According to the United Nations Office for Outer Space Affairs, there are currently 4,857 satellites orbiting the planet. Among them are two Sentinel-2 satellites, part of a space-borne mission provided by the Copernicus European Earth Observation programme. The two satellites visit the same spot on Earth every two to five days, depending on the location.
Their sensors acquire multispectral images with spatial resolution varying between 10, 20, or 60 metres, depending on the spectral band. The data produced by Sentinel satellites is freely available to the public and the volumes of data are staggering. Between Sentinel 1, 2 and 3, over 10 petabyte of new data are made available for download every year. With a single petabyte equalling 500 billion pages of standard typed text, this is Big Data worthy of its name.
Source – Modern Diplomacy - https://moderndiplomacy.eu/2019/02/10/eye-in-the-sky-using-satellites-to-better-manage-natural-resources/