Help Using Coastwatch

Top Ten Most Frequently Asked Questions
Order the Sea Grant CoastWatch Introductory Video

Key terms are identified and defined in detail below the map.

Key Terms and Definitions

	1. An isotherm is a graphic representation of temperature gradients. "Iso" (similar) "therms" (temperatures) are connected points forming lines that look to some people like the elevation lines on a topographic map. On the CoastWatch "port site" images, each line indicates a change in temperature of 1 degree fahrenheit.
	2. Fahrenheit temperatures presented to the nearest one-tenth degree. The grid pattern you see supplements the isothermic representation for ease of use. Learn more about water temperatures and thermal bars.
	3. The latitude and longitude grid provides both degrees (0) and minutes (') distance north and west of the equator and prime meridian. The example on the left locates you at 79 degrees, 30 minutes west (of the prime meridian).
	4. Cloud covered areas of the lake surface cannot be read accurately by NOAA satellites so the computer program colors them black. Areas near the black masked cloud cover may not be as precisely reported as those some distance from the clouds. CoastWatch images are generally representative of surface temperature conditions, they are not as accurate as your road atlas.
	5. Some areas are masked with grey color because the computer program has indicated the temperatures presented are probably cloud temperatures. The air temperature at the tops of clouds can sometimes be very nearly the same as the surface water temperature of the lakes below. The grey-scale masking indicates that the accuracy of temperature reporting is lower at this time. Watching CoastWatch temperature patterns over the days, weeks and seasons provides useful information on lake surface temperatures.
	6. Each area of coverage has a unique name. This is a "regional view" of Western Lake Ontario. CoastWatch also provides close-up "port views."
	7. The image date and time in this example is April 30, 1998 at 6:57 p.m. Images are drawn from satellite overflights that occur several times per day. We refer to these overflight images as "early evening" and "evening" images in our archives. The best available (usually the least cloudy) images are selected for presentation on CoastWatch, so when the clouds persist for several days, the image you see may be several days old.