ADCP资料处理中的船速计算

船载ADCP具有走航测流的特点,弥补了传统测流仪器只有停船才能观测的不足。它可以同时观测多层海流数据,获取连续性资料。ADCP测得流速是海水相对于船体的速度,在正常观测条件下,船速远大于海水流速,因而船速计算是ADCP资料处理的关键。本文对不同的船速计算方法进行了比较,对使用参考层法计算船速的原理、特点和效果进行了论述。     

Characteristics of SSH Anomaly Based on TOPEX/POSEIDON Altimetry and in situ Measured Velocity and Transport of Oyashio on OICE

An observation line along the TOPEX/POSEIDON (T/P) ground track 060 was set to estimate the Oyashio transport. We call this line the OICE (Oyashio Intensive observation line off-Cape Erimo) along which we have been conducting repeated hydrographic observations and maintaining mooring systems. T/P derived sea surface height anomaly (SSHA) was compared with velocity and transport on OICE. Although the decorrelation scale of SSHA was estimated at about 80–110 km in the Oyashio region, the SSHA also contains horizontal, small-scale noise, which was eliminated using a Gaussian filter. In the comparison between the SSHA difference across two selected points and the subsurface velocity measured by a moored Acoustic Doppler Current Profiler (ADCP), the highest correlation (0.92) appeared when the smoothing scale was set at 30 km with the two points as near as possible. For the transport in the Oyashio region, the geostrophic transport between 39°30′ N and 42°N was compared with the SSHA difference across the same two points. In this case the highest correlations (0.79, 0.88 and 0.93) occurred when the smoothing scale was set at 38, 6 and 9 km for reference levels of 1000, 2000 and 3000 db, respectively. The annual mean transport was estimated as 9.46 Sv in the 3000 db reference case. The Oyashio transport time series was derived from the T/P SSHA data, and the transports are smaller than that estimated from the Sverdrup balance in 1994–1996 and larger than that in 1997–2000. This difference is consistent with baroclinic response to wind stress field. This revised version was published online in July 2006 with corrections to the Cover Date.     

利用卫星高度计风速资料研究海面粗糙度

海面粗糙度对于海洋工程和海洋军事都非常重要,但对海面粗糙度的现场观测资料非常少, 这大大制约了对海面粗糙度的认识。利用 TOPEX 高度计风速资料实现了对海面粗糙度的反演,并利用 1993 年和1998 年两年的资料对西北太平洋海域的海面粗糙度进行了研究。     

Estimating the Kuroshio Axis South of Japan Using Combination of Satellite Altimetry and Drifting Buoys

By tracking the locally strongest part of the sea-surface velocity field, which was obtained by integrating data of satellite altimeters and surface drifting buoys, we extracted the Kuroshio axis south of Japan every 10 days from October 1992 to December 2000. The obtained axes clearly express the effect of the bottom topography; three modes were observed when the Kuroshio ran over the Izu Ridge. The axis was very stable to the south of ‘Tosa-bae,’ off the Kii Channel. Mean current speed at the Kuroshio axis gradually increased from 0.65 m/s south of Kyushu to 1.45 m/s off Enshu-nada. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于神经网络的卫星高度计海面风速反演算法

通过对TOPEX/Poseidon高度计资料与NDBC浮标实测数据进行时空匹配处理,得到同步数据集,利用人工神经网络方法试验得到海面风速反演算法,并与业务运行的M CW算法进行分析比较,指出考虑波浪状态影响因素的神经网络算法在均方根误差和对称性方面的优越性。研究表明利用神经网络方法反演海面风速是可行的。     

Comparison of Kuroshio surface velocities derived from satellite altimeter and drifting buoy data

Sea-surface geostrophic velocities for the Kuroshio region calculated from TOPEX/POSEIDON altimetry data together within situ oceanographic data are compared with surface velocities derived from drifting buoy trajectories. The geostrophic velocities agree well with the observed velocities, suggesting that the Kuroshio surface layer is essentially in geostrophic balance, within measurement error. The comparison is improved a little when the centrifugal acceleration is taken into account. The observed velocities are divided into the temporal mean and fluctuation components, and the partitioning of velocities between these two components is examined. For the Kuroshio region, most of the fluctuation components of the velocities derived from drifting buoys are found to be positive. This result suggests that Eulerian mean velocities for the Kuroshio region estimated from drifting buoy data tend to be larger than actual means, due to the buoy’s tendency to sample preferentially in the high-velocity Kuroshio.     

三峡河段表面流速流向数据处理

提出了三峡河段表面流速流向数据处理系统框架,制定了数据自动处理的流程,基于VB6.0实现了数据处理算法与系统,生成支持清华山维EPS2008的数据格式,最终生成流速流向图。最后,通过三峡—葛洲坝两坝间河段石牌水域四万五千流量级表面流速流向观测实例,验证了该数据处理方法的准确性和成图的快速性。     

关于表层声速对多波束测深影响及改正的探讨

通过分析波束形成的原理与实测数据处理得出结论：表层声速误差将对多波束测量产生不可挽回的错误;而当表层声速正确、声速剖面误差时,在后处理可以通过适当的声速剖面加以改正。     

太平洋波高分布及变化规律研究

使用 Topex/ Poseidon卫星高度计 1 992年 1 0月～ 1 998年 1 2月连续 75个月 ,2 30个重复周期的有效波高资料对南北太平洋的有效波高进行了统计 ,分析了太平洋有效波高的多年平均、多年各月平均和多年各季平均的空间分布特征和时间变化规律。结果表明 ,太平洋波高分布具有明显季节变化的规律 ,与太平洋的风速分布特征具有良好的对应关系     

利用漂流浮标资料对黑潮及其邻近海域表层流场及其季节分布特征的分析研究

利用1987年以来WOCE项目及我国自行投放或进入黑潮及其邻近海域(15°~36°N,114°~135°E)的共计323个卫星跟踪海表面漂流浮标资料,得到全年平均及季节平均的浮标轨迹及(1/4)°×(1/4)°格点平均的表层流矢量结果。分析认为:对于全年平均的表层流场,黑潮表层流路主要表现了对大洋西边界地形的适应,并呈现出6个较大的弯曲,其中在反气旋型弯曲处都发生分支或入侵现象、气旋型弯曲处这种现象却不明显。对于季节平均的表层流场,黑潮表层不同流段分别表现出各自显著的季节差异:吕宋海峡附近海域,表层水向南海的入侵只发生在秋、冬两季,而春、夏两季却不发生;在台湾以东海域,黑潮表层流路与黑潮右侧反气旋涡的存在与否密切相关,春季没有涡旋存在时,黑潮表层流路常出现气旋式大弯曲,其他三个季节反气旋涡存在时,黑潮表层流路相对平直;在台湾东北海域,黑潮表层水向东海南部陆架区的入侵以秋、冬季最强,春季次之,而夏季几乎不发生;在赤尾屿以北的东海黑潮中段,黑潮流动比较稳定,其表层平均流径走向由偏北到偏东依次约为冬(北偏东30°)、春(北偏东33°)、秋(北偏东38°)、夏(北偏东45°);流路宽度由宽至窄依次约为秋(90 km)、春(80 km)、冬(70 km)、夏(60 km),而流速由大至小依次为夏、春、秋、冬,且各季节都表现出北段流速大于南段的现象;在九州西南海域,春、秋两季黑潮表层水发生明显的向北入侵,入侵的黑潮水与东海外陆架水共同成为对马暖流的一部分来源,而夏季这种现象不明显,九州西南海域黑潮表层流路北界的位置以秋季最为偏北(但最北不超过31°N)、流路也最宽;在琉球群岛外缘海域,南半部基本没有北上的表层流存在,只有在冲绳群岛-奄美群岛以东海区,秋、夏、春三季表层反气旋涡旋都比较活跃,在涡旋的西侧有顺着冲绳群岛-奄美群岛的东北向流,其中秋季最为明显。这些结果可以为黑潮及其邻近海域的深入研究提供较为客观、直接的参考。     

Surface current field and seasonal variability in the Kuroshio and adjacent regions derived from satellite-tracked drifter data

The muhiyear averaged surface current field and seasonal variability in the Kuroshio and adjacent regions are studied. The data used are trajectories and （1/4） ° latitude by （1/4） ° longitude mean currents derived from 323 Argos drifters deployed by Chinese institutions and world ocean circulation experiment from 1979 to 2003. The results show that the Kuroshio surface path adapts well to the western boundary topography and exhibits six great turnings. The branching occurs frequently near anticyclonic turnings rather than near cyclonic ones. In the Luzon Strait, the surface water intrusion into the South China Sea occurs only in fall and winter. The Kuroshio surface path east of Taiwan, China appears nearly as straight lines in summer, fall, and winter, when anticyclonic eddies coexist on its right side; while the path may cyclonically turning in spring when no eddy exists. The Kuroshio intrusion northeast of Taiwan often occurs in fall and winter, but not in summer. The running direction, width and velocity of the middle segment of the Kuroshio surface currents in the East China Sea vary seasonally. The northward intrusion of the Kuroshio surface water southwest of Kyushu occurs in spring and fall, but not in summer. The northmost position of the Kuroshio surface path southwest of Kyushu occurs in fall, but never goes beyond 31 °N. The northward surface current east of the Ryukyu Islands exists only along Okinawa-Amami Islands from spring to fall. In particular, it appears as an arm of an anti- cyclonic eddy in fall.     

表层声速对多波束测深影响的研究

在多波束测深系统中,表层声速是线型接收换能器基阵对接收波束进行束控的重要参数。表层声速误差会直接造成接收波束的指向误差,也通过归算导致多波束脚印位置误差和回波图像的失真。在分析多波束信号处理流程和接收波束束控原理基础上,探讨表层声速对多波束指向和测深影响规律。     

Improvement of Sea Surface Height Measurements of HY-2A Satellite Altimeter Using Jason-2

Abstract

HY-2A, which was launched on 16 August 2011, is the Chinese first microwave ocean dynamics environment satellite. Analyses of HY-2A daily sea-level anomaly data and HY-2A–Jason-2 (H-J) dual crossover sea-level anomaly differences show that HY-2A has measurement differences that mainly refer to an orbit error. H-J crossover differences and HY-2A–HY-2A (H-H) crossover differences give an estimate of the HY-2A orbit error. Smoothing cubic-spline functions are then used to obtain a continuous estimation of the HY-2A orbit error over time. On the basis of the simultaneous global minimization of H-J dual crossover differences and H-H crossover differences, the HY-2A observation error is efficiently reduced and height measurement data that are more precise are obtained. Specifically, the range bias/trend of the HY-2A altimeter is removed effectively and the root mean square of H-J crossover sea-level anomaly differences decrease from above 60?cm to 5.64?cm, and the standard deviation of H-J crossover differences decreases from 6.68 to 5.64?cm. Furthermore, the rms and standard deviations of H-H crossover differences both decrease from 7.46 to 6.55?cm. The results show that HY-2A after correction has a measurement accuracy and precision that are comparable to those of Jason-2.     

海面噪声场条件下声压与振速的空间互相关函数

介绍了海面噪声场条件下的声压与质点振速的时空相关函数。论证了海面噪声场垂直与水平方向噪声的各向异性程度。结果表明,在垂直于海平面的方向上,噪声场表现为各向异性;在与海面的水平方向上,噪声场表现为各向同性。结果表明,各向同性噪声场条件下基于矢量水听器被动检测的声纳系统目标水平方位角估计是基本可靠的,但垂直方位角的计算需要修正。     

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.     

船载ADCP资料的潮流分离方法在厦门港断面重复走航中的应用

本文运用Candela等提出的潮流分离方法,选用高斯函数作为基函数,采用Matlab程序,首次对厦门港嵩鼓水道的船载ADCP断面重复走航资料进行潮流分离计算．通过对14个计算点的Candela方法计算结果与引进差比关系准调和分析方法计算结果的分析比较可见：（1）两种方法计算所得余流在大、小潮的相关系数分别为0．9882和0．8521,余流相对误差在大、小潮分别为0．065和0．150,而所得余流方向在大、小潮的相关系数分别为0．9982和0．9865,余流方向相对误差在大、小潮分别为0．023和0．027．两种方法计算的余流及其方向的相关性很高（在样本数为14,置信度为α=1％时,相关系数大于0．6610,结果是可信的）,而平均相对误差也很小．（2）对14个计算点的M2、S2、K1、O1、M4和MS4等6个分潮的计算结果（共有84个样本数据）进行分析比较,两种方法计算所得6个分潮的长轴、长轴方向和短轴在大潮的相关系数分别为0．9838、0．8960和0．2335,而在小潮的相关系数分别为0．9656、0．7555和0．2209．这两种方法计算所得6个分潮的长轴、长轴方向和短轴在大潮的平均相对误差分别为0．375、0．071和0．753,而在小潮的平均相对误差分别为0．287、0．254和0．845．两种方法计算的分潮长轴及其方向的相关性很高（在样本数为84,置信度为α=1％时,相关系数大于0．283,结果是可信的）．相应的分潮长轴的相关性略低,但是在样本数为84,置信度为α=5％时,相关系数均大于0．217．可认为在置信度为α=5％时,计算结果是可信的,而平均相对误差则略显较大．综上所述,我们认为采用Candela等的方法对船载ADCP断面重复走航资料进行潮流分离计算是可行的．     

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.     

Velocity structures and transports of the Kuroshio and the Ryukyu current during fall of 2000 estimated by an inverse technique

An inverse calculation using hydrographic section data collected from October to December 2000 yields velocity structure and transports of the Kuroshio in the Okinawa Trough region of the East China Sea (ECS) and south of central Japan, and of the Ryukyu Current (RC) southeast of the Ryukyu Islands. The results show the Kuroshio flowing from the ECS, through the Tokara Strait (TK), with a subsurface maximum velocity of 89 cm s⁻¹ at 460 dbar. In a section (TI) southeast of Kyushu, a subsurface maximum velocity of 92 cm s⁻¹ at 250 dbar is found. The results also show the RC flowing over the continental slope from the region southeast of Okinawa (OS) to the region east of Amami-Ohshima (AE) with a subsurface maximum velocity of 67 cm s⁻¹ at 400 dbar, before joining the Kuroshio southeast of Kyushu (TI). The volume transport around the subsurface velocity maximum southeast of Kyushu (TI) balances well with the sum of those in TK and AE. The temperature-salinity relationships found around these velocity cores are very similar, indicating that the same water mass is involved. These results help demonstrate the joining of the RC with the Kuroshio southeast of Kyushu. The net volume transport of the Kuroshio south of central Japan is estimated to be 64∼79 Sv (1 Sv ≡ 10⁶ m³s⁻¹), of which 27 Sv are supplied by the Kuroshio from the ECS and 13 Sv are supplied by the RC from OS. The balance (about 24∼39 Sv) is presumably supplied by the Kuroshio recirculation south of Shikoku, Japan.     

A Bathymetric Model for the South China Sea from Satellite Altimetry and Depth Data

A bathymetric model for the South China Sea is computed from altimeter-derived gravity anomalies, shipborne depths, ETOPO5, and the GMT shorelines using a procedure that includes downward continuation, linear regression, and data merging. The model best fits the GMT shorelines and is a compromise between smoothness, degree of agreement with ship data, and the seafloor features we wish to retain. The model is proven useful in studying the tectonics and modeling the ocean tide of the South China Sea.     

Improved Algorithms for the Measurement of Total Precipitable Water and Cloud Liquid Water from SARAL Microwave Radiometer Observations

SARAL carried onboard a radar altimeter that provides very precise measurements of the sea surface height (SSH). Like other altimetric missions, SARAL carries a passive microwave radiometer (PMR) for wet tropospheric correction to SSH. In the present study, new algorithms are developed for the retrieval of cloud liquid water (CLW) and total precipitable water vapor (TPW) over the global oceans from PMR measurements of the brightness temperatures. A radiative transfer and genetic algorithm based retrieval scheme is proposed for the estimation of CLW and TPW from SARAL PMR. The comparisons of CLW from PMR with independent measurements from GPM-GMI and SSMIS within and outside ±40° latitudes show correlation (R) of 0.86 and 0.83, bias of 0.7 and ?3.61?mg/cm², and root mean square error (RMSE) of 8.42 and 8.07?mg/cm², respectively. Similarly, TPW from PMR with GPM-GMI and SSMIS show R of 0.99 and 0.98, bias of ?0.04 and ?0.03?g/cm² and RMSE of 0.17 and 0.17?g/cm², respectively. The retrieval accuracy of CLW and TPW from the new algorithms is compared with these parameters provided in the SARAL geophysical data records as finished products, which showed substantial improvement in the quality of the parameters from the new algorithm.