基于分层EOF的深海声速剖面时变特征建模

Modeling of Time-Varying Characteristics of Deep-Sea Sound Velocity Profile Based on Layered-EOF

针对目前局部海域小时间尺度声速场建模方法未顾及不同深度区间内声速变化规律的问题,本文根据实测深海声速剖面的统计特征,提出了声速剖面分层方法,并进一步基于经验正交函数(Empirical Orthogonal Function,EOF)提出了局部小时间尺度的声速剖面分层时变模型构建方法。利用南海实测全海深声速剖面数据,分析了分层EOF第一模态系数和等效平均声速的日变化特征,并比较了不同拟合模型的精度。最后,利用试验海区的温度和潮汐数据分析了声速剖面周期变化的影响因素。结果表明:①声速剖面分层EOF第一模态系数及等效平均声速具有日周期变化特征,上层声速日周期变化特征不明显,中层声速日周期变化特征较明显,下层声速变化较小但仍具有日周期变化特征;②局部海域小时间尺度声速拟合应考虑长期变化项的影响;③试验海区声速剖面EOF第一模态系数变化与温度显著相关,提取的声速剖面时变特征与海区潮汐周期特征基本吻合。

In view of the problem that the variation of sound velocity in different depth intervals has not been taken into account in the existing methods for the modeling of small time-scale sound velocity field in local sea areas,a method for the layering of sound velocity profiles based on statistical characteristics of the measured deep-sea sound velocity profiles is proposed.Furthermore,a method for the construction of layered time-varying model of local small-scale sound velocity profiles is proposed based on the Empirical Orthogonal Function(EOF).The diurnal variation characteristics of the first mode coefficient of layered-EOF and the equivalent average sound velocity of the sound velocity profiles are analyzed by using the measured data of whole deep sound velocity profiles in the South China Sea,and the accuracy of different fitting models is compared.Finally,the factors affecting the periodic variations of the sound velocity profiles are analyzed by using temperature and tide data in the experimental sea area.The results show that:①Both the first mode coefficient of layered-EOF and the equivalent average sound velocity of the sound velocity profiles are characterized with daily periodic variation,with the daily periodic variation of sound velocity being not obvious in the upper layer,more obvious in the middle layer and small but still present in the lower layer.②The influence of long-term variation term should be taken into account in fitting the local and small time-scale sound velocity.③The change of the first mode coefficient of the EOF of the sound velocity profiles in the experimental sea area is significantly correlated to temperature.And the extracted time-varying characteristics of the sound velocity profiles are basically consistent with the periodic feature of tide in the experimental sea area.