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GOES 8

After successfully attaining orbit on 27 April 1994, the first of NOAA’s current series of Geostationary Operational Environmental Satellites was renamed GOES-8 from GOES-I.

GOES-8 operates as NOAA’s “eastern” satellite (stationed over 75 degrees W) and GOES-10 (stationed over 135 W) is the “western” satellite. Together, they cover the contiguous U.S., including portions of the Atlantic and Pacific Oceans off its coastlines.

 

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The material presented in this module is designed as a beginner’s guide to the use of GOES imagery. The GOES provide frequent images at five different wavelengths, including a visible wavelength channel and four infrared channels. The satellites scan the continental U.S. every 15 min.; most of the hemisphere, from near the north pole to ~ 20S latitude, every 30 min; and scan the entire hemisphere once every three hours in their “routine” scheduling mode. Optionally, special imaging schedules are available which allow data collection at more rapid time intervals (~7.5-min and 1-min), over reduced areal sectors. These will be discussed in more detail in the sections that follow.

You will have the option to proceed through the material, one “page” at a time, in the baseline order it was assembled or, you may go back to the Table Of Contents (TOC) and immediately go to a section of your choice from there. Throughout the module you will find links to more advanced material and various sub-topics. To “jump” to topics out of order from the baseline sequence (as outlined in the TOC), one may click the mouse over the hyper-text (bold, blue, underlined text) phrase of interest. You may return to the “page” you jumped from by clicking the PREVIOUS button; otherwise, clicking the PREVIOUS button takes you to the “page” just preceding the current one in the baseline sequence of the tutorial.

Much appreciation to Martin Holecko of Computer Graphics Group for his great work in developing and providing the image player (looper), jsImagePlayer 1.0, which is used so extensively throughout this module.

NOTE: You are invited to review two other RAMMT tutorials covering the GOES 3.9 micron Channel and the Advanced GOES Imagery Applications.

  • EARTH-ORIENTED SPACECRAFT – providing efficient duty cycles for imaging and sounding, yielding both high spatial resolution and high signal-to-noise ratios.
  • MULTISPECTRAL IMAGING CAPABILITY – a 5-channel, high-resolution imager allows for the development of a number of advanced products.
  • SOUNDING CAPABILITY – provides hourly, 19-channel operational soundings from geostationary altitude.
  • GROUND DATA PROCESSING SYSTEM – provides efficient dissemination of data and products to users.
  • DATA TRANSMISSION FORMATS FOR DIRECT BROADCAST USERS – allows users access to the entire data set at reasonable costs, with potential for growth over time.

GOES’ Imager Channel Characteristics

Channel Central Wavelength Sample Sub-pt. Res.
# µm (micrometers) km E/W x N/S
1 00.65 0.57 x 1.00
2 03.90 2.30 x 4.00
3 06.70 2.30 x 8.00
4 10.70 2.30 x 4.00
5 12.00 2.30 x 4.00

The Visible Wavelength Channel

Channel No. Central Wavelength (µm) Sample sub-point (E/W x N/S)
Resolution(km)
Common Reference
1 0.65 0.57 x 1.00 visible, VIS

The GOES visible wavelength channel produces images which can be thought of as black-and-white photographs of the earth and clouds from outer space. During the daylight hours, it is the most widely used channel because it has the highest resolution of the five imaging channels, and because it approximates what we see with the human eye.

The primary utility of the VIS channel imagery is in the day-time monitoring of thunderstorms and tropical cyclones. These applications are discussed in the following pages covering Channel 1. Some other interesting features that can be distinguished with the GOES visible imagery are shown in the imagery below. These image “thumbnails” may be individually clicked upon with the mouse in order to bring up a larger image that shows the feature/s defined under them.

Wet Ground

Wet Ground

Blowing Dust

Blowing Dust

Snow and Ice

Snow and Ice

Fog

Fog

Volcanic Ash

Volcanic Ash

 

The Shortwave Infrared Channel

Channel No. Central Wavelength (µm) Sample sub-point (E/W x N/S) Resolution (km) Common Reference
2 3.9 2.3 x 4.00 shortwave infrared, shortwave IR

The 3.9 µm channel is different from the other imaging channels, in that it responds to both emitted terrestrial radiation, and reflected solar radiation. Since the emissivity of water droplets at 3.9 µm is less than that for longer wavelengths, it is often easier to identify fog and stratiform cloudiness in the channel 2 imagery, and to discriminate between water and ice clouds. Many times fog can be identified on channel 2 imagery as cooler regions, though confusion can occur between stratus or fog, and cold ground. Combining this imagery with other channels resolves most of these problems (see COMBINED IMAGE PRODUCTS).

The 3.9 µm channel is also very sensitive to sub-pixel hot spots. Therefore, in cloud-free areas it can be used alone, or in combination with other channels, to identify fires when the fires are of large enough size or of great enough intensity.

The following 3.9 µm channel imagery examples (click upon them for enlargement) illustrate fog banks off the CA coast and wildfires in FL, respectively.

Coastal Fog

Coastal Fog

FL Wildfires

FL Wildfires

The Water Vapor (6.7 µm) Channel

Channel No. Central Wavelength (µm) Sample sub-point (E/W x N/S)
Resolution (km)
Common Reference
3 6.7 2.3 x 8.00 water vapor

The 6.7 µm channel responds to mid- and upper-level water vapor and clouds. Because organized atmospheric disturbances usually have large regions of upward (or downward) motion and consequent moistening (or drying), the water vapor data can often be used to locate and define synoptic features such as shortwave troughs, ridges, jet streams, etc. Mesoscale regions of moistening/drying at the 300-500 mb height (such as subsidence associated with thunderstorms’ anvils) have also recently come under close scrutiny using this channel’s imagery.

The Window (10.7 µm) Channel

Channel No. Central Wavelength (µm) Sample sub-point (E/W x N/S)
Resolution (km)
Common Reference
4 10.7 2.3 x 4.00 window, longwave IR

The 10.7 µm channel is a so-called “window channel” meaning that radiation at this wavelength is not absorbed (to any significant degree) by atmospheric gases. When we look at clouds, or the cloud-free ground, with this channel, we are “seeing” the actual temperature of the scene in the field-of-view. Channel 4 imagery has a wide variety of uses, including determination of cloud top heights, identification of cloud top features, tracking synoptic and mesoscale features at night, etc.

The Split Window (12.0 µm) Channel

Channel No. Central Wavelength (µm) Sample sub-point (E/W x N/S)
Resolution (km)
Common Reference
5 12.0 2.3 x 4.00 dirty window/split window IR

The 12.0 µm Channel 5 imagery is similar to that from Channel 4 (10.7 µm), except that this wavelength has a unique sensitivity to low-level water vapor. Used alone, it often appears identical to the Channel 4 imagery (see example below). However, when combined with the corresponding Channel 4 data, the subtle differences between them can be used to help the forecaster identify low-level moisture fields (as will be discussed further in the following section on Combined Image Products).

This example shows a Channel 4 and a Channel 5 image of the same scene at the same time. [Click on the “Forward” button to begin an automated sequencing between the two, or alternatively, click alternately between the “+1” and the “-1” buttons for a slower pace.] As you can see, the two are nearly indistinguishable.

Please download the latest version of Java Virtual Machine from http://www.java.com if you’re having trouble viewing this loop.