GOES West (GOES 17)

Like GOES-East, of the six instruments on GOES-West used 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).

The individual channels are as follows:

Visible Bands

There are two visible bands, blue and red, 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 respectively, but colors have been desaturated to appear in grayscale. Since these are "visible" channels, the images will appear black at night.

Near-Infrared Bands

Channel 3: The "Veggie" band

The centralized wavelength for this band is 0.86 µm (micrometers).

Although this is a "near-infrared" band (not visible to the eye), vegetation is readily seen at this wavelength, giving it 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 than nearby unaffected areas, which helps pinpoint locations where significant rainfall may lead to flooding and mudslides.

Water is very absorptive of this wavelength, which makes it appear dark in the image, resulting in a high contrast between land and water.

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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.

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Channel 5: The "Snow/Ice" band

The centralized wavelength for this band is 1.61 µm (micrometers).

This band takes advantage of the different way light is refracted between solid ice and liquid water. Snow and ice surfaces (solids) strongly absorb this wavelength. As a result, during daylight hours, ice crystals in snow and cirro-form clouds appear darker than clouds which consist of liquid water. During the nighttime hours, when it is too dark to distinguish snow/ice, very hot wildfires appear brightly against the dark background. Wildfires emit radiation at the same wavelength, so it is a dual-use band.

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Channel 6: The "Cloud Particle Size" band

The centralized wavelength for this band is 2.24 µm (micrometers).

The cloud particle size increases as they change from liquid to ice. This channel helps maximize the apparent difference so we can distinguish liquid clouds from ice crystal clouds. Small particles (liquid) appear bright while 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 at night. In fact, this channel is closer to the emitting energy of fires than channel 5.

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Channel 7: The "Shortwave window"

The centralized wavelength for this band is 3.9 µm (micrometers).

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 detecting volcanic ash, estimating sea-surface temperatures, and studying urban heat islands.

Water Vapor Bands

The satellites do not directly detect moisture but instead detect temperature. Water vapor absorbs radiation at these particular frequencies, and thus the satellite does not sense much radiation when there is high water vapor. It records this as a low temperature, which is interpreted as high water vapor content. When radiation is not absorbed and thus received by the satellite, it senses a high temperature and consequently interprets a low amount of water vapor.

As a result, the depth at which the satellite peers into the atmosphere will vary with the amount of moisture over any particular point from day to day.

Channel 8: The "Upper-Level" Water Vapor band

The centralized wavelength for this band is 6.2 µm (micrometers).

The primary use for this band is the detection of upper level atmospheric features such as jet streams, troughs/ridges, and signs of potential turbulence.

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Channel 9: The "Mid-level" Water Vapor band

The centralized wavelength for this band is 6.9 µm (micrometers).

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.

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Channel 10: The "Lower-level" Water Vapor band

The centralized wavelength for this band is 7.3 µm (micrometers).

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).

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Infrared Bands

The following channels in the infrared range will appear to look similar. There are subtle differences between the channels, but their value comes from comparison with each other.

Channel 11: "Cloud-top" phase

The centralized wavelength for this band is 8.5 µm (micrometers).

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.With multiple ways to apply this data, this band is widely used in day to day operations. This band is essential for generating many products.

The centralized wavelength for this band is 9.6 µm (micrometers).

This band provides information about the dynamics of the atmosphere near the tropopause (the atmospheric boundary between the troposphere below – where we live – and the stratosphere above). The ozone band on the ABI does not give exact information on total ozone; rather, multiple ABI IR bands are used to calculate an estimate. The Total Ozone product provides information to forecasters that helps them forecast areas of atmospheric turbulence and provide better forecasts of air quality.

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Channel 13: The "Clean" Infrared band

The centralized wavelength for this band is 10.3 µm (micrometers).

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.

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Channel 14: The "Traditional" Infrared band

 

The centralized wavelength for this band is 11.2 µm (micrometers).

Observations from this infrared window channel combined with other wavelengths, contribute 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.

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Channel 15: The "Dirty" Infrared band

The centralized wavelength for this band is 12.3 µm (micrometers).

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 highlight differences in moisture in clear skies.

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Channel 16: The "Carbon Dioxide" band

The centralized wavelength for this band is 13.3 µm (micrometers).

This band is typically not used for visual interpretation of weather events but for the generation of other derived GOES imagery. Its 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.

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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.

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