Validation of non-linear split window algorithm for land surface temperature estimation using Sentinel-3 satellite imagery: Case study; Tehran Province,Iran

In recent years, land surface temperature (LST) has become critical in environmental studies and earth science. Remote sensing technology enables spatiotemporal monitoring of this parameter on large scales. This parameter can be estimated by satellite images with at least one thermal band. Sentinel-3 SLSTR data provide LST products with a spatial resolution of 1 km. In this research, direct and indirect validation procedures were employed to evaluate the Sentinel-3 SLSTR LST products over the study area in different seasons from 2018 to 2019. The validation method was based on the absolute (direct) evaluation of this product with field data and comparison (indirect) evaluation with the MODIS LST product and the estimated LST using the non-linear split-window (NSW) algorithm. Also, two emissivity estimation methods, (1) NDVI thresholding method (NDVI-THM) and (2) classification-based emissivity method (CBEM), were used to estimate the LST using the NSW method according to the two thermal bands of Sentinel-3 images. Then, the accuracy of these methods in estimating LST was evaluated using field data and temporal changes of vegetation, which the NDVI-THM method generated better results. For indirect evaluation between the Sentinel-3 LST product, MODIS LST product, and LST estimated using NSW, four filters based on spatial and temporal separates between pairs of pixels and pixel quality were used to ensure the accuracy and consistency of the compared pairs of a pixel. In general, the accuracy results of the LST products of MODIS and Sentinel-3, and LST estimated using NSW showed a similar trend for LST changes during the seasons. With respect to the two absolute and comparative validations for the Sentinel-3 LST products, summer with the highest values of bias (?1.24 K), standard deviation (StDv = 2.66 K), and RMSE (2.43 K), and winter with the lowest ones (bias of 0.14 K, StDv of 1.13 K, and RMSE of 1.12 K) provided the worst and best results for the seasons in the period of 2018–2019, respectively. According to both absolute and comparative evaluation results, the Sentinel-3 SLSTR LST products provided reliable results for all seasons on a large temporal and spatial scale over our studied area.     

Influence of land surface parameters on the spatio-seasonal land surface temperature regime in rural West Bengal,India

The magnitude and causes of changes in the land surface temperature of rural areas have not been extensively studied. The thermal band of Landsat imagery is taken to extract winter, summer, and monsoon season land surface temperature (LST) and relate it to surface parameters over a 30-year period. From the extracted parameters constructed a prospective surface temperature (PST) model using Multivariate Adaptive Regression Splines. The Chandrabhaga river basin in West Bengal of the lateritic Rarh Tract at the Chota Nagpur Plateau fringe was chosen as the study area because it is far from urban influences, to avoid the well-known heat island effect. Over the study period, summer and winter average LST increased linearly by 0.085?°C/y and 0.016?°C/y respectively. These results were validated with air temperature (RMSE?=?x and y, respectively). Over time more of the area is in the higher temperature zones, e.g., in April 2011, 4% area exceeded >32°, whereas in 2015 this proportion reached 52%. PST models of all the seasons were moderate to highly correlate (0.57–0.87) with actual LST, showing the value of this model. It also revealed the relative importance of the regional factors. Based on this information factor management is a scientific step to restrict or minimize the temperature rise effect.     

Landsat 8地表温度产品验证与分析

Landsat系列卫星热波段具有60~120m的空间分辨率，对各种环境监测起到了重要的作用。随着Landsat系列卫星在全球范围内地表温度（land surface temperature，LST）产品的发布，其验证工作也随之展开，然而对于长时间序列的精度验证工作仍然缺乏。以黑河流域中游为研究区，利用研究区内湿地站（SD）、戈壁站（GB）和大满超级站（CJZ）三个气象站的地面测量数据对2013-2016年清晰无云的31景Landsat 8地表温度产品进行了验证与分析，并将Landsat 8地表温度产品与广泛使用的普适性单通道算法（JMS）反演结果进行了对比。结果表明，Landsat 8地表温度产品与普适性单通道算法反演结果精度均较高，在各个站点处R2均优于0.949。基于所有站点分析，Landsat 8地表温度产品精度稍高于普适性单通道算法反演结果。     

月基平台对地观测数据传输链路方案设计及分析

数据传输及处理能力是月基平台构建中的一个重要问题,如何高效准确地传输海量对地观测数据至地球供后续研究是开展月基对地观测的关键环节。通过STK和MATLAB软件联合仿真,模拟月基平台对地观测数据传输链路,首次提出适用于月基平台的下行链路通信方案:通过构建中纬度地球站、最小间隔经度值为40°的2颗中继卫星组的设计方案,可以最大程度地实现全天候、无时断的信号传输,满足下行链路接收端获取足够强度和低误码率的信息,从而保障月基平台的运行。      

Surface temperature estimation in Singhbhum Shear Zone of India using Landsat-7 ETM+ thermal infrared data

Land surface temperature (LST) is an important factor in global change studies, heat balance and as control for climate change. A comparative study of LST over parts of the Singhbhum Shear Zone in India was undertaken using various emissivity and temperature retrieval algorithms applied on visible and near infrared (VNIR), and thermal infrared (TIR) bands of high resolution Landsat-7 ETM+ imagery. LST results obtained from satellite data of October 26, 2001 and November 2, 2001 through various algorithms were validated with ground measurements collected during satellite overpass. In addition, LST products of MODIS and ASTER were compared with Landsat-7 ETM+ and ground truth data to explore the possibility of using multi-sensor approach in LST monitoring. An image-based dark object subtraction (DOS3) algorithm, which is yet to be tested for LST retrieval, was applied on VNIR bands to obtain atmospheric corrected surface reflectance images. Normalized difference vegetation index (NDVI) was estimated from VNIR reflectance image. Various surface emissivity retrieval algorithms based on NDVI and vegetation proportion were applied to ascertain emissivities of the various land cover categories in the study area in the spectral range of 10.4–12.5 μm. A minimum emissivity value of about 0.95 was observed over the reflective rock body with a maximum of about 0.99 over dense forest. A strong correlation was established between Landsat ETM+ reflectance band 3 and emissivity. Single channel based algorithms were adopted for surface radiance and brightness temperature. Finally, emissivity correction was applied on ‘brightness temperature’ to obtain LST. Estimated LST values obtained from various algorithms were compared with field ground measurements for different land cover categories. LST values obtained after using Valor’s emissivity and single channel equations were best correlated with ground truth temperature. Minimum LST is observed over dense forest as about 26 °C and maximum LST is observed over rock body of about 38 °C. The estimated LST showed that rock bodies, bare soils and built-up areas exhibit higher surface temperatures, while water bodies, agricultural croplands and dense vegetations have lower surface temperatures during the daytime. The accuracy of the estimated LST was within ±2 °C. LST comparison of ASTER and MODIS with Landsat has a maximum difference of 2 °C. Strong correlation was found between LST and spectral radiance of band 6 of Landsat-7 ETM+. Result corroborates the fact that surface temperatures over land use/land cover types are greatly influenced by the amount of vegetation present.     

风云三号C星GNOS北斗掩星电离层探测初步结果

利用风云三号卫星C星GNOS掩星探测仪电离层数据,分析了2013年10月FY-3C GNOS探测的北斗掩星电离层廓线分布,将2013年10月1日至2015年10月10日期间FY-3C GNOS观测的F₂层峰值电子密度（N_mF₂）与地面电离层测高仪观测结果进行对比,验证了FY-3C GNOS北斗电离层掩星的探测精度.结果表明,FY3-C GNOS北斗电离层掩星与电离层测高仪探测的N_mF₂数据相关系数为0.96,平均偏差为10.21%,标准差为19.61%.在不同情况下其数据精度有如下特征:白天精度高于夜晚;夏季精度高于分季,分季精度高于冬季;中纬地区精度高于低纬地区,低纬地区精度高于高纬地区; BDS倾斜同步轨道（IGSO）卫星精度高于同步轨道（GEO）卫星和中轨道（MEO）卫星.FY-3C GNOS北斗电离层掩星与国际上其他掩星电离层数据精度的一致性对GNSS掩星探测资料的综合利用具有重大意义.      

Update on Fengyun Meteorological Satellite Program and Development

China began to develop its meteorological satellite program since 1969. With 50-years' growing, there are 17 Fengyun (FY) meteorological satellites launched successfully. At present, seven of them are in orbit to provide the operational service, including three polar orbiting meteorological satellites and four geostationary meteorological satellites. Since last COSPAR report, no new Fengyun satellite has been launched. The information of the on-orbit FY-2 series, FY-3 series, and FY-4 series has been updated. FY-3D and FY-2H satellites accomplished the commission test and transitioned into operation in 2018. FY-2E satellite completed its service to decommission in 2019. The web-based users and Direct Broadcasting (DB) users keep growing worldwide to require the Fengyun satellite data and products. A new Mobile Application Service has been launched to Fengyun users based on the cloud technology in 2018. In this report, the international and regional co-operations to facilitate the Fengyun user community have been addressed especially. To strengthen the data service in the Belt and Road countries, the Emergency Support Mechanism of Fengyun satellite (FY_ESM) has been established since 2018. Meanwhile, a Recalibrating 30-years' archived Fengyun satellite data project has been founded since 2018. This project targets to generate the Fundamental Climate Data Record (FCDR) as a space agency response to the Global Climate Observation System (GCOS). At last, the future Fengyun program up to 2025 has been introduced as well.      

A comparison of different regression models for downscaling Landsat and MODIS land surface temperature images over heterogeneous landscape

Remotely sensed high spatial resolution thermal images are required for various applications in natural resource management. At present, availability of high spatial resolution (<200 m) thermal images are limited. The temporal resolution of such images is also low. Whereas, coarser spatial resolution (∼1000 m) thermal images with high revisiting capability (∼1 day) are freely available. To bridge this gap, present study attempts to downscale coarser spatial resolution thermal image to finer spatial resolution using relationships between land surface temperature (LST) and vegetation indices over a heterogeneous landscape of India. Five regression based models namely (i) Disaggregation of Radiometric Temperature (DisTrad), (ii) Temperature Sharpening (TsHARP), (iii) TsHARP with local variant, (iv) Least median square regression downscaling (LMS_DS) and (v) Pace regression downscaling (PR_DS) are applied to downscale LST of Landsat Thematic Mapper (TM) and Terra MODIS (Moderate Resolution Imaging Spectroradiometer) images. All the five models are first evaluated on Landsat image aggregated to 960 m resolution and downscaled to 480 m and 240 m resolution. The downscale accuracy is achieved using LMS_DS and PR_DS models at 240 m resolution at 0.61 °C and 0.75 °C respectively. MODIS data downscaled from 1000 m to 250 m spatial resolution results root mean square error (RMSE) of 1.43 °C and 1.62 °C for LMS_DS and PR_DS models, respectively. The LMS_DS model is less sensitive to outliers in heterogeneous landscape and provides higher accuracy when compared to other models. Downscaling model is found to be suitable for agricultural and vegetated landscapes up to a spatial resolution of 250 m but not applicable to water bodies, dry river bed sand sandy open areas.     

LEO enhanced Global Navigation Satellite System (LeGNSS) for real-time precise positioning services

Global Navigation Satellite System (GNSS) has been widely used in many geosciences areas with its Positioning, Navigation and Timing (PNT) service. However, GNSS still has its own bottleneck, such as the long initialization period of Precise Point Positioning (PPP) without dense reference network. Recently, the concept of PNTRC (Positioning, Navigation, Timing, Remote sensing and Communication) has been put forward, where Low Earth Orbit (LEO) satellite constellations are recruited to fulfill diverse missions. In navigation aspect, a number of selected LEO satellites can be equipped with a transmitter to transmit similar navigation signals to ground users, so that they can serve as GNSS satellites but with much faster geometric change to enhance GNSS capability, which is named as LEO constellation enhanced GNSS (LeGNSS). As a result, the initialization time of PPP is expected to be shortened to the level of a few minutes or even seconds depending on the number of the LEO satellites involved. In this article, we simulate all the relevant data from June 8th to 14th, 2014 and investigate the feasibility of LeGNSS with the concentration on the key issues in the whole data processing for providing real-time PPP service based on a system configuration with fourteen satellites of BeiDou Navigation Satellite System (BDS), twenty-four satellites of the Global Positioning System (GPS), and sixty-six satellites of the Iridium satellite constellations. At the server-end, Precise Orbit Determination (POD) and Precise Clock Estimation (PCE) with various operational modes are investigated using simulated observations. It is found out that GNSS POD with partial LEO satellites is the most practical mode of LeGNSS operation. At the user-end, the Geometry Dilution Of Precision (GDOP) and Signal-In-Space Ranging Error (SISRE) are calculated and assessed for different positioning schemes in order to demonstrate the performance of LeGNSS. Centimeter level SISRE can be achieved for LeGNSS.     

A topside investigation over a mid-latitude digisonde station in Cyprus

We examine the systematic differences between topside electron density measurements recorded by different techniques over the low-middle latitude operating European station in Nicosia, Cyprus (geographical coordinates: 35.14^oN, 33.2^oE), (magnetic coordinates 31.86^oN, 111.83 ^oE). These techniques include space-based in-situ data by Langmuir probes on board.European Space Agency (ESA) Swarm satellites, radio occultation measurements on board low Earth orbit (LEO) satellites from the COSMIC/FORMOSAT-3 mission and ground-based extrapolated topside electron density profiles from manually scaled ionograms. The measurements are also compared with International Reference Ionosphere Model (IRI-2016) topside estimations and IRI-corrected NeQuick topside formulation (method proposed by Pezzopane and Pignalberi (2019)). The comparison of Swarm and COSMIC observations with digisonde and IRI estimations verifies that in the majority of cases digisonde underestimates while IRI overestimates Swarm observations but in general, IRI provides a better topside representation than the digisonde. For COSMIC and digisonde profiles matched at the F layer peak the digisonde systematically underestimates topside COSMIC electron density values and the relative difference between COSMIC and digisonde increases with altitude (above hmF2), while IRI overestimates the topside COSMIC electron density but after a certain altitude (~150 km above hmF2) this overestimation starts to decrease with altitude. The IRI-corrected NeQuick underestimates the majority of topside COSMIC electron density profiles and relative difference is lower up to approximately 100 km (above the hmF2) and then it increases. The overall performance of IRI-corrected NeQuick improves with respect to IRI and digisonde.     

低轨卫星的北斗反射信号海洋覆盖分析

北斗系统作为我国自行研制的导航系统，具有独特的混合星座特性，其反射事件在海洋上的空间分布和覆盖性能的研究成果较少。针对上述问题，模拟了北斗三号（Beidou System 3，BDS3）以及全球定位系统（Global Positioning System，GPS）空间星座，模拟不同性能参数的低轨接收卫星，在此仿真系统的基础上，计算反射事件在各仿真场景下的海洋覆盖率以及同时发生反射事件的卫星数量。结果表明：BDS3与GPS相比具有更大的反射事件海洋覆盖率，覆盖性能更优；仿真周期7天与1天相比,前者卫星产生的反射事件海洋覆盖率约为后者5倍；低轨道卫星（Low Earth Orbit,LEO）轨道高度越高，天线波束角度越大，反射事件海洋覆盖率越大；3颗LEO卫星下同时发生反射事件卫星数的平均值约为单颗LEO卫星的3倍。可通过设计多星组网来提高反射事件海洋覆盖率。研究结果对星载反射技术海洋遥感应用方面有一定的参考价值。     

Substitution of satellite-based land surface temperature defective data using GSP method

Land surface temperature (LST) as an important environmental variable provides valuable information for earth environmental system modelling. Currently, LST is obtained through satellite thermal sensors at various spatial and temporal resolutions. Although spatially continuous satellite-based LST measurements are intended to overcome the shortcomings of sparse ground-based LST measurements, LST images often contain anomalous values due to the existence of clouds or sensor malfunctioning. The problem becomes more serious where the users deal with high spatial resolution characterized by low temporal resolution. This study examines the capability of a newly developed graph signal processing (GSP) method using two-dimensional single-date thermal data. For this purpose, four Landsat/TIRS datasets are analyzed. The data of five elliptical regions on thermal images are eliminated and then reconstructed through the GSP method and using the LST values of the enclosing rectangles containing the ellipsoids. The results indicate that the temperature variation determined by the GSP method generally conforms to the original image LST values. According to a correlation test conducted on the original image LST and those obtained through the GSP method, the values vary from 58% to 95%, which is an above-the-average rate (RMSE from 0.69 to 2.27). The statistical analysis of the original image LST in both the elliptical regions and the enclosing rectangles containing the ellipsoids indicates that an increase in the variance of LST data causes an increased error in the calculation of temperature by the GSP method, and vice versa. The results of the analysis of variance (ANOVA) and Duncan test indicated that an increase in the number of the non-zero spectral bins would result in increased RMSE values for all the dates and the regions. Moreover, the model errors were significant at the 0.05 level across all the image date and five elliptical study regions. Based on the results, the use of this method is recommended for the reconstruction of LST missing values, where dissimilarity of atmospheric conditions limits the use of other methods that depend on the time series data of various dates and a great deal of data calculation.     

基于DTW的HJ-1B卫星地表温度产品质量检验

HJ-1B卫星热红外数据应用广泛,但其地表温度反演产品的质量检验工作尚不完善。以黑河流域为研究区,利用普适性单通道算法得到HJ 1B地表温度,基于7个地面站点（下垫面为荒漠、沙漠、植被、农作物、雪地和湿地）同步观测资料和MODIS地表温度产品（MOD11A1）,引入动态时间规整方法（DTW）对站点处HJ 1B地表温度进行验证。试验结果表明：HJ 1B地表温度反演产品与地面观测值的偏差值在沙漠和荒漠站点为1K以内,均方根误差在05K左右;对于植被和农作物站点的偏差在2K以内,均方根误差为1~2K;基于DTW的验证对时序不匹配的数据评价结果与现有指标表现一致。HJ-1B地表温度反演产品与地面站点的相对偏差均低于其与MODIS地表温度反演产品的相对偏差。     

A method of estimating GPS instrumental biases with a convolution algorithm

This paper presents a method of deriving the instrumental differential code biases (DCBs) of GPS satellites and dual frequency receivers. Considering that the total electron content (TEC) varies smoothly over a small area, one ionospheric pierce point (IPP) and four more nearby IPPs were selected to build an equation with a convolution algorithm. In addition, unknown DCB parameters were arranged into a set of equations with GPS observations in a day unit by assuming that DCBs do not vary within a day. Then, the DCBs of satellites and receivers were determined by solving the equation set with the least-squares fitting technique. The performance of this method is examined by applying it to 361?days in 2014 using the observation data from 1311 GPS Earth Observation Network (GEONET) receivers. The result was crosswise-compared with the DCB estimated by the mesh method and the IONEX products from the Center for Orbit Determination in Europe (CODE). The DCB values derived by this method agree with those of the mesh method and the CODE products, with biases of 0.091?ns and 0.321?ns, respectively. The convolution method's accuracy and stability were quite good and showed improvements over the mesh method.     

MICROWAVE SENSOR DEVELOPMENT IN RECENT TWO YEARS IN CHINA

The development of microwave sensors in recent two years in China are in troduced with an emphasis on spaceborne sensors without the applications in cluded. The microwave sensors as the main payloads to be boarded on the future operational satellites, such as FY-3 meteorological satellites and HY-2 marine satellite are introduced with much in detail. Besides these, four new sensors are outlined, i.e. the imaging radar altimeter,synthetic aperture radiometer, and polarimetric radiometer. Two recently conducted flight experiment campaigns are also introduced with results shown.     

FY-3A卫星与NOAA系列卫星高能带电粒子实测结果的比较

FY-3A卫星是运行于830 km高度的太阳同步轨道气象卫星, 其搭载的空间环境监测器可观测3~300 MeV的高能质子和0.15~5.70 MeV的高能电子. FY-3A卫星在轨工作期间, 太阳活动处于由谷年向峰年过渡期, 空间环境非常平静, 探测结果显示3~300 MeV的高能质子分布主要集中在南大西洋辐射带异常区, 0.15~5.70 MeV的高能电子分布区域除南大西洋异常区外, 还分布在南北两极高纬区域. FY-3A与NOAA卫星测量结果反映出带电粒子强度及分布区域随投掷角变化的空间各向异性特征. 本文在充分考虑了带电粒子时间、空间分布差异以及比对探测器之间自身设计差异的前提下, 经过归一化处理后, 首次对两颗卫星同期探测结果进行相关性分析, 验证了两颗卫星相同时空条件下高能带电粒子通量分布的一致性; 说明FY-3A空间环境监测器不仅具备空间带电粒子辐射监测能力, 且探测结果有效可靠, 可用作辐射带环境数据源的组成部分, 为发展新的模型, 深入研究辐射带高能粒子的分布、起源和传输等提供新的观测依据.      

Waveform-based spaceborne GNSS-R wind speed observation: Demonstration and analysis using UK TechDemoSat-1 data

This paper explores two types of mathematical functions to fit single- and full-frequency waveform of spaceborne Global Navigation Satellite System-Reflectometry (GNSS-R), respectively. The metrics of the waveforms, such as the noise floor, peak magnitude, mid-point position of the leading edge, leading edge slope and trailing edge slope, can be derived from the parameters of the proposed models. Because the quality of the UK TDS-1 data is not at the level required by remote sensing mission, the waveforms buried in noise or from ice/land are removed by defining peak-to-mean ratio, cosine similarity of the waveform before wind speed are retrieved. The single-parameter retrieval models are developed by comparing the peak magnitude, leading edge slope and trailing edge slope derived from the parameters of the proposed models with in situ wind speed from the ASCAT scatterometer. To improve the retrieval accuracy, three types of multi-parameter observations based on the principle component analysis (PCA), minimum variance (MV) estimator and Back Propagation (BP) network are implemented. The results indicate that compared to the best results of the single-parameter observation, the approaches based on the principle component analysis and minimum variance could not significantly improve retrieval accuracy, however, the BP networks obtain improvement with the RMSE of 2.55 m/s and 2.53 m/s for single- and full-frequency waveform, respectively.     

Comparison between observed ionospheric foF2 and IRI-2001 predictions over periods of severe geomagnetic activities at Grahamstown,South Africa

The observed ionospheric F2 critical frequency (foF2) values over a South Africa mid-latitude station, Grahamstown, (geographic coordinates: 33.3°S, 26.5°E), were analysed and compared with International Reference Ionosphere (IRI) model, using the CCIR (Comite´ Consultatif International des Radio communications) and URSI (Union Radio-Scientifique Internationale) coefficients, during four geomagnetically disturbed days in the year 2000. These days are April 5, May 23, August 10 and September 15. The data were analysed for five days around the storm day. Comparisons between the IRI-2001 predicted foF2 values, using both CCIR and URSI coefficients and the observed values are shown with their root-mean-square error (RMSE) and the relative deviation module mean (rdmm) for the various storm periods. The CCIR option performed more accurately than the URSI option.     

应用双向时间传递的重力卫星时标误差自主测量

星间时标误差的自主测量对于中国自主研发地球重力卫星具有重要意义. 提出利用双向时间传递法实现重力卫星时标误差的自主测量, 设计了测量方案, 建立了包含卫星运动导致的链路非对称、电离层效应、设备零值以及随机测时误差在内的测量模型. 结合地球重力卫星相关特性, 分析了时标误差测量中各误差源的影响及相应的误差校正方法. 以GRACE重力卫星为例, 利用提出的方法和校正措施, 星间时标误差自主测量精度可以达到0.62ns, 其中误差主要来自系统零值标定误差和随机测时误差.