Improving the spaceborne GNSS-R altimetric precision based on the novel multilayer feedforward neural network weighted joint prediction model

Global navigation satellite system-reflection(GNSS-R)sea surface altimetry based on satellite constellation platforms has become a new research direction and inevitable trend,which can meet the altimetric precision at the global scale required for underwater navigation.At present,there are still research gaps for GNSS-R altimetry under this mode,and its altimetric capability cannot be specifically assessed.Therefore,GNSS-R satellite constellations that meet the global altimetry needs to be designed.Meanwhile,the matching precision prediction model needs to be established to quantitatively predict the GNSS-R constellation altimetric capability.Firstly,the GNSS-R constellations altimetric precision under different configuration parameters is calculated,and the mechanism of the influence of orbital altitude,orbital inclination,number of satellites and simulation period on the precision is analyzed,and a new multilayer feedforward neural network weighted joint prediction model is established.Secondly,the fit of the prediction model is verified and the performance capability of the model is tested by calculating the R2 value of the model as 0.9972 and the root mean square error(RMSE)as 0.0022,which indicates that the prediction capability of the model is excellent.Finally,using the novel multilayer feedforward neural network weighted joint prediction model,and considering the research results and realistic costs,it is proposed that when the constellation is set to an orbital altitude of 500 km,orbital inclination of 75and the number of satellites is 6,the altimetry precision can reach 0.0732 m within one year simulation period,which can meet the requirements of underwater navigation precision,and thus can provide a reference basis for subsequent research on spaceborne GNSS-R sea surface altimetry.

Coastal bathymetry inversion using SAR-based altimetric gravity data:A case study over the South Sandwich Island

The global bathymetry models are usually of low accuracy over the coastline of polar areas due to the harsh climatic environment and the complex topography.Satellite altimetric gravity data can be a supplement and plays a key role in bathymetry modeling over these regions.The Synthetic Aperture Radar(SAR)altimeters in the missions like CryoSat-2 and Sentinel-3A/3B can relieve waveform contamination that existed in conventional altimeters and provide data with improved accuracy and spatial resolution.In this study,we investigate the potential application of SAR altimetric gravity data in enhancing coastal bathymetry,where the effects on local bathymetry modeling introduced from SAR altimetry data are quantified and evaluated.Furthermore,we study the effects on bathymetry modeling by using different scale factor calculation approaches,where a partition-wise scheme is implemented.The numerical experiment over the South Sandwich Islands near Antarctica suggests that using SARbased altimetric gravity data improves local coastal bathymetry modeling,compared with the model calculated without SAR altimetry data by a magnitude of 3:55 m within 10 km of offshore areas.Moreover,by using the partition-wise scheme for scale factor calculation,the quality of the coastal bathymetry model is improved by 7.34 m compared with the result derived from the traditional method.These results indicate the superiority of using SAR altimetry data in coastal bathymetry inversion.

Parallel-Dynamic Interpolation Algorithm of Sea Surface Height for Future 2D Altimetry Mapping of Sea Surface Height

The sea surface height data volume of the future wide-swath two-dimensional(2D)altimetric satellite is thousands of times greater than that of nadir altimetric satellites.The time complexity of the 2D altimetry mapping reaches O(n^(3)).It is challenging to map the global grid products of future 2D altimetric satellites.In this study,to improve the efficiency of global data mapping,a new algorithm called parallel-dynamic interpolation(PA-DI)was designed.Through the use of 2D data segmentation and fine-grained data mosaic methods,the parallel along-track DI processes were accelerated,and a fast and efficient spatial-temporal high-resolution and low-error enhanced mapping method was obtained.As determined from a comparison of the single-threaded DI with the PA-DI,the new algorithm optimized the time complexity from O(n^(3))to O(n^(3)/KL),which improved the mapping efficiency and achieved the expected results.According to the test results of the observing system simulation experiments,the PA-DI algorithm may provide an efficient and reliable method for future wide-swath 2D altimetric satellite mapping.

Analysis of the merged quasi-geoid of neighbouring areas

Employing the merged quasi-geoid, we analyses the causes of systematic errors in modelling of quasigeoid of neighbouring areas in the paper, and the efficient method is introduced to improve the accuracy of quasi-geoid. First, the systematic error is weakened with the moving window method applied to established quasi-geoids in two adjacent regions, and the accuracy of the merged quasi-geoid in the stitching region is checked using the measured GPS benchmark data; Second, the whole quasi-geoid is recomputed with data obtained from two adjacent regions if the accuracy of the quasi-geoid obtained from the first step in the stitching region is low; Finally, the quasi-geoids in two adjacent regions are recomputed respectively using GPS benchmark data of own region and adjacent region with the same solution if the accuracy of whole quasi-geoid obtained from the second step also is low. Actual data sets from Sichuan Province and Chongqing City are employed to test the moving window method. It is shown that the quasi-geoid models with high resolution and accuracy were obtained.

Direct regional quasi-geoid determination using EGM2008 and DEM:A case study for China's Mainland and its vicinity areas

Earth＇s gravity model（EGM） helps people better determine the figure of Earth, which is generally represented by a global geoid. For a considerable amount of practical applications, people use quasi-geoid to approximate the geoid, thus the quasi-geoid is also treated as an important height datum. In this study we revisit the method to directly determine regional quasi-geoid using EGM and digital elevation model（DEM）, on the basis of Molodensky theory. According to the method we obtain a 50 50quasi-geoid for China's Mainland and its vicinity areas, based on the EGM2008 gravitational potential model and the Shuttle Radar Topography Mission（SRTM） DEM model. By comparing height anomalies derived from EGM2008 with observations at 70 GPS/leveling points in areas including northwest,mid-west, mid-east and southeast of China, we find that the 50 50EGM2008 quasi-geoid well fits the GPS/leveling results, with average deviations less than 10 cm for the selected areas in east China（with mainly plain topography） and ~20 cm for the selected areas in west China（highland or mountainous areas）. We also discuss a few technical issues for directly determining height anomalies based on EGM and DEM, under the frame of Molodensky theory.

海洋重力似大地水准面与区域测高似大地水准面的拟合问题

研究了将陆地重力似大地水准面与GPS水准似大地水准面拟合的处理方法推广到海洋的问题,首先从理论上证明了当存在海面地形,则海洋大地水准面与似大地水准面不重合,导出了在海洋上大地水准面差距与高程异常之间差值的公式,由此给出了求定平均海面相对于区域高程基准的正常高以及测高似大地水准面的计算公式。由于测高平均海面与GPS大地高有相近的精度,提出了将海洋重力似大地水准面与区域测高似大地水准面拟合的处理方法,并利用当前最新的海面地形模型和测高平均海面模型做了数值估计。

由多卫星测高大地水准面推断西太平洋边缘海构造动力格局

由于卫星观测技术的发展 ,现在已能利用测高大地水准面简捷可靠地研究海底构造与动力问题 .根据GeosatT2 ERM、Topex Poseidon和ERS 1 2测高数据给定的 0°N～ 4 5°N、10 0°E～ 15 0°E范围内 4′× 4′大地水准面 ,采用全球地形 均衡的重力位效应改正 ,计算布格、格莱尼和均衡大地水准面 .由格莱尼大地水准面反演Moho面埋深 ,再从均衡大地水准面起伏推算小尺度地幔流应力场 .结果表明 ,菲律宾海和南海显示了与磁条带、扩张脊对应或斜交的高频成分大地水准面起伏条带 .各边缘海盆的Moho面埋深有往南变浅的趋势 ,与菲律宾海各海盆的Moho面埋深大致相当 ,说明琉球—台湾—菲律宾岛弧两侧的构造动力强度基本相近 .从各种构造特征和大、中、小尺度的地幔流应力场的驱动机制 ,可以证明岛弧内侧的边缘海具有不同于大洋、大陆的独特构造动力格局和特征 .

WAVEWATCHⅢ同化模块的建立和检验

将基于最优插值（OI）的同化并行模块植入全谱空间的第三代海浪模式 WAVEWATCH III ver-sion3.14,建立数据同化的海浪模式预报系统,并通过实际的预报个例对同化系统进行检验。个例实验是以5°S以北的印度洋海域为目标计算区域,海面风场强迫采用业务单位的中尺度天气预报模式WRF （weather research and forecast）提供的逐时海面风场预报产品。模式积分过程中连续同化2010年12月15日、16日和17日过境北印度洋的Jason-2卫星高度计沿轨有效波高（SWH）数据（需要指出的是,每次同化得到新的SWH分析场后需重构相应的二维海浪谱用于谱模式）。SWH同化分析值和无同化的对照组分别与高度计沿轨观测数据比较发现,就日平均统计来看,同化较无同化使SWH分析值的均方根误差减小约25%-50%。以 SWH同化分析场作为初始场的预报表明,同化对预报影响的时效性可延长至48-60 h。本研究目的是通过将高度计测量的SWH数据同化到海浪模式进一步提升海浪数值预报的准确度。

单臂架起重机起升-变幅系统的设计与仿真

从单臂架起重机吊重高度补偿的数学模型出发,求解分析得到了一种总体结构形式,并结合差动减速箱的传动方式,实现用一个减速器完成单臂架起重机的变幅和起升,在此基础上通过ADAMS/cable绳索模块仿真分析了系统变幅过程中吊重高度位移变化,并与数学模型MATLAB仿真结果对比,验证所设计的差动减速器满足工程实际需要。

联合多代卫星测高数据构建中国近海及邻域海平面异常序列

首先给出海面高的计算方法,并引入基于高斯滤波的粗差探测方法,有效地剔除了各弧段测高数据存在的粗差。通过对3颗卫星同步运行段测高数据的分析,得到3组数据在中国近海及邻域的平均偏差分别为:Jason-1相对T/P需改正-8.77 cm;Jason-2相对Jason-1需改正-7.33 cm,两者均小于其在全球海域的改正值。以T/P测高数据所得平均海平面为基础,利用改正后的Jason-1、Jason-2数据,得到该海域18年海平面异常时间序列,海平面平均上升速率约为4.9 mm/a。分别对中国近海各海域海平面异常时间序列进行分析,得到渤海、黄海、东海及南海的海平面平均上升速率分别为:2.5 mm/a、3.2 mm/a、3.6 mm/a和6.2 mm/a。将所得每周期离散正常点的观测数据格网化,然后逐格网计算海平面异常时间序列,得到研究海域18年来海平面异常平均上升速率的分布情况。结果表明,研究海域海平面上升速率高于全球平均水平。

基于虚拟仪器技术的无线电高度表动态测试系统

从无线电高度表工作原理的分析与研究出发,提出了基于虚拟仪器技术和I/Q调制器的无线电高度表动态测试系统的总体设计,同时对测试数据的处理理论进行了一定的分析和研究。结合高度表测试实例,采用基于数据采集卡的虚拟仪器方式完成了系统的构建。

近海多种卫星测高联合数据处理技术

海域海况复杂多变 ,潮汐不但受外海能量输入的控制 ,而且在复杂的海岸线、浅海海底和内陆河流运输的作用下变得异常复杂。卫星测高由于受复杂的海洋动力环境和陆地反射的影响 ,数据质量普遍较深海差。将多种卫星测高数据联合处理 ,可以大大提高近海海域平均海面高的精度与分辨率 ,增强测高卫星监测近海复杂动力现象与反演近海复杂动力机制的能力。本文讨论近海多种卫星联合数据处理的技术与方法 ,分别从提取海平面稳态和时变信息的角度较系统地研究了多种卫星测高联合数据处理方法 ,通过提取不同测高卫星海平面观测数据中与时间无关的系统偏差 ,建立多种卫星测高数据的海平面时变基准 ,从而将多种测高卫星海面监测数据融合到一个动力系统中。大大提高测高卫星海平面监测的时空分辨率 ,为联合多种卫星测高数据在大地测量与近海海洋动力学研究中的应用创造基本条件。

CQG2000似大地水准面模型在青藏高原地区区域重力调查中的应用

区域重力调查中,GPS高程测量的精度直接影响重力测量成果的精度。用国内最新研制的测绘科技成果——CQG2000似大地水准面模型,对GPS测得的大地高程进行改算,可得到较高精度的正常高成果。方法应用于青海三江流域1∶20万区域重力调查工作中,取得了较好的效果。

基于回归分析的卫星测高布格重力异常求取

根据海洋卫星测高技术推算出具有较高分辨率的海洋大地水准面高,基于重力场理论可计算得到卫星测高自由空气重力异常,再进行相关的校正可得到卫星测高布格重力异常。提出了一种新的方法计算卫星测高布格重力异常:基于一元线性回归分析方法,对已知海域船测布格重力异常和卫星测高自由空气重力异常间的相关性进行研究,计算出回归方程,进而求取相邻未知海域的卫星测高布格重力异常。研究结果表明,在海底地形起伏变化不大时,利用一元线性回归分析方法求取的卫星测高布格重力异常,能满足中等或者小比例尺的海洋地质与资源调查。

Comparing the steric height in the Nordic Seas with satellite altimeter sea surface height

In this study the steric height anomaly which is calculated from the hydrological data （EN3） is compared with the sea level anomaly derived from satellite altimetry in the Nordic Seas. The overall pattern of steric height is that it is higher in the margin area and lower in the middle area. The extreme values of steric height linear change from 1993 to 2010 occur in the Lofoten Basin and off the Norwegian coast, respectively. Such a distribution may be partly attributed to the freshening trend of the Nordic Seas. The correlation between SLA （sea level anomaly） and SHA （steric height anomaly） is not uniform over the Nordic Seas. The time series of SLA and SHA agree well in the Lofoten Basin and northern Norwegian Basin, and worse in the northern Norwegian Sea, implying that the baroclinic effect plays a dominant role in most areas in the Norwegian Sea and the barotropic effect plays a dominant role in the northern Norwegian Sea. The weaker correlations between SLA and SHA in the Greenland and Iceland Seas lead a conclusion that the barotropic contribution is significant in these areas. The area-mean SHA over the entire Nordic Seas has similar amplitudes compared with the SLA during 1996-2002, but SHA has become lower than SLA, being less than half of SLA since 2006.

Refining geoid and vertical gradient of gravity anomaly

We have derived and tested several relations between geoid （N） and quasi-geoid （~） with model validation. The elevation correction consists of the first-term （Bouguer anomaly） and second-term （vertical gradient of gravity anomaly）. The vertical gradient was obtained from direct measurement and terrain calcula- tion. The test results demonstrated that the precision of geoid can reach centimeter-level in mountains less than 5000 meters high.

Unification of national surveying vertical datum

The vertical datum of China is composed of leveling datum for heights and chart datum for depths. The determination of national leveling datum and its disadvantages were discussed firstly. The local mean sea level and chart datum with its guarantee rate of navigation safety were studied secondly. The models of unification of national surveying vertical datum, such as optimization model of mean sea level, adoption of New Chinese quasi-geoid of 2000(CQG2000) and time-invariant global geoid were suggested finally.

直升机气压高度速度传感器原位校准方法研究

针对气压高度速度传感器定期校准的要求,在考虑实际工作环境条件改变及传统校准方法存在风险的基础上,提出了一种可在试验现场原位校准的方法。在该方法中,为了提高校准结果的准确性,计入了环境温度变化对结果的影响且计算了整套校准装置的不确定度,验证了其符合性。利用该套校准装置完成了气压高度速度传感器的原位校准,通过与实验室校准数据比对,计算各点校准结果的|En|值且均小于1,验证了该方法的有效性。

Engineering coordinate system for vertical mine region based on GPS technique

For the problems existing in control network of vertical mine region established by conventional way, this paper advances a new scheme of establishing engineering coordinate system for vertical mine region. Based on the GPS positioning technique, through the relationship of coordinate transformation about a group of connecting points, the transforming parameters between the WGS-84 system and the Beijing54 system or Xi’an80 system about the region were calculated. The plane coordinate systems about the region can be maintained with a few of GPS control points using the method of GPS level, and fits the quasi-geoid about the region based on the Ellipsoid WGS-84. Huanghai Vertical Datum 1985 about the region can be maintained with the Ellipsoid WGS-84 as datum plane. Practice proves that there are advantages using the scheme to establish engineering coordinate system: the coordinate system as engineering foundation for vertical mine region will be in preservation for a long time; it is convenient and easy to carry out daily surveying work based on this coordinate system.

Tidal Analysis of High and Low Water Data

The harmonic analysis method based on high and low water levels is discussed in this paper. In order to make full use of the information of high and low water observations (the time derivative of water level at the observation time is zero), the weight coefficient, w, is introduced to control the importance of the part related to this information in the error formula. The major diurnal constituents, O 1 and K 1, and semi diurnal constituents, N 2, M 2 and S 2 are selected directly from the monthly data analysis, and some other important constituents, P 1, ν 2 and K 2, are included as the inferred constituents. The obtained harmonic constants of the major constituents are very close to those obtained from the analysis of hourly data, and this shows that high and low water data can be used to extract tidal constants with high accuracy. The analysis result also shows that the inference and the weighting coefficient are important in the high and low water data analysis, and it is suggested that w ≥1 should be taken in monthly high and low water data analysis. This analysis method can be used directly to analyze altimetric data with w =0.