Two European Space Agency (ESA) satellites are flying in formation to study Earth and its environment, ESA announced.

ERS-2 and Envisat are flying in formation for the second time.

The constellation includes ERS-2, ESA’s veteran spacecraft, and Envisat, the largest environmental satellite ever built, ESA announced.

Both carry Synthetic Aperture Radar (SAR) instruments that provide high resolution images of the Earth’s surface.

By combining two or more SAR images of the same site, slight alterations that may have occurred between acquisitions can be detected. This technique, known as SAR interferometry, or InSAR, aids applications such as glacier monitoring, surface deformation detection and terrain mapping.