以相邻海面高度差为观测量的沿迹调和分析新方法(英文)

An algorithm (differential mode) is presented for the improvement of harmonic tidal analysis along T/P tracks, in which the differences between the observed sea surface heights at adjacent points are taken as observations. Also, the observation equations are constrained with the results of the crossover analysis; the parameter estimations are performed at 0.1° latitude intervals by the least squares. Cycle 10 to 330 T/P altimeter data covering the China Sea and the Northwest Pacific Ocean (2°-50°N,105°-150°E) are adopted for a refined along-track harmonic tidal analysis, and harmonic constants of 12 constituents in 8 474 points are obtained, which indicates that the algorithm can efficiently remove non-tidal effects in the altimeter observations, and improve the precision of tide parameters. Moreover, parameters along altimetry tracks represent a smoother distribution than those obtained by traditional algorithms. The root mean squares of the fitting errors between the tidal height model and the observations reduce from 11 cm to 1.3 cm.     

Absolute sea level variability of Arctic Ocean in 1993–2018 from satellite altimetry and tide gauge observations

Arctic absolute sea level variations were analyzed based on multi-mission satellite altimetry data and tide gauge observations for the period of 1993–2018. The range of linear absolute sea level trends were found ?2.00 mm/a to 6.88 mm/a excluding the central Arctic, positive trend rates were predominantly located in shallow water and coastal areas, and negative rates were located in high-latitude areas and Baffin Bay. Satellite-derived results show that the average secular absolute sea level trend was (2.53±0.42) mm/a in the Arctic region. Large differences were presented between satellite-derived and tide gauge results, which are mainly due to low satellite data coverage, uncertainties in tidal height processing and vertical land movement (VLM). The VLM rates at 11 global navigation satellite system stations around the Arctic Ocean were analyzed, among which 6 stations were tide gauge co-located, the results indicate that the absolute sea level trends after VLM corrected were of the same magnitude as satellite altimetry results. Accurately calculating VLM is the primary uncertainty in interpreting tide gauge measurements such that differences between tide gauge and satellite altimetry data are attributable generally to VLM.     

基于逆Vening-Meinesz公式的测高重力中央区效应精密计算

为提高利用逆Vening-Meinesz公式反演测高重力中央区效应的精度,视中央区为矩形域,将垂线偏差分量表示成双二次多项式插值形式,引入非奇异变换,推导出了重力异常的计算公式。以低纬度区域2′×2′的垂线偏差实际数据为背景场进行了计算,结果表明,当中央区包含4个网格时,传统公式与推导出的重力异常计算公式误差的最大值大于1 mGal。推导出的公式可为高精度测高重力中央区效应的计算提供理论依据。     

基于ERS-2和Envisat测高卫星提取西太平洋潮汐信息

对两颗太阳同步轨道测高卫星ERS-2和Envisat 1995～2010年169个重复周期（共近15 a）的数据进行沿轨正交响应分析,得到中国海及西太平洋地区的海洋潮汐调和常数,并利用交叉点位置上升轨迹与下降轨迹提取的潮汐信息和验潮站数据分析了结果的准确度。结果表明,除S2、K1分潮外,基于ERS-2和Envisat测高卫星能够提取出可靠和分布合理的潮汐调和常数,结合交叉轨迹与邻近地面轨迹将有效改善采样规律和观测样本数量,进一步提高潮汐参数的准确度。     

Assessment of Cryosat-2 and SARAL/AltiKa altimetry for measuring inland water and coastal sea level variations: A case study on Tibetan Plateau lake and Taiwan Coast

Satellite altimetry has been proven as an effective technology to accurately measure water level, ice elevation, and flat land surface changes since the 1990s. To overcome limitations of pulse-limited altimetry, new altimetric missions such as Cryosat-2 and Satellite with ARgos and AltiKa (SARAL/AltiKa), have been designed to have higher along-track spatial resolution to measure more accurately inland water levels for small water bodies, and coastal sea level changes. In this study, we evaluate the performance of Cryosat-2 low-resolution (LRM) and SARin modes and SARAL/AltiKa Ka-band data on two connected lakes in central Tibetan Plateau, and in the coastal region of Taiwan. Results are compared with in situ tide gauge data in Taiwan and altimetric lake level time series from the CNES Hydroweb database. Our results show that water level change trends observed by Cryosat-2 20-Hz retracked observations, the SARAL/AltiKa 40-Hz Ice-1 retracked data, and the Hydroweb measurements are consistent with the estimated water level trend of ～0.30?m/y, during 2011–2017, and 2013–2015, for the Tibetan Migriggyangzham Co and Dorsoidong Co, respectively. For the coastal region, the performance of SARAL/AltiKa is better than that of Cryosat-2 LRM data in Taiwan. This finding demonstrates the superiority of the Ka-band over Ku-band radar altimetry.     

基于T/P和Jason-1/2卫星高度计海面高度数据获取南海同潮图的研究

随着卫星高度计资料的不断丰富,通过对卫星高度计所得潮汐调和常数进行插值或拟合得到潮汐同潮图成为可能。本文拟对T/P(TOPEX/POSEIDON)、Jason-1和Jason-2卫星高度计数据进行分析,得到南海区域星下观测点处四个主要分潮(M2、S2、K1和O1分潮)的调和常数,进而利用双调和样条插值方法对其进行插值,获取南海同潮图。首先,以1992～2016年T/P和Jason卫星高度计所得海面高度数据为基础,利用调和分析方法计算了南海星下观测点处M2、S2、K1和O1四个主要分潮的调和常数,并与40个验潮站数据进行了对比,最大矢量均差为4.99cm,说明分析所得调和常数与利用验潮站资料提取的调和常数的误差较小。进而采用双调和样条插值方法对星下点调和常数进行插值,得到了南海四个主要分潮的同潮图,所得结果与全球潮汐模型TPXO7.2模式结果的矢量均差分别为4.69、2.46、3.13和2.42 cm,与141个验潮站处观测结果的矢量均差分别为22.59、10.26、10.24和8.51 cm。此外,插值所得四个主要分潮的无潮点位置与前人研究结果相近。上述实验结果表明:利用双调和样条插值方法对卫星高度计所得调和常数进行插值能够获取较为准确的同潮图。     

资源三号02星激光测高数据质量分析

近几年来,中国的对地观测卫星激光测高技术发展较快,资源三号02星上搭载了国内首台对地观测的卫星激光测高试验载荷,在后续的高分七号、陆地生态系统碳监测卫星上均装备业务化应用的激光测高仪,开展国产对地观测卫星激光测高数据质量分析研究非常必要,能有效填补国内空白并推动相关技术发展。本文对资源三号02星载荷的激光测高数据进行了严密几何处理,重点从夜间观测、卫星小角度侧摆、海面区域等不同条件下的数据质量进行了分析,对数据的平均可用率进行了统计分析。试验表明,资源三号02星激光测高仪能获得约30%有效测高数据,在夜间数据有效利用率略有提高,在大型水面也能获得有效数据,经后处理后在平坦地区验证的绝对高程精度优于1.0 m,部分点高程精度优于0.5 m,硬件本身的测距精度和卫星姿态测量误差是主要的误差源。相关结论对于后续国产卫星激光测高载荷的研制以及数据后处理和应用具有参考价值。     

我国东部海域高精度地转流的确定方法

针对目前带有高频信息的全球稳态海面地形模型的计算过程比较复杂的问题,该文采用移去恢复法,对由全球海面高模型得到稳态海面地形模型添加高频信息,并用新模型计算我国东部海域的地转流,分析其精度。结果表明:使用卫星重力场模型GOCE_TIM5,全球平均海面高模型CNES-CLS15,计算出分辨率为15′×15′我国东部海域的地转流,高频信息不明显;采用移去恢复法,利用GOCE_TIM5模型、CNES-CLS15模型、全球稳态海面地形模型CNES-CLS13,得到相同分辨率我国东部海域的地转流,与未采用移去恢复法相比,其结果中细节信息明显,与全球实测浮标数据更为接近,其精度与由全球稳态海面地形模型CNES-CLS13得到结果相当。     

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).     

基于海面高度数据的全球海洋多核涡旋探测和统计

This study produced a statistical analysis of multicore eddy structures based on 23 years' altimetry data in global oceans. Multicore structures were identified using a threshold-free closed-contour algorithm of sea surface height, which was improved for this study in respect of certain technical details. Meanwhile a more accurate definition of eddy boundary was used to estimate eddy scale. Generally, multicore structures, which have two or more closed eddies of the same polarity within their boundaries, represent an important transitional stage in their lives during which the component eddies might experience splitting or merging. In comparison with global eddies, the lifetimes and propagation distances of multicore eddies were found to be much smaller because of their inherent structural instability. However, at the same latitude, the spatial scale of multicore eddies was found larger than that of single-core eddies, i.e., the eddy area could be at least twice as large. Multicore eddies were found to exhibit some features similar to global eddies. For example, multicore eddies tend to occur in the Antarctic Circumpolar Current, some western boundary currents, and mid-latitude regions around 25°N/S, the majority(70%) of eddies propagate westward while only 30% propagate eastward, and large-amplitude eddies are restricted mainly to reasonably confined regions of highly unstable currents.