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

该项目建议建造漂流浮标，以精确测量海面高度（SSH）和可降水量（PWV）含量。海面高度是全球海洋观测系统（GOOS）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。海面高度与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GOOS的第二个基本海洋变量。DOT观测与密度剖面相结合，例如由海洋学浮标测量的密度剖面（例如，Argo浮标在温带海洋中，冰系剖面仪在冰雪覆盖的海洋中）来推断速度切变，这使得测量绝对水速与深度的关系成为可能，这是GOOS的第三个基本海洋变量。在冰雪覆盖的海域，除大风期间外，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波弗特海环流的圆顶方面发挥着越来越重要的作用。此外，DOT中的跨陆架梯度驱动次级环流（如上升流和下升流），负责陆架-盆地交换，这对维持北冰洋冷盐斜至关重要。要了解全球特别是北极地区大气条件的变化，需要对可降水量（PWV）含量进行观测。为了了解大气条件的变化、全球水循环以及作为主要温室气体的水蒸气，需要对对流层可降水量进行观测。这一点在北冰洋上空尤其如此，在那里，通过其他方式进行的观测基本上是不存在的。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理解云在地表热收支、水循环、大气动力学及其对海冰、业务天气预报和无线电传播的影响中的作用至关重要。云中的PWV含量反射入射的太阳辐射，并捕获地表附近的长波辐射，因此探测水分含量对于理解云在地表热收支、水循环、大气动力学及其对海冰的影响中的作用至关重要。这些影响对天气预报和无线电传播的业务至关重要。尽管DOT和PWV含量很重要，但还没有对这些变量进行完全自主的原位测量。卫星高度计极大地扩大了DOT观测的面积覆盖范围，但原位DOT和PWV含量观测对于为卫星提供地面真实值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、电力系统和经过验证的APL漂流浮标的冰能力浮标外壳，并使用双频GPS接收器，类似于由太平洋海洋环境实验室（PMEL）的合作伙伴建造的经过验证的系泊内部记录GPS浮标。PMEL浮标过去的数据将用于设计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年计划中的ONR (SODA， SIZRS), NASA （ICESat-2， SWOT）和NOAA （IABP）计划中的应用。DOT浮标将使用精确的双频GPS和PPP处理GPS数据，以确定DOT精度为1厘米，PWV精度为1毫米。PPP和接收机的双频能力解决了GPS误差的主要来源。PPP处理依赖于世界范围内的固定GPS接收器阵列来确定GPS卫星轨道和时钟的误差。对这些错误的修正将应用于来自DOT浮标GPS接收的原始代码和相位信息，以获得精度达到1厘米的位置。然而，这需要从漂流浮标遥测完整的代码和相位信息，以便在1周的延迟时间内进行后处理。基本硬件和PPP方案都得到了很好的验证。挑战在于设计一个铱遥测系统和采样策略，在适当的空间和时间尺度上测量DOT和可降水量，并缓冲通过铱数据链传输的数据。建议的浮标将适用于海面或空中部署在海冰或开阔水域。这些浮标将立即加强许多联邦机构（ONR， NASA， NOAA， NSF）对北冰洋的研究。该奖项反映了美国国家科学基金会的法定使命，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.