Inversion of multimegameter-range acoustic data for ocean temperature
Inversion of multimegameter-range acoustic data for ocean temperature
复制标题
海洋温度的多兆米范围声学数据反演
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
B. Dushaw
中科院分区：
文献类型：
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作者：
B. Dushaw
当参考海洋状态不足以进行线性化反演时，由声传输获得的射线传播时间推导出的海洋声速（代替温度）可能不准确。当参考（例如，Levitus海洋地图集）与“真实”海洋明显不同时，参考射线路径不能准确地代表真实采样。此外，海洋的自然变化，如夏季混合层的演变，可以随时间显著改变射线采样。反演的指导原则是与反演解相关的射线旅行时间必须与测量的旅行时间相匹配。随时间变化的参考海洋可以减少非线性和解的不确定性，因为可以假定模式方差较小。利用Levitus海洋地图集，探讨了非线性对多兆欧米级声波数据反演的影响，并找到了精确的反演方法。这些方法应用于海洋气候声学测温（ATOC）项目期间在北太平洋获得的声学数据，该项目使用加利福尼亚海岸外先锋海山的声源。为了使反演线性化，通过参考测量的旅行时间和使用Levitus月度海洋地图集计算的旅行时间来去除年周期。这种线性化的结果是更精确的范围和深度平均温度的时间序列，但是范围和深度平均温度的解决方案与使用与时间无关的一组射线的解决方案只有轻微的不同。0-1000 m深度平均温度的标准不确定度通常为/spl plusmn/0.012/spl℃，而年峰间温度变化约为0.4/spl℃。由于走时数据本质上是平均的，范围和深度平均温度的时间序列对正演模型中的不同假设（如模型参数化、方差、波数谱和数据不确定性）不敏感。
Ocean sound speed (a surrogate for temperature) derived from the ray travel times obtained from acoustic transmissions may be inaccurate when the reference ocean state is inadequate for linearized inversion. When the reference (e.g., the Levitus ocean atlas) is significantly different from the "true" ocean, the reference ray paths inaccurately represent the true sampling. In addition, natural oceanic variations, such as the evolution of a summer mixed layer, can significantly change the ray sampling over time. The guiding principle for inversion is that ray travel times associated with the inverse solution must match the measured travel times. A time-dependent reference ocean can reduce both the nonlinearities and the solution uncertainties since the model variances may be assumed to be less. The Levitus ocean atlas was employed to explore the effects of nonlinearities when inverting multimegameter-range acoustic data and to find accurate inversion methods. These methods were applied to acoustic data obtained in the North Pacific during the acoustic thermometry of ocean climate (ATOC) project using an acoustic source on Pioneer Seamount off the coast of California. In order to linearize the inversions, the annual cycle was removed by referencing the measured travel times to travel times computed using the Levitus monthly ocean atlas. This linearization results in a more accurate time series of range- and depth-averaged temperatures, but the solution for range- and depth-averaged temperature is only slightly different from that using a time-independent set of rays. Standard uncertainties for the 0-1000-m depth-averaged temperature are typically /spl plusmn/0.012/spl deg/C, while the annual peak to-peak temperature variation is about 0.4/spl deg/C. Because the travel time data are inherently averaging, the time series of range- and depth averaged temperature is insensitive to different assumptions made in the forward model, such as the model parameterization, variances, wavenumber spectra, and the data uncertainties.