The Challenge of Watching Storms
Since the 1960s, satellites have been our eyes in the sky for tracking powerful cyclones. Instruments that capture images in visible and infrared light have been essential, showing us the vast, swirling cloud tops of a developing storm. However, this
method has a fundamental weakness: these sensors can't see what’s happening underneath the dense cloud cover. For forecasters trying to determine a cyclone's true strength and predict its next move, only seeing the top of the storm is like trying to understand an engine by only looking at the car's roof. ISRO's current operational satellites, like the INSAT series and Oceansat series, use a variety of sensors, including scatterometers, which are a type of radar that measures wind speed and direction over the ocean. While incredibly useful, they provide a lower-resolution view and can be hampered by the very weather they are trying to observe. To truly understand a cyclone's intensity, you need to see the ocean surface itself, right at the base of the storm.
Enter Synthetic Aperture Radar (SAR)
The game-changing upgrade is a technology called Synthetic Aperture Radar, or SAR. Unlike passive cameras that rely on sunlight or heat, SAR is an active system. It works by sending its own microwave energy pulses down to the Earth's surface and capturing the signals that bounce back. Because it provides its own illumination, SAR can see perfectly day or night. More importantly, its microwave signals can penetrate clouds, smoke, and haze, providing a clear view of the ground and sea surface regardless of the weather. The "synthetic aperture" part is a clever processing technique where the satellite's own movement is used to simulate a much larger antenna than it could physically carry. This allows it to create incredibly detailed, high-resolution images from hundreds of kilometres in space. For storm monitoring, this means we can finally get a clear picture of the ocean surface right inside the cyclone's most violent regions.
A Clearer Picture of Danger
By piercing the cloud wall, high-resolution SAR provides two critical pieces of information. First, it reveals the texture of the ocean surface. Rough, choppy water, whipped up by extreme winds, reflects the radar signal differently than calmer water. This allows scientists to create highly detailed maps of surface wind speeds, helping them locate the storm's eye with greater precision and estimate its maximum wind intensity. This is a huge leap forward for predicting how dangerous a cyclone will be when it makes landfall. Second, SAR can identify the storm's core structure, including the eyewall, rainbands, and even smaller vortices within the storm that are completely hidden from other sensors. Having this detailed structural information helps forecasters understand if a storm is intensifying or weakening, leading to more accurate and timely warnings for coastal communities.
ISRO's New Radar Powerhouse: NISAR
ISRO is embracing this technology through a landmark collaboration with NASA called the NISAR (NASA-ISRO Synthetic Aperture Radar) mission. This powerful satellite, which is now in its science operations phase as of July 2026, is the world's first to use dual-frequency L-band and S-band radars. ISRO provided the S-band radar component, while NASA supplied the L-band. This dual-frequency capability allows it to observe a wide range of changes on Earth's surface, from tiny shifts in the ground that might precede an earthquake to the structure of forests. For storm monitoring, NISAR provides all-weather, day-and-night imaging with a rapid 12-day repeat cycle over the entire globe, offering an unprecedented ability to monitor the ocean surface. Data from NISAR's S-band radar is already being released by ISRO, providing crucial insights for disaster management and environmental monitoring. While Oceansat series satellites like Oceansat-3 (also called EOS-06) continue to provide vital data on ocean colour, temperature, and wind vectors using scatterometers, the addition of high-resolution SAR from missions like NISAR represents a quantum leap in capability.
