GOES BAND IMAGERY
Of the six instruments on GOES-East satellite for observing the earth and sun, it is the “Advanced Baseline Imager” (ABI) instrument that provides visible and infrared views the earth. The ABI produces images at 16 different wavelengths (called bands and/or channels). Those available via HRIT are marked as such.
The individual channels are as follows:
There are two visible bands, blue and red. These two wavelengths are named relative to their location on the visible portion of the electromagnetic spectrum.
While in their natural state these images would appear in blue and red hues respectfully, colors have been desaturated to appear in grayscale. Since these are “visible” channels the images will appear black at night.
Channel 1: The “Blue” band
One of the two visible channels, this one is located in the blue portion of the visible spectrum. It provides nearly continuous daytime observations of dust, haze, smoke and clouds. It also includes measurements of “aerosol optical depths” will help air quality monitoring and tracking. Measurements in the blue band may provide estimates of visibility as well.
Channel 2: The “Red” band (Available via HRIT)
The second of the two visible channels, this one is located near the red portion of the visible spectrum. While it looks similar to channel 1, when you think “visible imagery” this is the band to choose. It is used for daytime snow and ice cover, detection of severe weather, low-level cloud-drift winds, smoke, volcanic ash, hurricane analysis, and winter storm analysis.
This band is also the highest resolution band coming from GOES-16. Directly beneath the satellite (70°W, 0°N) the resolution is 1,600 feet (0.5 km). There is no “green” channel. That is important as all three colors, red, green and blue, are needed to product a true color image. The information made available by the next channel below, the “Veggie” band is used to simulate the “green” color needed to produce a “color” image.
Channel 3: The “Veggie” band
Although this is a “near-infrared” band (not visible to the eye) vegetation is readily seen at this wavelength and therefore given the nickname “veggie” band. It is useful in assessing land characteristics when determining fire and flood potential. For example, forest fire damage will appear darker as compared to nearby unaffected areas. This helps pinpoint areas where significant rainfall may lead to flooding and mudslides.
Water is very absorbing at this wavelength which makes it appear dark. So, there is a high contrast between land and water. Channel 3 is also used to simulate a “green” band needed to produce a red-green-blue (RBG) color image.
Channel 4: The “Cirrus” band
This band is centered in a strong water vapor absorption of the electromagnetic spectrum. What this means is radiation from water vapor (water in a gaseous state) is absorbed and therefore not routinely visible at this wavelength. Therefore, this channel provides excellent daytime sensitivity to high, very thin cirrus under most circumstances, hence the “cirrus” band. This also means it is easier to distinguish between low and high clouds or other bright objects and high clouds.
Channel 5: The “Snow/Ice” band
This band takes of advantage of the different way light is refracted between ice and water. Snow and ice surfaces are strongly absorbing this wavelength. With their radiation being absorbed, in daytime, ice crystals (snow and cirro-form clouds) appear darker than clouds which consist of liquid water. At night hours forest fires are particularly noticeable against the dark background.
Channel 6: The “Cloud Particle Size” band
The size of cloud particles increases as it changes from liquid to ice. This channel helps maximize this difference so we can see liquid clouds verses ice crystal clouds. Small particles (liquid) appear bright. Larger ice crystals appear dark. Also, similar to the 1.6 µm band, the 2.2 µm band can be useful in determining hot spots as night. In fact, this channel is closer to the emitting energy of fires than channel 5.
Channel 7: The “Shortwave Window” band (Available via HRIT)
This infrared channel is sensitive to temperature and therefore able to see the slight thermal differences between the ground and low stratus clouds. This makes it useful for identifying night time fog and low clouds. It is also useful for detection of volcanic ash and estimating sea-surface temperatures. This band can be used to study urban heat islands as well.
Water Vapor Bands
The satellites do not directly detect moisture but actually detect temperature. Water vapor (water in a gaseous state) absorbs radiation at these particular frequencies. When much radiation has been absorbed by water vapor the satellite does not sense much radiation and therefore records a low temperature.
The satellite interprets a low temperature as high water vapor content. When much radiation is received by the satellite, it senses a high temperature and consequently a low amount of water vapor.
As a result, the depth at which the satellite peers into the atmosphere will vary with amount of moisture over any particular point from day to day.
Channel 8: The “Upper-Level” Water Vapor band (Available via HRIT)
The primary use for this band is upper level feature detection such as jet streams, troughs/ridges, and signs of potential turbulence.
Channel 9: The “Mid-Level” Water Vapor band (Available via HRIT)
The middle water vapor channel. Unless higher-level clouds obscure the view, this band can view as low as 500 mb level (about 18,000 feet/5,500 meters). It is used for mid and upper-level water vapor tracking, jet stream identification, hurricane track forecasting, mid-latitude storm forecasting, severe weather analysis, and mid-level moisture estimation.
Channel 10: The “Lower-level” Water Vapor band
This channel peers deepest into the atmosphere. Unless higher-level clouds obscure the view, this band can view as low as 750 mb level (about 8,000 feet/2,400 meters). As such it is useful to view and estimate lower-level moisture and jet streaks (small areas embedded in the jet stream that can lead to severe weather). It can also be used to highlight volcanic plumes that are rich in sulfur dioxide (SO2).
The following channels in the infrared range will appear to look similar. There are subtle differences between the channels but their value is when are compared to each other.
Channel 11: The “Cloud-Top Phase” band
Clouds can consist of the following phases; liquid water, super-cooled water (droplets remain in liquid form although the temperature is BELOW freezing) or frozen. This band is similar to the “traditional” infrared band (channel 14, below) but with the added benefit of helping to determine cloud phase. It is used in combination with channels 14 and 15 to help derive cloud phases during both day and night. This band is essential for generating many products.
Channel 12: The “Ozone ” band
At present this band provides information about the dynamics of the atmosphere near the tropopause (the boundary between the troposphere below – where we live – and the stratosphere above). In the future, this channel, along with other infrared channels and weather model information, will provide the amount of ozone in a column. The Total Ozone product is expected to provide information to forecasters that will help them forecast areas of atmospheric turbulence and to provide better forecasts of air quality.
Channel 13: The “Clean” band (Available via HRIT)
This channel is considered “clean” because it is less sensitive than other infrared window channels to water vapor. Because of this, when compared to channel 11, it can see through some clouds to view ice. This helps to improve corrections to atmospheric moisture and is useful for the estimation of cloud particle sizes. Channel 13 will be used in many composite and band differences views.
Channel 14: The “IR Longwave Window ” band (Available via HRIT)
The traditional infrared view channel. Observations from this infrared window channel, with other wavelengths, contributes to many satellite derived products, such as precipitation estimates, cloud-drift winds, hurricane intensity and track analyses, cloud-top heights, and volcanic ash detection, as well as fog detection, cloud phase, and cloud particle size estimates.
Channel 15: The “Dirty” band (Available via HRIT)
This channel is considered “dirty” because it is more sensitive than other infrared window channels to water vapor. When compared to the “clean” window (channel 13) it is used to compute the split window difference. A split window difference is where the values for any particular location on the “dirty” channel are subtracted from the values at the same location on the “clean” channel. This helps to can highlight differences in moisture in clear skies.
Channel 16: The “Carbon” band
This band is typically not used for visual interpretation of weather events but used in the generation of other derived GOES imagery. It is primary use is for air temperature estimation, determining the location of the tropopause and cloud observations for cloud top height, cloud-drift (for determining wind speed and direction) and supplementing ASOS observations.
Geo-Color (almost true color)
This image is not a single channel but a combination of several GOES-R channels along with a polar-orbiting satellite. During daytime, bands 1, 2 and 3 (red, blue and “veggie”) are combined to produce an approximation of how it would appear if viewed with human eyes from space.
At night, bands 7 and 13 are combined and colorized. The nighttime blue colors represent liquid water clouds such as fog and stratus, while gray to white indicate higher ice clouds. Finally, from a polar-orbiting NASA satellite, the nighttime city lights are added.
In HRIT bands 02 and 13 are combined along with a Color Look up Table to produce a false-color image.