长江口EnviSat测高数据的波形分类重构分析

采用波形分类重构算法处理EnviSat卫星从2002年10月至2010年5月在长江口近岸海域28°N~32°N、121°E~125°E范围内的波形数据。该区域内海洋波形、波形后缘前端出现峰值的波形、波形后缘后端出现峰值的波形、似镜面波形和复杂波形分别占89.03%、2.95%、0.45%、3.31%和4.26%。根据不同的波形类别采用不同波形算法进行波形重构。同时,分析了不同重构算法之间的系统偏差,并据此确定OCOG算法、Threshold算法和子波形算法的最优阈值水平分别为65%、45%和50%。重构结果表明,波形分类重构算法优于其他波形重构算法,能有效改善原始海面高的精度,改善程度在16.62%~53.86%之间。此外,重构后交叉点差值小于重构前的交叉点差值,与轨迹P089、P411形成的交叉点的海面高差值由1m降低到25cm左右,其余交叉点的差值均在2~6cm。     

湖冰厚度遥感反演进展与展望

湖冰是对气候变化十分敏感的冰冻圈水文变量,起到调节区域气候和湖泊生态系统的作用,并作为一种自然资源服务于冰上生产生活。湖冰覆盖和湖冰厚度是研究湖冰过程的关键变量,目前大多数湖冰研究集中在湖冰覆盖领域,湖冰厚度领域由于缺乏实测资料和专门的遥感观测平台还存在诸多空白,大量缺资料地区湖冰厚度仍处于未知状态,亟待方法和数据上的突破与创新。本文综述了近20年国内外湖冰厚度遥感反演领域的进展,介绍了各类反演方法的原理机理及主要优缺点,其中被动微波遥感方法具有良好的时间分辨率但空间分辨率较粗,难以覆盖中小型湖泊;基于SAR影像的主动微波方法空间分辨率较高但物理机制复杂,可靠性有待进一步验证;基于测高雷达的主动微波方法观测时段较长,物理机制明确,易于拓展到无实测资料湖泊,但空间覆盖相对有限;热红外遥感方法时空分辨率较好,但容易受云和湖冰表面积雪的影响,反演精度和可靠性有待提升。在此基础上,本文分析湖冰厚度遥感反演领域面临的主要挑战和发展方向包括：（1）厘清湖冰表面积雪相关的物理过程;（2）实现大范围实测冰厚和遥感资料的集成;（3）实现多源遥感冰厚反演方法的交叉融合。     

Influence of Tide Models on the Use of Altimetry Data to Research Sea Level Anomaly

A tide model (named DN1.0), which contains 12 principal constituents over China seas and the Northwest Pacific is estimated by along-track harmonic analysis with TOPEX/Poseidon altimetry data taken from 1993 to 2002. CSR3.0, FES95.2 and DN1.0 are used respectively to detide the data for the time series of sea level anomaly (SLA) in the Yellow Sea, East China Sea, South China Sea and Northwest Pacific. The SLA curves and the power spectral density show that the major components that exist in SLA in China seas arise from the error of the tide models.     

星载激光光斑影像特征参数提取与分析

激光指向、足印大小和形状、能量等参数的精确提取是评估星载激光测高数据质量的重要指标.然而,对这些参数的研究和理解目前还不明确,为准确提取和理解这些参数,本文依托ICESat/GLAS的激光剖面阵列(LPA)影像数据,采用激光能量最大强度的1/e2弱化背景噪声影响,利用灰度加权一阶矩阵法和椭圆拟合法提取LPA影像的5个特...     

Combining multisource satellite data to estimate storage variation of a lake in the Rift Valley Basin,Ethiopia

Integration of remote sensing data sets from multiple satellites is tested to simulate water storage variation of Lake Ziway, Ethiopia for the period 2009-2018. Sixty Landsat ETM+/OLI images served to trace temporal variation of lake surface area using a water extraction index. Time series of lake levels were acquired from two altimetry databases that were validated by in-situ lake level measurements. Coinciding pairs of optical satellite based lake surface area and radar altimetry based lake levels were related through regression and served for simulating lake storage variation. Indices for extracting lake surface area from images showed 91–99 % overall accuracy. Lake water levels from the altimetry products well agreed to in-situ lake level measurements with R² = 0.92 and root mean square error of 11.9 cm. Based on this study we conclude that integrating satellite imagery and radar altimetry is a viable approach for frequent and accurate monitoring of lake water volume variation and for long-term change detection. Findings indicate water level reduction (4 cm/annum), surface area shrinkage (0.08km²/annum) and water storage loss (20.4Mm³/annum) of Lake Ziway (2009–2018).     

西太平洋海域卫星测高重力垂直梯度分布

从地球重力场基本理论出发,推导了重力垂直梯度计算的数值积分公式,并利用由多颗测高卫星联合反演的2'×2'海洋重力异常资料,解算了西太平洋海域重力垂直梯度.将计算所得的重力异常垂直梯度与现有资料进行比较,其差值均方根为±10.08E,表明两者精度相当.此外,还对差值大小和空间分布进行了深入分析.     

利用卫星测高技术确定浙江海域大地水准面

利用多颗卫星的测高数据,经共线平均及交叉点平差,建立浙江深海海域2.5′×2.5′格网分辨率的平均海面高模型,在扣除海面地形影响后得到海域的大地水准面起伏,并与EGM2008所得计算结果进行对比;利用移去-恢复技术及SVR方法,联合验潮站GPS/水准数据与EGM2008大地水准面模型,计算浙江近岸海域大地水准面起伏;最终建立浙江海域2.5′×2.5′格网分辨率的大地水准面模型。     

Contributions of Satellite Laser Ranging to Past and Future Radar Altimetry Missions

Satellite laser ranging (SLR) has proven avery efficient method for contributingto the tracking of altimetric satellites anddetermining accurately their orbitalthough hampered by the non-worldwide coverageand the meteorologicalconditions. Indeed, in some cases it is the onlymethod available to determinethe satellite orbit (e.g., the orbits of the ERS-1and Geosat-Follow-On missions).Moreover, any operational and non-weather dependenttechniques, like GPS,DORIS, PRARE, can exhibit systematic errors inpositioning and orbitography. Acomparison with SLR results allows to evidence sucherrors and vice versa. Fordoing that, two different approaches for determiningprecise orbits can beconsidered: one based on global orbit determination,the other on a short-arctechnique used to locally improve a global orbitdetermined by another trackingtechniques, such as DORIS or GPS. We can thusvalidate a global orbit andachieve orbit quality control to a level of2 to 3 centimeters at present and expectto achieve a level of 1 to 2 centimeters inthe near future. Errors induced bystation coordinates or by the gravity field(geographically correlated errors, forexample) can be estimated from SLR tracking data.Colocation experiments withdifferent techniques in the same geodetic siteplay also a key role to ensure preciserelationships between the geodetic referenceframes linked to each technique. Inparticular, the role of the SLR technique is tostrengthen the vertical component(including velocity) of the positioning, whichis crucial for altimetry missions.The role of SLR data in the modelling of the firstterms of the gravity field has finally to be emphasized,which is of primary importance in orbitography,whatever the tracking technique used.Another application of SLR technology is thesatellite altimeter calibration. Examples of past calibrationand future experiments are given, including theaccuracy we can expect from the Jason-1 and EnviSatspace oceanography missions.     

Assimilation of altimetry data for nonlinear shallow-water tides: Quarter-diurnal tides of the Northwest European Shelf

Non-linear tidal constituents, such as the overtide M₄ or the compound tide MS₄, are generated by interaction in shallow seas of the much larger astronomically forced “primary” tidal constituents (e.g., M₂, S₂). As such, errors in modeling these “secondary” shallow-water tides might be expected to be caused first of all by errors in modeling the primary constituents. Thus, in the context of data assimilation, observations of primary-constituent harmonic constants can indirectly constrain shallow-water constituents. Here we consider variational data assimilation for primary and secondary tidal constituents as a coupled problem, using a simple linearized perturbation theory for weak interactions of the dominant primary constituents. Variation of the resulting penalty functional leads to weakly non-linear Euler–Lagrange equations, which we show can be solved approximately with a simple two-stage scheme. In the first stage, data for the primary constituents are assimilated into the linear shallow water equations (SWE), and the resulting inverse solutions are used to compute the quadratic interactions in the non-linear SWE that constitute the forcing for the secondary constituents. In the second stage, data for the compound or overtide constituent are assimilated into the linear SWE, using a prior forced by the results of the first stage. We apply this scheme to assimilation of TOPEX/Poseidon and Jason altimetry data on the Northwest European Shelf, comparing results to a large set of shelf and coastal tide gauges. Prior solutions for M₄, MS₄ and MN₄ computed using inverse solutions for M₂, S₂, and N₂ dramatically improve fits to validation tide gauges relative to unconstrained forward solutions. Further assimilation of along-track harmonic constants for these shallow-water constituents reduces RMS differences to below 1 cm on the shelf, approaching the accuracy of the validation tide gauge harmonic constants.     

南海海盆重力异常场特征及构造演化

卫星重力测高能提供高分辩率的空间重力异常资料。本文解译了南海地块细结构的重力异常特征 ,并探讨了南海海盆的形成与演化