Sristi Raj Rai, Amity University Kolkata
We still need to monitor our Earth for minute changes that occur, while we are wondering what NASA’s Perseverance rover is doing on Mars. A job of monitoring and reporting the data is essential for any study, whether done manually or by automated machines. When it comes to monitoring our planet which cannot be done manually, we need man-made satellites to do the job. The European Space Agency (ESA) planned for a new set of missions – Sentinel, each with twin satellite launches. The goal of this next-generation observational series was to update the previous records about Earth which might have become outdated. Each Sentinel’s mission has a different set of targets to achieve covering the atmosphere, oceans, and lands.
The Sentinel-1 (A launched on 3rd April 2014 followed by B on 25th April 2016) program produces images every 6 days. This polar-orbiting satellite works day-and-night in all weather conditions to collect data from oceans and ground. So, are these images the same as the ones taken from our camera? No, the technology used by the satellite for imaging is different and is called synthetic aperture radar (SAR). Synthetic Aperture Radar is getting a lot of attention all around the world in various fields. The technology which was initially developed for military surveillance is now being used by glaciologists, geophysicists, and many more.
Unlike, optical imagery satellites (like the U.S. Geological Survey’s Landsat) that use reflected light to take photos passively and cannot penetrate the clouds, Synthetic Aperture Radar penetrates the clouds and uses radars to actively take photos of the Earth. SAR’s antennas emit microwaves which on hitting the ground bounce back to produce colorful images. The resolution is directly dependent on the number of signals. Moreover, for a given place the instrument captures two images at two different times that can be compared to produce a better result. This technique is known as interferometric SAR (InSAR). Changes in the landscape over time (like swelling/sinking of land), even a few millimeters, and surface movements can easily be detected. Thus, topographical changes due to a natural disaster (volcanic eruptions, ground shifts due to earthquake, flood) and human activities can be closely monitored. Their future goal is to produce snapshots with greater ≥50 cm resolution that to several times a day. The team also looks forward to coming up with real-time information which will even help to prepare in case of natural disasters.
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SOURCE – A technique to track Earth’s subtle movements with orbiting radars is heating up. (2021). Retrieved 7 March 2021, from https://www.sciencemag.org/news/2021/03/technique-track-earth-s-subtle-movements-orbiting-radars-heating
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