Help Using Coastwatch
Top Ten Most Frequently Asked Questions
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
||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
||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.