Satellite images provide a unique, dramatic perspective of our Earth and its atmosphere. The images used to piece together this view of the United States were generated using data gathered from an advanced sensor that flies aboard the satellites in NASA’s Earth Observing System, Terra and Aqua. Traveling north to south, Terra loops over the equator in the morning. Aqua moves in the opposite direction, passing south to north over the equator in the afternoon. Both satellites carry the Moderate Resolution Imaging Spectroradiometer (MODIS). Together, the Terra MODIS and Aqua MODIS provide a complete view of the Earth every one to two days across a wide spectrum of energy.
During a given day, both Terra and Aqua will make two to four passes each over the continental USA during daylight hours, and another two to four during the night. The MODIS Today United States composite features the latest image available from either Terra or Aqua, allowing users to toggle between satellites. You will occasionally notice distinct boundaries in the composite because the images that comprise the composite originate from different passes. By combining the images acquired from the blue, red and green portions of the energy spectrum, SSEC generates a “true” or “natural” representation of the Earth’s land, ocean, and atmosphere.
In addition to the images available on the website, we also provide a daily link to a KML (Keyhole Markup Language) file which can loaded into the freely available Google Earth application. When the daily KML file for Terra or Aqua is loaded into Google Earth, you can browse the entire continental USA (depending on the satellite pass positions for that particular day) at up to 250-meter resolution. The images for Google Earth are tiled into small subsets so they download quickly to your desktop.
More information on the instrument and data processing
The MODIS instruments are able to capture images at a maximum resolution of 250 meters per pixel at the Earth’s surface. This website features MODIS images at 4000 meter resolution over the entire continental United States as well as 2000-, 1000-, and 250-meter resolution images for eight subset regions. Several processing steps are needed to create the images from the raw data collected by the MODIS instrument. First, the raw digital counts acquired by MODIS are calibrated to physical units known as reflectance. Next, the images are processed to remove some (but not all) of the image features introduced by the atmosphere, such as haze. Then the images are transformed from the projection geometry of the instrument (which includes distortions due to phenomena such as earth curvature) into a standard map projection, known as the equirectangular projection. Finally, the images are enhanced using contrast adjustment and image sharpening techniques. As new images become available from Terra and Aqua throughout the day, they automatically appear on the website. The images are usually available within 60 minutes of the time they are acquired onboard the spacecraft.