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Asymmetries between Wavenumber Spectra of Along- and Across-Track Velocity from Tandem Mission Altimetry

机译：串联任务测高的沿线速度和跨线速度波数谱之间的不对称性

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摘要

Satellite altimetry has proven to be one of the most useful oceanographic datasets, providing a continuous, near-global record of surface geostrophic currents, among other uses. One limitation of observations from a single satellite is the difficulty of estimating the full geostrophic velocity field. The 3-yr Jason-1-Ocean Topography Experiment (TOPEX)/Poseidon tandem mission, with two satellites flying parallel tracks, promised to overcome this limitation. However, the wide track separation severely limits the tandem mission's resolution and reduces the observed velocity variance. In this paper, the effective filter imposed by the track separation is discussed and two important consequences for any application of the tandem mission velocities are explained. First, while across-track velocity is simply low-pass filtered, along-track velocity is attenuated also at wavelengths much longer than the track separation. Second, velocity wavenumber spectral slopes are artificially steepened by a factor of k~(-2) at wavelengths smaller than the track separation. Knowledge of the effective filter has several applications, including reconstruction of the full velocity spectrum from the heavily filtered observations. Here, the hypothesis that the tandem mission flow field is horizontally nondivergent and isotropic is tested. The effective filter is also used to predict the fraction of the eddy kinetic energy (EKE) that is captured for a given track separation. The EKE captured falls off rapidly for track separations greater than about 20 km.
机译：事实证明，卫星测高是最有用的海洋数据集之一，除其他用途外，它还提供了连续的，近乎全球的地面地转流记录。单颗卫星观测的局限性在于难以估计整个地转速度场。为期3年的Jason-1-Ocean地形实验（TOPEX）/ Poseidon串联任务，由两颗人造卫星平行飞行，有望克服这一限制。但是，宽轨道分离严重限制了串联任务的分辨率，并减小了观察到的速度变化。在本文中，讨论了由航迹分离施加的有效滤波器，并解释了串联任务速度在任何应用中的两个重要后果。首先，跨轨速度只是简单地低通滤波，而沿轨速度在比轨距更长的波长处也会衰减。其次，在小于轨道间隔的波长处，人工将速度波数频谱斜率以k〜（-2）的比例人工变陡。关于有效滤波器的知识有多种应用，包括从经过大量滤波的观测值重建全速谱。在此，检验了串联任务流场水平不发散且各向同性的假设。有效滤波器还用于预测在给定的磁道间隔中捕获的涡动能（EKE）的比例。所捕获的EKE会在轨道间距大于20 km时迅速下降。

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  • 来源
    《Journal of Physical Oceanography》 |2014年第4期|1151-1160|共10页
  • 作者

    Cimarron Wortham; Joern Callies; Martin G. Scharffenberg;

  • 作者单位

    Applied Physics Laboratory, University of Washington, Seattle, Washington;

    Massachusetts Institute of Technology/WHOI Joint Program in Oceanography, Cambridge, Massachusetts Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139;

    Institut fuer Meereskunde, Universitaet Hamburg, Hamburg, Germany;

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