Estimation of Sea Ice Thickness from SARAL/AltiKa in Drifting Orbit Phase

Abstract

Intra and inter-annual variations in the sea ice thickness are highly sensitive indicators of climatic variations undergoing in the earth’s atmosphere and oceans. This paper describes the method of estimating sea ice thickness using radar waveforms data acquired by SARAL/Altika mission during its drifting orbit phase from July 2016 onwards yielding spatially dense data coverage. Based on statistical analysis of return echoes, classification of the surface has been carried out in three different types, viz. floe, lead and mixed. Time delay correction methods were suitably selected and implemented to make corrections in altimetric range measurements and thereby freeboard. By assuming hydrostatic equilibrium, freeboard data were converted into sea ice thickness. Results show that sea ice thickness varies from 4 to 5?m near ice shelves and 1 to 2.5?m in the marginal sea ice regions. Freeboard and sea ice thickness estimates were also validated using NASA’s Operation Ice Bridge (OIB) datasets. Freeboard measurements show very high correlation (0.97) having RMSE of 0.13. Overestimation of approximately 1–2?m observed in the sea ice thickness, which could be attributed to distance between AltiKa footprint and OIB locations. Moreover, sensitivity analysis shows that snow depth and snow density over sea ice play crucial role in the estimation of sea ice thickness.     

Diet of albacore Thunnus alalunga from the waters of Mauritius (western Indian Ocean) inferred from stomach contents and fatty acid analysis

The diet of albacore Thunnus alalunga from their spawning ground in the waters of Mauritius was investigated. The stomach contents of 249 albacore individuals, caught by industrial longliners and artisanal fishers, was analysed, and the dominant prey taxa were selected for lipid and fatty acid (FA) analysis. The FA profiles of prey were compared with those of liver tissue of spawning-capable and post-spawning female albacore, using multivariate analysis. Whereas stomach content analysis identified cephalopods and crustaceans as the dominant prey items in number, FA-profile analysis identified crustaceans and fishes as the most-frequently consumed prey of post-spawning female albacore. In contrast, the FA profiles of spawning-capable albacore and those of prey showed very low similarity. Analysis of the prey suggests that although cephalopods, crustaceans and fishes could all provide albacore with the required lipids and FAs, cephalopod prey seem to be less desirable owing to their lower energy content (i.e. low in total lipid, triacylglycerol, 16:0, 18:0 and 18:1ω9). Instead, the most beneficial food appeared to be locally available fishes, which are more energy-rich and have a higher docosahexaenoic acid/ eicosapentaenoic acid ratio. These results provide new information on the trophic ecology of albacore, promote our understanding of the importance of prey type for successful reproduction of albacore, and highlight the advantages of FA profiling to study diet.     

满足给定数字特征和谱的随机信号的产生

本文给出了满足给定数字特征和谱的随机序列的产生方法，即用无记忆非线性变换实现非正态随机信号的模拟．该法与Ｇｕｊａｒ法相比较，放宽了变量概率分布的限制，只要求变量矩的存在。同时考虑无记忆非线性变换对谱的影响，用异于Ｌｉｕ的方法在频域上求解输入正态分布随机序列的谱．     

风暴期间黄河水下三角洲波浪变形

为确定适用黄河三角洲的波动理论，对黄河三角洲风暴期间及前后波浪连续观测资料进行了处理，将其投在komar波浪理论分区图中后，分析了风暴期间黄河水下三角洲波浪的波形特征，发现站位所在地适合的波浪理论主要为艾里波和斯托克斯波，风暴期间波浪变形，还存在少量超过极限波陡线的波浪，通过比较常见的极限波陡线，看出Miche曲线比较适合该研究区。     

广西沿岸海平面变化的关联维数研究

采用相空间重构和关联维数方法，研究了广西沿岸月平均海平面变化的分形特征，结果表明，相空间重构的延迟时间τ为3△t，当关联维数趋于饱和时，石头埠，北海和龙尾的相空间维数为7，而涠洲岛为9，它们的关联维数平均值平均值分别为6.6507,6.5414,6.7059.     

碳水化合物的组合合成

碳水化合物的组合合成是一项新兴技术，该技术可以在短时间内合成大量用于进行生物活性筛选的寡糖及拟糖物。液相与固相合成技术可以极大地加快药物研究与开发进程。作者针对该技术在碳水化合物合成方面的研究进展情况进行讨论。     

An unsteady wave driver for narrowbanded waves: modeling nearshore circulation driven by wave groups

In this paper, we derive an unsteady refraction–diffraction model for narrowbanded water waves for use in computing coupled wave–current motion in the nearshore. The end result is a variable coefficient, nonlinear Schrödinger-type wave driver (describing the envelope of narrow-banded incident waves) coupled to forced nonlinear shallow water equations (describing steady or unsteady mean flows driven by the short-wave field). Comparisons with experimental data show that good accuracy can be obtained for cases of nonbreaking wave transformation. Numerical simulations show that the interaction of wave groups with longshore topographic nonuniformities generates strong edge wave resonances, providing a generating mechanism for low-order edge waves.     

新生相形成的模拟实验研究

通过模拟实验制备了硅酸盐类不溶性固体，从Ｘ射线衍射特征和红外光谱特征两方面看，制得的硅酸盐类与河口新生相成分，结构相似，表明铁水解成的β－ＦｅＯＯＨ胶体吸附Ｓｉ，Ａｌ，Ｍｇ，Ｋ等元素，经结构重组可形成硅酸盐矿物，这可能是河口体系新生相的形成原因。