舟山群岛海域峡道密布,峡道边坡失稳现象普遍发育,规模不一。多发的水下滑坡对海底光缆、港口码头等海岸工程设施都有较大威胁。2012年12月,使用浅地层剖面仪对六横岛周边峡道区进行探测,划分出3个主要声学反射界面以及4个地层单元,上部3个地层为全新世沉积层。发现6处水下滑坡,分布于六横岛沿岸边坡及毗邻的潮流深槽边坡。滑坡结构均为整体性滑坡,部分具多级性。从滑坡体规模看,滑坡体体积介于1.6×10⁵~2.7×10⁷ m³之间,其中超大型滑坡2处、大型滑坡3处、中型滑坡1处。根据界面与滑坡体的相关性,推测水下滑坡均发生在距今2.5 ka以来的全新世晚期。

For more than 20 years, the multi-satellite Data Unification and Altimeter Combination System (DUACS) has been providing near-real-time (NRT) and delayed-time (DT) altimetry products. DUACS datasets range from along-track measurements to multi-mission sea level anomaly (SLA) and absolute dynamic topography (ADT) maps. The DUACS DT2018 ensemble of products is the most recent and major release. For this, 25 years of altimeter data have been reprocessed and are available through the Copernicus Marine Environment Monitoring Service (CMEMS) and the Copernicus Climate Change Service (C3S). Several changes were implemented in DT2018 processing in order to improve the product quality. New altimetry standards and geophysical corrections were used, data selection was refined and optimal interpolation (OI) parameters were reviewed for global and regional map generation. This paper describes the extensive assessment of DT2018 reprocessing. The error budget associated with DT2018 products at global and regional scales was defined and improvements on the previous version were quantified (DT2014; Pujol et al., 2016). DT2018 mesoscale errors were estimated using independent and in situ measurements. They have been reduced by nearly 3 % to 4 % for global and regional products compared to DT2014. This reduction is even greater in coastal areas (up to 10 %) where it is directly linked to the geophysical corrections applied to DT2018 processing. The conclusions are very similar concerning geostrophic currents, for which error was globally reduced by around 5 % and as much as 10 % in coastal areas.