Today's sensors can capture details as small as one-half mile across, and technological advances have increased the number of ways of probing the lower atmosphere. Satellite sensors detect and record the radiation reflected and radiated by clouds and water vapor in the troposphere. Infrared radiation emitted by clouds reveals their temperatures, which can then be used to calculate cloud heights. Cruising at altitudes of 300 to 500 miles, POES can reveal details about cloud cover and water vapor in higher latitudes, where GOES images are usually distorted because of Earth's curvature. As the table below shows, thick clouds and fresh snow reflect more light than thin clouds, so they appear brighter in the images.
Thin clouds appear gray, and areas with no shading are generally clear.
The U.S. operates two geostationary satellites, GOES 8 covers the eastern U.S. and Atlantic, GOES 9 the West and part of the Pacific. The Europeans and Japanese operate similar satellites that cover most of the rest of the world. The close imaging from POES and the lack of easily accessible images mean they are not very useful to pilots. We'll focus on GOES imagery because it's easier to understand and is much easier to find. The image in Figure 1 is a visible GOES image.