HY-2A卫星雷达高度计海面高度测量分析与评估

HY-2A卫星是我国首颗自主海洋动力环境卫星,已连续运行6年多。卫星上搭载的主载荷雷达高度计能够实现全天候、全天时全球海面高度、有效波高和海面风速的观测,这些观测数据已经广泛用于海洋防灾减灾、资源开发和海上安全等领域。为了全面了解HY-2A卫星雷达高度计多年来的整体观测性能,本文选取了2012年10月26日至2017年8月27日间的全部观测数据IGDR产品进行综合评价。通过自交叉和与Jason-2互交叉两种手段对HY-2A卫星雷达高度计测高能力进行评估。计算HY-2A升降轨自交叉点的测高不符值,发现HY-2A卫星雷达高度计在近全球海域内、升降轨高度异常差小于30cm的限制条件下,平均绝对高度误差为5.81cm,高度异常标准差为7.76cm;限制观测区域为南北纬60°范围内、海面高度异常升降轨交叉点处的差小于10cm的情况下,平均绝对误差可达3.95cm,海面高度异常标准差达4.76cm。通过和Jason-2卫星的互交叉,发现在南北纬66°范围内,交叉点高度异常差小于30cm的情况下,HY-2A和Jason-2的海面高度异常平均绝对误差为5.86cm,标准差为7.52cm,如果在该海域内将海面高度异常差限制在10cm内,平均绝对误差和标准差分别达到4.19cm和4.98cm。HY-2A卫星雷达高度计已经达到国际同类卫星雷达高度计测高水平,可以满足海洋科学研究、海洋环流反演等的需求。     

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-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。     

HY-2A/GM高度计数据反演的初步海洋重力场

HY-2 A(Haiyang-2 A), launched in 2011, is the first ocean dynamic environment satellite of China and is equipped with a radar altimeter as one of the primary payloads. HY-2 A shifted the drift orbit in March 2016 and has been accumulating geodetic mission(GM) data for more than three years with 168-day cycle. In this paper, we present the preliminary gravity field inverted by the HY-2 A/GM data from March 2016 to December 2017 near Taiwan(21°–26°N, 119°–123°E). The gravity anomaly is computed by Inverse Vening Meinesz(IVM) formula with a onedimensional FFT method during remove-restore procedure with the EGM2008 gravity model as the reference field. For comparison, CryoSat-2 altimeter data are used to inverse the gravity field near Taiwan Island by the same method. Comparing with the gravity field derived from CryoSat-2, a good agreement between the two data sets is found. The global ocean gravity models and National Geophysical Data Center(NGDC) shipboard gravity data also are used to assess the performance of HY-2 A/GM data. The evaluations show that HY-2 A and CryoSat-2 are at the same level in terms of gravity field recovery and the HY-2 A/GM altimeter-derived gravity field has an accuracy of 2.922 mGal. Therefore, we can believe that HY-2 A will be a new reliable data source for marine gravity field inversion and has the potentiality to improve the accuracy and resolution of the global marine gravity field.     

HY-2A卫星高度计有效波高信息提取业务化算法

2011年8月16日我国成功发射了第一颗自主海洋动力环境卫星HY-2A,有效波高是其搭载的雷达高度计可获取的重要海洋动力环境参数之一。本文详细介绍了应用于HY-2A雷达高度计的有效波高信息提取业务化算法,该算法通过迭代最小二乘拟合方法提取有效波高信息。同时,基于HY-2A雷达高度计业务化运行获取的有效波高数据,分别与Jason-2卫星高度计有效波高和NDBC浮标海浪波高数据进行了比对分析。比较结果表明,HY-2A雷达高度计与Jason-2有效波高的标准偏差为-0.26m,RMS为0.58m;HY-2A高度计与NDBC浮标数据间的标准偏差为-0.22m,RMS为0.37m。结果证明了目前应用于HY-2A雷达高度计业务化运行中的有效波高信息提取算法的可行性。     

中国HY-2卫星雷达高度计有效波高真实性检验

Chinese Haiyang-2(HY-2) satellite is the first Chinese marine dynamic environment satellite. The dual-frequency(Ku and C band) radar altimeter onboard HY-2 has been working effective to provide operational significant wave height(SWH) for more than three years(October 1, 2011 to present).We validated along-track Ku-band SWH data of HY-2 satellite against National Data Buoy Center(NDBC) in-situ measurements over a time period of three years from October 1, 2011 to September 30, 2014, the root mean square error(RMSE) and mean bias of HY-2SWH is 0.38 m and(–0.13±0.35) m, respectively. We also did cross validation against Jason-2 altimeter SWH data,the RMSE and the mean bias is 0.36 m and(–0.22±0.28) m, respectively. In order to compare the statistical results between HY-2 and Jason-2 satellite SWH data, we validated the Jason-2 satellite radar altimeter along-track Ku-band SWH data against NDBC measurements using the same method. The results demonstrate the validation method in this study is scientific and the RMSE and mean bias of Jason-2 SWH data is 0.26 m and(0.00±0.26) m,respectively. We also validated both HY-2 and Jason-2 SWH data every month, the mean bias of Jason-2 SWH data almost equaled to zero all the time, while the mean bias of HY-2 SWH data was no less than –0.31 m before April2013 and dropped to zero after that time. These results indicate that the statistical results for HY-2 altimeter SWH are reliable and HY-2 altimeter along-track SWH data were steady and of high quality in the last three years. The results also indicate that HY-2 SWH data have greatly been improved and have the same accuracy with Jason-2SWH data after April, 2013. SWH data provided by HY-2 satellite radar altimeter are useful and acceptable for ocean operational applications.     

基于核函数NPSSB模型的HY-2A卫星雷达高度计海况偏差研究

利用机器学习的方法,对14个周期HY-2A卫星高度计数据:风速、有效波高和海面高度差值进行训练,探究海况偏差和风速、有效波高之间的关系,创建海况偏差核函数非参数模型(NPSSB),并与参数模型中具有代表性的BM3、BM4模型进行对比。研究表明:(1)核函数NPSSB模型能够很好的反映SSB与U、SWH之间的关系,SSB与U呈二次函数关系,SSB与SWH呈反比例函数关系;(2)核函数NPSSB模型对SSB的模拟能力与训练数据集相关,数据量越多,模拟能力越好;(3)核函数NPSSB模型与BM3、BM4模型都存在0～-0.03 m的差值,随着风速和有效波高的增加,差值的绝对值越大。     

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。     

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。     

基于HY-2卫星高度计机载校飞数据的有效波高信息提取及初步分析

利用HY-2卫星雷达高度计校飞数据,开展了有效波高信息提取及精度比对研究。首先对其进行波形筛选、1s平均和去噪,然后基于Hayne海面回波模型进行波形拟合,提取出波高均方根并得到有效波高,并与浮标和同轨迹的Jason-1卫星高度计有效波高进行了比较。结果表明,本次校飞其高度计测波精度存在系统偏差,初步分析可能是其数据未经仪器校正等原因导致。     

Preliminary results of the global ocean tide derived from HY-2A radar altimeter data

The HY-2A satellite, which is equipped with a radar altimeter and was launched on August 16, 2011, is the first Chinese marine dynamic environmental monitoring satellite. Extracting ocean tides is one of the important applications of the radar altimeter data. The radar altimeter data of the HY-2A satellite from November 1, 2011 to August 16, 2014 are used herein to extract global ocean tides. The constants representing the tidal constituents are extracted by HY-2A RA data with harmonic analysis ...     

基于浮标数据的卫星雷达高度计海浪波高数据评价与校正

卫星雷达高度计是海浪有效波高（significant wave height,SWH）观测的重要手段之一,本文利用时空匹配方法对T/P、Jason-1、Envisat、Jason-2、Cryosat-2和HY-2A共6颗卫星雷达高度计SWH数据与NDBC（National Data Buoy Center,NDBC）浮标SWH数据进行对比验证,并对雷达高度计SWH数据进行校正。全部卫星雷达高度计SWH数据时间跨度为1992年9月25日到2015年9月1日,对比验证NDBC浮标共53个,包括7个大洋浮标。精度评价发现除T/P外,各卫星雷达高度计SWH的RMSE都在0.4~0.5 m之间,经过校正后,RMSE都有显著下降,下降程度最大为13.82%;对于大洋浮标,评价结果RMSE在0.20~0.28 m之间,结果明显优于全部NDBC浮标的精度评价结果;HY-2A卫星雷达高度计SWH在经过校正后数据质量与国外其他5颗卫星雷达高度计SWH数据质量差异较小。     

Assessment of reprocessed sea surface height measurements derived from HY-2A radar altimeter and its application to the observation of 2015–2016 El Ni?o

Haiyang-2A(HY-2A) is China's first ocean dynamic environment satellite and the radar altimeter is one of its main payloads. One of the main purposes of the radar altimeter is to measure the sea surface height(SSH). The SSH determined from the altimeter range measurements includes some range and geophysical corrections. These corrections largely affect the accuracy of the SSH measurements. The range and the geophysical corrections are reprocessed and the altimeter waveforms in HY-2A sensor interim geophysical data set records(S-IGDR) are retracked from June 1, 2014 to June 14, 2014, and the accuracy of the reprocessed SSH measurements is evaluated.The methods of the range and geophysical corrections used to reprocess HY-2A altimeter data are validated by using these methods to reprocess the Jason-2 range and geophysical corrections and comparing the results with the range and geophysical corrections in Jason-2 geophysical dataset records(GDR) product. A crossover analysis is used to evaluate the accuracy of the reprocessed HY-2A SSH measurements. The standard deviation(STD) of the crossover SSH differences for HY-2A is around 4.53 cm while the STD of the SSH differences between HY-2A and Jason-2 is around 5.22 cm. The performance of the reprocessed HY-2A SSH measurements is significantly improved with respect to the SSH measurements derived from HY-2A interim geophysical dataset records(IGDR)product. The 2015–2016 El Ni?o has been the strongest El Ni?o event since 1997–1998. The range and the geophysical corrections in HY-2A IGDR are reprocessed and sea level anomalies are used to monitor the2015–2016 El Ni?o. The results show that the HY-2A altimeter can well observe the 2015–2016 El Ni?o.