Wind wave characteristics based on visual Observations and satellite altimetry

Joint analysis of wind wave characteristics derived from the Voluntary Observing Ship data (VOS) and satellite altimetry is presented as the first step of the synthesis of different data sources. Global distributions of significant wave heights and periods along with wind speed are constructed using various techniques and empirical parameterizations. Good qualitative and quantitative agreement of VOS and satellite altimetry is found especially for regions with high spatio-temporal density of observations. The problems and prospects of the further development of the study are discussed in the context of global wave climatology and marine safety.     

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。     

Detection of ocean waves using satellite altimetry: Application to equatorial Kelvin waves

A new method for wave motion detection from satellite altimetric measurements of sea surface height is presented. The essence of the approach is to construct a two‐dimensional traveling‐wave Fourier series representation of the amplitude field within a prespecified oceanic region. The method employs an iterative, nonlinear least‐squares technique based on the Marquardt‐Levenberg algorithm to solve for model parameters describing characteristic features of the evolving wave system. The Marquardt‐Levenberg Fourier series (MLFS) algorithm was applied to Kelvin waves active during the 1986–1987 El Nino event in the equatorial Pacific ocean using GEOSAT Exact Repeat Mission altimetry data. Characteristics of the wave system were found to be in essential agreement with earlier field measurements and the observations of Cheney and Miller (1987) obtained using time series developed from GEOSAT data. The advantage of the present detection scheme lies in its speed and ability to determine a wave system's dispersion relation over a finite range of wavenumbers, and hence the group velocity of that system.     

Estimating trends of the Mediterranean Sea level changes from tide gauge and satellite altimetry data (1993-2015)

The impact of climate change on sea level has received a great deal of attention by scientists worldwide. In this context, the problem of sea levels on global and regional scales have been analyzed in a number of studies based on tide gauges observations and satellite altimetry measurements. This study focuses on trend estimates from 18 high-quality tide gauge stations along the Mediterranean Sea coast. The seasonal Mann-Kendall test was run at a 5% significance level for each of the 18 stations for the period of 1993-2015 (satellite altimetry era). The results of this test indicate that the trends for 17 stations were statistically significant and showed an increase (no significant trend was observed only at one station). The rates of sea level change for the 17 stations that exhibit significant trends, estimated using seasonal Sen's approach, range after correction for Vertical Land Motion (VLM) from 1.48 to 8.72 mm/a for the period 1993-2015. Furthermore, the magnitude of change at the location of each tide gauge station was estimated using the satellite altimetry measurements. Thus, the results obtained agree with those from the tide-gauge data analysis.     

Altimetric Algorithm and Errors of Ocean Altimetry Using GNSS Reflection Signals

As a new remote sensing technology, the global navigation satellite system (GNSS) reflection signals can be used to collect the information of ocean surface wind, surface roughness and sea surface height. Ocean altimetry based on GNSS reflection technique is of low cost and it is easy to obtain large amounts of data thanks to the global navigation satellite constellation. We can estimate the sea surface height as well as the position of the specular reflection point. This paper focuses on the study of the algorithm to determine the specular reflection point and altimetry equations to estimate the sea surface height over the reflection region. We derive the error equation of sea surface height based on the error propagation theory. Effects of the Doppler shift and the size of the glistening zone on the altimetry are discussed and analyzed at the same time. Finally, we calculate the sea surface height based on the simulated GNSS data within the whole day and verify the sea surface height errors according to the satellite elevation angles. The results show that the sea surface height can reach the precision of 6 cm for elevation angles of 55° to 90°, and the theoretical error and the calculated error are in good agreement.     

HY-2卫星高度计波高资料在集合最优插值同化中的应用研究——以台风“Lipee”为例

基于海浪模式SWAN（Simulating Waves Nearshore）,以台风“Lipee”为例,开展了集合最优插值（EnOI）同化HY-2卫星高度计有效波高（SWH）资料的台风浪数值预报影响研究。结果表明,利用HY-2卫星高度计波高资料结合EnOI方法进行同化,可有效改善海浪初始场质量,同化对绝对误差的改进可达15%,均方根误差改进14%。同化对预报误差、均方根误差都有一定程度的改进,其中在0~24 h预报时效内的改进最为明显,绝对误差可改进12%,均方根误差改进13%。研究结果不仅可为海洋预报、同化提供参考,而且可为进一步加强HY-2卫星高度计资料的应用提供技术支持。     

Determining the Gravitational Gradient Tensor Using Satellite-Altimetry Observations over the Persian Gulf

With the advent of satellite altimetry in 1973, new scientific applications became available in oceanography, climatology, and marine geosciences. Moreover, satellite altimetry provides a significant source of information facilitated in the geoid determination with a high accuracy and spatial resolution. The information from this approach is a sufficient alternate for marine gravity data in the high-frequency modeling of the marine gravity field quantities. The gravity gradient tensor, consisting of the second-order partial derivatives of the gravity potential, provides more localized information than gravity measurements. Marine gravity observations always carry a high noise level due to environmental effects. Moreover, it is not possible to model the high frequencies of the Earth's gravity field in a global scale using these observations. In this article, we introduce a novel approach for a determination of the gravity gradient tensor at sea level using satellite altimetry. Two numerical techniques are applied and compared for this purpose. In particular, we facilitate the radial basis functions (RBFs) and the harmonic splines. As a case study, the gravitational gradient tensor is determined and results presented in the Persian Gulf. Validation of results reveals that the solution of the harmonic spline approach has a better agreement with a theoretical zero-value of the trace of the Marussi gravitational gradient tensor. However, the data-adaptive technique in the RBF approach allows more efficient selection of the parameters and 3-D configuration of RBFs compared to a fixed parameterization by the harmonic splines.     

基于MASNUM海浪预报系统的北印度洋波浪特征模拟与预报分析

基于MASNUM海浪数值预报系统的全球10 a后报数据库资料,分析了北印度洋区域波浪分布特征.由于该地区受季风控制显著,夏季波浪大于冬季;在空间分布上,西部比东部风大、浪大,在亚丁湾、索马里外海波浪最大.基于Janson-1卫星高度计有效波高观测资料,对MASNUM海浪预报系统的预报性能进行了检验,检验结果表明,预报波高均方根误差在0.5 m左右,短期的24 h预报效果好于48 h和72 h,冬季好于夏季.另外,对预报误差进行了相应的概率分布分析.     

Estimation of extreme wave heights using GEOSAT measurements

Satellite technology has yielded a large database of global ocean wave heights which may be used for engineering applications. However, the sampling protocol used by the satellite leads to some difficulties in making use of these data for practical applications. These difficulties and techniques to estimate extreme wave heights using satellite measurements are discussed. Significant wave heights for a 50-year return period are estimated using GEOSAT measurements for several regions around North America. Techniques described here may be used for estimation of wave heights associated with any specified return interval in regions where buoy data are not readily available.     

Estimation of extreme wave heights using GEOSAT measurements

Satellite technology has yielded a large database of global ocean wave heights which may be used for engineering applications. However, the sampling protocol used by the satellite leads to some difficulties in making use of these data for practical applications. These difficulties and techniques to estimate extreme wave heights using satellite measurements are discussed. Significant wave heights for a 50-year return period are estimated using GEOSAT measurements for several regions around North America. Techniques described here may be used for estimation of wave heights associated with any specified return interval in regions where buoy data are not readily available.     

Absolute sea level variability of Arctic Ocean in 1993–2018 from satellite altimetry and tide gauge observations

Arctic absolute sea level variations were analyzed based on multi-mission satellite altimetry data and tide gauge observations for the period of 1993–2018. The range of linear absolute sea level trends were found ?2.00 mm/a to 6.88 mm/a excluding the central Arctic, positive trend rates were predominantly located in shallow water and coastal areas, and negative rates were located in high-latitude areas and Baffin Bay. Satellite-derived results show that the average secular absolute sea level trend was (2.53±0.42) mm/a in the Arctic region. Large differences were presented between satellite-derived and tide gauge results, which are mainly due to low satellite data coverage, uncertainties in tidal height processing and vertical land movement (VLM). The VLM rates at 11 global navigation satellite system stations around the Arctic Ocean were analyzed, among which 6 stations were tide gauge co-located, the results indicate that the absolute sea level trends after VLM corrected were of the same magnitude as satellite altimetry results. Accurately calculating VLM is the primary uncertainty in interpreting tide gauge measurements such that differences between tide gauge and satellite altimetry data are attributable generally to VLM.     

利用卫星测高、GRACE和GOCE资料估计全球海洋表面地转流

重力恢复和气候试验GRACE(gravity recovery and climate experiment)卫星极大地提高了地球重力场的精度和分辨率,特别是中长波分量,联合卫星测高数据可获得全球海洋表面大尺度洋流循环。另外,新一代地球重力和海洋环流探测卫星GOCE(gravity field and steady-state ocean circulation explorer)于2009年3月成功发射,采用卫星重力梯度测量原理,对重力场的高频部分非常敏感,使其高分辨率监测全球海洋循环成为可能。本文利用1~7年GRACE观测数据确定的重力场模型和18个月GOCE观测数据确定的地球重力场模型GO_CONS_GCF_2_TIM_R3,联合卫星测高确定的平均海面高模型MSS_CNES_CLS_11,分别估计全球海洋表面地转流,并且与实测浮标数据结果进行比较。分析表明GOCE重力卫星确定的重力场模型具有更高的空间分辨率,能够确定高精度和高空间分辨率的全球海洋地转流,如墨西哥湾暖流的细节和特征,并且与实测浮标结果基本一致。而基于1~4年GRACE观测资料的模型不能很好估计全球地转流特征,基于7年GRACE观测资料的重力场模型ITG-Grace2010s确定的全球地转流的精度仍低于18个月GOCE观测数据确定的地球重力场模型GO_CONS_GCF_2_TIM_R3的结果,估计的全球地转流仍含有较大的噪声,不能很好地反应中小尺度地转流细节特征。并计算ITG_Grace2010s和GOCE_TIM3的稳态海面地形和全球平均地转流的内符合精度,结果显示,在全球范围内,GOCE_TIM3的稳态海面地形和全球平均地转流的精度都比ITG_Grace2010s结果的精度有着很大的改善,其中ITG_Grace2010s的稳态海面地形的精度为21.6cm,而GOCE_TIM3的结果则为7.45cm,ITG_Grace2010s的全球平均地转流的精度为40.7cm/s,而GOCE_TIM3的结果则为19.6cm/s。     

几款全球海底地形模型比较分析

近几十年,随着卫星测高技术和相关数据精密处理技术发展,依托卫星测高技术业已成为快速获取全球海底地形数据的可靠手段,国内外相关组织机构已发布了一系列全球海底地形模型。整理评述了多款全球海底地形的基本情况,以及相互间的内在联系,包括DBDB系列模型、ETOPO系列模型、Sandwell系列模型、GEBCO系列模型、SRTM+系列模型、EARTH地形球谐系数模型、BAT_VGG模型、BAT_WHU2020模型、STO_IEU2020模型等。通过对全球海底地形模型的认识和梳理,以期为下一步全球海底地形模型高效、低成本构建提供方法参考。     

Impact of Multisatellite Altimeter Data Assimilation on Wave Analysis and Forecast

Satellite altimetry has become an important discipline in the development of sea-state forecasting or more generally in operational oceanography. Météo-France Marine and Oceanography Division is much involved in altimetry, in which it is also one of the main operational customers. Sea-state forecasts are produced every day with the help of numerical models assimilating Fast Delivery Product altimeter data from ESA ERS-2 satellite, available in real-time (3–5 h). These forecasts are transmitted to seamen as part of safety mission of persons and properties, or specific assistance for particular operations. With the launch of ENVISAT (from ESA, launched on 1 March 2002, to take over the ERS mission) and JASON-1 (from CNES/NASA, launched on 7 December 2001, successor of TOPEX/Poseidon), we have an unprecedented opportunity of improved coverage with the availability in quasi-real-time of data from several altimeters. The objective of this study is to evaluate the impact of using multisources of altimeter data in real-time, to improve wave model analyses and forecasts, at global scale. Since July 2003, Météo-France injects the wind/wave JASON-1 Operational Sensor Data Record on the WMO Global Transmitting System, making them available in near real-time to the international meteorological community. Similarly, fast delivery altimeter data of ENVISAT will improve coverage and contribute to the constant progress of marine meteorology. For this purpose, significant wave height time series were generated using the Wave Model WAM and the assimilation of altimeter wave heights from two satellites ERS-2 and JASON-1. The results were then compared to Geosat Follow-On (GFO, U.S. Navy Satellite) and moored buoy wave data. It is shown that the impact of data assimilation, when two (ERS-2 and JASON-1) or three (ERS-2 with JASON-1 and GFO) sources of data are used instead of one (ERS-2), in term of significant wave height, is larger in wave model analyses but smaller in wave model forecasts. However, there is no improvement in terms of wave periods, both in the analysis and forecast periods.     

Reconstruction of mean dynamic topography of the Black Sea for altimetry measurements

In this study a new approach for reconstructing the Mean Dynamic Topography of the Black Sea is applied. Constant observations (SVP measurements), drifters, and data of vertical sounding of the temperature and salt content together with measurements of sea level anomalies received from Topex/Poseidon mission satellite data were used. The absolute sea level received by altimetry data using the mean dynamic topography received during work was compared to the dynamic level received according to independent marine surveys. The comparison showed that the method represented in the study permits one to define more exactly the dynamic topography of the Black Sea when compared with the studies of previous authors. The results of this study will be useful to reconstruct the areas of the geostrophic currents according to satellite altimetry.     

Evaluation of vertical crustal movements and sea level changes around Greenland from GPS and tide gauge observations

To better monitor the vertical crustal movements and sea level changes around Greenland, multiple data sources were used in this paper, including global positioning system(GPS), tide gauge, satellite gravimetry, satellite altimetry, glacial isostatic adjustment(GIA). First, the observations of more than 50 GPS stations from the international GNSS service(IGS) and Greenland network(GNET) in 2007–2018 were processed and the common mode error(CME) was eliminated with using the principal component analysis(PCA). The results show that all GPS stations show an uplift trend and the stations in southern Greenland have a higher vertical speed. Second, by deducting the influence of GIA, the impact of current Gr IS mass changes on GPS stations was analysed, and the GIA-corrected vertical velocity of the GPS is in good agreement with the vertical velocity obtained by gravity recovery and climate experiment(GRACE). Third, the absolute sea level change around Greenland at 4 gauge stations was obtained by combining relative sea level derived from tide gauge observations and crustal uplift rates derived from GPS observations, and was validated by sea level products of satellite altimetry. The results show that although the mass loss of Gr IS can cause considerable global sea level rise, eustatic movements along the coasts of Greenland are quite complex under different mechanisms of sea level changes.     

Seafloor mapping from high-density satellite altimetry

In this paper, we publish the results of a bathymetry survey based on the processing of satellite altimetry data. Data gathered from GEOSAT (Geodetic Mission), SEASAT, ERS-1 and TOPEX/POSEIDON satellites were processed to recover the seafloor topography over new seamounts in a test area located in the south central Pacific. We show that by processing high-density satellite altimetry data, alone or in combination with shiptrack bathymetric data, it is possible to produce full coverage bathymetric maps.     

基于卫星测高与卫星测温的表层流产品生成方法应用评估

提高海洋表层流的精度与分辨率对于相关应用领域至关重要.研究引入海表面温度(sea surface temperature,SST)信息对高度计导出流场的改进效果,计算了 2018年每日无间隔的全球海洋表层流速度.通过增加热量守恒方程约束,引入卫星测温产品,在地转流基础上生成表层流产品,并与现场漂流浮标速度比较,评估了使...     

多源数据推求的西太平洋区域海面动力地形比较分析

简述利用空间大地测量观测数据和海洋水文数据推求海面动力地形的方法。基于EGM96重力场模型和卫星重力恢复的重力场模型GL04C,联合卫星测高平均海面高模型分别推算西太平洋海域的平均海面动力地形,并与根据海洋水文数据推算之结果进行比较分析。结果表明:卫星重力场模型GL04C更好地表现了海面地形的细节特征。卫星重力和卫星测高的联合应用将成为确定海面动力地形的有效途径之一。     

Global historical archive of wind waves based on Voluntary Observing Ship data

A new global archive of wind wave characteristics has been developed based on Voluntary Observing Ship (VOS) data for the period of 1888–2015. In addition to the basic meteorological variables, we have derived the records of visually observed heights, periods, and wind sea and swell directions. The main parameters have been supplemented by significant wave height and dominant period estimates, as well as wave geometry characteristics: steepness, wave age, and wavelength. Multistage quality control has been applied to correct or eliminate spurious values. Data are presented as individual records for every month and as original monthly means fields for every parameter. Easy access and use, along with representative data, make the new archive particularly special and applicable in different ways without any additional preprocessing. Visual wave observations assimilated in the new archive can be used to develop global and regional climatologies, estimate extreme wave characteristics and long-term trends in wave climate, verify and compare them with satellite measurements and model analysis, and test the theoretical laws of ocean wave development and propagation.