Collaborative Research: LIDAR Studies of Lateral Dispersion in the Seasonal Pycnocline

知识价值。在30米至3公里的尺度上，层状海洋中的横向搅拌和混合知之甚少。然而，在这些尺度上的混合是海洋生态学的一个重要方面。此外，在海洋环流和海洋生物地球化学的数值模式中，通常必须将这些尺度上的混合参数化，因为在大多数模式中没有明确地解决这种小尺度。提出的工作的目的是可视化和理解在这些小尺度上控制横向搅拌和混合的过程。需要验证的一个假设是，横向搅拌是由垂直混合事件产生的弱分层水的松弛所驱动的。另一种说法是由于水平速度中垂直混合和垂直剪切的共同作用。也可能有独立于垂直混合的搅拌过程。Drs。Ledwell和Sundermeyer将测试这些假设和想法，并准备在他们的实验基础上制定其他假设和想法。该方法是在百慕大附近的分层上层海洋中释放荧光染料，那里的水非常清澈。将使用一架低空飞行的飞机携带的扫描激光雷达（光探测和测距）系统对不断变化的染料斑块进行快速调查。一艘小船在小块区域内绘制的剖面图将为空中测量提供校准数据，并将对小块区域内感兴趣的水文结构进行采样。这艘小船将由一艘科考船看管，科考船将测量水的固有光学特性、水流速度剖面、环境辐射和斑块附近的气象条件。机载激光雷达系统将是由NAVAIR飞行设施操作的地形测绘系统的改进版。它的深度分辨率为1米，横向分辨率为2到3米，可以探测到30米深处的染料。染料斑块的导航和测绘将与一组漂流浮标相关，浮标在释放物的深处设置了液力计，并配有GPS接收器和无线电发射器，用于与船只、小船和飞机通信。实验将在七月进行，那时通常是水最清澈的时候，也是风混合层最薄的时候。释放将在地表以下10到20米之间，每次实验将持续大约24小时。染料分布将从发射和荧光频段返回信号的复杂反转中推断出来。更广泛的影响。了解在海洋中小规模横向混合中起作用的物理过程，对那些试图研究海洋生态系统的人，从而对那些致力于保护海洋健康的人，以及那些试图为此和其他各种实际目的开发海洋数值模型的人，将有直接的好处。我们将通过ARMADA项目培训本科生和/或研究生以及一名学校教师，让他们在暑假期间进行实地工作。将培养一名博士后进行实地考察和分析。Wallops飞行设施的NASA激光雷达系统的发展，无论是否使用染料，都可以有效地看到海洋上层，这将是海洋学家可用的研究工具的重要补充。

Intellectual Merit. Lateral stirring and mixing in the stratified ocean at scales of 30 m to 3 km are poorly understood. Yet mixing at these scales is an important aspect of marine ecology. Also, mixing at these scales must usually be parameterized in numerical models of ocean circulation and ocean biogeochemistry, since such small scales are not explicitly resolved in most models. The aim of the proposed work is to visualize and to understand the processes governing lateral stirring and mixing at these small scales. One hypothesis to test is that lateral stirring is driven by the relaxation of patches of weakly stratified water created by vertical mixing events. Another is that it is due to the combined action of vertical mixing and vertical shear in the horizontal velocities. There may also be stirring processes independent of vertical mixing. Drs. Ledwell and Sundermeyer will test these hypotheses and ideas and be prepared to formulate others on the basis of their experiments. The approach is to release patches of fluorescent dye in the stratified upper ocean off Bermuda, where the water is very clear. Rapid surveys of the evolving dye patches will be made with a scanning LIDAR (LIght Detecting and Ranging) system carried by a low-flying aircraft. Profiles made by a small boat in the patches will provide calibration data for the airborne measurements and would sample hydrographic structures of interests within the patches. The small boat will be tended by a research vessel, from which measurements will be made of inherent optical properties of the water, water velocity profiles, ambient radiation and meteorological conditions near the patches. The airborne LIDAR system will be a modification of a topographic mapping system operated by the NAVAIR Flight Facility. It will have a depth resolution of 1 m and a lateral resolution of 2 to 3 meters, and will sense dye to depths of 30 meters. Navigation and mapping of the dye patches will be relative to a set of drifting buoys with drogues set at the depth of the releases, and with GPS receivers and radio transmitters for communication with the ship, the small boat, and the aircraft. The experiments will be conducted during the month of July when the water is usually the clearest and when the wind-mixed layer is the thinnest. The releases will be between 10 and 20 meters below the surface, and each experiment will last on the order of 24 hours. The dye distribution will be inferred from sophisticated inversions of the returned signal in both the transmitted and fluoresced frequency bands. Broader Impacts. Understanding of the physical processes at work in small scale lateral mixing in the ocean will be of direct benefit to those trying to study ocean ecosystems and hence to those working to protect the health of the ocean, as well as those trying to develop numerical models of the ocean for this and a great variety of other practical purposes. We will entrain undergraduate and/or graduate students and a school teacher, through the ARMADA program, into the field work, which will be conducted during the summer break. A post doctoral fellow will be entrained for the field work and analysis. Development of the NASA LIDAR system at Wallops Flight Facility into one that can effectively see into the upper ocean, whether dye is used or not, will be a substantial addition to the research tools available to oceanographers.