Radar Time Series Measurements Collected at Duck, North Carolina – Beginning of Pier (x = 200 meters)

DEPLOYMENT - An instrument package was developed by the USGS consisting of a commercially available, non-contact oceanographic radar sensor, a data logger, a cellular modem, and an external battery housed inside a water-tight box, with a cellular antenna and solar panel affixed on the outside of the lid. Multiple radar instrument packages were built, with one each being deployed at three locations along the USACE FRF research pier including at the seaward ocean-facing end (x=600m) from August 18, 2022, to present, and at the middle (x=300m) and near the beginning (x=200m) from January 18, 2024, to April 23, 2024. Each box was attached to the FRF pier railing using specially fabricated stainless-steel L-shaped mounting arms that can be installed quickly and do not require drilling into the structure. Each radar was deployed such that the sensor extends over the water surface with no obstructions below (e.g., pier deck, piling, rocks) and with the box secured and as level as possible. The elevation of each sensor was surveyed to a known datum (NAVD88) using differential leveling.

DATA COLLECTION - The non-contact oceanographic radar sensor (Geolux® LX-80-15 10 Hz) directly measured the elevation of the sea surface using a frequency-modulated electromagnetic (radio) wave to detect the distance from the sensor to the water surface and relating that to the surveyed elevation of the radar sensor. The radar sampled continuously at 10 Hz, and a data logger was used to save down-sampled 5 Hz time series data, which was transmitted in near real-time over a cellular network connection.

DATA PROCESSING - The 5 Hz time series data were minimally quality-controlled, with erroneous spikes (when distance = 15 and/or water level = 7999, which are the instrument default values for bad data) replaced with the fill value (not-a-number) and gaps in the water level time series of less than 60 seconds filled with linear interpolation; longer time gaps are due to insufficient power when the solar panel was dirty or sensor maintenance. Then, the data were processed to compute mean water levels and wave conditions and converted into network common data form (netCDF, .nc) files with stglib python libraries (Nowacki and others, 2024), a package of code to process data consistent with procedures of the USGS Coastal/Marine Hazards and Resources Program. More information about stglib can be found here: https://stglib.readthedocs.io/en/latest/. Attributes describing the variables and conforming to CF (Climate and Forecast) Metadata Convention (version 1.8) were added to each file by stglib. Times are in Coordinated Universal Time (UTC) and water levels are in meters, referenced to NAVD88. NetCDF filenames include location (FRFx200 to represent the local FRF cross-shore coordinate of x=200m), deployment date (YYYYMM), an abbreviation of the instrument type ("glx" for Geolux® radar), and a designation for the file type, which is either "cont" for continuous time series data, or "spec" for wave spectra and statistics.