From the Coastline to the Cosmos
Traditionally, tides were measured using fixed gauges along the coast. These stations provide incredibly valuable and long-term data for specific locations, with some records stretching back over a century. However, they have a major limitation: they only
tell us what's happening at that single point. The vast expanse of the open ocean remained largely unmeasured. Since 1992, satellite technology has filled this gap, offering a global perspective on the rise and fall of the seas, creating a continuous, comprehensive record of sea surface height across the entire planet.
The Science of Seeing the Sea
The primary technology behind satellite tide mapping is radar altimetry. A satellite sends a microwave radar pulse towards the ocean and measures the precise time it takes for the signal to bounce off the surface and return. Knowing the satellite's exact altitude, scientists can calculate the sea surface height with remarkable accuracy. This process is repeated continuously as the satellite orbits Earth, piecing together a dynamic map of the ocean's topography. This isn't just a single snapshot; missions are designed to pass over the same ocean points repeatedly, building a rich history of data over time. For this data to be as accurate as possible, it is constantly cross-referenced with ground-based tide stations to calibrate the measurements.
The Eyes in the Sky
A series of international satellite missions has been dedicated to this task for decades. The legacy began with missions like TOPEX/Poseidon and has been continued by the Jason series of satellites (Jason-1, 2, and 3). These missions are a partnership between agencies like NASA in the U.S. and CNES in France. More recently, the Sentinel-6 Michael Freilich satellite, a joint U.S.-European mission launched in 2020, has taken up the mantle. A second identical satellite, Sentinel-6B, was launched in 2025 to ensure this critical data stream continues into the next decade, aiming to create a nearly 40-year continuous record of sea level observations.
Beyond Predicting High and Low Tide
While predicting tides for shipping and coastal activities is a key benefit, the data from these satellites has far broader applications. It is fundamental to understanding global sea-level rise, one of the most critical indicators of climate change. Scientists use this data to distinguish between the natural cycle of tides and the long-term trend of rising oceans. The information also helps improve the forecasting of ocean currents, hurricane intensity, and climate patterns like El Niño. By providing a clearer picture of ocean dynamics, satellite altimetry strengthens weather models and our ability to predict future conditions.
A New Wave of Innovation
Recent breakthroughs have even found ways to use decades of satellite imagery, not just altimetry data, to map tides with unprecedented local detail. A new method analyzes over 40 years of images from programs like the U.S. Landsat series. By tracking how the boundary between land and water shifts in thousands of images and combining that with the beach's slope, researchers can calculate tidal variations at a very local scale. This technique turns what was once considered 'noise' in satellite photos into a valuable signal, allowing for detailed tidal maps even in remote areas with no physical gauges.
Challenges and the Coastal Zone
Despite its power, satellite altimetry does face challenges. Getting accurate readings very close to the coast can be difficult, as the radar signal can be contaminated by interference from land. This coastal zone, where most human activity occurs, is precisely where the most detailed information is often needed. Furthermore, a number of complex corrections must be applied to the raw data to account for factors like atmospheric water vapour and the shape of the ocean floor, which can all affect the signal. To overcome this, scientists are constantly refining their models and combining data from multiple satellite missions to improve resolution and accuracy.
