These global composite images are created by the University of Wisconsin-Madison (UW) Space Science and Engineering Center (SSEC) Data Center. The images are a collection of approximately 14 satellites—both geostationary (GEO) and low earth-orbiting (LEO)—over the course of 1-hour intervals. Every hour, at 30min past, new imagery is uploaded to SSEC's RealEarth™ map server. Over the course of the hour the most recent satellite imagery is remapped into the composite. At any one point in each image, the source of the measurement may come from any of the satellites in the collection. Infrared imagery are provided at approximately 4 km resolution.
Infrared images measure thermal radiation: cooler areas appear lighter while warmer areas appear darker. Clouds at lower altitudes have warmer temperatures and thus appear relatively darker than clouds higher in the atmosphere. Because this method does not rely on reflected sunlight (as visible imagery does), clouds can be seen in infrared imagery even during the nighttime.
time period: current; updates hourly.