Satellite wave measurements for coastal engineering applications

Measurements from the GEOSAT, ERS-1 and 2 and Topex/Poseidon satellites have now accumulated to over 15 years of global ocean wave and wind data. Extraction of wave height, wind speed and wave period from the satellite altimeters and directional wave spectra from the synthetic aperture radars are reviewed along with recent validation and calibration efforts. Applications of the data to a variety of problems illustrate the potential of satellite wave measurements.     

关于NWW向昌平-丰南隐伏断裂的新证据和分析

ＮＷＷ向昌平－丰南断裂是根据卫星图像解译发现的一条隐伏活断层,是迄今为止发现的ＮＷＷ向张家口－蓬莱断裂带中规模最大的断裂,为一条第四纪左旋走滑正断层。深地震测深表明,断裂已延伸至上地幔顶部     

Temporal variation of chlorophyll a concentration in the coastal waters affected by the Hebei Spirit oil spill in the West Sea of Korea

Time series changes in chlorophyll a concentration before and after the Hebei Spirit oil spill that occurred in December 2007 were analyzed using NCEP wind and SeaWiFS/MODIS ocean color data. Prevailing southwesterly winds and northeast/southwestward tidal currents pushed the oil towards Korea’s West Sea coast of Taean. After the oil spill, daily chlorophyll a concentration decreased about 45-50% compared to the normal condition before the oil spill, and this decrease continued for about two weeks. Monthly mean chlorophyll a concentration in December 2007 was lower compared to the average value for the same month between 1998 and 2007, but, in October and November 2007 before the spill and in January-February 2008 after the spill, the concentration value was higher than average for the same period between 1998 and 2007.     

用一维变分法校正卫星资料反演地球大气湿度场的试验研究

本文采用一维变分法,并将MM5模式的相对湿度6小时预报作为背景信息,对1998年6~7月两种卫星反演地球大气相对湿度资料进行偏差校正试验,以提高其精度.这两种反演资料分别是用统计反演法反演GMS-5静止气象卫星多通道遥感信息得到的GMS反演地球大气湿度,和用同步物理反演法反演NOAA-14极轨卫星的TOVS晴空测值所得的TOVS反演湿度.校正试验结果表明,一维变分法能有效减小两种卫星反演湿度相对于匹配的NCEP/DOE再分析相对湿度的平均偏差和均方根偏差：850~300 hPa GMS反演湿度的绝对平均偏差下降了0.59%~2.87%;各层GMS反演湿度的均方根偏差的减少量为3.26%~7.49%,其中925~400 hPa从11%~14%降为6%~9%,300~200 hPa从20%~24%降为13%~18%;500~300 hPa TOVS反演湿度的绝对平均偏差从7%~13%降至1%~5%;各层TOVS反演湿度的均方根偏差减少了12.61%~15.1%,其中1000~500 hPa从21%~24%降至8%~10%,400~300 hPa从25%~29%降至11%~14%.校正分别使925~400 hPa GMS反演湿度和1000~500 hPa TOVS反演湿度的均方根偏差降至10％以下,达到了WMO对卫星资料反演地球大气湿度垂直分布的可用精度要求.     

Floating marine debris surface drift: Convergence and accumulation toward the South Pacific subtropical gyre

Whatever its origin is, a floating particle at the sea surface is advected by ocean currents. Surface currents could be derived from in situ observations or combined with satellite data. For a better resolution in time and space, we use satellite-derived sea-surface height and wind stress fields with a 1/3° grid from 1993 to 2001 to determine the surface circulation of the South Pacific Ocean. Surface currents are then used to compute the Lagrangian trajectories of floating debris. Results show an accumulation of the debris in the eastern-centre region of the South Pacific subtropical gyre ([120°W; 80°W]–[20°S; 40°S]), resulting from a three-step process: in the first two years, mostly forced by Ekman drift, the debris drift towards the tropical convergence zone (30°S). Then they are advected eastward mostly forced by geostrophic currents. They finally reach the eastern-centre region of the South Pacific subtropical gyre from where they could not escape.     

Combined electromagnetic, geochemical and thermal surveys of Taal volcano (Philippines) during the period 2005–2006

Since 1572, 33 phreatic to phreatomagmatic eruptions have occurred on Taal volcano (Philippines), some of them causing several hundred casualties. Considering the time delay between two consecutive eruptions, there is an 88% probability that Taal volcano should have already erupted. Since 1992, several phases of seismic activity have been recorded accompanied by ground deformation, opening of fissures, and surface activity. The volcanic activity of Taal appears to be controlled by dike injections and magma supply, buffered by a hydrothermal system that releases fluids and heat through boiling and subsequent steaming. In early 2005, a multidisciplinary project was launched for studying the hydrothermal activity. To map the hydrothermal system, combined surveys were carried out to investigate self-potential, total magnetic field, ground temperature and carbon dioxide soil degassing, along with satellite thermal imaging of the Main Crater Lake. The elevated temperatures and high concentrations of carbon dioxide, as well as electromagnetic anomalies, indicate large-scale hydrothermal degassing. This process is enhanced along the tectonic features (e.g., crater rim and faults) of the volcano, while active fissures opened along the E–W northern flank during the 1992–1994 seismic activity. Heat and fluids from the hydrothermal system are essentially released in the northern part of the crater, which is bounded to the South by a suspected NW–SE fault along which seismicity seems to take place, and dikes are thought to be intruded. During the January 2005 surveys, a new seismic crisis started, and the felt earthquakes prompted spontaneous evacuation of hundreds of inhabitants living on the volcano. Repeated surveys show changes of self-potential, total magnetic field, and ground temperature with time, without any noticeable spatial enlargement. These observations suggest that the northern flank located between the crater rim and the 1992–1994 fissures is connected with a deep thermal source in Main crater and is reactivated during seismic crises. This sector could be subjected to flank failure.     

Global surface currents: a high-resolution product for investigating ocean dynamics

A global 1/4° resolution product of surface currents has been developed by the Centre de Topographie des Océans et de l’Hydrosphère. The surface current is calculated from a combination of Ekman currents derived from wind estimates from QuikSCAT satellite, geostrophic current anomalies derived from altimetry, and a mean geostrophic current derived from climatology. In the equatorial band, the currents are adjusted following the methodology proposed by Lagerloef et al. (J Geophys Res, 104(C10):22313–22326, 1999). These satellite-derived currents have been compared to different types of in situ current observations. A global validation is performed using Lagrangian surface drifting buoys and acoustic Doppler current profiler current observations along ship tracks. The comparison shows a very good agreement in the subtropical and mid-latitude bands. The correlation between the satellite-derived currents and the drifter currents in zonal mean bands is around 0.7 for most of the world oceans, both for the zonal and the meridional components. This correlation rises up to 0.8 in the regions of strong boundary currents. In the equatorial band, the correlation with the surface drifting buoys is reduced. A direct comparison with the TOGA/TAO moored current meter data at the equator shows that the low frequency currents are captured by the satellite current product, but there is a substantial high-frequency signal (<20 days), which is not reproduced. This is especially the case for the meridional component and is mainly related to the tropical instability waves. We also show that using daily QuikSCAT wind forcing improves the satellite current product, particularly in the high-latitude westerly wind belt and in the tropical Indian Ocean.     

Glacial isostatic adjustment at the Laurentide ice sheet margin: Models and observations in the Great Lakes region

Glacial Isostatic Adjustment (GIA) modelling in North America relies on relative sea level information which is primarily obtained from areas far away from the uplift region. The lack of accurate geodetic observations in the Great Lakes region, which is located in the transition zone between uplift and subsidence due to the deglaciation of the Laurentide ice sheet, has prevented more detailed studies of this former margin of the ice sheet. Recently, observations of vertical crustal motion from improved GPS network solutions and combined tide gauge and satellite altimetry solutions have become available. This study compares these vertical motion observations with predictions obtained from 70 different GIA models. The ice sheet margin is distinct from the centre and far field of the uplift because the sensitivity of the GIA process towards Earth parameters such as mantle viscosity is very different. Specifically, the margin area is most sensitive to the uppermost mantle viscosity and allows for better constraints of this parameter. The 70 GIA models compared herein have different ice loading histories (ICE-3/4/5G) and Earth parameters including lateral heterogeneities. The root-mean-square differences between the 6 best models and the two sets of observations (tide gauge/altimetry and GPS) are 0.66 and 1.57 mm/yr, respectively. Both sets of independent observations are highly correlated and show a very similar fit to the models, which indicates their consistent quality. Therefore, both data sets can be considered as a means for constraining and assessing the quality of GIA models in the Great Lakes region and the former margin of the Laurentide ice sheet.     

地震应急卫星通信系统远端小站的故障诊断与处理

本文对地震应急卫星通信系统进行了简要介绍.针对系统运行过程中遇到的远端小站的各类故障进行了诊断分析.文中主要通过介绍设备状态及链路层状态两方面,来对如何解决此类故障问题提出了处理方案.     

A comparison of GOCE gravitational models with EGM2008

Four new gravity field models from GOCE, two of them combined with GRACE, are compared here with EGM2008. The objectives are to look into the differences in consecutive ranges of the spherical harmonic expansion globally as well as in selected geographical regions and in the regions of the various data sources used for EGM2008. In general, GOCE is able to contribute to improved global gravity models in the spherical harmonic range between 120 and 200 (and above). The agreement between EGM2008 and the GOCE models is very good in well-surveyed regions such as North America, Europe and Australia, with geoid RMS-differences on the order of 4–6 cm. In other regions, where the surface gravity data available for the development of EGM2008 were poor, such as South America, Africa, South-East Asia or China the RMS-differences are on a level of 30 cm. Here GOCE leads to a significant improvement. These findings are confirmed by the analysis of the areas of the various EGM2008 data sources. In the regions of the so-called “fill-in” data of EGM2008 RMS-geoid height differences are high. In Antarctica GOCE also gives important improvements in terms of spatial resolution and accuracy. In general, the agreement between EGM2008 and the GOCE-models up to degree and order (d/o) 200 is good, with a global (excluding the polar gaps of GOCE orbits, throughout) geoid difference RMS of 11 cm, in the ocean areas 8 cm and 20 cm in the continental areas. GOCE models are better suited for ocean circulation studies because no prior ocean information enters into the data reduction process, as it is the case when deducing gravity anomalies from an altimetric mean sea surface. On the other hand, the good consistency between GOCE-models and EGM2008 in ocean areas very likely indicates that the influence of ocean circulation information on EGM2008 is rather small. The four tested GOCE models behave similarly except at the highest latitudes where GOCE lacks data due to its orbit inclination of 96.5° and some form of regularization which has to be applied.