From Seashore to Space
Traditionally, our knowledge of tides came from tide gauges—devices installed along coastlines to measure the local rise and fall of sea level. While essential, these gauges provide a limited, point-based view of a global phenomenon. They can't tell us
what's happening in the vast open ocean or along remote, unmonitored coastlines. This left significant gaps in our understanding. Since the 1990s, and especially with recent advancements, satellite technology has completely transformed the field. Missions like TOPEX/Poseidon and the Jason series began using radar altimetry to measure sea surface height from orbit, offering the first truly global perspective on tides.
How Satellites 'See' the Tides
A satellite altimeter works by sending a radar pulse down to the ocean and measuring the precise time it takes to bounce back. Knowing the satellite's exact altitude allows scientists to calculate the sea surface height with astonishing accuracy, often to within a few centimetres. By repeatedly passing over the same locations, these satellites build a detailed map of the ocean's surface, capturing the rhythmic bulging and dipping caused by the gravitational pull of the moon and sun. A newer technique even analyzes decades of satellite images from programs like Landsat, tracking the shifting line between water and land to map tides at a highly local scale. This method cleverly turns what was once seen as 'noise' in coastal imagery into a valuable signal for tidal patterns.
Why Global Tide Maps Matter
This new vantage point from space is about much more than just creating better tide calendars. For a country like India with a 7,500-kilometre coastline, accurate tidal knowledge is critical for several reasons. It is vital for safe navigation in busy shipping lanes and ports. Furthermore, it drastically improves models that predict storm surges and coastal flooding, which is essential for protecting vulnerable communities. Better tide models also help scientists separate long-term sea-level rise from daily fluctuations, providing a clearer picture of climate change's impact. The data also supports industries like fishing and the planning of offshore renewable energy projects.
Uncovering the Ocean's Hidden Rhythms
Perhaps the most exciting discoveries have been about phenomena that were previously difficult or impossible to observe. Satellites have unveiled the world of 'internal tides.' These are massive waves that move below the ocean surface, not on it. They are generated when surface tides push water over underwater topography like ridges and seamounts, creating waves that can be hundreds of feet high underwater. These internal tides play a crucial role in mixing ocean water, which affects ocean temperature, nutrient distribution, and climate. Missions like SWOT (Surface Water and Ocean Topography), launched in 2022, are designed with unprecedented resolution to map these complex features, which are vital for understanding ocean energy and circulation.
The Future: Higher Resolution, Better Forecasts
The science of satellite tide mapping is continuously evolving. The SWOT mission, a partnership between NASA and the French space agency CNES, uses a revolutionary wide-swath radar interferometer that can see the ocean in high-definition 2D, a major leap from the single-point measurements of older altimeters. This will provide unparalleled detail on coastal tides and small-scale ocean features. A recent study even showed that by analysing 30 years of altimetry data, scientists can detect how internal tides have strengthened, likely in response to ocean warming. As data from missions like Sentinel and SWOT gets integrated with improved models, our ability to forecast everything from coastal flooding in Bangladesh to the dynamics of glaciers in Greenland will improve dramatically.
