Decoding the inconsistency of six cropland maps in China

Accurate cropland information is critical for agricultural planning and production,especially in foodstressed countries like China.Although widely used medium-to-high-resolution satellite-based cropland maps have been developed from various remotely sensed data sources over the past few decades,considerable discrepancies exist among these products both in total area and in spatial distribution of croplands,impeding further applications of these datasets.The factors influencing their inconsistency are also unknown.In this study,we evaluated the consistency and accuracy of six cropland maps widely used in China in circa 2020,including three state-of-the-art 10-m products(i.e.,Google Dynamic World,ESRI Land Cover,and ESA WorldCover)and three 30-m ones(i.e.,GLC_FCS30,GlobeLand 30,and CLCD).We also investigated the effects of landscape fragmentation,climate,and agricultural management.Validation using a ground-truth sample revealed that the 10-m-resolution WorldCover provided the highest accuracy(92.3%).These maps collectively overestimated Chinese cropland area by up to 56%.Up to 37%of the land showed spatial inconsistency among the maps,concentrated mainly in mountainous regions and attributed to the varying accuracy of cropland maps,cropland fragmentation and management practices such as irrigation.Our work shed light on the promotion of future cropland mapping efforts,especially in highly inconsistent regions.

Development of Integrated and Intelligent Geodetic and Photogrammetry Satellites with Corresponding Key Technologies

Aerospace surveying and mapping has become the main method of global earth observation.It can be divided into the geodetic observation satellites and the topographic surveying satellites according to the disciplines.In this paper,the geodetic satellites and photographic satellites are introduced respectively.Then,the existing problems in Chinese earth observation satellites are analyzed,and the comprehensive satellite with integrated payloads,the intensive microsatellite constellation and the intelligent observation satellite are proposed as three different development ideas for the future earth observation satellites.The possibility of the three ideas is discussed in detail,as well as the related key technologies.

Development of Comprehensive PNT and Resilient PNT

Any single Positioning,Navigation and Timing(PNT)technology has its vulnerability and limits,even the powerful Global Navigation Satellite System(GNSS)is no exception.To provide continuous and reliable PNT information to users,the theory and technique of comprehensive PNT information system and resilient PNT application system have attracted great attention from Chinese scholars.We try to summarize the progress and development of the synthetic PNT system,including the proposal,the modification and the improvement of the comprehensive PNT,as well as the follow-up resilient PNT.The frame of China’s comprehensive PNT system consisted of comprehensive PNT infrastructure and comprehensive PNT application system is initially described;the achievements on some main PNT technologies are introduced;the conceptual models of resilient PNT are given;besides,existing researches on resilient function models and stochastic models are summarized according to different user scenarios.

Predicting bathymetry based on vertical gravity gradient anomaly and analyses for various influential factors

The prediction of bathymetry has advanced significantly with the development of satellite altimetry.However,the majority of its data originate from marine gravity anomaly.In this study,based on the expression of vertical gravity gradient(VGG)of a rectangular prism,the governing equations for determining sea depths to invert bathymetry.The governing equation is solved by linearization through an iterative process,and numerical simulations verify its algorithm and its stability.We also study the processing methods of different interference errors.The regularization method improves the stability of the inversion process for errors.A piecewise bilinear interpolation function roughly replaces the low-frequency error,and numerical simulations show that the accuracy can be improved by 41.2%after this treatment.For variable ocean crust density,simulation simulations verify that the root-mean-square(RMS)error of prediction is approximately 5 m for the sea depth of 6 km if density is chosen as the average one.Finally,two test regions in the South China Sea are predicted and compared with ship soundings data,RMS errors of predictions are 71.1 m and 91.4 m,respectively.

An improved typhoon monitoring model based on precipitable water vapor and pressure

The potential of monitoring the movement of typhoons using the precipitable water vapor(PWV) has been confirmed. However, monitoring the movement of typhoon is focused on PWV, making it difficult to describe the movement of a typhoon in detail minutely and resulting in insufficient accuracy. Hence,based on PWV and meteorological data, we propose an improved typhoon monitoring mode. First, the European Centre for Medium-Range Weather Forecasts Reanalysis 5-derived PWV(ERA5-PWV) and the Global Navigation Satellite System-derived PWV(GNSS-PWV) were compared with the reference radiosonde PWV(RS-PWV). Then, using the PWV and atmospheric parameters derived from ERA5, we discussed the anomalous variations of PWV, pressure(P), precipitation, and wind speed during different typhoons. Finally, we compiled a list of critical factors related to typhoon movement, PWV and P. We developed an improved multi-factor typhoon monitoring mode(IMTM) with different models(i.e.,IMTM-I and IMTM-II) in different cases with a higher density of GNSS observation or only Numerical Weather Prediction(NWP) data. The IMTM was evaluated through the reference movement speeds of HATO and Mangkhut from the China Meteorological Observatory Typhoon Network(CMOTN). The results show that the root mean square(RMS) of the IMTM-I is 1.26 km/h based on ERA5-P and ERA5-PWV,and the absolute bias values are mostly within 2 km/h. Compared with the models considering the single factor ERA5-P/ERA5-PWV, the RMS of the IMTM-I is improved by 26.3% and 38.5%, respectively. The IMTM-II model manifests a residual of only 0.35 km/h. Compared with the single-factor model based on GNSS-PWV/P, the residual of the IMTM-II model is reduced by 90.8% and 84.1%, respectively. These results propose that the typhoon movement monitoring approach combining PWV and P has evident advantages over the single-factor model and is expected to supplement traditional typhoon monitoring.

Prediction of earth rotation parameters based on improved weighted least squares and autoregressive model

In this paper, an improved weighted least squares （WLS）, together with autoregressive （AR） model, is proposed to improve prediction accuracy of earth rotation parameters（ERP）. Four weighting schemes are developed and the optimal power e for determination of the weight elements is studied. The results show that the improved WLS-AR model can improve the ERP prediction accuracy effectively, and for different prediction intervals of ERP, different weight scheme should be chosen.

Heterogeneous strain regime in the eastern margin of Tibetan Plateau and its tectonic implications

The eastern margin of Tibetan Plateau is one of the most active zones of tectonic deformation and seismicity in China. To monitor strain buildup and benefit seismic risk assessment, we constructed 14 survey-mode global position system （GPS） stations throughout the northwest of Longmenshan fault. A new GPS field over 1999-2011 is derived from measurements of the newly built and pre-existing stations in this region. Sequentially, two strain rate fields, one preceding and the other following the 2008 MwT.9 Wenchuan earthquake, are obtained using the Gausian weighting approach. Strain field over 1999-2007 shows distinct strain partitioning prior to the 2008 MwT.9 Wenchuan earthquake, with compression spreading over around Longmenshan area. Strain fieldderived from the two measurements in 2009 and 2011 shows that the area around Longmenshan continues to be under striking compression, as the pattern preceding the Wenchuan earthquake, implying a causative factor of the sequent of 2013 Mw6.7 Lushan earthquake. Our GPSderived dilatation shows that both the Wenchuan and Lushan earthquakes occurred within the domain of pro- nounced contraction. The GPS velocities demonstrate that the Longriba fault underwent slight motion with the faultnormal and -parallel rates at 1.0 -4- 2.5 mm and 0.3 4-2.2 mm/a; the Longmenshan fault displayed slow activity, with a fault-normal rate at 0.8 ± 2.5 mm/a, and a fault-parallel rate at 1.8 4- 1.7 mm/a. Longriba fault is on a par with Longmenshan fault in strain partitioning to accommodate the southeastward motion of eastern margin of the Tibetan Plateau. Integrated analysis of principal strain tensors, mean principal stress, and fast directions of mantle anisotropy shows that west of Sichuan is characterized as mechanically strong crust-mantle coupling.

Scenario simulation of water retention services under land use/cover and climate changes: a case study of the Loess Plateau, China

Comprehensive assessments of ecosystem services in environments under the influences of human activities and climate change are critical for sustainable regional ecosystem management. Therefore,integrated interdisciplinary modelling has become a major focus of ecosystem service assessment. In this study, we established a model that integrates land use/cover change(LUCC), climate change, and water retention services to evaluate the spatial and temporal variations of water retention services in the Loess Plateau of China in the historical period(2000–2015) and in the future(2020–2050). An improved Markov-Cellular Automata(Markov-CA) model was used to simulate land use/land cover patterns, and ArcGIS 10.2 software was used to simulate and assess water retention services from 2000 to 2050 under six combined scenarios, including three land use/land cover scenarios(historical scenario(HS), ecological protection scenario(EPS), and urban expansion scenario(UES)) and two climate change scenarios(RCP4.5 and RCP8.5, where RCP is the representative concentration pathway). LUCCs in the historical period(2000–2015) and in the future(2020–2050) are dominated by transformations among agricultural land, urban land and grassland. Urban land under UES increased significantly by 0.63×10^(3) km^(2)/a, which was higher than the increase of urban land under HS and EPS. In the Loess Plateau, water yield decreased by 17.20×10^(6) mm and water retention increased by 0.09×10^(6) mm in the historical period(2000–2015),especially in the Interior drainage zone and its surrounding areas. In the future(2020–2050), the pixel means of water yield is higher under RCP4.5 scenario(96.63 mm) than under RCP8.5 scenario(95.46mm), and the pixel means of water retention is higher under RCP4.5 scenario(1.95 mm) than under RCP8.5 scenario(1.38 mm). RCP4.5-EPS shows the highest total water retention capacity on the plateau scale among the six combined scenarios, with the value of 1.27×10^(6) mm. Ecological restoration projects in the Loess Plateau have enhanced soil and water retention. However, more attention needs to be paid not only to the simultaneous increase in water retention services and evapotranspiration but also to the type and layout of restored vegetation. Furthermore, urbanization needs to be controlled to prevent uncontrollable LUCCs and climate change. Our findings provide reference data for the regional water and land resources management and the sustainable development of socio-ecological systems in the Loess Plateau under LUCC and climate change scenarios.

Soil physicochemical properties and vegetation structure along an elevation gradient and implications for the response of alpine plant development to climate change on the northern slopes of the Qilian Mountains

Elevation is one of key factors to affect changes in the environment, particularly changes in conditions of light, water and heat. Studying the soil physicochemical properties and vegetation structure along an elevation gradient is important for understanding the responses of alpine plants andtheir growing environment to climate change. In this study, we studied plant coverage, plant height, species richness, soil water-holding capacity, soil organic carbon(SOC) and total nitrogen(N) on the northern slopes of the Qilian Mountains at elevations from2124 to 3665 m. The following conclusions were drawn:(1) With the increase of elevation, plant coverage and species richness first increased and then decreased, with the maximum values being at 3177 m.Plant height was significantly and negatively correlated with elevation(r=–0.97, P<0.01), and the ratio of decrease with elevation was 0.82 cm·100 m-1.(2) Both soil water-holding capacity and soil porosity increased on the northern slopes of the Qilian Mountains with the increase of elevation. The soil saturated water content at the 0-40 cm depth first increased and then stabilized with a further increase of elevation, and the average ratio of increase was2.44 mm·100 m-1. With the increase of elevation, the average bulk density at the 0-40 cm depth first decreased and then stabilized at 0.89 g/cm3.(3) With the increase of elevation, the average SOC content at the 0-40 cm depths first increased and then decreased,and the average total N content at the 0-40 cm depth first increased and then stabilized. The correlation between average SOC content and average total N content reached significant level. According to the results of this study, the distribution of plants showed a mono-peak curve with increasing elevation on the northern slopes of the Qilian Mountains. The limiting factor for plant growth at the high elevation areas was not soil physicochemical properties, and therefore,global warming will likely facilitate the development of plant at high elevation areas in the Qilian Mountains.

High-Order Radial Derivatives of Harmonic Function and Gravity Anomaly

The first through ninth radial derivatives of a harmonic function and gravity anomaly are derived in this paper. These derivatives can be used in the analytical continuation application. For the downward continuation of gravity anomaly, the Taylor series approach developed in the paper is equivalent theoretically to but more efficient and storage-saving computationally than the well-known gradient operator approach. Numerical simulation shows that Taylor series expansion constructed by the derived formulas for the radial derivatives of gravity disturbance is still convergent for height up to 4 km.

Quantizing and analyzing the feature information of coastal zone based on high-resolution remote sensing image

On the basis of realization of beach information and its differentiating of high-resolution remote sensing image on coastal zone, extracting objects are carried through RS multi-scale diagnostic analysis, and fast information extraction methods and key technologies are put forward. Meanwhile image segmentation methods are set forth for objects of coastal zone. And through the application of Otsu2D to the segmentation of water area and dock and the applying of Gabor filter to the separation and extraction of construction, some typical applications of high-resolution RS image are presented in the field of coastal zone surface objects＇ recognition. Quantizing high-resolution RS information on the coastal zone proved to be of great scientific and practical significance for coastal development and management.

Black Spot Determination of Traffic Accident Locations and Its Spatial Association Characteristic Analysis Based on GIS

In general, the location of traffic accidents is described as an address with text, so they are difficult to display on the map. The paper discusses how to utilize the geocoding technology and VRS-GPS positioning technology to record the traffic accidents with Geo-spatial information. Based on the spatial relationship between traffic accidents and road network elements, two-way association relationship is defined by spatial relationship computation. Then the paper presents the method which takes the potential of reducing accidents as an index to extract the black spots. Finally, in the discussion, the association relationship between black spots and traffic attributes is used to analyze the factors that resulting in traffic accidents.

Construction of nonsingular formulae of variance and covariance function of disturbing gravity gradient tensors

When the computational point is approaching the poles, the variance and covariance formulae of the disturbing gravity gradient tensors tend to be infinite, and this is a singular problem. In order to solve the problem, the authors deduced the practical non-singular computational formulae of the first- and second-order derivatives of the Legendre functions and two kinds of spherical harmonic functions, and then constructed the nonsingular formulae of variance and eovarianee function of disturbing gravity gradient tensors.

GPR Surveying in the kernel area of Grove Mountains,Antarctica

The Grove Mountains, located between the Zhongshan Station and Dome A, are a very important area in inland Antarctic research. China has organized ifve investigations of the Grove Mountains, encompassing the geological structure, ancient climate, meteorites, ice-movement monitoring, basic mapping, meteorological observations, and other multi-disciplinary observational studies. During the 26th Chinese National Antarctic Research Expedition in 2010, the Grove Mountains investigation team applied specialized ground-penetrating radar （GPR） to survey subglacial topography in the eastern kernel area of the Grove Mountains. In this paper, we processed GPS and GPR data gathered in the ifeld and drew, for the ifrst time, two subglacial topographic maps of the Grove Mountains kernel area using professional graphics software. The preliminary results reveal the mystery of the nunatak landform of this area, give an exploratory sense of the real bedrock landforms, and indicate a possible sedimentary basin under the Pliocene epoch fossil ice in the Grove Mountains area. Additionally, it has been proven from cross-sectional analysis between Mount Harding and the Zakharoff ridge that the box-valley shape between two nunataks has already matured.

Design and Implementation of mobile GIS application based on Android

This paper analyzes the key technology of mobile GIS development, discusses the design method of mobile GIS spatial data management, visualization of spatial data And Spatial data query, tinder Object oriented mode. And we develop a set of mobile GIS basic software platform in the Android platform, and tested in the mainstream smart mobile phone with Android operating system, test results show that the software platform can run smoothly. Other users can development a variety of mobile GIS to call the platform through an application service interface.

Progresses and Prospects of Marine Geodetic Datum and Marine Navigation in China

Territorial water is a significant part of national sovereignty of China,thus the infrastructures of national space datum and location services should cover the sea areas except for the land areas.China has established relatively complete geodetic coordinate frame in land areas over the past decades,including the lastest developed China Geodetic Coordinate System 2000(CGCS 2000)with its reference frame and the national gravity datum 2000.However,the currently used geodetic infrastructures have not well covered the sea areas of China.The marine geodetic datum and marine navigation technologies need to be further developed and extended to satisfy the national demands of marine environment and resources detection,scientific investigation as well as marine economy development in new era of China.This paper mainly reviews the development and the progress of Chinese marine geodetic datum and marine navigation,analyses related key technologies in establishing our national marine geodetic datum.Some current trends and future directions for independently developing our national marine geodetic datum and marine navigation technologies are discussed.

A Two-step Estimation Method of Troposphere Delay with Consideration of Mapping Function Errors

Mapping function errors are usually not taken into consideration, when space geodetic data observed by VLBI, GNSS and some other techniques are utilized to estimate troposphere delay, which could, however, probably bring non-ignorable errors to solutions. After analyzing the variation of mapping function errors with elevation angles based on several-year meteorological data, this paper constructed a model of this error and then proposed a two-step estimation method of troposphere delay with consideration of mapping function errors. The experimental results indicate that the method put forward by this paper could reduce the slant path delay residuals efficiently and improve the estimation accuracy of wet tropospheric delay to some extent.

Results and Analyses of BDS Precise Orbit Determination with the Enhancement of Fengyun-3C

Global navigation satellite system occultation sounder (GNOS) Fengyun-3C was launched successfully on September 23, 2013, which carried GPS/BDS receiver for the first time. This provides the convenience to study the enhancement results of low earth orbiter satellite (LEO) to BDS precise orbit determination (POD). First the data characteristic and code observation noise of GNOS are analyzed. Then the enhancement experiments in the case of global and regional ground observation stations layout are processed with four POD schemes: BDS single system, GPS/BDS double system, BDS single system with GNOS observations, GPS/BDS double system with GNOS observations. The precision of BDS orbits and clocks are compared via overlapping arcs. Results show that in the case of global station layout the along directional precision of GEO satellite has the biggest improvement, with the improvement percentage 60%. Then the precision of cross direction and the along direction of remaining satellites shows the second biggest improvement. The orbit precision of BDS-only POD in part of observation arcs some satellite even suffers a slight decline. The root mean square (RMS) of overlapping clock difference of visible arcs in GPS/BDS POD experiments improves by 0.1 ns level. As to the experiments of regional station layout with 7 ground stations, the orbit and clock overlapping precision and orbit predicting precision are analyzed. Results show that the predicting precision of BDS GEO satellites in the along direction improves by 85%. The remaining also has a substantial improvement, with the average percentage 21.7%. RMS of overlapping clock difference of visible arcs improves by 0.5 ns level.

Research on Error Analysis and Correction Technique of Atmospheric Refraction for InSAR Measurement with Distributed Satellites

SAR interferometry with distributed satellites is a technique based on the exploitation of the interference pattern of two SAR images acquired synchronously. The interferogram contains geometric, atmospheric, topographic and land defomation. This paper focuses on atmospheric effects on SAR interferometry, which shows theoretically that the relationship among ionosphere TEC and troposphere parameters such as temperature, relative humitdity and pressure with respect to slant rang changes. An atmospheric correction method is given in the end.

Feasibility Analysis of Performance Validation for Satellite Altimeters Using Tide Gauge and Deep-ocean Bottom Pressure Recorder

Independent of traditional approach of satellite altimeter calibration, the feasibility of altimeter validation using tide gauge located on solitary island at open sea (TGSI) and deep-ocean bottom pressure recorder (DBPR) separately is initially studied. Bias of Jason-3 sea surface height (SSH) and relative SSH bias (Δbias) between Jason-2 and Jason-3 is calculated using the data of tide gauge on Harvest oil platform, tide gauge No. 1890000 and DBPR No. 21419. The standard deviations of calculated SSH bias sequence are 3.98 cm, 2.87 cm and 8.61 cm respectively, and Δbias (Jason-3—Jason-2) is -3.62± 2.17 cm , -2.58±1.97 cm and -2.60±1.30 cm respectively. Comparing to the results reported by international calibration sites, the results show that Jason-3 SSH is 3.0 cm lower than that of Jason-2, the selected DBPR is appropriate to the calculation of relative SSH bias between Jason-2 and Jason-3, but it is not suitable for calibration or validation of single satellite, TGSI is appropriate to both.