The Mexican capital, Mexico City, is sinking at an alarming rate: a radar satellite has just revealed the exact scale of this phenomenon. Far from being a mere geological curiosity, this city of 20 million inhabitants is subsiding by up to 14 inches (35 cm) per year in some places. Thanks to the NISAR satellite – a collaboration between NASA and ISRO – scientists can now track this movement millimeter by millimeter.
To achieve these precise measurements, the NISAR satellite was launched in July 2025. It is equipped with two synthetic aperture radars, one in L-band and the other in S-band. The L-band radar, developed by NASA, is particularly sensitive to changes in rock and ice – it enabled the mapping of Mexico City's subsidence. The satellite overflies the entire Earth every 12 days, providing a global and regular view of surface deformations.
Since 1925, it has been known that the city is sinking due to the extraction of groundwater from a former dried-up lake. Excessive pumping compresses the sedimentary layers, and the weight of buildings worsens the phenomenon. The damage is visible: cracks in roads, subsidence of the metro.
The radar image of Mexico City resembles a blue and yellow paint stain. Blue areas indicate a subsidence of at least 0.8 inches (2 cm) between October 2025 and January 2026, during the dry season, revealing an annual rate that can reach 14 inches (35 cm) in some places. Yellow and green areas represent residual noise, which will decrease with subsequent satellite passes. These initial data confirm that NISAR is working perfectly.
According to mission scientists, NISAR is the first satellite to combine two radar frequency bands. The L-band (1-2 GHz) penetrates the ground better, while the S-band (2-4 GHz) is more suitable for vegetation. This dual capability will allow monitoring of densely forested coastal regions, where subsidence exacerbates sea level rise.
Visualization of the NISAR satellite above Earth.
Credit: NASA/JPL-Caltech
The images of Mexico City are just the beginning. With its global coverage every 12 days, NISAR promises many discoveries, whether on glacier retreat, tectonic movements, or the spread of wildfires.