“海翼号”水下滑翔机盐度数据的热滞后效应偏差订正方法探讨

水下滑翔机可以高效地观测海水的温度、盐度和压强等海洋参数,但由于热滞后效应,盐度数据,特别是在温度梯度较大的温跃层,会出现一定程度的偏差。本研究选取了3种目前常用的盐度热滞后订正方法,对带泵的“海翼号”水下滑翔机,于2019年8月在中北太平洋所观测的盐度数据因热滞后效应引起的偏差进行订正处理,与船载911型温盐深测量仪(Instrument for Measuring Conductivity Temperature and Depth,CTD)观测盐度进行对比,在比较了3种方法对滑翔机盐度订正前后下降和上升剖面偏差的减少程度、订正后剖面与船载CTD观测剖面的偏差大小和下降上升温盐曲线(T-S曲线)的一致程度后,得出了水下滑翔机盐度订正的最优方法,即在订正电导池中实际温度的前提下,采用计算机图形分割方法,最小化滑翔机机载CTD测得的下降和上升两个剖面T-S曲线围成面积所确定的目标函数,来确定合适的热滞后修正振幅和时间常数,从而修正下降和上升两个剖面之间盐度偏差。

Discussion on the correction method of thermal lag effect deviation in salinity data of sea-wing glider

The underwater glider can record the data of temperature, salinity and pressure of sea water efficiently.However, due to the thermal lag effect, the salinity data, especially in the thermocline with large temperature gradient, should have produced a certain degree of deviation. In this study, three commonly used salinity thermal lag correction methods were selected to correct the deviation caused by thermal lag effect of salinity data observed by sea-wing underwater glider with pump in the central North Pacific Ocean in August 2019. The results are compared with the salinities recorded by shipborne 911 conductivity, temperature and depth measuring instruments (CTD). The reduction degrees of deviation of upcast and downcast profiles before and after the application of three methods for salinity correction of glider are compared. The optimal method of salinity correction for the underwater glider is obtained. That is, on the premise of correcting the actual temperature in the conductivity cell, the computer graphic segmentation method is used to minimize the objective function determined by the area surrounded by T-S curves of the downcast and upcast profiles. Finally, the thermal lag correction amplitude and time constant could be determined to correct the salinity deviation between the downcast and upcast profiles.