Development of Drifting Buoys to Measure Dynamic Ocean Topography and Precipitable Water Vapor

该项目建议建造漂流浮标，精确测量海面高度和可吸入水汽含量。海平面高度是全球海洋观测系统（GOOS）的十大基本海洋变量之一。它是衡量长期海平面上升和较短时间尺度的潮汐和风暴潮的重要指标。海面高度和大地水准面高度之间的差异是动态海洋地形（DOT），它构成了驱动地转表面速度的表面压力梯度，这是全球海洋观测系统的第二个基本海洋变量。DOT观测与密度分布相结合，例如通过海洋学浮标测量（例如，阿尔戈浮标在温和的海洋中漂浮，冰系剖面仪在冰封的海洋中漂浮）来推断速度切变，从而有可能测量绝对水速度与深度的关系，这是全球海洋观测系统的第三个基本海洋变量。在冰覆盖的海洋中，除了在大风期间，海冰漂移（Vice）主要遵循地转表面速度（Vgeo）。Vice和Vgeo之间的差异在稳定北冰洋博福特海环流的隆起方面起着越来越关键的作用。此外，DOT中的跨大陆架梯度驱动二次循环（例如，上升流和下降流）负责陆架盆地交换，这是至关重要的维持北冰洋冷盐跃层。为了了解全球特别是北极地区大气条件的变化，需要观测可吸入水汽（PWV）含量。对流层可降水水汽含量的观测需要了解大气条件的变化，全球水循环，水蒸气作为主要的温室气体。在北冰洋尤其如此，因为在那里基本上不存在通过其他手段进行的此类观测。凝结的水蒸气（在云中）反射入射的太阳辐射，并在地表附近捕获长波辐射，使得水分含量的探测对于了解云在地表热收支，水循环，大气动力学中的作用至关重要，以及它们对海冰，业务天气预报和无线电传播的影响。云中的PWV含量反映了入射的太阳辐射，并将长波辐射捕获在表面附近，使得探测水分含量对于了解云在表面热收支，水循环，大气动力学及其对海冰的影响中的作用至关重要。这些影响在天气和无线电传播的业务预报中至关重要。尽管DOT和PWV含量的重要性，这些变量的完全自主的原位测量还没有。卫星高度计极大地扩大了DOT观测的区域覆盖范围，但现场DOT和PWV含量观测对于为卫星提供地面实况和填补高频时间空白至关重要。应用物理实验室（APL）将建造6个DOT浮标，结合铱数据遥测、动力系统、和冰能力浮标船体的一个证明APL漂流浮标与双-频率GPS接收器，类似于太平洋海洋环境合作伙伴建造的经过验证的系泊内部记录GPS浮标中使用的接收器实验室（PMEL）。PMEL浮标的过去数据将用于设计DOT浮标的最佳采样策略。喷气推进实验室（JPL）的合作伙伴将执行精确单点定位（PPP）处理。APL和JPL将评估DOT浮标的性能，并促进浮标在2019-2021年计划的ONR（SODA，SIZRS），NASA（ICESat-2，SWOT）和NOAA（IABP）计划中的应用。DOT浮标将使用精密双频全球定位系统和对全球定位系统数据进行PPP处理，以确定精度为1厘米的DOT和1毫米的PWV。PPP和接收机的双频能力解决了GPS误差的主要来源。PPP处理依赖于全球范围内的固定GPS接收器阵列来确定GPS卫星轨道和时钟的误差。对这些误差的校正将应用于DOT浮标GPS接收的原始码和相位信息，以得出精度为1厘米的位置。然而，这要求必须从漂移浮标遥测完整的代码和相位信息，以进行具有1周延迟的后处理。基本硬件和PPP方案得到了很好的验证。面临的挑战是设计一个铱遥测系统和采样策略，以适当的空间和时间尺度测量DOT和可蒸发水汽含量，并缓冲数据，通过铱数据链传输。拟议的浮标将适合在海冰或开放水域的水面或空中部署。这些浮标将立即加强一些联邦机构（ONR、NASA、NOAA、NSF）在北冰洋的研究。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project proposes to build drifting buoys making precise measurements of sea surface height (SSH) and Precipitable Water Vapor (PWV) content. Sea surface height is one of the ten Global Ocean Observing Systems (GOOS) Essential Ocean Variables. It is important as the measure of long-term sea level rise and on shorter time scales, tides and storm surges. The difference between sea surface height and the height of the geoid is dynamic ocean topography (DOT), which constitutes the surface pressure gradient that drives geostrophic surface velocity, a second GOOS Essential Ocean Variable. DOT observations are combined with density profiles, such as measured by oceanographic buoys (e.g., Argo floats in temperate oceans and Ice Tethered Profilers in ice-covered seas) to infer velocity shear, which makes it possible to measure absolute water velocity versus depth, a third GOOS Essential Ocean Variable. In ice-covered seas, except during high winds, the sea ice drift (Vice) largely follows the geostrophic surface velocity (Vgeo). The difference between Vice and Vgeo plays an increasingly critical role in stabilizing the doming of the Beaufort Sea Gyre in the Arctic Ocean. Furthermore, cross-shelf gradients in DOT drive secondary circulations (e.g., upwelling and downwelling) responsible for shelf-basin exchanges, which are critical to maintaining the Arctic Ocean cold halocline. Observations of Precipitable Water Vapor (PWV) content are needed to understand changes in atmospheric conditions globally and in the Arctic in particular. Observations of tropospheric precipitable water vapor content are needed to understand changes in atmospheric conditions, the global water cycle, and water vapor as the dominant greenhouse gas. This is particularly true over the Arctic Ocean where such observations by other means are largely non-existent. Condensed water vapor (in clouds) reflects incoming solar radiation and traps long-wave radiation near the surface, making soundings of moisture content critical to understanding the role of clouds in the surface heat budget, the water cycle, atmospheric dynamics, and their effect on sea ice, operational weather forecasts, and radio propagation. PWV content in clouds reflects incoming solar radiation and traps long-wave radiation near the surface, making soundings of moisture content critical to understanding the role of clouds in the surface heat budget, the water cycle, atmospheric dynamics, and their effect on sea ice. These effects are critical in operational forecasts of weather and radio propagation. In spite of the importance of DOT and PWV content, wholly autonomous in situ measurements of these variables have not been made. Satellite altimeters greatly expand the areal coverage of DOT observations, but in situ DOT and PWV content observations are critical to provide ground truth for the satellites and fill high-frequency temporal gaps.The Applied Physics Lab (APL) will build six DOT Buoys combining the Iridium data telemetry, power systems, and ice-capable buoy hull of a proven APL drifting buoy with a dual-frequency GPS receiver similar to what is used in a proven moored internally recording GPS buoy built by partners at the Pacific Marine Environmental Laboratory (PMEL). Past data from the PMEL buoy will be used to design the optimum sampling strategy for the DOT Buoy. Partners at the Jet Propulsion Laboratory (JPL) will perform the Precise Point Positioning (PPP) processing. APL and JPL will evaluate the DOT Buoy performance and facilitate application of the buoys to planned ONR (SODA, SIZRS), NASA (ICESat-2, SWOT), and NOAA (IABP) programs in 2019-2021. The DOT Buoys will use precision dual-frequency GPS and PPP processing of GPS data to determine DOT to 1-cm accuracy and PWV to 1-mm accuracy. PPP and the dual frequency capability of the receiver address the key sources of GPS errors. PPP processing relies on a worldwide array of stationary GPS receivers to determine the errors in GPS satellite orbits and clocks. Corrections for these errors will be applied to raw code and phase information from the DOT Buoy GPS receptions to derive positions good to 1-cm accuracy. However, this requires that full code and phase information must be telemetered from the drifting buoy for post processing with 1-week latency. The basic hardware and PPP scheme are well proven. The challenge is to design an Iridium telemetry system and sampling strategy that measure DOT and Precipitable Water Vapor content at appropriate spatial and temporal scales and buffers the data for transmission through an Iridium data link. The proposed buoys will be suitable for surface or air deployment in sea ice or open water. The buoys will immediately enhance research in the Arctic Ocean by a number of federal agencies (ONR, NASA, NOAA, NSF).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.