Monitoring Water Levels and Space Weather Using Global Position Satellite Receivers - Alaska Ocean Observing System
Original (non-English) name
Acronym
Monitoring Water Levels and Space Weather Using GPS Receivers - AOOS
Citation
Abstract
Larson et al. [2012; 2013;2017] demonstrated that reflected GPS signals can be utilized to monitor changes in the height of the reflecting surface, thereby allowing GPS receivers located near the shoreline to be used as ‘tidal gauges.’ ASTRA, LLC has developed and commercialized dual-frequency GPS receivers that are designed for space weather monitoring activities, but also provide other observations, including soil moisture, snow depth measurement, and ocean water level. In April 2017, AOOS contracted with ASTRA to install two discrete dual-frequency GPS receivers in Seward, Alaska to test this technology near an existing NWLON station 9455090 for comparison. These installations were deployed for one year, then one was relocated to Homer, AK to test the method on a beach with a long tidal excursion, to mimic similar topography in western Alaska. These trial deployments informed on installation requirements and limitations, endurance, and data processing methods and requirements to maximize data quality. ASTRA continues to work on automating and operationalizing both the data processing and data telemetry components of their system to provide the capability to report converted water level observations directly from the installation site. In 2020-21, AOOS is working to deploy a permanent, real time operational ASTRA GPS installation in Utqiaġvik, Alaska.
The basic approach for using GPS for water level observing uses reflected GPS satellite signals to determine the height of a reflecting surface, such as the ocean, relative to a stable GPS antenna of fixed local height. The total received GPS signal measured by the antenna is the sum of the direct signal and the reflected signal. The interference between these two signals depends on the satellite altitude in the sky and on the receiver height above the ground. Given the satellite altitude is known, the observed interference pattern as the satellite rises/sets is used to extract the receiver height, after which the antenna height is subtracted to determine the true water level.