During this period, the microwave payload data of FY-3 satellite played an active role in disaster prevention and mitigation and numerical weather forecast assimilation.Based on the review of the international satellite borne microwave radiometer historical data recalibration technology, the characteristics of the microwave load of FY-3 satellite is introduced, the common technologies of operational radiation calibration and historical data recalibration are summarized, and the microwave load of the FY-3 satellite that passes through the entire link radiation transfer simulation of the instrument system is expounded. After constructing the radiation correction model under special conditions in orbit, the technical route of rescaling historical data to eliminate the radiation difference between generations based on the international reference load, the basic operational status of the FY-3 microwave payload in orbit, and the research results of historical data recalibration are introduced.The long-time sequence L1 scientific dataset of FY-3 microwave generated by recalibration is cross compared with similar international loads. Results show that the RMSE of long-time series brightness temperature data of oxygen absorption channel is 0.77 k, and the standard deviation is 0.28 k. After rescaling the water vapor absorption channel, the optimal RMSE of the long-time series data is 0.80 k, and the standard deviation is 0.20 k. In the window channel, considering the 23.8 ghz V polarization channel as an example, the RMSE of the long-time series data after re calibration is the best up to 1.29 k, and the standard deviation is 0.15k. After calibration, the maximum RMSE shall not exceed 1.5 k.Conclusion The microwave load of the FY-3 satellite has very good radiation consistency with the reference load. The recalibration results of the historical data of the FY-3 satellite microwave load provide basic support for the subsequent establishment of the FY-3 satellite microwave load basic climate data set (FCDR), Climate Data Set (CDR), and climate variable data set (ECV).  
      关键词:FY-3 meteorological satellite;microwave atmosphere detector;microwave imager;historical data re calibration;cross calibration   
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      发布时间:2023-12-05
    • WANG Ling,HU Xiuqing,XU Na,CHEN Lin,ZHANG Peng,XU Hanlie
      Vol. 27, Issue 10, Pages: 2270-2282(2023) DOI: 10.11834/jrs.20221587
      Construction of directional reflectance reference model for desert stable earth targets
      摘要:Accurate and consistent calibration for long-term satellite remote sensing data is critical to accurately estimate multi-decadal climate variability. However, for the historical optical satellite sensors, the lack of or limited number of synchronous in situ observation of surface Bidirectional Reflectance Distribution Function (BRDF) model data is the main difficulty to recalibrate their radiance products. This study aims to build a surface directional reflectance reference model for some typical stable earth targets worldwide, providing a uniform surface reflectance reference for the historical remote sensing satellites to perform a consistent recalibration of their long-term TOA radiance products.The long-term data products from MODIS satellite instrument, well known for its high calibration accuracy and stability, are used to establish the surface directional reflectance reference model for the selected stable earth targets. Specifically, for the desert sites, the MODIS surface BRDF products (MCD43A1) from 2008 to 2012 are used to build a monthly climatology of the BRDF parameters as the surface directional reflectance reference. Then, independent MODIS products, i.e., the data time is different from that used in the model construction, are applied to verify the accuracy of the established directional reflectance reference model. Finally, to check the applicability of this model in the radiometric calibration of satellite instruments, it was used to carry out calibration experiments on the Visible Infrared Radiometer (VIRR) on the FY-3C, and compared with the calibration results obtained based on real-time MODIS BRDF products.The uncertainty estimation of the surface directional reflectance reference model over desert sites shows that the model uncertainty of foreign desert targets is lower than that of domestic desert targets. The reference model uncertainty of foreign targets is below 3%, and the domestic desert sites are below 4% (except TKLM_3). The model accuracy verification of the radiometric reference model shows that among the 13 foreign desert targets, except Tinga_Tingana in Australia, the relative errors are basically within ±3%, and that in Libya 4 can be less then ±1%. Six domestic desert sites, i.e., BDJL_1, BDJL_2, TNGR_1, TNGR_2, WULBHE, and LBPO_W, can achieve a sound accuracy of within ±3%, which is comparable to the stable earth targets frequently used by the international research. The radiometric calibration test on FY-3C VIRR shows that using the directional reflectance reference model of the stable target is in good agreement with the radiometric calibration results based on the real-time MODIS BRDF product, and the difference between the two calibration results is very small, i.e., the average relative bias is basically within ±0.6%.The results indicate that established directional reflectance reference model over the stable earth targets can be used in the application of radiometric calibration of the optical satellite instruments and can solve the problem of consistent recalibration of historical data from domestic optical satellite instruments.  
      关键词:remote sensing instrument;radiometric calibration;reflectance;BRDF;stable targets;MODIS   
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      发布时间:2023-12-05
    • WANG Zhenzhan,XIAO Yuwei,WANG Kexin,ZHANG Shengwei
      Vol. 27, Issue 10, Pages: 2283-2294(2023) DOI: 10.11834/jrs.20221446
      Recalibration Model of MWHTS’ historical data onboard FY-3C Satellite
      摘要:The microwave radiation data of the earth’s surface and atmosphere observed by the spaceborne microwave radiometer are a basic source for numerical weather prediction and climate research. Certain bias exists between the data of different or the same radiometers over a long period of time due to the difference in the response characteristics and calibration absolute reference between each sounder and variation of the on-orbit working conditions. If these biases are not corrected, then they will have significant implications for long time series applications (such as climate studies) and may even lead to erroneous results. In addition, absolute calibration of onboard data cannot be performed because the absolute reference for calibration is unobtainable at present. Therefore, other relative calibration methods should be used to evaluate the stability and variation characteristics of the radiometer. In this paper, a correction model for the calibration biases of the microwave humidity sounder is established, considering the principle of system responses and on-orbit calibration, which is also called re-calibration methods, based on OMB technique (observed brightness temperature (O) minus simulated brightness temperature (B)). Using the re-calibration methods, L1 level observation data of the FY-3C microwave humidity sounder were analyzed and the re-calibration coefficients were calculated. Then, the re-calibration coefficients were verified using two data sets. The residual and validation results show that the time series of the recalibration findings is stable, and some abnormal fluctuations in the original OMB biases have been well corrected after re-calibration, indicating that the re-calibration methods are valid. The method is based on the system responses of microwave humidity sounder. Therefore, it is also applicable to other FY-3 series satellite microwave humidity sounders for calibration bias correction. When using the same Radiative Transfer (RT) model, this re-calibration methods can achieve consistent calibration of FY-3 series satellite microwave humidity sounder data.  
      关键词:FY-3C microwave humidity sounders;re-calibration methods;system responses;consistency of satellite data   
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      发布时间:2023-12-05
    • WANG Yang,NIU Xinhua,ZHANG E,CHEN Shuaishuai,HU Xiuqing,ZHANG Dongdong,WANG Xianghua,XIONG Qianqian
      Vol. 27, Issue 10, Pages: 2295-2306(2023) DOI: 10.11834/jrs.20231599
      Uniformity correction of radiance responsivity in vacuum infrared calibration for FY-3B/VIRR
      摘要:In vacuum infrared calibration, factors, such as test contamination and non-uniformity of instrument temperature, cause response changes for scanning radiometer system, resulting in inaccurate calibration coefficients and platinum resistance conversion coefficients for each channel. The non-uniformity of the responsivity is corrected using the stability of the blackbody as a reference source in the constant temperature mode and the responsivity invariance in the single calibration state for the infrared detection system. The transfer algorithm of the consistent response from the internal to external blackbody measurement for the infrared channels is established by the data of variable temperature test for the surface blackbody and on-board blackbody in the infrared calibration. For the prelaunch calibration data of FY-3B visible infrared radiometer (VIRR), the non-uniformity of system responsivity is corrected during the calibration. At the temperature change stage, the uniformity of the correction signal for the surface blackbody between the heating-up and cooling-down stages is better than 0.7 digital number. In the radiance transfer stage, the uniformity of the correction signal for the on-board blackbody is better than 0.3 digital number in the reference condition. The difference between the correction method and other traditional methods in calculating the equivalent blackbody temperature of the on-board blackbody is analyzed. This algorithm ensures the transfer accuracy from the space-based radiance standard to the infrared detection system and on-board blackbody, and the technical support is provided to effectively improve the accuracy of vacuum infrared calibration.  
      关键词:remote sensing;infrared calibration;stability;scanning radiometer;responsivity;uniformity   
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      发布时间:2023-12-05
    • XU Hannlie,HU Xiuqing,XU Na,ZHANG Liyang,QI Chengli
      Vol. 27, Issue 10, Pages: 2307-2317(2023) DOI: 10.11834/jrs.20231589
      Construction and validation of FY-3C/VIRR infrared window channel refinement re-calibration model
      摘要:FY-3 visible infrared scanning radiometer (FY-3/VIRR) has provided Earth-observation data in orbit for more than 10 years since the launch of FY-3A in 2008. These data are important for atmospheric, surface, and environmental product inversion, weather, and climate change research. In this study, the calibration bias characteristics of FY-3/VIRR thermal infrared channel were analyzed, and the main sources of error were preliminarily identified in combination with the operational calibration model in day-night difference and seasonal variation of the operational calibration bias. In addition, the on-board calibration model and the on-board blackbody radiation model were optimized to construct the fine re-calibration model of the thermal infrared channel. In the linear calibration model plus nonlinear correction adopted by the FY-3/VIRR infrared channel, the quadratic term is related to the calibrated blackbody radiation. When the satellite is in orbit, the temperature change of the blackbody causes change in the quadratic term coefficient. As a result, the shape of the quadratic response of the infrared channel is changed. When the blackbody temperature changes, the quadratic term coefficient is changed, thereby introducing calibration deviation. In addition, the blackbody radiation on the infrared channel is calculated using the equivalent brightness temperature coefficient of the blackbody obtained from the pre-launch test. In fact, the radiation in the blackbody observation path is reflected in a set of polynomial fitting coefficients. This fitting process is based on the pre-launch vacuum test, and the on-orbit application results in calibration deviation. The FY-3/VIRR re-calibration model of thermal infrared channel directly uses quadratic calibration equation for on-board calibration model and considers the influence of instrument environmental radiation. The blackbody radiation model on the planet is reconstructed by considering the blackbody temperature as the proxy ambient temperature given that traditional instruments lack temperature measurement points on the planet. Based on the matching samples of Simultaneous Nadir Observation (SNO) recommended by GSICS, The parameters of the refined re-calibration model were determined using the internationally recognized high-precision Infrared Atmospheric Sounding Interferometer (IASI) as the reference instrument. The results show that the refined re-calibration model has a significant correction effect on the systematic deviation, diurnal difference, and seasonal variation of the operational calibration model, and the monthly mean deviation is within ±0.3K after re-calibration using the refined re-calibration model. In 2018, for example, the difference between day and night in winter decreased from approximately 0.4 K of the service calibration to less than 0.1 K.  
      关键词:Visible and Infra-Red Radiometer (VIRR);infrared calibration;on-board calibration;refinement calibration model;re-calibration;onboard blackbody radiance model   
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      发布时间:2023-12-05
    • LIU Mingxu,ZHANG Shengwei,HE Jieying
      Vol. 27, Issue 10, Pages: 2318-2326(2023) DOI: 10.11834/jrs.20221660
      Striping noise analysis and mitigation for microwave humidity sounder
      摘要:Noise analysis and mitigation play an important role in meteorological satellite data processing. This study is based on the idea of noise mitigation by using Principal Component Analysis (PCA), Ensemble Empirical Mode Decomposition (EEMD) algorithm, and improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN). The modified method is used to observe data of the microwave humidity sounder (MWHS-2) of the Fengyun-3C and 3D satellites (FY-3C, FY-3D) to analyze the striping noise in its observed brightness temperature. In this study, the effectiveness of this method for MWHS-2 data is confirmed, and a performance analysis of the improved method for data processing and noise mitigation is conducted.The striping noise has a very high correlation with scan line; thus, using PCA can not only effectively isolate the noise-related principal components, but also reduce the dimension of the processed data. When the noise containing principal components is extracted, the empirical mode decomposition method can be used to adaptively separate each component into multiple modes with different frequencies. The noise can be easily separated from the signal by a method that calculates and compares the average period and energy density by using the differences in energy between noise and signal modes. Finally, the remaining modes are combined to reconstruct the principal components, which reconstruct the observed brightness temperature data.When this method is applied to the MWHS-2 data, we used the hourly global reanalysis data of ERA5 with RTTOV model to generate the simulated brightness temperature data and compared with the observed brightness temperature before and after processing. The result shows that the algorithm successfully extracts the striping noise in the signal, and the noise histogram exhibits a Gaussian distribution. The noise mitigation effect between the original EEMD algorithm and various improved mode decomposition methods is compared, and the results show that the use of ICEEMDAN can effectively avoid some problems in EEMD, such as the residue noise, and can reduce reconstruction errors. Numerical analysis results show that compared with the EEMD method, this improved method further reduces the variance by 0.020 K2, and the Signal-to-Noise Ratio (SNR) increases by 0.031 dB, which further improves the noise mitigation capability of the algorithm.PCA combined with ensemble empirical mode decomposition can effectively mitigate the striping noise. Although the mode decomposition method is affected by some of its own properties and has certain limitations in accuracy, it has a more convenient operation and higher adaptability. Moreover, the test result shows that this method can achieve satisfactory results. The improvement using ICEEMDAN and calculating the energy density with average period can also be helpful to noise analysis and mitigation and can enhance the reconstruction accuracy. This condition may have certain value for the further improvement of noise reduction algorithm and may improve the accuracy of meteorological data analysis and forecasting.  
      关键词:FY-3;MWHS-2;microwave radiation measurement;data processing;noise mitigation;PCA;empirical mode decomposition;striping noise   
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      发布时间:2023-12-05
    • WANG Zhenzhan,XIAO Yuwei,ZHANG Shengwei,HE Jieying,GU Songyan
      Vol. 27, Issue 10, Pages: 2327-2336(2023) DOI: 10.11834/jrs.20221447
      Analysis on applicability of nonlinearity coefficients derived from prelaunch calibration tests to onboard calibration of Microwave Humidity Sounder (MWHS-Ⅲ) on FY-3E satellite
      摘要:Nonlinearity is one of the most important errors in calibrating a microwave radiometer. It cannot be corrected in orbit through direct measurements, and its correction usually uses a set of coefficients derived from prelaunch calibration tests, namely, thermal vacuum test. The main difference between prelaunch and on-board calibration of a microwave radiometer is that of the cold calibration target used in two-point calibration. On board calibration usually uses the cold sky, which is also called cosmic background temperature of 2.7 K, as the lower end in the response of a microwave radiometer, whereas in the prelaunch calibration, a blackbody at a temperature between 80 K and 100 K is used in the calibration practice. Therefore, the applicability of the nonlinear coefficients derived from the prelaunch calibration test for on-board calibration is a long-standing concern that has never been validated. In this study, a special program of prelaunch calibration was designed, adding a validation blackbody target, which works at ambient temperature of 180—200 K in the thermal vacuum chamber, in addition to the traditional cold blackbody target, a warm blackbody target, and a varied-temperature blackbody target. This validation target provides an opportunity to compute nonlinear coefficients directly through three-point calibration and to evaluate the errors in applying the nonlinear coefficients by the traditional calibration method. Furthermore, a novel method is invented through extrapolating the measurements to the cold sky temperature by the equation of three-point calibration during a scan. It serves as a virtual on-board calibration target to calibrate the radiometer and to produce nonlinear coefficients combined with three other calibration targets. The nonlinear coefficients of the traditional and novel methods are compared, and the two groups of nonlinearities are applied to the same data sets. Thus, the errors in applying the nonlinear coefficients by the traditional calibration method can be evaluated. The results show a deviation between the two group of nonlinear coefficients; the greater absolute value of the nonlinear coefficients indicates greater error. The nonlinear coefficients of the traditional and novel methods are compared, and discrepancies are found in applying the two groups of nonlinearities to the same data sets. The finding implies that errors exist in the prelaunch coefficients when using the traditional method. The novel method simplifies the procedure of prelaunch calibration and improves the accuracy of nonlinear coefficients using for on-board calibration.  
      关键词:Microwave radiometer calibration;FY-3E Microwave Humidity Sounder;Prelaunch calibration;Nonlinearity;On-board calibration   
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      发布时间:2023-12-05
    • LI Guorong,HE Yuqing,HU Xiuqing,WANG Junwei
      Vol. 27, Issue 10, Pages: 2337-2349(2023) DOI: 10.11834/jrs.20221585
      Cross calibration technology for the same platform of FY-3 optical imager based on IR-MAD no-change pixels
      摘要:During the operation of the satellite in orbit, the radiation detection performance and stability of the sensor changes, and the accuracy of the acquired radiation observation signal decreases. Accurate on-orbit calibration of sensors is crucial to ensure the validity of their data products. The stable target site based cross calibration method is limited by the pseudo-invariant target, which is manually selected by the satellite synchronous transit and has simple spectral characteristics. Thus, multi-frequency and high-precision cross calibration are difficult to carry out.MethodThis study proposes a cross calibration method based on iterative reweighted multivariate alteration detection (IR-MAD). Taking the FY-3B medium resolution spectral imager (MERSI) as the reference, the cross-calibration of visible and infrared radiometer (VIRR) on the same platform is studied. Initially, the IR-MAD algorithm linearly combines the simultaneous multi-channel images of the two sensors to construct canonical correlation variables and performs canonical correlation analysis to eliminate the correlation between different channels of a single sensor and unmatched channels of different sensors. Then, through multiple probability reweighting iterations, the IR-MAD algorithm can automatically identify the no-change pixels (NCPs) in the same phase scene of the two sensors. The radiance of the NCPs has the largest linear correlation between VIRR and MERSI matching channels. The cross-calibration coefficients can be obtained using a linear regression model based on the apparent reflectance information of the NCPs by correcting the spectral differences between matched channels of two sensors. This study implements this procedure with data from Northwest China region and North Africa region and compares it with the calibration results obtained from other related studies.ResultExperimental results show that the proposed method is consistent with the operational calibration and the Dunhuang desert site calibration. The relative deviation of the radiometric information between VIRR and MERSI after calibration exceeds 2%. The cross-calibration results of IR-MAD obtained in northwest China and north Africa are consistent (most channels are better than 2%), verifying the generalization and stability of this method. The long-time sequence results show a correlation between the channel response decay trend and wavelength. In general, the shorter wavelength indicates a more serious decay. In addition, some seasonal fluctuations are found in the relative calibration slope time series of near-infrared and shortwave infrared channels.ConclusionThis method can automatically and efficiently select pseudo-invariant targets in satellite observation scenes and realize high precision cross calibration based on the selected pseudo-invariant targets. It is applicable to the re-calibration of historical satellite data and the relative response monitoring of sensors on the same platform. Our future work will focus on the application of algorithms in different platforms and nonlinear problems.  
      关键词:visible and infra-red radiometer (VIRR);medium resolution spectral imager (MERSI);IR-MAD;no-change pixels;cross calibration   
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      发布时间:2023-12-05
    • WANG Wei,WANG Lijuan,GUO Ni,HU Xiuqing,WANG Ling
      Vol. 27, Issue 10, Pages: 2350-2362(2023) DOI: 10.11834/jrs.20231867
      Selection and evaluation of pseudo-invariant calibration sites in the Badain Jaran and Tengger Desert of China based on Sentinel satellite data
      摘要:The selection of ground sites conforming to the radiometric calibration of long time series remote sensing data is greatly important to establish a unified radiometric calibration reference standard, improve the accuracy of satellite radiometric calibration, and promote the application of quantified products. In this study, Sentinel-2 A/B MSI remote sensing data covering the entire study from November 2018 to October 2021 were used to combine the coefficient of variation (CV) index and the Getis-Ord Gi* spatial clustering method to comprehensively evaluate the study area in terms of spatial and temporal stability and spatial consistency and to select sites that could be used for radiometric calibration in the visible and short-wave infrared bands of long time series meteorological satellite data. Results showed that: (1) the PICS with spatial and temporal stability and spatial uniformity in the study area are mainly located in the western and northern parts of the Badain Jaran Desert and Tengger Desert, as well as the connection zone between the southern edge of the desert and the Zhongwei and Hexi Corridor of China. (2) This study reduces the uncertainty of site evaluation results by improving the site selection method. The average spatio-temporal coefficient of variation for the 16 sites selected was only 1.59%. (3) The CVSR_b1-12_avg of TNGR_1 and TNGR_3 sites in the study area is ≤1.19%, which is better than the evaluation results of similar international sites. These sites have an average number of cloud-free days close to 300 d throughout the year, with the attributes of large spatial area, good spatial and temporal stability, homogeneous surface, dry and clean atmosphere, and few cloudy and rainy days. Therefore, these sites provide relatively rich brightness quasi-invariant calibration sites for conducting historical meteorological satellite data recalibration studies.  
      关键词:desert;calibration field;Sentinel-2;spatial clustering;coefficient of variation   
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      发布时间:2023-12-05

      Research Progress

    • HE Ze,LI Shihua
      Vol. 27, Issue 10, Pages: 2363-2382(2023) DOI: 10.11834/jrs.20221701
      Research progress on radar remote sensing for rice growth monitoring
      摘要:Rice is one of the most productive food crops of Asian countries. Timely and accurate access to rice cultivation information can provide professional support for farming management and agricultural policy-making. Space-borne Synthetic Aperture Radar (SAR) imaging is free from meteorological interference and can sensitively respond to rice plant development and soil moisture changes. Therefore, satellites equipped with various SAR sensors are important data sources for rice growth monitoring in cloudy and foggy areas. The research progress of microwave remote sensing in rice growth monitoring has been made on all fronts, but the technical evolution and relationship of different research topics are complex and relatively confusing.The development history, current focus, and innovation prospect of rice radar remote sensing should be reviewed and analyzed, considering the key scientific problems and main experimental approaches. Based on the collation and statistics of relevant literature in the recent 30 years, the key problems of rice radar remote sensing are summarized into three study focuses: planting area identification, biophysical parameter retrieval, and phenology and cropping intensity recognition. Then, the technical methods are summarized into three research strategies: mathematical and physical analysis, machine learning, and multisource data synergism.Specifically, rice planting area identification methods are divided into four schemes: time domain change analysis, machine learning, object-oriented classification, and multisource data synergism. Rice biophysical parameter retrieval methods are divided into five models: empirical model, physical model, semi-empirical model, data assimilation, and multi-source data synergism. Rice phenology and cropping intensity recognition methods are divided into two algorithms: time-series feature detection and multi-temporal machine learning. From the perspective of data attributes and model structure, the theoretical basis and applicable conditions of different methods are introduced, and their advantages and limitations are explained. Finally, in view of the rapid advancement of SAR imaging capability and computer science, the future research issues are discussed.Therefore, the three difficult points to be solved in rice radar remote sensing monitoring are as follows: (1) fragmented farmlands and fluctuant terrain; (2) diverse cultivation conditions, and (3) asynchronous phenology and complex interplant. The future study should focus on the following: (1) high temporal-spatial resolution of rice planting area identification relying on less prior information; (2) dynamic retrieval of rice biophysical parameters balancing model efficiency and accuracy; (3) automatic recognition of rice phenology and cropping intensity combining plant growth mechanism and time series observation. The improvement of these research topics profoundly promotes the practical application of rice radar remote sensing.  
      关键词:SAR;rice;Planting area;biophysical parameters;phenology;cropping intensity   
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      发布时间:2023-12-05

      Models and Methods

    • XIAO Rulin,GAO Jixi,LIU Aijun,HOU Peng,ZHANG Wenguo,YANG Yong,LI Yunbao,FU Zhuo,JIN Chuanping,YANG Xu,ZHENG Shuhua,YIN Shoujing
      Vol. 27, Issue 10, Pages: 2383-2394(2023) DOI: 10.11834/jrs.20222099
      Remote sensing monitoring method of livestock in grassland based on multi-scale features and multi-models fusion
      摘要:China is a large country of grassland and animal husbandry. Overloading and overgrazing is one of the main causes of grassland degradation in China. To protect the grassland, it is necessary to precisely monitoring livestock carrying capacity, which is the key to evaluation and control grass-livestock balance. However, traditional method of livestock carrying capacity such as hierarchical statistics, sampling field survey and online camera monitoring is whether time-consuming, labor-intensive, costly or poor quality. So it is very urgent to find a kind of efficient and precise monitoring method of livestock carrying capacity in grassland.To achieve this goal, this research proposes an efficient and precise monitoring method of the livestock in grassland by using of sub-meter resolution satellite image. The method not only fuses multi-scale features of livestock in sub-meter resolution satellite image such as “blob feature”、“flock feature”、“moving feature” , but also integrates deep learning technology and object oriented recognition technology. Firstly, considering that the livestock in satellite image is a kind of small (tiny) target, it uses kinds of image enhancement method such as bi-lateral filtering and Laplace of Gaussian (LoG) operator to enhance the weak livestock signal successfully. Secondly, in consideration of “flock feature” of livestock flock, it use a kind of “livestock flock detection model” based on deep learning technology to get the rough distribution area of livestock flocks. Thirdly, in consideration of “blob feature” and “moving feature” of livestock, it use a kind of “livestock blob detection method” based on LoG Gradient Difference and object oriented recognition technology to get the possible livestock blobs. Finally, by integrating the detecting result of both livestock flocks and livestock blobs, it uses the livestock blobs result to enhance and verify the livestock flocks result, and the enhanced and verified livestock flocks and the livestock blobs within them is finally get by using some simple manually revising work.Through an experiment in Xilingol grassland, it is found that the approach has good effect on livestock flock detection: with positive detection rate about 0.802 and false detection rate about 0.244, especially as to big livestock flock, the positive detection rate is up to 0.937, the false detection rate is low to 0.072.It is very helpful for the monitoring and supervision of livestock flock in grassland, and can also provide reference for remote sensing monitoring of other “small (tiny) targets”. It is of great significance both in terms of technological innovation and business application. It makes a litter effort in promoting the livestock satellite remote sensing monitoring into an intuitive and fine monitoring era-“Number-Counting Era”.  
      关键词:livestock;remote sensing;livestock carrying;grassland;small (tiny) target   
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    • WU Kai,JI Ce,LUO Lei,WANG Xinyuan
      Vol. 27, Issue 10, Pages: 2395-2405(2023) DOI: 10.11834/jrs.20210553
      Comprehensive analysis of wide-area observation development for solid earth tides by space technology
      摘要:The observation and research for solid earth tides (SETs), which have always been the focus of earth science, can provide an important basis for understanding the structure of the earth’s interior. However, unavoidable limitations exist when observations are operated to capture the global-scale SET information only with ground instruments. At present, the distribution of ground stations is sparse and uneven. Moreover, the observations of different stations are affected by the local environment. Thus, achieving large-scale, time-consistent, and space-continuous SET observation is difficult. SET observation must rely on the development of space technology. In this study, the temporal and spatial distribution characteristics of the SET are obtained using the theoretical model. This model considers the earth’s ellipticity, rotation, inelasticity of the mantle, nonhydrostatic equilibrium, and lateral inhomogeneity. Combined with the lunar ephemeris, the space–time coordinate system and the influence factors, such as precession, polar shift, nutation, and lunar libration, are considered. After the optimization of the model accuracy and efficiency, the theoretical model of the millimeter accuracy is obtained. Based on these characteristics, the macroscopic observation potential of space technology is discussed. It mainly includes the wide-area displacement monitoring ability by combining InSAR technology and ranging technologies, such as GNSS, VLBI, and SLR. The time-varying gravity acquisition ability solved from the gravity satellite data is also included. According to the requirements of InSAR technology on time baseline and swath width, three kinds of platforms, namely, low Earth orbit satellite, inclined geosynchronous satellite, and moon-based platform, are simulated. The advantages and disadvantages of various platforms are also analyzed. Results showed that the network of new gravity satellites and the new conceptual platform of remote sensing have the macro-observation potential for SETs. Compared with inclined geosynchronous satellite orbit, the moon-based platform can easily design the SAR system. The moon-based SAR has long service life and small orbit error. Given the change in declination, the moon-based platform can realize global continuous angle observation. It can also extract high-precision horizontal displacement from the deformation in line of sight. The multiangle observation area of the inclined geosynchronous satellite orbit is only one-third of that of the moon-based platform. Moreover, the land area corresponding to the ascending and descending nodes for inclined geosynchronous satellites has an inherent blind area. As the main force source of SETs, the moon can be used to separate the coupled solar and lunar tides. Given the observation effect and platform characteristics, the moon-based platform can become the best platform for earth tide observation if a series of key problems related to lunar landing, such as energy supply, temperature control, data transmission, material transportation, and dust environment, are solved. Given the cooperation of multiple platforms, the macro-observation of the earth tide in most areas can be realized with a temporal resolution lower than 1 day. Moreover, space technology development can supplement the spatial decorrelation period of the moon-based platform and realize complementary advantages.  
      关键词:solid earth tides;space technology;orbit ephemeris;wide-area observation;earth science   
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    • LI Sihui,DONG Jie,ZHANG Lu,LIAO Mingsheng
      Vol. 27, Issue 10, Pages: 2406-2417(2023) DOI: 10.11834/jrs.20221736
      Time-series InSAR tropospheric atmospheric delay correction based on common scene stacking
      摘要:Synthetic Aperture Radar Interferometry (InSAR) technology has the advantages of high resolution, high precision, and wide coverage; it has been widely used in the field of ground deformation monitoring. However, the tropospheric atmospheric delay has always been one of the main factors limiting the accuracy of deformation measurement of InSAR. Given that the interferograms sharing a common scene contain the same contribution of atmospheric delay, the Common Scene Stacking (CSS) method uses simple summation to estimate the atmospheric delay phase of the common date and improves the estimation accuracy through iterations with the advantages of simple implementation and high computational efficiency. The CSS method estimates the atmospheric delay phase point by point, thereby introducing more noise. The estimated atmospheric delay phase by CSS is spatially low-pass filtered in this study given the characteristics of the atmospheric delay phase as a low-frequency component in the spatial dimension, and the phase unwrapping and CSS atmospheric delay phase estimation are iterated to improve the deformation estimation results. The influence of different parameters on the tropospheric atmospheric delay correction results of CSS is analyzed using simulated data. The results show that satisfactory results can be obtained after five iterations. Then, this method is applied to real SAR data. The comparison of the results of different time windows indicates that using a larger time window smoothens the time series of stable points. However, at the same time, it leads to distortion at both ends of the time series of deformation points. The proposed method is compared with spatio-temporal filtering, GACOS, and IPTA methods, and the correction result of the CSS method is found to be significantly better than that of spatio-temporal filtering and GACOS. After correction by the CSS method, the spatial phase standard deviation is reduced by 62% on the average, and the time-series standard deviation of the stable points is reduced by 58% on the average. Compared with IPTA, the CSS method can obtain similar results and improve the problem of underestimation of deformation. On this basis, the applicability of the CSS method for the vertically stratified tropospheric delay is discussed. The simulation results show that the CSS method can only correct the turbulent mixing delay, but cannot effectively remove the vertically stratified delay. Therefore, the CSS method is unsuitable for the steep mountainous areas, where the vertically stratified component is evident and the atmospheric delay presents a seasonal oscillation trend.  
      关键词:time-series InSAR;tropospheric atmospheric delay;common scene stacking;parameters setting;deformation estimation   
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    • ZHU Fang,SI Fuqi,ZHOU Haijin,ZHAO Minjie,DOU Ke,LUO Yuhan,ZHAN Kai
      Vol. 27, Issue 10, Pages: 2418-2430(2023) DOI: 10.11834/jrs.20231649
      Tangent height correction and sensitivity studies from SCIAMACHY limb scattering detection
      摘要:A tangent height retrieved by UV narrow bands (THRUNB) method is proposed to correct the tangent height from SCIAMACHY limb instrument to solve the tangent height offset caused by misalignment and other reasons in the pointing process of limb UV-VIS scattering detection instrument.In this method, a narrow band (300—305 nm) and a new engineering tangent height sequence (43, 46, 49, 52, and 55 km) are proposed to maintain measurement vectors that are more sensitive and with less dimension by analyzing the influence of the limb radiance profile shape and engineering pointing information of multiple UV bands on the tangent height correction. At the same time, the optimal estimation algorithm combined with SCIATRAN model is used to retrieve the tangent height deviation from the limb radiance.The experimental results show that the average accuracy of tangent height correction by the THRUNB method is improved by 45%, and the running time of the algorithm is reduced by 20%, compared with TRUE (tangent height retrieved by UV-B exploitation) method. Compared with SCIAMACHY L1B tangent height data provided by ESA, the average deviation of tangent height is less than 150 m. Compared with the SCIAMACHY v3.5 ozone profile product provided by University of Bremen, the average relative error of the retrieved ozone profile with tangent height correction is less than 10% in the range of 13—38 km, and the average relative error without tangent height correction is as high as 22% in the same range. At the same time, the effects of atmospheric pressure, temperature, and ozone profile on tangent height retrieved are investigated. The experimental results show that the influence of pressure and ozone on TH retrieval is positively correlated, whereas the temperature is negatively correlated. The ozone profile has the greatest influence on TH retrieval, followed by pressure and temperature.The THRUNB method can effectively reduce the tangent height offset caused by the instrument pointing information error. The accuracy of the retrieved atmospheric trace gas profile can be improved by correcting tangent height. The effective ozone and neutral density profiles are very important for tangent height correction.  
      关键词:limb radiance;tangent height;Correction;knee method;ozone profile;atmospheric remote sensing   
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    • ZHANG Tingwei,ZHANG Wangfei,ZHANG Yongxin,HUANG Guoran
      Vol. 27, Issue 10, Pages: 2431-2444(2023) DOI: 10.11834/jrs.20211335
      Bayesian analysis for uncertainty of forest height inversed by polarimetric interferometric SAR data
      摘要:Polarimetric Interferometry Synthetic Aperture Radar (PolInSAR) has been widely used in forest height inversion. Accurate evaluation of the uncertainty caused by model input parameters, model assumptions, stand structure, and site conditions can improve the accuracy of forest height inversion with PolInSAR technology. In practical application, the study on uncertainty of forest height inversion is as important as of forest height estimation methods. Quantification of global carbon stocks based on forest biomass calculations usually requires reducing the error in biomass estimates through forest height. The uncertainty of forest height may be attributed to model input parameters, model assumptions, observed data, and forest scene factors. However, comprehensive collaborative impact analyses on the uncertainty of forest height inversion results are few. On this basis, the uncertainty of forest height inversion should be studied using PolInSAR technique. We initially analyze the uncertainty caused by the input parameters of the RVoG (Random Volume over Ground) model based on the Bayesian model using the simulated L-band full PolInSAR data, and then prior knowledge (value of the forest height in the imaging) is applied to fix the extinction of the RVoG model. Subsequently,we inversed the forest height. The results show that a priori knowledge can greatly reduce canopy height uncertainties in some cases. On this basis, we combine the RVoG model and Bayesian framework, use L-band simulated PolInSAR data, and comprehensively explore the uncertainties that result from the input parameters of the RVoG model, model hypothesis, observation value, changes in forest tree species, forest density, surface properties, ground moisture content, and other factors in the process of forest height inversion. The research results indicated that: (1) prior knowledge can reduce the uncertainty of the forest height inversion (by fix the extinction value) with RVoG model and L-band PolInSAR data. (2) The forest height inversion results are greatly affected by forest tree species, and the inversion results on the uncertainty of coniferous forest are lower than those of broad-leaved forest. (3) The change in forest stand density has a significant influence on the uncertainty of the forest height inversion results. The higher density indicates lower uncertainty, especially in the pure coniferous forest. When the forest density is small, the uncertainty of the forest height retrieved by the RVoG model is large. When the forest stand density increases from 150 plants/hm² to 1200 plants/hm², the uncertainty decreased to approximately 67.5%. (4) The change in surface roughness has a positive correlation with the uncertainty of the forest height inversion results, the greater roughness indicates higher uncertainty. (5) The uncertainty caused by ground moisture content is smaller than those by the other factors and can be ignored.  
      关键词:PolInSAR;RVoG;forest height;Tree Species;Forest Stand Density;Surface roughness;Ground Moisture Content   
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