Researcher Shane Elipot, from the Rosenstiel School of Marine and Atmospheric Science at the University of Miami, has proposed a new technique in monitoring the global rise of sea levels.
Elipot recommends the use of already-available 1,200 buoys from the Global Drifter Program by the National Oceanic and Atmospheric Administration (NOAA). The deployed buoys, drifting with the ocean currents, will require additional instruments to record their height, which corresponds to the sea level of the waters these buoys are currently riding on. These updated buoys will provide long-term data on the sea levels around the world.
The study that prompted Elipot's recommendation is published in the journal Geophysical Research Letters.
A Model for Measuring the Global Mean Sea Level
In his report, Elipot explains the current global mean sea level (GMSL) rise as an intrinsic measure of man-made climate change. Increasing sea levels in the past decades have been attributed to a variety of factors, with most common assumptions pointing toward the thermal expansion of the ocean's increasing temperature and the increasing mass due to melting icebergs and ice shelves.
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There are two observational systems in place, aimed at monitoring sea level changes. The first one uses an array of coastal and island tidal gauges. While these gauges pick up precise readings with its high temporal resolution, its representation of the GMSL is biased toward the coasts and the Northern Hemisphere, where these systems are mostly installed. The other system uses satellite radar altimeters, which has a global coverage but is limited to providing its view once in every ten days.
With the Global Drifter Program, Elipot illustrates its potential for recording a variety of significant data: its geographical coordinates via GPS, its altitude with respect to the mean sea surface. The drifters' size and distribution offers an independent and resilient system for monitoring GMSL over extended periods of time.
Through the NOAA Global Drifter Program
To demonstrate his proposal, Elipot used the NOAA global drifter program as an example. The drifter array originally relied on the Argos system, which was a global monitoring system focused on environmental applications such as meteorological and wildlife applications. It later transitioned to using Global Positioning System (GPS) in localizing its data monitoring and also to the Iridium satellite system for data transmission. However, despite the GPS system's capability for altitude data transmission, only the latitude and longitude data remains in the NOAA data stream.
In implementing a measure of global sea levels through the drifting buoys, an important parameter is the height of the sea surface relative to a defined reference mean sea surface (MSS). This is taken from the sum of the geoid - an equigeopotential surface that the ocean would take based on gravity and Earth's rotation alone, without winds and tides factoring in - and a mean dynamic topography.
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A technical limitation in the proposal, however, is the assumption that altitude measurements of an acceptable accuracy, gathered at regular intervals. To ensure this constraint, considerable computing power must be installed on each drifter to allow regular computation and transmission of its 3D position.
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