Trends in Extreme Mean Sea Level Quantiles from Satellite Altimetry

Satellite altimetry allows the study of sea-level long-term variability on a global and spatially uniform basis. Here quantile regression is applied to derive robust median regression trends of mean sea level as well as trends in extreme quantiles from radar altimetry time series. In contrast with ordinary least squares regression, which only provides an estimate on the rate of change of the mean of data distribution, quantile regression allows the estimation of trends at different quantiles of the data distribution, yielding a more complete picture of long-term variability. Trends derived from basin-wide averaged regional mean sea level time series are robust and similar for all quantiles, indicating that all parts of the data distribution are changing at the same rate. In contrast, trends are not robust and diverge across quantiles in the case of local time series. Trends are under- (over-)estimated in the western (eastern) equatorial Pacific. Furthermore, trends in the lowermost quantile (0.05) are larger than the median trend in the western Pacific, while trends in the uppermost quantile (0.95) are lower than the median trend in the eastern Pacific. These differences in trends in extreme mean sea level quantiles are explained by the exceptional effect of the strong 1997–1998 El Niño–Southern Oscillation (ENSO) event.     

A New Methodology for Incorporating Tide Gauge Data in Sea Surface Topography Models

As part of the Vertical Offshore Reference Frames (VORF) project sponsored by the U. K. Hydrographic Office, a new model for Sea Surface Topography (SST) around the British Isles has been developed. For offshore areas (greater than 30 km from the coast), this model is largely derived from satellite altimetry. However, its accuracy and level of detail have been enhanced in coastal areas by the inclusion of not only the 60 PSMSL tide gauges with long-term records around the coasts of the United Kingdom and Ireland but also some 385 gauges established at different epochs and for different observation spans by the U. K. Admiralty. All tide gauge data were brought into a common reference frame by a combination of datum models and direct GPS observations, but a more significant challenge was to bring all short-term sea level observations to an unbiased value at a common epoch. This was achieved through developing a spatial-temporal correlation model for the variations in mean sea level around the British Isles, which in turn meant that gauges with long-term observation spans could be used as control points to improve the accuracy of Admiralty gauges. It is demonstrated that the latter can contribute point observations of mean sea level (MSL) with a precision of 0.078 m. A combination of least squares collocation and interpolation was developed to merge the coastal point and offshore gridded data sets, with particular algorithms having to be developed for different configurations of coastal topology. The resulting model of sea surface topography is shown to present a smooth transition from inshore coastal areas to offshore zones. Further benefits of the techniques developed include an enhanced methodology for detecting datum discontinuities at permanent tide gauges.     

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.     

Book reviews

R. Donaghe, R. Chaney, and M. Silver, eds. 1988. Advanced Triaxial Testing of Soil and Rock, STP 977. Philadelphia: American Society for Testing and Materials. Hard Cover, 904 pp., 625 illus. $120.00.

Adrian F. Richards, ed. 1988. Vane Shear Strength Testing in Soils: Field and Laboratory Studies, STP 1014. Philadelphia: American Society for Testing and Materials. Hard Cover, 312 pp., 253 illus. $79.00.     

First Calibration Results for the SARAL/AltiKa Altimetric Mission Using the Gavdos Permanent Facilities

This work presents the first calibration results for the SARAL/AltiKa altimetric mission using the Gavdos permanent calibration facilities. The results cover one year of altimetric observations from April 2013 to March 2014 and include 11 calibration values for the altimeter bias. The reference ascending orbit No. 571 of SARAL/AltiKa has been used for this altimeter assessment. This satellite pass is coming from south and nears Gavdos, where it finally passes through its west coastal tip, only 6 km off the main calibration location. The selected calibration regions in the south sea of Gavdos range from about 8 km to 20 km south off the point of closest approach. Several reference surfaces have been chosen for this altimeter evaluation based on gravimetric, but detailed regional geoid, as well as combination of it with other altimetric models.

Based on these observations and the gravimetric geoid model, the altimeter bias for the SARAL/AltiKa is determined as mean value of ?46mm ±10mm, and a median of ?42 mm ±10 mm, using GDR-T data at 40 Hz rate. A preliminary cross-over analysis of the sea surface heights at a location south of Gavdos showed that SARAL/AltiKa measure less than Jason-2 by 4.6 cm. These bias values are consistent with those provided by Corsica, Harvest, and Karavatti Cal/Val sites. The wet troposphere and the ionosphere delay values of satellite altimetric measurements are also compared against in-situ observations (?5 mm difference in wet troposphere and almost the same for the ionosphere) determined by a local array of permanent GNSS receivers, and meteorological sensors.     

Altimetry-observed semi-annual cycle in the South China Sea: Real signal or alias of K1 tidal error?

There have been a number of applications of satellite altimetry to seasonal and interannual sea level variability in the South China Sea. However, these applications usually exclude shallow waters along the coast, with one of the concerns being large aliased tide-correction error. In this study the authors analyzed 14 years of merged satellite altimeter data to obtain the amplitude and phase of the semi-annual cycle and to examine the variation at the K1 alias frequency (close to the semi-annual frequency). The results indicate that the amplitude of the semi-annual cycle ranges from 3-7 cm, substantial compared with that of the annual cycle; while the amplitude at the K1 alias frequency (error of the K1 tidal correction) is essentially 1 cm only. Altimeter–derived semi-annual cycle is in good agreement with that from independent tide-gauge observations, pointing to the competent ability of satellite altimetry in observing semi-annual sea level variations in the South China Sea.     

利用T/P卫星测高资料构造中国近海及邻域平均海平面和海面地形

在对T/P卫星4年1992年10月–1996年10月测高数据的编辑及预处理基础上,采用stacking处理技术构造出中国近海及邻域（0°–40°N,105°–135°E）相对于GRS80参考椭球的30'×30'年平均海平面,其总体精度达到±8.3cm（均方根）水平。验证了中国近海及邻域的平均海平面在总体上呈东南高、西北低的趋势。利用JGM-3和OSU91A混合模型的重力大地水准面,直接从平均海平面中扣除大地水准面起伏的影响,并采用“剪切”法得到中国近海及邻域完整到20阶次的海面地形模型的球谐函数表达式,验证了中国近海及邻域海面地形在总体上为正的格局,并对其构造特征作了初步探讨。     

A Review of: “Numerical Modeling of Water Waves,Second Edition”

Optimal interpolation in the spatial domain is limited by computer storage requirements and the computational effort to invert the autocovariance matrix. The procedure can be simplified by use of the fast Fourier transform (FFT), where matrix inversion is replaced by a quotient of power spectral density (PSD) functions in the spectral domain. Such a methodology is developed and utilized to estimate an altimetric mean sea surface from a single 35‐day cycle of ERS‐1. ERS‐1 radial orbit error is first reduced by minimizing dual crossover residuals with TOPEXIPoseidon through solution for a sinusoidal correction for each ascending and descending arc along with the relative altimeter bias. A regular grid for ascending (descending) arcs is then formed by use of the equator‐crossing longitudes and the along‐track displacement. Gaps in the altimeter data set are filled by use of a reference model. PSDs derived from the data and reference surface enable computation of the least‐Squares estimator in the spectral domain, from which the optimally interpolated surface heights for ascending (descending) arcs are derived by the inverse Fourier operator. The resolution is bounded across track by the Nyquist frequencies, which for the 35‐day repeat period correspond to 1.44° longitudinal spacings or 160 km. For consistency, the along‐track resolution is reduced to a comparable level. The combination of the ascending and descending sea surface heights yields a surface up to the isotropic frequency that corresponds to surface spherical harmonics of degree and order 250. Comparisons show that the model performs almost as well as the Ohio State University model present on the TOPEXIPoseidon CD‐ROMs.     

海洋卫星测高新概念——GPS浮标

本文选定定义ＧＰＳ测高的概念,然后介绍ＧＰＳ测高技术之一的浮标ＧＰＳ测高的基本原理及其应用实例,最后讨论浮标ＧＰＳ测高在我国的应用前景。     

机载GNSS反射信号海面测高模型的研究

相对于岸基GNSS-R技术,机载GNSS-R优势在于其空间分辨率高、监测范围广,可对特定区域范围进行高分辨率监测,兼具了灵活的高度和方位调节的同时保障了更高的数据质量。本文主要研究了机载GNSS-R测高模型,依据岸基GNSS-R码测高原理,针对大气延迟、天线距离等进行修正,优化机载测高模型,同时采用DTU10全球海面平均高度及潮汐模型验证机载GNSS-R测高模型的精度。通过分析2011年11月11日,CSIC-IEEC在芬兰波罗的海的GNSS-R机载数据,针对不同仰角下的实验数据进行反演,成功地实现了亚米级机载海面高度反演,得出仰角大小会对测高结果精度产生较大影响的结论,定性分析了仰角大小所引起的误差范围。本文的结果证明了机载GNSS-R的海面测高的可行性。     

Sea Level Prediction in the Yellow Sea From Satellite Altimetry With a Combined Least Squares-Neural Network Approach

Accessible high-quality observation datasets and proper modeling process are critically required to accurately predict sea level rise in coastal areas. This study focuses on developing and validating a combined least squares-neural network approach applicable to the short-term prediction of sea level variations in the Yellow Sea, where the periodic terms and linear trend of sea level change are fitted and extrapolated using the least squares model, while the prediction of the residual terms is performed by several different types of artificial neural networks. The input and output data used are the sea level anomalies (SLA) time series in the Yellow Sea from 1993 to 2016 derived from ERS-1/2, Topex/Poseidon, Jason-1/2, and Envisat satellite altimetry missions. Tests of different neural network architectures and learning algorithms are performed to assess their applicability for predicting the residuals of SLA time series. Different neural networks satisfactorily provide reliable results and the root mean square errors of the predictions from the proposed combined approach are less than 2?cm and correlation coefficients between the observed and predicted SLA are up to 0.87. Results prove the reliability of the combined least squares-neural network approach on the short-term prediction of sea level variability close to the coast.     

Near-Real–Time GPS-Based Orbit Determination and Sea Surface Height Observations from the Jason-1 Mission Special Issue: Jason-1 Calibration/Validation

The Jason-1 Operational Sensor Data Record (OSDR) is intended as a wind and wave product that is aimed towards near-real–time (NRT) meteorological applications. However, the OSDR provides most of the information that is required to determine altimetric sea surface heights in NRT. The exceptions include a sufficiently accurate orbit altitude, and pressure fields to determine the dry troposphere path delay correction. An orbit altitude field is provided on the OSDR but has accuracies that range between 8–25 cm (RMS). However, tracking data from the on-board BlackJack GPS receiver are available with sufficiently short latency for use in the computation of NRT GPS-based orbit solutions. The orbit altitudes from these NRT orbit solutions have typical accuracies of < 3.0 cm (RMS) with a latency of 1–3 h, and < 2.5 cm (RMS) with a latency of 3–5 h. Meanwhile, forecast global pressure fields from the National Center for Environmental Prediction (NCEP) are available for the NRT computation of the dry troposphere correction. In combination, the Jason-1 OSDR, the NRT GPS-based orbit solutions, and the NCEP pressure fields can be used to compute sea surface height observations from the Jason-1 mission with typical latencies of 3–5 h, and have differences with those from the 2–3 day latency Interim Geophysical Data Records of < 5 cm (RMS). The NRT altimetric sea surface height observations are potentially of benefit to forecasting, tactical oceanography, and natural hazard monitoring.     

渤海海面风场的一种动力诊断方法

给出一种动力诊断获取渤海海面风场的简便方法.首先建立一个简单的水平二维地面风场诊断模式,根据由微机支持的数字化仪输入的地面格点气压场,诊断出地面风场;然后利用渤海沿岸和岛屿海洋观测站(含石油平台站)实测风资料,运用简单的资料同化方法(张驰逼近方法)对诊断风场进行调整,从而得到渤海海面风场.结果表明,此方法简便有效.     

基于多颗在轨高度计数据的中国近海平均海平面模型建立

联合使用Jason-2成功发射3 a来的Jason-2(cycle 001-113)、轨道调整前后的Envisat(cycle 070-107)以及轨道调整后的Jason-1(cycle 263-352)等在轨高度计卫星数据,首先对电离层延迟校正项进行平滑处理,再经过数据编辑和各项地球物理及环境改正后,对周期(cycle)逐一进行统计验证并剔除交叉点不符值异常的数据周期,采用共线处理和交叉点平差削弱海面时变和径向轨道误差的影响,再经参考椭球和参考框架基准的统一,最后选用Shepard方法建立了我国海域及邻海海域(0°~45°N,100°~140°E)2'×2'分辨率的平均海平面模型。将所建立模型与MSS_CNES_CLS01模型和MSS_CNES_CLS10模型进行了比较,不符值RMS分别为8.28和11.65 cm,验证了所开展模型的正确性。     

Extension of Satellite Altimetry Jason-2 Sea Level Anomalies Towards the Red Sea Coast Using Polynomial Harmonic Techniques

Satellite altimetry data are facing big challenges near the coasts. These challenges arise due to the fundamental difficulties of correction and land contamination in the foot print, which result in rejection of these data near the coast. Several studies have been carried out to extend these data towards the coast. Over the Red Sea, altimetry data consist of gaps, which extend to about 30–50 km from the coast. Two methods are used for processing and extending Jason-2 satellite altimetry sea level anomalies (SLAs) towards the Red Sea coast; Fourier Series Model (FSM), and the polynomial sum of sine model (SSM). FSM model technique uses Fourier series and statistical analysis reflects strong relationship with both the observation and AVISO data, with strong and positive correlation. The second prediction technique, SSM model, depends on the polynomial sum of sine, and does not reflect any relationship with the observations and AVISO data close to the coast and the correlation coefficient (CC) is weak and negative. The FSM model output results in SLA data significantly better and more accurate than the SSM model output.     

Book reviews

Behavioural biology of killer whales. Editors: C. Kirkevold and J. S. Lockard. Zoo Biology Monographs, Volume 1. Alan Liss Inc., New York, 1986. 457 p. ISBN 0–8451–3100–1. Price: US$79.50.

Aquaculture of Cyprinids. Editors: R. Billard and J. Marcel. Institut National de la Recherche Agronomique, 1986. 504 p. Price FF150.00. Available from INRA Publications, Route de St Cyr, 78000 Versailles, France.

The Peruvian anchoveta and its upwelling ecosystem: three decades of change. Editors: D. Pauly and I. Tsukayama. Institute) del Mar del Peru (IMARPE); Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ); International Center for Living Aquatic Resources Management (ICLARM) 1987.351 p. ISBN 971–1022–34–6, ISSN 0115–4389. Price US$17.50 surface; US$36 airmail. Available from ICLARM, MCP.O. 1501, Makati, Metro Manilla, Philippines.

The freshwater planktonic blue‐greens (Cyanophyta/Cyanobacteria) of New Zealand: a taxonomic guide. By M. K. Etheredge and R. D. Pridmore. Published for the National Water and Soil Conservation Authority, 1987. 122 p, including 93 figures. ISSN0110–4705. Price $38.50. Available from DSIR Publishing, P.O. Box 9741, Wellington, New Zealand.     

Book reviews

Glossary of aquatic habitat inventory terminology. Compiled by Neil B. Armantrout. Published in 1998 by American Fisheries Society. 150 p. ISBN 1–888569–11–5. Price: US$33.00 (available from: APS Publication Fulfillment, P. O. Box 1020, Sewickley, PA 15143, United States).

Studying temperate marine environments— a handbook for ecologists. Edited by Michael Kingsford and Christopher Battershill. Published in 1998 by Canterbury University Press, Private Bag 4800, Christchurch, New Zealand (email: m.bradstock@cup.canterbury.ac.nz). 344 p., limpbound. ISBN 0–908812–54‐X. Price: NZ$49.95.     

Book reviews

Theory and management of tropical fisheries. Edited by D. Pauly and G. I. Murphy. Proceedings of the ICLARM/CSIRO Workshop on the Theory and Management of Tropical Multispecies Stocks. 12–21 January 1981, Cronulla, Australia. 1982. 360 p. $US21.50 surface; hardbound.

Animals of the estuary shore : illustrated guide and ecology. By Malcolm B. Jones, 1983. University of Canterbury publication No. 32. 162p., 140 figures, 11 keys. ISBN 0900–392–32–0 (soft cover, spiral bound). Price NZ$7.50.

Numerical ecology. By L. Legendre and P. Legendre, 1983. Elsevier Scientific Publishing Company, Amsterdam. $US83.00.

The control of oil pollution (revised edition). Edited by J Wardley‐Smith. Graham & Trot‐man Limited, London. 1983. 285 p., 98 figures, 17 tables. ISBN 0.86010 3382. £19.00/$US35.00.

Physical oceanography in Australia. Edited by J. Imberger. Reprinted from the Australian Journal of Marine and Freshwater Research, Volume 34, 1–230, 1983. CSIRO, Melbourne 1983.     

1.5 Ma以来南海南北上部水体温度变化对比

浮游有孔虫表层海水古温度转换函数、表层暖水种属种含量比值,以及次表层暖水种含量的变化,表明南海北部1．5Ma以来表层、次表层海水温度逐渐降低,其主要变化阶段为0．86～0．94Ma和0．64～0．68Ma。与南海南部西太平洋暖池区的17957站研究结果对比．发现南海南部1．5Ma以来表层、次表层海水温度逐渐增加．发生的主要时间为1．23～1．3Ma和0．64～0．68Ma。南海北部的上部海水结构变化主要受东亚冬季风影响,而南海南部则主要受西太平洋暖池影响,因此,南海南、北上部海水温度的变化说明0．9Ma后尤其是0．68Ma以来东亚冬季风强化,西太平洋暖池加强。     

基于T/P卫星海面测高的黄东海海面地形变化探讨

利用Topex/Posedion卫星的SSHA数据对黄、东海1993-2001年期间的平均海面地形的空间形态特征、变化速率的空间分布特征及年内变化特征等3个方面进行了分析.研究结果表明,该海区9a平均海面地形的基本特征为：东南高、西北低,由东南向西北倾斜,最大高差超过90 cm;1993-2001年期间全海区均呈现海面上升趋势,上升速率值在5～8.6 mm/a之间,海面上升的空间分异表现为南快北慢,东快西慢.海面地形的年内变化在时间上呈正弦波动,空间上中、北部区域变化速度快,年较差大;南部区域变化速度慢,年较差小;变化空间特征复杂.