The Moderate-resolution Imaging Spectroradiometer's (MODIS') cloud detection capability is so sensitive that it can detect clouds that would be indistinguishable to the human eye. This pair of images highlights MODIS' ability to detect what scientists call ''sub-visible cirrus.'' The image on top shows the scene using data collected in the visible part of the electromagnetic spectrum--the part our eyes can see. Clouds are apparent in the center and lower right of the image, while the rest of the image appears to be relatively clear. However, data collected at 1.38microns (lower image) show that a thick layer of previously undetected cirrus clouds obscures the entire scene. These kinds of cirrus are called ''sub-visible'' because they can't be detected using only visible light. MODIS' 1.38microns channel detects electromagnetic radiation in the infrared region of the spectrum. These images were made from data collected on April 4, 2000.