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Sea Grant CoastWatch Frequently Asked Questions

1. How are the surface temperature images created?
Sea Grant CoastWatch surface temperature images are the result of a partnership between Sea Grant, the Michigan State University Remote Sensing & Geographic Information Science Research and Outreach Services (RS&GIS), the Great Lakes Environmental Research Laboratory (GLERL) in Ann Arbor, and the National Oceanic and Atmospheric Administration (NOAA).

NOAA Polar Orbiter satellites carry Advanced Very High Resolution Radiometers (AVHRRs), and these provide Sea Surface Temperature (SST) imagery to GLERL, which in turn uses an electronic dissemination system to make the data available to RS&GIS. A fully automated system is in place, so that the RS&GIS computer can download SST images and cloud masks four times each day. The data is converted to isoline imagery and posted to the Sea Grant CoastWatch website.

2. When are the surface temperature images updated?
The RS&GIS computer asks the GLERL computer for data twice an hour.

The satellite images are transmitted on a regular basis and the exact time of each transmittal is presented at the top of each image posted to the website. The satellite transmission times vary by several minutes with each orbit.

3. Can the satellite flights be adjusted so morning images can be posted earlier?
No. The CoastWatch program is just one of several users of the satellite, and we have no control over when the data can be made available.
4. Sometimes images are a few days old, why?
The computer "decides" to replace an existing website image only if the new image would be of equal or better quality. Cloud cover sometimes obscures too much of the lake surface to make posting the new flight data reliable or worthwhile.
5. How far is it between lat/long lines?
This varies with your position on the globe, but approximately 11 miles north and south between latitude lines and 8 miles east and west between longitude lines at Lansing Michigan. Remember, don't use CoastWatch for navigation, use your charts....CoastWatch is not accurate at very fine resolution.
6. Why do I sometimes get a different temperature reading off my temperature gauge than CoastWatch shows on the contour image map?
The satellite scans the top millimeter of the water temperature. Your temp gauge might be through the hull or down on your transom; several inches or a few feet below the surface. That explains some of the differences. Also, don't forget that the afternoon CoastWatch images are going to display reflected and surface heat, so evening or early morning imagery will more likely be similar to what you find out on the lake using your temp gauge. And remember, CoastWatch gives you general insight on a fairly large scale. Don't try to make it work right down to the resolution of your temperature gauge.
7. Where can I learn more about using surface temperature data?
Ask your Sea Grant Office, visit our page about temperatures, or visit a few of our Favorite Links for more information.


Most questions can be answered by your Sea Grant Agent or on our CoastWatch Help Pages. Please send comments or bug reports to Please include the name of the location or file that's giving you trouble, as well as the type of software you are running. This is a cooperative project between the NOAA CoastWatch Great Lakes Regional Node located at the NOAA Great Lakes Environmental Research Laboratory in Ann Arbor and the Sea Grant Network.
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