Three types of images are available from weather satellites on a nearly real-time, operational basis. Those sensors on board the satellite that operate within the visible range of the electromagnetic spectrum sense sunlight reflected back to the satellite from the various components of the earth-atmosphere system, including cloud tops and the earth's surface. The processed image from these visible sensors is essentially a black and white photograph of the earth. The brightest and most white elements appearing in these images indicate the most reflective surfaces, where a greater intensity of sunlight is being reflected back into space from clouds or a fresh snow cover. Conversely, the darkest parts of the image indicate the least reflective surfaces, such as nearly black ocean surfaces where much of the sunlight penetrates the surface and is not reflected back.
Land surfaces tend to appear gray.
Visible satellite images obtained from geosynchronous satellites typically have less than a 1 kilometer resolution. That is, a landmark that has a horizontal dimension of 1 kilometer could be detected on a visible satellite image. These images are used by meteorologists to locate and identify cloud masses. From these cloud masses, some information as to the circulation regime can be inferred. Differences in the shading of clouds usually relate to cloud thickness.