Arctic Dynamic Ocean Topography (DOT) Buoy Data, Beaufort Sea & Laptev Sea (2019-2024)

We have developed for deployment in ice-covered seas Dynamic Ocean Topography (DOT) Buoys which make precise measurements of sea surface height (SSH) and precipitable water vapor (PWV) content. Our motivation is to improve measurements of DOT, the departure of sea surface height from the height of the geoid time-invariant geopotential surface (e.g., the EGM-2008 model). The spatial gradient of DOT is the sea surface tilt that drives surface geostrophic current. Satellite altimeters such as CryoSat-2, ICESat-2, and SWOT measure DOT, but they require ground truth observations for calibration and validation. These are difficult anywhere, but in ice-covered oceans they have been nonexistent. We have developed the DOT buoys to fill this gap. The methodology is in principle very simple, that is to measure the height of a drifting buoy with a precise Global Positioning System (GPS) receiver and the changes in height of the buoy relative to the water surface with a pressure sensor at the bottom of the buoy. The major components of the buoys include the dual channel GPS receiver and the Iridium transmitter receiver, which is used for transmission of the full GPS data including phase of the carrier frequencies. In addition, the buoys have a pressure sensor at the bottom of the buoy hull for determination of the GPS antenna freeboard, tilt and heading sensors, and atmospheric pressure and temperature sensors. To conserve power, we typically sample GPS data at 30-second intervals but on a duty cycle of for example 2 days on and 5-days off. The GPS data have been processed by Bruce Haines at Jet Propulsion Laboratory (JPL) using GYPSY Precise Point Positioning (PPP). The dual frequencies allow determination of the position error due to wet tropospheric delay. PPP uses GPS data from a worldwide array of receivers fixed to bedrock to determine the GPS satellite clock and ephemerae errors that are the other main source of position errors. This results in accuracies of SSH measurement approaching 1-centimeter (cm). The wet tropospheric delay measurement when multiplied by -0.18 is approximately the precipitable water vapor content (PWV) of the atmosphere. All the GPS-derived parameters, the buoy orientation measurements where available, the met measurements, buoy draft pressure, and initial GPSS antenna freeboard, and the constant GPS phase center height above the GPS antenna base are included in the data submission.