A New Eye in the Sky
The latest breakthrough in understanding our oceans comes from the SWOT (Surface Water and Ocean Topography) satellite mission, a joint effort by NASA and the French space agency CNES. Launched in late 2022, SWOT is now delivering some of the most detailed,
comprehensive views of Earth's water ever seen. While previous satellites could measure sea level, SWOT’s advanced radar interferometry technology allows it to see the ocean's surface in high-resolution, detecting variations in height with centimetre-level accuracy. This is a dramatic leap forward, enabling scientists to map not just large ocean currents but also smaller, more complex features like eddies and, crucially, the intricate patterns of coastal tides.
How Satellites Actually See Tides
It might seem impossible for a satellite orbiting hundreds of kilometres above Earth to measure a small rise or fall in sea level. The technology, known as altimetry, works by sending a radar pulse to the ocean surface and measuring the precise time it takes to bounce back. SWOT takes this a step further with its Ka-band Radar Interferometer (KaRIn), which uses two antennas spread 10 metres apart to survey a wide 120-kilometre swath of the ocean. This creates a 3D picture of the water's surface, revealing subtle bumps and dips. These variations in height are caused by many factors, including currents, temperature, and the gravitational pull of undersea mountains, but they also capture the unmistakable signature of the tides. A separate new technique even uses historical satellite images to track how the waterline moves up and down a beach, effectively turning the shore itself into a giant tide gauge.
Beyond Traditional Tide Gauges
For over a century, our understanding of tides has relied on coastal tide gauges—fixed instruments in ports and harbours that measure water level at a single point. While reliable, this network has huge gaps, leaving vast stretches of the world's coastlines, including in developing regions, unmonitored. Previous satellites improved on this by providing global coverage but had a coarse resolution, blurring details over tens of kilometres. This meant that the highly localised and often dramatic variations in tides near the coast remained largely invisible. The new high-resolution data from missions like SWOT fills this critical gap, revealing that tides can vary by as much as a metre over just a few kilometres within the same bay—a detail that older systems would completely miss.
What This Means for India's Coastline
For a country with a 7,500-kilometre coastline and around 170 million people living in coastal regions, this technology is more than an academic exercise. India is highly vulnerable to sea-level rise, coastal erosion, and extreme weather events like cyclones. Cities like Mumbai and Kolkata are at significant risk of increased flooding. Accurate, high-resolution tide data is essential for protecting these communities. It allows for vastly improved flood models, helping to forecast storm surges with greater precision. It aids in safer navigation for shipping in and out of busy ports, and provides crucial information for managing coastal erosion, which already affects over a third of India's shoreline. This data can also help protect fragile ecosystems like the Sundarbans, which are threatened by rising seas and saltwater intrusion.
The Future of Coastal Safety
The data flowing from SWOT and other advanced satellite systems represents a new frontier in climate resilience. As sea levels continue to rise, understanding how tidal patterns themselves are changing will be critical. This information will allow governments and planners to make smarter decisions about where and how to build coastal defences, manage freshwater resources threatened by saltwater intrusion, and improve early warning systems for natural disasters. India is already expanding its own ocean observation network with more buoys and gauges. Integrating this on-the-ground data with the comprehensive view from space will create a powerful, multi-layered system for safeguarding lives and livelihoods against the challenges of a changing climate.
