False Color: Red = Band 3, Green = Band 6, Blue = Band 7
This combination is used to map snow and ice. Snow and ice are very reflective in the visible part of the spectrum (Band 3), and very absorbent in Bands 6 and 7 (short-wave infrared, or SWIR). This band combination is good for distinguishing liquid water from frozen water, for example, clouds over snow, ice cloud versus water cloud; or floods from dense vegetation. This band combination is only available for MODIS (Terra) because 70% of the band 6 sensors on the MODIS instrument on the Aqua satellite failed shortly after launch.
The MODIS Corrected Reflectance imagery is available only as near real-time imagery. The imagery can be visualized in Worldview and the Global Imagery Browse Services (GIBS. The sensor resolution is 500 m and 250 m (Bands 1 and 2 have a sensor resolution of 250 m, Bands 3 – 7 have a sensor resolution of 500 m, and Bands 8 - 36 are 1 km. Band 1 is used to sharpen Band 3, 4, 6, and 7), imagery resolution is 250 m, and the temporal resolution is daily.
Since the only visible light used in these images (Band 3) is assigned to red, snow and ice appear bright red. The more ice, the stronger the absorption in the SWIR bands, and the more red the color. Thick ice and snow appear vivid red (or red-orange), while small ice crystals in high-level clouds will appear reddish-orange or peach.
Vegetation will appear green in this band combination, as vegetation is absorbent in Bands 3 and 7, but reflective in Band 6. Bare soil and deserts will appear bright cyan in the image since it much more reflective in Band 6 and 7 than Band 3.
Liquid water on the ground will appear very dark since it absorbs in the red and the SWIR, but small liquid water drops in clouds scatter light equally in both the visible and the SWIR, and will therefore appear white. Sediments in water appear dark red.
The MODIS Corrected Reflectance algorithm utilizes MODIS Level 1B data (the calibrated, geolocated radiances). It is not a standard, science quality product. The purpose of this algorithm is to provide natural-looking images by removing gross atmospheric effects, such as Rayleigh scattering, from MODIS visible bands 1-7. The algorithm was developed by the original MODIS Rapid Response team to address the needs of the fire monitoring community who want to see smoke. Corrected Reflectance shows smoke more clearly than the standard Surface Reflectance product. In contrast, the MODIS Land Surface Reflectance product (MOD09) is a more complete atmospheric correction algorithm that includes aerosol correction, and is designed to derive land surface properties. In clear atmospheric conditions the Corrected Reflectance product is very similar to the MOD09 product, but they depart from each other in presence of aerosols. If you wish to perform a complete atmospheric correction, please do not use the Corrected Reflectance algorithm. An additional difference is that the Land Surface Reflectance product is only tuned for calculating the reflectance over land surfaces.
References: NASA Earthdata - FAQ; AMNH - Biodiversity Informatics, Band Combination; NASA Earthdata - Creating Reprojected True Color MODIS Images: A Tutorial