NOAA CoastWatch produces near real-time true color satellite images
for U.S. coastal regions
from the Visible Infrared Imaging Radiometer Suite (VIIRS)
on-board the polar-orbiting Suomi-NPP satellite.
True color satellite images are like a camera photo.
The instrument's visible measurements at the red, green, and blue
wavelengths are combined to create a color-realistic image, just
like a digital photograph.
Land and water features can be seen in these images. Because cloud
coverage is very obvious, these images can be used to quickly determine
if a particular day's image is useful for observing a land or water feature.
CoastWatch generates data files of both top-of-atmosphere radiance
and surface reflectance of the VIIRS red, green and blue bands.
The surface reflectance is corrected for atmospheric effects, such
as a Rayleigh correction, whereas the top-of-atmosphere radiance is
uncorrected for atmospheric effects. True color
made from surface reflectance offers clearer, brighter images.
Below is a comparison of the two approaches.
NOAA CoastWatch East Coast Node began featuring true color images made
with surface reflectance on November 9, 2018, but then reverted to
true color images made with top-of-atmosphere radiance on
April 11, 2019.
The intention is to again offer true color images made
with surface reflectance in the future.
Starting September 14, 2021, an improved image enhancement was implemented to
generate true color images from top-of-atmosphere radiance that accentuates
coastal in-water features similar to true color images from surface
reflectance. However, it is still intended to again offer true color images
made with surface reflectance at some point in the future.