卫星测高研究应用新进展

卫星测高是利用空间技术进行海洋观测的崭新技术手段。GEOSAT卫星的升空又使得这一研究向前大大地推进。本文简要介绍卫星测高在确定大地水准面精度、研究岩石圈特性、探测海底深部构造、研究海洋动力环境以及其经济效益和社会效益的最新进展。     

基于Laplace方程的垂线偏差法反演全球海域重力异常

海洋重力场模型反演的质量主要依赖于采用测高数据的精度、空间分辨率和数据分布密集程度。本文联合Geosat GM/ERM、ERS-1 GM/ERM、TOPEX/Poseidon、Envisat、Cryosat-2、Jason-1 ERM/GM和SARAL/AltiKa等多种测高观测数据集,深入比较了多种波形重跟踪算法的效果,回波数据重跟踪处理后的沿轨海面高标准差。统计表明,Sandwell算法优于MLE-4算法、Davis阈值法、改进阈值法和β参数拟合法;基于不同测高数据波形重采样的结果给出了沿轨海面梯度计算中低通滤波的参数选择方法,并采用Sandwell提出的垂线偏差法,反演了全球海域1′×1′的重力场模型。检核表明,反演结果与DTU13和SIO V23.1模型检核的差值均方根分别为3.4、1.8 mGal,与NGDC船测数据的检核精度为4~8 mGal,且本文模型在部分典型海区内精度更优。     

Bathymetric inversion of South China Sea from satellite altimetry data

1　ＩｎｔｒｏｄｕｃｔｉｏｎＴｏｄｅｖｅｌｏｐｔｈｅｏｃｅａｎｗｉｄｅｌｙａｎｄｄｅｅｐｌｙ ,ｗｅｎｅｅｄａｂｕｎｄａｎｔｏｃｅａｎｉｎｆｏｒｍａｔｉｏｎ .Ａｓａｎｅｓｓｅｎｔｉａｌｐａｒｔｏｆｓｕｃｈｉｎｆｏｒｍａｔｉｏｎ ,ｓｅａｆｌｏｏｒｔｏｐｏｇｒａｐｈｙｐｌａｙｓａｖｅｒｙｉｍｐｏｒｔａｎｔｒｏｌｅｉｎａｖａｒｉｅｔｙｏｆｍａｒｉｎｅａｃｔｉｖｉｔｉｅｓ .Ｈｏｗｅｖｅｒ,ｔｈｅｈｉｇｈｃｏｓｔｆｏｒｏｃｅａｎｂａｔｈｙｍｅｔｒｉｃｓｕｒｖｅｙｉｎｇｌｉｍｉｔｓｔｈｅａｐｐｌｉｃａｔｉｏｎｏ…     

Topex/Poseidon Altimetry and Dynamics of the Ocean-Atmosphere System

The T/P altimeter data 1993 – 1997 (cycles 11 – 194) has been analyzed with emphases on seasonal variations in sea surface topography (SST). The amplitude of the annual variations amounted to (5.9±0.3) mm when inverted barometer (IB) corrections were applied and (2.0±0.4) mm without any IB corrections. The amplitude of the semi-annual variations in SST was small with IB corrections applied: (0.6±0.3) mm. However, when no IB corrections were applied, it was (1.8±0.4) mm, i.e. the semiannual variations are at the same level as the annual variations with no IB corrections. The phase angle offset of the annual term has shifted by about 180° when IB correction was applied. The dynamics of the ocean-atmosphere system is discussed and it is concluded that it could, at least partly, be responsible for the above observed effects.     

用不变矩从机载激光扫描测高点云数据中重建规则房屋

介绍了不变矩的概念，结合实例，基于机载激光扫描测高的三雏点云数据，用不变矩实现了规则房屋的模型重建。对不变矩重建房屋模型的精度进行了讨论和分析．得出了一些有益的结论。     

一种多前缘多阈值的波形重构算法

为了改善近海测高精度,本文对近海测高波形的特征进行了研究,并在现有算法的基础上提出基于波前缘识别算法的多前缘多阈值波形重构方法.然后将该方法用于中国近海的卫星测高波形数据的处理,得到精度与分辨率更好的海面高数据.作为验证,将此海面高数据换算为重力异常并与船测重力进行比较,结果显示该方法可以明显提高卫星测高精度.     

The 2013 Ibiza Calibration Campaign of Jason-2 and SARAL Altimeters

This study presents the results of the 2013 Ibiza (Western Mediterranean) calibration campaign of Jason-2 and SARAL altimeters. It took place from 14 to 16 September 2013 and comprised two phases: the calibration of the GNSS (Global Navigation Satellite System) buoys to estimate the antenna height of each of them and the absolute calibration to estimate the altimeter bias (i.e., the difference of sea level measured by radar altimetry and GNSS). The first one was achieved in the Ibiza harbor at a close vicinity of the Ibiza tide gauge and the second one was performed at ～ 40 km at the northwest of Ibiza Island at a crossover point of Jason-2 and SARAL nominal groundtracks. Five buoys were used to delineate the crossover region and their measurements interpolated at the exact location of each overflight. The overflights occurred two consecutive days: 15 and 16 September 2013 for Jason-2 and SARAL, respectively. The GNSS data were processed using precise point positioning technique. The biases found are of (?0.1 ± 0.9) and (?3.1 ± 1.5) cm for Jason-2 and SARAL, respectively.     

Use of SARAL/AltiKa Observations for Modeling River Flow

In the absence of many gauging stations in the major and mighty river systems, there is a need for satellite-based observations to estimate temporal variations in the river water storage and associated water management. In this study, SARAL/AltiKa application for setting up hydraulic model (HEC-RAS) and river flow simulations over Tapi River India has been discussed. Waveform data of 40 Hz from Ka band altimeter has been used for water levels retrieval in the Tapi river. SARAL/AltiKa retrieved water levels were converted to discharge in the upstream location (track-926) using the rating curve available for the nearby gauging site and using linear spatial interpolation technique. Steady state simulations were done for various flow conditions in the upstream. Validation of river flow model was done in the downstream location (track-367) by comparing simulated and altimeter retrieved water levels (RMSE 0.67 m). Validated model was used to develop rating curve between water levels and simulated discharge for the downstream location which enables to monitor discharge variations from satellite platform in the absence of in situ observations. It has been demonstrated that SARAL/AltiKa data has potential for river flow monitoring and modeling which will feed for flood disaster forecasting, management and planning.     

Mesoscale surface circulation and variability of Southern Indian Ocean derived by combining satellite altimetry and drifter observations

High resoultion Eulerian mean velocity field has been derived by combining the satellite tracked surface drifter data with satellite altimetry and ocean surface winds. The drifter data used in this study includes Argos and surface drifter data from Global Drifter Program. Maps of Sea Level Anomaly(MSLA) weekly files with a resolution of(1/3)° in both Latitude and Longitude for the period 1993–2012 have been used. The Ekman current is computed using ocean surface mean wind fields from scatterometers onboard ERS 1/2,Quikscat and ASCAT. The derived mean velocity field exhibits the broad flow of Antarctic Circumpolar Current with speeds up to 0.6 m/s.Anomalous field is quite significant in the western part between 20° and 40°E and in the eastern part between 80°E and 100°E with velocity anomaly up to 0.3 m/s. The estimated mean flow pattern well agrees with the dynamic topography derived from in-situ observations. Also,the derived velocity field is consistent with the in-situ ADCP current measurements. Eddy kinetic energy illustrates an increasing trend during 1993–2008 and is in phase coherence with the Southern Annular Mode by three month lag. Periodic modulations are found in the eddy kinetic energy due the low frequency Antarctic Circumpolar Wave propagation.     

CryoSat-2卫星海冰区域波形识别及海冰干舷高确定

利用40%阈值法对CryoSat-2卫星波形数据进行重跟踪,将波形特征参数和海冰浓度相结合,对海冰和Lead(浮冰之间的开阔水域)进行有效识别。利用沿轨前后搜索算法计算海冰干舷高,并引用AWI结果,绘制2011~2013年北冰洋多年冰区域和一年冰区域平均海冰干舷高变化趋势图。比较本文结果与AWI结果的各年同期数据,验证本文结果的可靠性。