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

点击翻译按钮获取中文摘要

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.