Bancroft算法在多卫星导航定位系统解算中的推广应用

提出了一种改进的Bancroft算法运用于组合双系统SPP解算。为检验新算法的解算精度,选取2013年2月采集于武汉大学实验大楼楼顶的GPS/BD双频双模接收机实测数据进行解算。实验结果表明改进的Bancroft算法与传统的最小二乘算法的解算精度相当,其解算效率与最小二乘算法相比提高了22%,从而验证了改进的Bancroft算法在组合双系统SPP解算中的可行性及优越性。     

基于现场观测与MyOcean模式数据的印度洋东南部Aquarius反演海表盐度的评价与纠正

The in situ sea surface salinity(SSS) measurements from a scientific cruise to the western zone of the southeast Indian Ocean covering 30°–60°S, 80°–120°E are used to assess the SSS retrieved from Aquarius(Aquarius SSS).Wind speed and sea surface temperature(SST) affect the SSS estimates based on passive microwave radiation within the mid- to low-latitude southeast Indian Ocean. The relationships among the in situ, Aquarius SSS and wind-SST corrections are used to adjust the Aquarius SSS. The adjusted Aquarius SSS are compared with the SSS data from My Ocean model. Results show that:(1) Before adjustment: compared with My Ocean SSS, the Aquarius SSS in most of the sea areas is higher; but lower in the low-temperature sea areas located at the south of 55°S and west of 98°E. The Aquarius SSS is generally higher by 0.42 on average for the southeast Indian Ocean.(2) After adjustment: the adjustment greatly counteracts the impact of high wind speeds and improves the overall accuracy of the retrieved salinity(the mean absolute error of the Zonal mean is improved by 0.06, and the mean error is-0.05 compared with My Ocean SSS). Near the latitude 42°S, the adjusted SSS is well consistent with the My Ocean and the difference is approximately 0.004.     

GPS positioning accuracy using precise real‐time ephemeris and clock correction

Global positioning system (GPS) has found applications in various areas including marine geodesy. GPS positioning accuracy, however, is greatly degraded by GPS ephemeris and clock errors, particularly errors due to Selective Availability (SA). Thus, it is crucial to use precise ephemeris and clock corrections for users who require high position accuracy. Presently, precise ephemeris and clock corrections are available only in post‐mission. This paper investigates the generation of precise real‐time ephemeris and clock corrections and the positioning accuracy using them. In this research, precise real‐time ephemeris is generated from accurate dynamic orbit prediction and clock corrections are calculated using instantaneous GPS measurements. Numerical analysis using data from an actual GPS tracking network is performed that indicates use of precise ephemeris and clock corrections can improve the positioning accuracy to the one meter level. This accuracy is attainable in real‐time as the precise real‐time ephemeris and clock corrections become available in the future.     

Relative Sea Level Changes in Maldives and Vulnerability of Land Due to Abnormal Coastal Inundation

Oceanic Islands in the Pacific and Indian Oceans have extremely small land areas, usually less than 500 km2, with maximum height about 4 m above sea level. The Republic of Maldives is an independent island nation in the Indian Ocean south of Sri Lanka which stretches vertically in the Indian Ocean from 07° 06'N - 0° 42'S. The land area of this island country is about 300 km2, and none of Maldives' 1190 islands has an elevation more than 3 m above sea level. In fact the Maldives has the distinction of being the flattest country on earth, making it extremely vulnerable to the effects of global warming. Of the south Asian countries, the Maldives is the most vulnerable nation, facing severe consequences as a result of global warming and sea level rise (SLR). Because of their obvious vulnerability to SLR, the Government of Maldives is very much concerned about climate change. As global warming and the related SLR is an important integrated environmental issue, the need of the hour is to monitor and assess these changes. The present article deals mainly with the analysis of the tidal and Sea Surface Temperature (SST) data observed at Male and Gan stations along the Maldives coast in the northern and southern hemispheres, respectively. The objective of the analysis is to study the trends of these parameters. Trend analysis is also performed on the corresponding air temperature data of both stations. The results show that Maldives coastal sea level is rising in the same way (rising trend) as the global sea level. The mean tidal level at Male has shown an increasing trend of about 4.1 mm/year.Similarly at Gan, near the equator,it has registered a positive trend of about 3.9 mm/year.Sea level variations are the manifestations of various changes that are taking place in the Ocean-Atmosphere system. Therefore, the variations in SST and air temperature are intimately linked to sea level rise. It is found that SST and air temperature have also registered an increasing trend at both stations. The evidence of rising trends suggest that careful future monitoring of these parameters is very much required. Tropical cyclones normally do not affect the Maldives coast. However, due to its isolated location, the long fetches in association with swells generated by storms, that originated in the far south have resulted in flooding. Thus the rising rate of sea level with high waves and flat topography have increased the risk of flooding and increased the rate of erosion and alteration of beaches.     

Relative Sea Level Changes in Maldives and Vulnerability of Land Due to Abnormal Coastal Inundation

Oceanic Islands in the Pacific and Indian Oceans have extremely small land areas, usually less than 500 km2, with maximum height about 4 m above sea level. The Republic of Maldives is an independent island nation in the Indian Ocean south of Sri Lanka which stretches vertically in the Indian Ocean from 07° 06'N - 0° 42'S. The land area of this island country is about 300 km2, and none of Maldives' 1190 islands has an elevation more than 3 m above sea level. In fact the Maldives has the distinction of being the flattest country on earth, making it extremely vulnerable to the effects of global warming. Of the south Asian countries, the Maldives is the most vulnerable nation, facing severe consequences as a result of global warming and sea level rise (SLR). Because of their obvious vulnerability to SLR, the Government of Maldives is very much concerned about climate change. As global warming and the related SLR is an important integrated environmental issue, the need of the hour is to monitor and assess these changes. The present article deals mainly with the analysis of the tidal and Sea Surface Temperature (SST) data observed at Male and Gan stations along the Maldives coast in the northern and southern hemispheres, respectively. The objective of the analysis is to study the trends of these parameters. Trend analysis is also performed on the corresponding air temperature data of both stations. The results show that Maldives coastal sea level is rising in the same way (rising trend) as the global sea level. The mean tidal level at Male has shown an increasing trend of about 4.1 mm/year.Similarly at Gan, near the equator,it has registered a positive trend of about 3.9 mm/year.Sea level variations are the manifestations of various changes that are taking place in the Ocean-Atmosphere system. Therefore, the variations in SST and air temperature are intimately linked to sea level rise. It is found that SST and air temperature have also registered an increasing trend at both stations. The evidence of rising trends suggest that careful future monitoring of these parameters is very much required. Tropical cyclones normally do not affect the Maldives coast. However, due to its isolated location, the long fetches in association with swells generated by storms, that originated in the far south have resulted in flooding. Thus the rising rate of sea level with high waves and flat topography have increased the risk of flooding and increased the rate of erosion and alteration of beaches.     

南印度洋副热带偶极子型海温异常与全球环流和我国降水变化的关系

用1951~2001年观测资料,研究了南印度洋副热带偶极子型(IOSD)海温异常对全球500hPa环流和我国降水的影响.结果表明,冬季IOSD激发出极显著的南北半球环绕太平洋的波列结构(CP),其年际变化周期是2.0和6.5 a,与赤道中东太平洋海温也有密切联系.北半球冬季异常峰值后的第二年春季欧亚中高纬度地区500 hPa环流出现显著的EUP型低频流型持续异常,同时中太平洋和北美地区出现CPNP流型和澳大利亚南部的南半球中高纬地区呈现极显著的西南太平洋遥相关型(SWP).当冬季赤道南印度洋副热带呈极显著的西负东正海温距平分布时,后期春季欧亚中高纬地区负EUP型遥相关波列持续偏强,导致东亚大槽明显偏弱,长江以北地区(特别是黄河中上游地区)多雨.反之,春季东亚大槽加强且稳定,我国东部地区大范围少雨.它反映了南印度洋地区海气系统相互作用与东亚热带内外环流低频变化的联系.因此,上一年冬季南印度洋副热带偶极子型(IOSD)海温异常强度是预测春季华北地区旱涝变化的重要因子之一.     

GPS测速精度分析与应用

全球定位系统(GPS)技术的出现,为速度测量提供了新的手段。基于GPS测速的基本原理,采用单点定位模式、无线电信标/差分GPS模式和GPS RTK模式,研究了不同模式下速度测量的方法和精度概况,重点分析了GPS RTK模式下的测速精度,并对高精度速度测量应用提出了建议。     

A study of increasing the precision of navigation position for submerged body

Currently, most submerged bodies use the long-baseline acoustic position system (LBL) to identify the navigation position for submerging. A precise navigation position is always the target pursued by underwater technology. The conventional long-baseline acoustic position systems normally use Kalman filter correction to handle the problem of positional errors. This article proposes a new modification, which is based on the periodically measured actual navigation distance, and associated with the three-dimensional geometrical relations between the transponder on the seabed and the navigation distance. This new modification employs the iterative approximation to modify the errors of the measured navigation position from the conventional long-baseline acoustic position system. In order to verify the availability of the modified model by the essay, the study uses the navigation position for an underwater surveying submerged body as the study object. After the numerical simulation analysis, the result shows that the modification was presented by the article can only use very few iterations to precisely modify the errors of the measured navigation position from the conventional long-baseline acoustic position system, which is highly applicable for positioning in long-term and long-distance submersion. Moreover, the modification method proposed by the paper can also help submersion positioning for the underwater vehicle, as well as the military submerged body.     

车辆导航系统中地图匹配新算法

根据网格思想将道路网络进行分块并融合GPS所提供的定位数据,利用车辆行驶的位置、方向和实际道路网络的拓扑特性,提出一种快速实用地图匹配算法。使GPS数据实时地与G IS地图数据匹配,有效地提高车辆导航的定位精度。     

赤道印度洋海温偶极子的气候影响及数值模拟研究

在分析研究印度洋海温变化的基本特征,尤其是在分析赤道印度洋海温偶极子及其影响的基础上,利用IAP9L大气环流模式模拟研究了赤道印度洋海温偶极子异常对亚洲季风区气候变化的影响.其结果表明,印度洋、亚洲南部和东部地区的流场和降水都对印度洋海温异常的强迫作用比较敏感.正位相印度洋偶极子的作用使得赤道东印度洋-印度次大陆南部-阿拉伯海一带出现距平东风,孟加拉湾-中南半岛出现异常反气旋性环流,从而对减少印度南部和中南半岛南部、印度尼西亚地区的夏季降水,以及增加中国南部和东非的夏季降水有十分重要的作用.与此相反,负位相印度洋偶极子的作用将使赤道东印度洋附近出现西风异常,孟加拉湾-中南半岛存在异常气旋性环流,从而使印度次大陆和中南半岛南部、印度尼西亚地区的降水增加,使中国西部和孟加拉湾的降水减少.数值模拟结果与资料分析相互映证,切实地揭示了印度洋海温偶极子对亚洲季风区的气候变化有重要影响.     

热带印度洋偶极子事件和副热带印度洋偶极子事件的联系

分别对热带印度洋偶极子事件和副热带印度洋偶极子事件的时间序列进行了周期分析。结果表明,热带印度洋偶极子事件的主要振荡周期为2 a和4 a,而副热带偶极子事件的主要振荡周期为8 a;对整个印度洋海区的海表温度距平进行2~8 a的带通滤波,发现未滤波之前,2个事件的相关性很低,而在进行了滤波之后,2个事件的相关性有很大的提高,并且当副热带印度洋偶极子事件超前热带印度洋偶极子事件9个月时,二者具有很强的相关性。通过对温度场和风场的分析,从物理上解释了2个事件之间的相互联系。     

How does the Indian Ocean subtropical dipole trigger the tropical Indian Ocean dipole via the Mascarene high？

The variation in the Indian Ocean is investigated using Hadley center sea surface temperature(SST)data during the period 1958–2010.All the first empirical orthogonal function(EOF)modes of the SST anomalies(SSTA)in different domains represent the basin-wide warming and are closely related to the Pacific El Ni o–Southern Oscillation(ENSO)phenomenon.Further examination suggests that the impact of ENSO on the tropical Indian Ocean is stronger than that on the southern Indian Ocean.The second EOF modes in different domains show different features.It shows a clear east-west SSTA dipole pattern in the tropical Indian Ocean(Indian Ocean dipole,IOD),and a southwest-northeast SSTA dipole in the southern Indian Ocean(Indian Ocean subtropical dipole,IOSD).It is further revealed that the IOSD is also the main structure of the second EOF mode on the whole basin-scale,in which the IOD pattern does not appear.A correlation analysis indicates that an IOSD event observed during the austral summer is highly correlated to the IOD event peaking about 9 months later.One of the possible physical mechanisms underlying this highly significant statistical relationship is proposed.The IOSD and the IOD can occur in sequence with the help of the Mascarene high.The SSTA in the southwestern Indian Ocean persists for several seasons after the mature phase of the IOSD event,likely due to the positive wind–evaporation–SST feedback mechanism.The Mascarene high will be weakened or intensified by this SSTA,which can affect the atmosphere in the tropical region by teleconnection.The pressure gradient between the Mascarene high and the monsoon trough in the tropical Indian Ocean increases(decreases).Hence,an anticyclone(cyclone)circulation appears over the Arabian Sea-India continent.The easterly or westerly anomalies appear in the equatorial Indian Ocean,inducing the onset stage of the IOD.This study shows that the SSTA associated with the IOSD can lead to the onset of IOD with the aid of atmosphere circulation and also explains why some IOD events in the tropical tend to be followed by IOSD in the southern Indian Ocean.     

印度洋海温异常对西北太平洋台风的影响及机制研究

基于近40 a NCEP/NCAR再分析月平均高度场、风场、涡度场、垂直速度场以及NOAA重构的海面温度(sea surface temperature,SST)资料和美国联合台风预警中心(Joint Typhoon Warning Center,JTWC)热带气旋最佳路径资料,利用合成分析方法,研究了前期春季及同期夏季印度洋海面温度同夏季西北太平洋台风活动的关系。结果表明:1)前期春季印度洋海温异常(sea surface temperature anomaly,SSTA)尤其是关键区位于赤道偏北印度洋和西南印度洋地区对西北太平洋台风活动具有显著的影响,春季印度洋海温异常偏暖年,后期夏季,110°～180°E的经向垂直环流表现为异常下沉气流,对应风场的低层低频风辐散、高层辐合的形势,这种环流形势使得低层水汽无法向上输送,对流层中层水汽异常偏少,纬向风垂直切变偏大,从而夏季西北太平洋台风频数偏少、强度偏弱,而异常偏冷年份则正好相反。2)春季印度洋异常暖年,西北太平洋副热带高压加强、西伸;而春季印度洋异常冷年,后期夏季西北太平洋副热带高压减弱、东退,这可能是引起夏季西北太平洋台风变化的另一原因。     

Performance of Real-Time Precise Point Positioning

The IGS Real-time Pilot Project (IGS-RTPP) provides real-time precise orbits and clocks, which support real-time positioning for single stations over large areas using the Precise Point Positioning (PPP) technique. This paper investigates the impact of real-time orbits, network configuration, and analysis strategies on real-time PPP implementation and demonstrates the real-time PPP performance. One month of data from the IGS network is analyzed in a real-time simulation mode. Results reveal the following: (1) In clock estimation, differential approaches are much more efficient than the zero-differenced approach. (2) The precision of IGS Ultra rapid (IGU) orbits could meet the IGS-RTPP requirement for precise clock estimation and PPP positioning. (3) Considering efficiency and precision, a network with 50 stations is recommended for the IGS-RTPP. It is demonstrated that the real-time satellite clock precision is 0.1 ns supporting hourly static PPP with a mean precision of 2–3 cm in the North component and 3–4 cm in the other components. Kinematic PPP assessed with onboard GPS data collected from a buoy provided mean coordinate precision of 2.2, 4.2, 6.1 cm in the North, East and Up directions, compared to the RTK solutions.     

近45 年南海-北印度洋波浪能资源评估

利用 ERA-40海表10 m 风场驱动第三代海浪数值模式(WAVEWATCH-,Ⅲ简称 WW3),得到南海–北印度洋1957年9月~2002年8月的海浪资料,计算该海域的波浪能,分析波浪能流密度的四季分布特征、不同能级出现的频率及波浪能流密度的稳定性,为海浪发电、海水淡化等选址提供依据.研究发现,南海–北印度洋海域蕴藏着较为丰富的波浪能:(1)南海–北印度洋大部分海域的年平均波浪能流密度在2 kW/m 以上,大值区位于南海、孟加拉湾、索马里附近海域.(2)南海–北印度洋海域波浪能流密度大于2 kW/m 和大于4 kW/m 出现的频率都较高.(3)南海–北印度洋的波浪能流密度具有较好的稳定性,春季、秋季、冬季的稳定性好于夏季,南海的稳定性好于北印度洋     

HiPAP100水下定位系统在海底摄像中的应用

分析了HiPAP100高精度声学定位系统及其水下定位原理,阐述了影响水声传播的因素及HiPAP100的解决办法,介绍了水下定位系统在我国海洋区域地质调查海底摄像测站作业中的应用,分析比较海底摄像常规定位与HiPAP100超短基线的定位精度,说明水下定位在海底摄像等水下拖曳和定点作业中的必要性和重要性。     

Western Indian Ocean SST signal and anomalous Antarctic sea-ice concentration variation

Teleconnection between El Nino/La Nina-Southern Oscillation (ENSO) phenomenon and anomalous Antarctic sea-ice variation has been studied extensively.In this study,impacts of sea surface temperature in the Indian Ocean on Antarctic sea-ice change were investigated during Janaury 1979 and October 2009.Based on previous research results,sea areas in the western Indian Ocean (WIO;50°–70°E,10 °–20 °S) are selected for the resreach.All variables showed 1-10 year interannual timescales by Fast Founer Tranaform (FFT) transformation.Results show that i) strong WIO signals emerged in the anomalous changes of Antarctic sea-ice concentration;ii) significant positive correlations occurred around the Antarctic Peninsula,Ross Sea and its northwest peripheral sea region iii) negative correlation occurred in the Indian Ocean section of the Southern Ocean,Amundsen Seas,and the sea area over northern Ross Sea;and iv) the atmospheric anomalies associated with the WIO including wind,meridional heat flux,and surface air temperature over southern high latitudes were the possible factors for the teleconnection.     

印度洋海表温度的变化及其对印度夏季季风降水影响的诊断研究

对印度洋海表温度(SST)的主要特征及变化趋势进行分析,并研究了其与印度夏季季风降水(ISMR)和季风环流的关系,揭示出:从北印度洋到南半球中高纬度印度洋,SST最显著的变化模态是全海盆一致的变化,近50 a来总体趋势是上升的,在1976,1986年以及1996年间分别有一次跳跃性增温,与太平洋SST变化趋势基本一致.除了长期变化趋势外,南印度洋中高纬度比热带地区有更显著的模态分布.在印度洋SST升温的背景下,ISMR具有逐渐减少的趋势,但两者相关较弱.印度洋SST发生跳跃后的不同阶段,许多海区SST与ISMR相关均发生变化,但在春季,热带外南印度洋具有一对相对稳定区,其分布与EOF分析的第2模态相似.根据它们的分布,文中定义了春季南半球偶极子(SIOD),在正SIOD(PSIOD)情况下印度降水偏多,而负SIOD(NSIOD)则反之.环流分析表明,PSIOD(NSIOD)通过与大气的相互作用,对夏季马斯克林高压具有增强(减弱)作用,进而使得索马里越赤道气流增强(减弱),在印度地区低空产生异常的辐合(辐散),高层辐散(辐合),从而影响印度季风环流,使得印度季风降水偏多(少).     

印度洋赤道潜流年际变化特征及其与印度洋偶极子的联系

印度洋赤道潜流(equatorial undercurrent,EUC)是赤道流系的重要组成部分,对印度洋物质输运和能量交换有着重要意义.基于SODA 3.4.2海洋再分析数据,对印度洋EUC的三维空间结构和年际变化特征进行分析,并揭示其年际变率与印度洋偶极子(Indian Ocean dipole,IOD)的联系.结...     

Natural thermoluminescence of fossil foraminiferals as a potential proxy for deep-sea temperature changes

Foraminiferal shells from two piston cores separately located at the Ninetyeast Ridge and the Bengal Fan of the Indian Ocean were selected and purified for measurements of natural thermoluminescence （NTL） intensity by a high precision thermoluminescence meter （RGD-3）. Variations of the NTL intensity along the two core sequences both spanning the last two glacial--interglacial cycles displayed a strong, identical signal of the global ice volume cycles, which matched well with their corresponding oxygen isotope data. As higher NTL intensity occurred within interglacial periods and changes in an NTL signal were most likely influenced by the temperature of ambient seawater in which the planktonic foraminiferal shells long existed, the NTL signal could be considered as a potential proxy for orbital scale temperature changes of bottom seawater in the tropical Indian Ocean.