Sea Grant CoastWatch Frequently Asked Questions
1. How are the surface temperature
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
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,
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
|5. How far is it between
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
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
|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