基于GNSS浮标和验潮资料的HY-2A卫星高度计绝对定标

为探测我国HY-2A卫星高度计海面高测量绝对偏差及其在轨运行状态,本文利用GNSS浮标星下点同步测量和验潮资料海面高传递方法在山东千里岩和珠海担杆岛海域开展定标研究。为验证GNSS浮标定标方法的准确性,还对国外卫星Jason-2和Saral进行了定标实验。实验表明GNSS浮标绝对海面高测量精度达2 cm,对Jason-2和Saral高度计多个周期定标得到的海面高偏差均值分别为5.7 cm和-2.3 cm,与国际专门定标场的结果符合较好。2014年9月和2015年5月HY-2A卫星高度计浮标定标结果分别是-65 cm和-91 cm,因两次结果差异显著,故又利用千里岩验潮站资料对HY-2A卫星高度计第56至73周期进行了定标分析,结果证明HY-2A卫星海面高存在约-51 cm/a的漂移,置信度为95%的回归分析表明浮标和验潮定标结果符合。本文研究结果表明在我国尚无专门定标场的情况下,可利用GNSS浮标对我国高度计实施灵活、精准的在轨绝对定标,在有高度计轨迹经过验潮站的情况下可使用验潮资料结合精密大地水准面模型进行绝对定标。     

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。     

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。     

基于珠海万山定标场沿岸验潮仪的HY-2B雷达高度计定标研究

随着我国海洋二号B卫星(HY-2B)于2018年10月发射成功,国家卫星海洋应用中心于珠海万山进行了HY-2B的在轨测试。试验利用沿岸验潮仪,在珠海万山直湾岛HY-2B过境轨道375的星下点附近进行了由2018年11月3日至12月12日的验潮仪定标试验。在试验期间,HY-2B共重访定标场星下点3次,定标结果表明:3个周期的HY-2B雷达高度计测量海面高度定标结果良好,定标参数分别为(3.06±3.48) cm、(2.85±1.03) cm、?7.41 cm;定标参数在前3个周期存在一定漂移,需要后续的定标工作以确定漂移原因。     

卫星高度计海上定标场及定标方法研究进展

介绍了卫星高度计定标中海面高度和后向散射系数的定标方法。在后向散射系数的定标中介绍了利用有源定标器和微波辐射计定标两种方法。结合卫星高度计的特点,提出了海上定标场选取所需注意的问题,并介绍了目前比较成功的几个定标场及其定标结果,旨在为我国今后发射的卫星高度计绝对定标和定标场的选取提供依据。     

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。     

中国海洋水色遥感器瑞利散射定标研究

水色遥感是海洋环境监测的主要技术手段之一.对于任何海洋水色遥感器来说,监测其在轨期间的定标系数变化是非常重要的,否则无法得到精确的定量产品.以我国“HY-1B”卫星水色遥感器为研究对象,开展了基于大洋水体上空的瑞利散射定标方法研究,利用通过对SeaWiFS数据叶绿素、离水辐亮度和气溶胶产品进行分析,选择了符合条件的7个海区实施大气瑞利散射定标,根据2010年12月份选定的4个区域定标结果得到不同海区/不同时间获得的定标系数一致性较好,CH1至CH6的定标系数标准差分布在0.9％～2.1％的范围内,因此瑞利散射定标是有效的非现场定标方法,具有较高的定标精度,其总误差在4.09％.     

HJ-1A星辐射定标及近海水体大气校正的精度验证

以应用HJ-1A星数据进行近海水体定量反演为目的,对HJ-1A星CCD的星上定标系数的精度进行验证,并基于Landsat-5TM数据对其进行交叉定标。在此基础上反演近海水体的反射率,将反演结果与实测水体反射率进行比较发现:对HJ-1A星CCD数据进行交叉定标能在一定程度上能提高近海水体反射率反演的精度。结果表明,HJ-1A星CCD影像的星上定标系数不够精确,在利用该数据进行近海水体的定量反演研究时,需要利用交叉定标对星上定标参数进行修正。     

利用南海石油平台的卫星雷达高度计定标与检验

在对南海石油平台所处的南海北部海域海底地形、平均海平面、风浪时空分布等进行分析基础上,利用南海石油平台水位计对Jason-2卫星高度计进行了测高绝对定标,定标结果为30.9 cm±7.8 cm,分析发现南海北部中尺度涡可能对定标结果产生影响;利用南海石油平台测波雷达对Jason-1高度计有效波高进行了精度检验,Jason-1高度计Ku波段和C波段有效波高测量的均方根误差分别为0.43 m和0.45 m。分析和检验结果表明,南海石油平台所处海洋环境条件、平台上装载的水位计和测波雷达均满足卫星雷达高度计定标与检验要求。南海石油平台定标场预期可用于中国海洋二号卫星和其他卫星高度计的定标与检验。     

卫星测高定标场选址中有效波高因素分析

利用Jason-3卫星在国外4个主要卫星高度计定标场所在海域的测量数据,分析了这些海域的有效波高变化特性。在我国大陆沿岸选取了Jason-3卫星经过的12个海域,分析了它们的有效波高变化特性,给出了在我国大陆沿岸建设卫星测高定标场的选址建议。Bass、Corsica、Gavdos等3个定标场海域的平均有效波高约为1.1 m,说明平均有效波高1.1 m及以下的海域适用于建设定标场。选定的12个沿岸海域中,渤海及黄海海域平均有效波高小于0.8 m,显著小于东海及南海1.3～1.5 m平均有效波高,单独从有效波高的角度渤海及黄海海域更适合于建设卫星高度计定标场。     

Statistical Evaluation of the Jason-1 Operational Sensor Data Record

The Jason-1 satellite altimeter mission represents a first step towards operational oceanography from satellite altimeter missions. An operational data product, the Operational Sensor Data Record (OSDR), provides measurements from the on-board altimeter and radiometer within 3-5 h of real time. This data product is a wind and wave product that is aimed towards near-real-time meteorological applications. A higher accuracy and more detailed data product, the Interim Geophysical Data Record (IGDR), that is better suited to detailed scientific studies of ocean topography, is available no sooner than 2-3 days from real time. The measurements reported on the OSDR primarily differ from those on the IGDR in that the OSDR reports measurements derived from on-board processing of the altimeter waveforms, while ground retracking of the waveforms is performed for the IGDR. The altimeter-derived measurements on the OSDR are validated through a statistical evaluation of the differences between data on the OSDR and IGDR. In doing so, the impact of ground retracking of the altimeter waveforms is also illustrated.     

Statistical Evaluation of the Jason-1 Operational Sensor Data Record Special Issue: Jason-1 Calibration/Validation

The Jason-1 satellite altimeter mission represents a first step towards operational oceanography from satellite altimeter missions. An operational data product, the Operational Sensor Data Record (OSDR), provides measurements from the on-board altimeter and radiometer within 3–5 h of real time. This data product is a wind and wave product that is aimed towards near-real–time meteorological applications. A higher accuracy and more detailed data product, the Interim Geophysical Data Record (IGDR), that is better suited to detailed scientific studies of ocean topography, is available no sooner than 2–3 days from real time. The measurements reported on the OSDR primarily differ from those on the IGDR in that the OSDR reports measurements derived from on-board processing of the altimeter waveforms, while ground retracking of the waveforms is performed for the IGDR. The altimeter-derived measurements on the OSDR are validated through a statistical evaluation of the differences between data on the OSDR and IGDR. In doing so, the impact of ground retracking of the altimeter waveforms is also illustrated.     

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。     

Absolute Calibration of the Jason-1 Altimeter Using UK Tide Gauges

This article describes an “absolute” calibration of Jason-1 (J-1) altimeter sea surface height bias using a method developed for TOPEX/Poseidon (T/P) bias determination reported previously. The method makes use of U.K. tide gauges equipped with Global Positioning System (GPS) receivers to measure sea surface heights at the same time, and in the same geocentric reference frame, as Jason-1 altimetric heights recorded in the nearby ocean. The main time-dependent components of the observed altimeter-minus-gauge height-difference time series are due to the slightly different ocean tides at the gauge and in the ocean. The main harmonic coefficients of the tide differences are calculated from analysis of the copious TOPEX data set and then applied to the determination of T, P, and J-1 bias in turn. Datum connections between the tide gauge and altimetric sea surface heights are made by means of precise, local geoid differences from the EGG97 model. By these means, we have estimated Jason-1 altimeter bias determined from Geophysical Data Record (GDR) data for cycles 1–61 to be 12.9 cm, with an accuracy estimated to be approximately 3 cm on the basis of our earlier work. This J-1 bias value is in close agreement with those determined by other groups, which provides a further confirmation of the validity of our method and of its potential for application in other parts of the world where suitable tide gauge, GPS, and geoid information exist.     

Comparison of Sea Surface Heights Derived from Satellite Altimetry and from Ocean Bottom Pressure Gauges: The SW Pacific MOTEVAS Project

A bottom pressure gauge (BPG) was installed in proximity (3.7 km at closest approach) of Jason-1 and formerly TOPEX/Poseidon (T/P) ground track No. 238 at the Wusi site, located ∼ 10 km offshore off the west coast of Santo Island, Vanuatu, Southwest (SW) Pacific. Sea level variations are inferred from the bottom pressure, seawater temperature, and salinity, corrected for the measured surface atmospheric pressure. The expansion of the water column (steric increase in sea surface height, SSH) due to temperature and salinity changes is approximated by the equation of state. We compare time series of SSH derived from T/P Side B altimeter Geophysical Data Records (GDR) and Jason-1 Interim Geophysical Data Records (IGDR), with the gauge-inferred sea level variations. Since altimeter SSH is a geocentric measurement, whereas the gauge-inferred observation is a relative sea level measurement, SSH comparison is conducted with the means of both series removed in this study. In addition, high-rate (1-Hz) bottom pressure implied wave heights (H_1/3) are compared with the significant wave height (SWH) measured by Jason-1. Noticeable discrepancy is found in this comparison for high waves, however the differences do not contribute significantly to the difference in sea level variations observed between the altimeter and the pressure gauge. In situ atmospheric pressure measurements are also used to verify the inverse barometer (IB) and the dry troposphere corrections (DTC) used in the Jason IGDR. We observe a bias between the IGDR corrections and those derived from the local sensors. Standard deviations of the sea level differences between T/P and BPG is 52 mm and is 48 mm between Jason and BPG, indicating that both altimeters have similar performance at the Wusi site and that it is feasible to conduct long-term monitoring of altimetry at such a site.     

Absolute Calibration of the Jason-1 Altimeter Using UK Tide Gauges

This article describes an “absolute” calibration of Jason-1 (J-1) altimeter sea surface height bias using a method developed for TOPEX/Poseidon (T/P) bias determination reported previously. The method makes use of U.K. tide gauges equipped with Global Positioning System (GPS) receivers to measure sea surface heights at the same time, and in the same geocentric reference frame, as Jason-1 altimetric heights recorded in the nearby ocean. The main time-dependent components of the observed altimeter-minus-gauge height-difference time series are due to the slightly different ocean tides at the gauge and in the ocean. The main harmonic coefficients of the tide differences are calculated from analysis of the copious TOPEX data set and then applied to the determination of T, P, and J-1 bias in turn. Datum connections between the tide gauge and altimetric sea surface heights are made by means of precise, local geoid differences from the EGG97 model. By these means, we have estimated Jason-1 altimeter bias determined from Geophysical Data Record (GDR) data for cycles 1-61 to be 12.9 cm, with an accuracy estimated to be approximately 3 cm on the basis of our earlier work. This J-1 bias value is in close agreement with those determined by other groups, which provides a further confirmation of the validity of our method and of its potential for application in other parts of the world where suitable tide gauge, GPS, and geoid information exist.     

Comparison of Sea Surface Heights Derived from Satellite Altimetry and from Ocean Bottom Pressure Gauges: The SW Pacific MOTEVAS Project

A bottom pressure gauge (BPG) was installed in proximity (3.7 km at closest approach) of Jason-1 and formerly TOPEX/Poseidon (T/P) ground track No. 238 at the Wusi site, located ～ 10 km offshore off the west coast of Santo Island, Vanuatu, Southwest (SW) Pacific. Sea level variations are inferred from the bottom pressure, seawater temperature, and salinity, corrected for the measured surface atmospheric pressure. The expansion of the water column (steric increase in sea surface height, SSH) due to temperature and salinity changes is approximated by the equation of state. We compare time series of SSH derived from T/P Side B altimeter Geophysical Data Records (GDR) and Jason-1 Interim Geophysical Data Records (IGDR), with the gauge-inferred sea level variations. Since altimeter SSH is a geocentric measurement, whereas the gauge-inferred observation is a relative sea level measurement, SSH comparison is conducted with the means of both series removed in this study. In addition, high-rate (1-Hz) bottom pressure implied wave heights (H _1/3 ) are compared with the significant wave height (SWH) measured by Jason-1. Noticeable discrepancy is found in this comparison for high waves, however the differences do not contribute significantly to the difference in sea level variations observed between the altimeter and the pressure gauge. In situ atmospheric pressure measurements are also used to verify the inverse barometer (IB) and the dry troposphere corrections (DTC) used in the Jason IGDR. We observe a bias between the IGDR corrections and those derived from the local sensors. Standard deviations of the sea level differences between T/P and BPG is 52 mm and is 48 mm between Jason and BPG, indicating that both altimeters have similar performance at the Wusi site and that it is feasible to conduct long-term monitoring of altimetry at such a site.     

TOPEX/Poseidon and Jason-1: Absolute Calibration in Bass Strait, Australia

Updated absolute calibration results from Bass Strait, Australia, are presented for the TOPEX/Poseidon (T/P) and Jason-1 altimeter missions. Data from an oceanographic mooring array and coastal tide gauge have been used in addition to the previously described episodic GPS buoy deployments. The results represent a significant improvement in absolute bias estimates for the Bass Strait site. The extended methodology has allowed comparison between the altimeter and in situ data on a cycle-by-cycle basis over the duration of the dedicated calibration phase (formation flight period) of the Jason-1 mission. In addition, it has allowed absolute bias results to be extended to include all cycles since the T/P launch, and all Jason-1 data up to cycle 60. Updated estimates and formal 1-sigma uncertainties of the absolute bias computed throughout the formation flight period are 0 ± 14 mm for T/P and +152 + 13 mm for Jason-1 (for the GDR POE orbits). When JPL GPS orbits are used for cycles 1 to 60, the Jason-1 bias estimate is 131 mm, virtually identical to the NASA estimate from the Harvest Platform off California calculated with the GPS orbits and not significantly different to the CNES estimate from Corsica. The inference of geographically correlated errors in the GDR POE orbits (estimated to be approximately 17 mm at Bass Strait) highlights the importance of maintaining globally distributed verification sites and makes it clear that further work is required to improve our understanding of the Jason-1 instrument and algorithm behavior.     

卫星高度计绝对定标中海面高梯度的计算

给出了通过平均海面高模型计算海面高梯度的具体方法,选择DTU13、CNES_CLS15、WHU2013 3种模型计算了不同海域近岸比较点海面高梯度值,随机选择的30个近岸比较点处的计算结果表明:使用3种模型计算得到的海面高梯度值之间的标准差均值为0.19cm/km。在卫星高度计定标的具体应用中,由海面高梯度得到的海面高差改正量的误差应不超过0.3cm。     

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.