联合多代卫星测高资料反演中国南海重力异常

联合HY-2A、Geosat、ERS1/2、Envisat、T/P、Jason1/2等多颗测高卫星,通过共线处理和交叉点平差削弱海面时变效应和径向轨道误差等影响,以Jason-1测高卫星作为参考,对多代测高卫星进行基准统一,消除测高数据的不一致性,基于全球EGM2008重力场模型,采用移去恢复技术和逆Vening-Meinesz公式反演中国南海(0°~23°N,103°~120°E)2'×2'重力异常,与船测重力数据比较,均方根误差为4.9m Gal。     

HY-2A卫星海面高度数据质量评估

对HY-2A卫星雷达高度计数据进行筛选获取有效的观测点,利用HY-2A卫星第18~23周期数据和同时在轨的Jason-2数据进行交叉点选取,对两颗卫星在交叉点海面高度异常值的差值进行统计与分析,提出了基于交叉点差值统计特征的筛除HY-2A轨道数据方法,评估了HY-2A卫星雷达高度数据质量。结果显示,HY-2A卫星18~23周期阈值筛选去除的点个数占总海洋观测点约12%,HY-2A海面高度异常与Jason-2海面高度异常的标准偏差在7.0 cm,数据精度满足设计精度要求。     

HY-2A测高数据对重力异常反演精度的影响分析

通过联合HY-2A、TP、Envisat卫星的高度计数据,分析HY-2A测高数据对中国南海重力异常影响。首先,将HY-2A和TP、Envisat数据进行对比,通过共线处理和交叉点平差前后的不符值RMS统计分析表明,HY-2A数据精度优于TP变轨后及Envisat数据精度;利用逆Venning-Meinesz公式分别计算中国南海海域(0°~23°N,103°E~120°E)15'×15'的重力异常,将反演结果与船测结果对比,HY-2A数据加入反演得到的重力异常精度在±6.13m Gal,其精度要优于没有HY-2A反演得到的结果,并分析反演重力异常与船测重力差值分布规律。结果表明,HY-2A数据对于提高海洋重力异常计算精度具有一定意义。     

一种建立南海浅海海域高精度潮汐模型方法的研究

针对应用高度计数据建立的海潮模型在浅海海域精度较低的现状,提出采用移去-恢复技术联合利用19a T/P、Jason-1卫星原始轨道、变轨轨道高度计数据建立南海浅海海域高精度潮汐模型的方法。处理卫星高度计数据时以平均海平面为基准面,按纬差0.1°间隔采用沿迹分析提取南海海域原始轨道2 184个正常点和变轨轨道1 626个正常点;分别对原始轨道、变轨轨道正常点进行调和分析以及响应分析,得到潮汐主要分潮调和常数;进一步建立网格潮汐模型,讨论了不同分辨率潮汐模型的精度差异。基于验潮站数据集结果运用移去-恢复技术对所建潮汐模型进行改进,改进后潮汐模型4个最主要分潮O_1,K_1,M_2和S_2的RMS分别提高至7.76,9.40,13.86和8.51cm,RSS达到20.32cm,表明移去-恢复技术能够明显改善潮汐模型在浅海海域的精度。     

基于Jason-2的Saral/AltiKa高度计全球统计评估与交叉定标

利用Jason-2同期观测的GDR数据对Saral/AltiKa观测的有效波高、后向散射系数、电离层延迟、对流层延迟等参数进行对比分析,发现各参数存在不同程度的差异,并在文中对差异原因进行了讨论分析。计算了Saral/AltiKa卫星升轨与降轨间的交叉点海面高差异,结果表明,其交叉点差值为(1.22±65.00)mm,与同期Jason-2的交叉点海面高差异(0.25±58.60)mm相当,同时计算Saral/AltiKa和Jason-2之间的交叉点海面高差异进行星间交叉定标,发现存在(-58.64±66.53)mm的交叉点不符值,研究结果与国外定标场的绝对定标结果一致。     

GM测高数据反演中国近海及邻域精细重力场

综合对比4种波形重跟踪算法,选择改进阈值法处理Jason-1GM数据,联合波形重跟踪后的Geosat和ERS-1GM数据,沿轨2Hz重采样以提高数据空间分辨率。通过数据质量控制剔除粗差数据,考虑海表面地形的影响,基于移去-恢复法和维宁-曼齐兹公式反演了中国近海及邻近海域(0°~45°N,100°~140°E)1′×1′的精细重力场。船测数据检核表明反演结果在开阔海域精度约4mGal,近岸浅水区约10mGal,均优于DTU10和V21.1模型。     

HY-2卫星雷达高度计时标偏差估算

卫星雷达高度计是海洋遥感监测的重要传感器之一,测高系统和定轨系统是高度计重要的组成部分。若两系统使用不同的系统时钟,则获得的轨道高度和卫星测距值之间可能会存在一个时标偏差,该时标偏差会降低卫星雷达高度计的海面高度测量精度。针对HY-2卫星雷达高度计的时标偏差问题,本文分析了时标偏差对测高精度的影响,介绍了一种使用自交叉点数据估算时标偏差值的方法,并基于HY-2卫星雷达高度计第21个周期数据开展了时标偏差修正实验。时标偏差修正后HY-2自交叉点的海面高度差值(也称"不符值")分布收敛程度有了明显的提高,其RMS均方根值从24.7 cm减小到了7.0 cm,HY-2与Jason-2互交叉点的不符值的RMS也从16.6 cm减小到了7.3 cm。这表明本文介绍的时标偏差修正方法可有效地提高HY-2卫星雷达高度计的测高精度。     

基于与Jason-2数据比对的Jason-3卫星高度计全球数据质量评估

Jason-3卫星高度计于2016年1月17日成功发射,2016年2月12日进入预定轨道,与Jason-2高度计同轨进入编队飞行阶段,并落后Jason-2高度计约1分20秒,两者相距约560 km。2016年9月1日,Jason-2高度计变换轨道,编队飞行阶段结束,两高度计进入平行轨道,以增加卫星高度计对地观测的空间覆盖。本研究主要开展了Jason-3高度计的数据质量的评估与检验,包括Jason-3高度计数据可用性和有效性的验证,以及Jason-3高度计和校正辐射计各参数的数据质量监测。重点开展了Jason-2与Jason-3高度计各项参数的综合比较,利用Jason-2与Jason-3高度计编队飞行阶段的数据精确评估了两高度计参数的一致性,并从全球数据角度分析了Jason-3高度计获取各参数的能力以及稳定性;通过与Jason-2互交叉点比较分析评估Jason-3高度计海面高度数据质量情况,验证Jason-3高度计数据精度。结果表明,Jason-3高度计的数据质量满足高度计测高的要求,具有与Jason-1、Jason-2、T/P等高度计相同或更高的测高精度以监测全球海平面变化,此外,Jason-3有效波高参数数据质量明显优于Jason-2高度计。     

中国近岸海域高度计JASON-1测量数据的波形重构算法研究

卫星雷达高度计的测量数据目前已被广泛应用于各个领域,但高度计在近海的测量数据却一直不可用,一方面是因为高度计在近岸海域的回波波形测量受陆地回波的影响,另一方面是因为一些校正量对近海不准确,如大气湿对流层校正、海洋潮汐校正以及大气高频因数校正等。通过对高度计在近海测量的回波波形进行重构处理,可以缩短近海数据不可用的距离,提高数据的数量和质量。以我国海域及邻近海域(14°~45°N,105°~130°E)为研究区域,采用四种波形重构算法(海洋算法、重力中心偏离算法、冰层算法二和阈值算法)对JASON-1高度计1 a共31个周期的测量波形重新进行了计算,比较了轨道交叉点处升轨和降轨的海面高度异常值以及海面高度值与验潮站的实测水位,结果表明重力中心偏离法比其他三种算法更适合我国近海的测高波形重构:计算结果精度最高,有效数目最多。     

联合多卫星测高数据确定中国近海及其邻域垂线偏差

联合T/P数据、T/P新轨道数据、Jason-1数据、Jason-1新轨道数据、Jason-2数据、Geosat/GM数据、Geosat/ERM数据、Envisat RA-2数据、ERS-1/ERM和ERS-2/ERM数据,基于EGM2008重力场模型,用相邻测高点大地水准面高度的一次差分求沿轨垂线偏差,然后基于最小二乘原理,采用求最小范数逆的方法,直接解算中国近海及其邻域(0°～42°N,102°～138°E)2′×2′分辨率网格点垂线偏差子午分量和卯酉分量。计算结果与EGM2008模型垂线偏差相比,子午分量的RMS为0.91″,卯酉分量的RMS为0.27″。     

Global Statistical Assessment and Cross-Calibration with Jason-2 for Reprocessed HY-2 A Altimeter Data

HY-2 A (Haiyang-2 A) satellite was launched on August 16, 2011 and radar altimeter is one of its main payloads. We reprocessed two years of HY-2 A altimeter sensor geophysical dataset records (SGDR) data. This paper presents the main results in terms of reprocessed HY-2 A altimeter data quality: verification of data availability and validity, monitoring several relevant altimeter parameters, and assessment of the HY-2 A altimeter system performances. A cross-calibration analysis of reprocessed HY-2 A altimeter data with Jason-2 was conducted. The reprocessed HY-2 A altimeter data show good quality and have a low level of noise with respect to Jason-2. The same geophysical correction methods were used to calculate the sea surface height (SSH) for the two missions. The mean standard deviations of the crossover differences for HY-2 A and Jason-2 are 5.24 cm and 5.34 cm, respectively. The mean standard deviation of the crossover differences between HY-2 A and Jason-2 is 5.37 cm. These show that HY-2 A can provide SSH measurements at almost the same level of accuracy as Jason-2. The relative SSH bias between HY-2 A and Jason-2 due to the Ultra Stable Oscillator (USO) drift is obviously observed, and it can affect the calculation of mean sea level and should be further studied and corrected.     

利用GPS拖体在万山区域测量平均海面技术研究

Wanshan area has been chosen to be the specified field to calibrate and validate(Cal/Val) the HY-2 altimeter and its follow-on satellites. In March 2018, an experiment has been conducted to determine the sea surface height(SSH) under the HY-2 A ground track(Pass No. 203). A GPS towing-body(GPS-TB) was designed to measure the SSH covering an area of about 6 km×28 km wide centered on the HY-2 A altimeter satellite ground track. Three GPS reference stations, one tide gauge and a GPS buoy were placed in the research area, in order to process and resolve the kinematic solution and check the precision of the GPS-TB respectively. All the GPS data were calculated by the GAMIT/GLOBK software and TRACK module. The sea surface was determined by the GPS-TB solution and the tide gauge placed on Zhiwan Island. Then the sea surface of this area was interpolated by Arc GIS10.2 with ordinary Kriging method. The results showed that the precision of the GPS-TB is about 1.10 cm compared with the tide gauge placed nearby, which has an equivalent precision with the GPS buoy. The interpolated sea surface has a bias of –1.5–4.0 cm with standard deviation of 0.2–2.4 cm compared with the checking line. The gradient of the measured sea surface is about 1.62 cm/km along the HY-2 orbit which shows a good agreement compared with the CLS11 mean sea surface(MSS). In the Cal/Val of satellites, the sea surface between the tide gauge/GPS buoy and the footprint of altimeter can be improved by this work.     

HY-2A卫星雷达高度计数据的全球统计评价及质量分析

自HY-2A卫星发射以来,针对HY-2A卫星雷达高度计产品的交叉定标、真实性检验及质量评估工作一直在持续开展。本文主要以HY-2A卫星高度计第44周期的IGDR产品数据为例,通过使用全球分布图、二维直方图和每日均值统计的方法完成了与Jason-2IGDR产品的比对验证,同时对主要环境校正参数及地球物理产品的数据质量稳定性进行了分析,结果显示高度计产品数据质量较稳定,此外利用HY-2A卫星升降轨交叉点海面高度差、与Jason-2卫星交叉点海面高度差以及沿轨海平面异常数据分析的方法进行了HY-2A卫星高度计观测系统的性能评估,结果显示,HY-2A卫星海面高度精度约为7.48cm,精度接近Jason-2,能满足海洋应用与科学研究的需要。     

HY-2C卫星海面高度数据的质量分析

卫星海面高度数据对于监测全球海面高度具有重要的意义,所以卫星高度数据的定标和检验变得至关重要。海洋二号C（HY-2C）卫星是继海洋二号B卫星后的第二颗业务卫星,于2020年成功发射升空。然而,目前对HY-2C卫星高度计的数据质量了解甚少,所以对HY-2C卫星的海面高度数据进行质量分析具有重要的意义。本文以同期观测的HY-2B卫星和Jason-3卫星的地球物理数据（GDR）为参考,对HY-2C卫星遥感地球物理数据（SGDR）中的海面高度数据进行质量分析。结果显示,在星星交叉定标中使用3种常见的交叉定标插值方法对HY-2C卫星的海面高度异常数据进行自交叉点分析时,HY-2C卫星海面高度异常数据质量分析的结果不同。其中使用三次样条插值方法进行质量分析的结果最优,得到海平面高度异常差的平均值为0.03 cm,标准差为6.17 cm。此外,对HY-2C卫星和HY-2B卫星互交叉点海面高度异常差异的平均值为?0.47 cm,标准差为5.32 cm;HY-2C卫星SGDR与Jason-3卫星GDR的海面高度异常数据进行互交叉点分析,得到海平面高度异常差的平均值为?0.3 cm,标准差为5.32 cm,这些数据表明HY-2C卫星的测高精度与HY-2B卫星、Jason-3卫星一致。因此HY-2C高度计产品数据质量稳定,能满足海洋应用和科学研究的需要。     

Absolute calibration of HY-2A and Jason-2 altimeters for sea surface height using GPS buoy in Qinglan,China

GPS buoy methodology is one of the main calibration methodologies for altimeter sea surface height calibration. This study introduces the results of the Qinglan calibration campaign for the HY-2A and Jason-2 altimeters. It took place in two time slices;one was from August to September 2014, and the other was in July 2015. One GPS buoy and two GPS reference stations were used in this campaign. The GPS data were processed using the real-time kinematic (RTK) technique. The fi nal error budget estimate when measuring the sea surface height (SSH) with a GPS buoy was better than 3.5 cm. Using the GPS buoy, the altimeter bias estimate was about -2.3 cm for the Jason-2 Geophysical Data Record (GDR) Version ‘D' and from -53.5 cm to -75.6 cm for the HY-2A Interim Geophysical Data Record (IGDR). The bias estimates for Jason-2 GDR-D are similar to the estimates from dedicated calibration sites such as the Harvest Platform, the Crete Site and the Bass Strait site. The bias estimates for HY-2A IGDR agree well with the results from the Crete calibration site. The results for the HY-2A altimeter bias estimated by the GPS buoy were verifi ed by cross-calibration, and they agreed well with the results from the global analysis method.     

Global Calibration of SARAL/AltiKa Using Multi-Mission Sea Surface Height Crossovers

SARAL/AltiKa completed its first year in orbit in March 2014. The 1 Hz GDR-T data of the first 10 cycles of the mission are used to perform a comprehensive quality assessment by means of a global multi-mission crossover analysis. Within this approach, SARAL sea surface heights are compared with data from other current missions, mainly Jason-2 and Cryosat-2, to reveal its accuracy and consistency with the other altimeter systems. Alongside with global mean range bias and instrumental drifts, investigations on geographically correlated errors as well as on the realization of the systems origin are performed. The study proves the high quality and reliability of SARAL. The mission shows only a small range bias of about ?5 cm with respect to Jason-2 and neither significant time-tag bias nor instrumental drifts. With 1.3 cm the scatter of radial errors is in the same order of magnitude as for Cryosat-2 and Jason-1 GM and will probably further improve using an enhanced sea state bias (SSB) model. However, the wet tropospheric corrections from SARAL radiometer still show some systematic effects influencing the range bias as well as geographically correlated error patterns and the z-component of the origin. Improved inflight calibration will be necessary to overcome these effects.     

Absolute Calibration of Jason-1 and TOPEX/Poseidon Altimeters in Corsica Special Issue: Jason-1 Calibration/Validation

The double geodetic Corsica site, which includes Ajaccio-Aspretto and Cape Senetosa (40 km south Ajaccio) in the western Mediterranean area, has been chosen to permit the absolute calibration of radar altimeters. It has been developed since 1998 at Cape Senetosa and, in addition to the use of classical tide gauges, a GPS buoy is deployed every 10 days under the satellites ground track (10 km off shore) since 2000. The 2002 absolute calibration campaign made from January to September in Corsica revealed the necessity of deploying different geodetic techniques on a dedicated site to reach an accuracy level of a few mm: in particular, the French Transportable Laser Ranging System (FTLRS) for accurate orbit determination, and various geodetic equipment as well as a local marine geoid, for monitoring the local sea level and mean sea level. TOPEX/Poseidon altimeter calibration has been performed from cycle 208 to 365 using M-GDR products, whereas Jason-1 altimeter calibration used cycles from 1 to 45 using I-GDR products. For Jason-1, improved estimates of sea-state bias and columnar atmospheric wet path delay as well as the most precise orbits available have been used. The goal of this article is to give synthetic results of the analysis of the different error sources for the tandem phase and for the whole studied period, as geophysical corrections, orbits and reference frame, sea level, and finally altimeter biases. Results are at the millimeter level when considering one year of continuous monitoring; they show a great consistency between both satellites with biases of 6 ± 3 mm (ALT-B) and 120 ± 7 mm, respectively, for TOPEX/Poseidon and Jason-1.     

Ku– and Ka-band Altimeter Data in the Northwestern Mediterranean Sea: Impact on the Observation of the Coastal Ocean Variability

The strong increase in altimeter measurement errors near land surfaces is a limiting factor for coastal applications. We analyze the performance of the new Ka-band SARAL/AltiKa (SRL) mission in the northwestern Mediterranean Sea. SRL sea surface height (SSH) measurements are compared with those from the Jason-2 Ku-band satellite mission. The results show a significant increase in both quantity and quality of SSH data available near coastlines when using SRL data. Available edited data are 95.1% of SRL compared with 88.6% for Jason-2. Closer than 10 km to the coastline, available SRL data are still about 60% and only about 31% for Jason-2. Comparisons of the altimeter sea level variations are made with available coastal tide gauge data. The differences obtained between altimeter and tide gauge SLA time series are reduced for SRL (3.3 cm in average) compared with Jason-2 (4.2 cm in average), especially closer than 30 km to the land. It results in higher correlations (by 30%) obtained with SRL data. The coastal circulation derived from altimetry using SRL data shows an offshore meandering, which is more stable in time and with larger velocities close to the coast than that derived from Jason-2 observations.     

卫星高度计海面风速的校准与验证

为了改善不同卫星高度计海面风速数据之间的一致性,以浮标数据为基准,对国内的HY-2A和国外的T/P、GFO、Jason-1、Envisat、Jason-2、CryoSat-2共7颗卫星高度计的海面风速数据进行了分析,给出了各个卫星高度计的海面风速校准公式,并对其校准效果进行了验证。验证结果表明:各个卫星高度计的海面风速在经过校准后,与浮标海面风速差异的均值和均方根都有所降低,其中HY-2A最为显著。经过校准后所有卫星高度计的海面风速与浮标海面风速差异的均值都在±0.2m/s以内。除了HY-2A、GFO和Jason-1,其余4颗卫星高度计校准后的海面风速与浮标海面风速差异的均方根都在1.6m/s以下。由此可以得出结论,利用本文的校准公式对各个卫星高度计(特别是HY-2A卫星高度计)的海面风速进行校准,可以有效减少其与浮标海面风速之间的差异。