 The Atmospheric Correction Intercomparison Exercise, ACX, is an international initiative designed to compare the performance of different atmospheric correction algorithms. 12 participants were invited to apply their algorithms to Landsat 8 and Sentinel, two images from various locations around the world. The results showed that each approach has its own strengths and weaknesses, and further improvements can be made by optimizing the algorithms used. This article was authored by Georgia Doxonee, Eric Vremont, John Claude Roger, and others.