Modeling Ground Temperature
How would I go about calculating the change in temperature of
the ground surface over time, for example 10 square meters of asphalt,
as it is heated by the sun? I understand that I can use asphalt's
emissivity to calculate the energy transfer at a certain temperature,
but how would I calculate (estimate) the actual change in temperature
over time? (assuming the sun is directly overhead, and ignoring weather
Capturing useful energy is actually very easy. The hard part is
capturing it in a cost-effective way. There are lots of sources of
useful energy around us -- the problem is that it costs to much to use
them. (electricity and gasoline are just too darn cheap!).
Using an optical measurement is certainly not the simplest approach. It is
full of possible experimental difficulties. A simpler approach would be to
use a thermocouple, or resistance thermometer buried a few centimeters
beneath the surface of the ground. This would be accurate to (+/-) 0.1 to
(+/-) 0.05 C. This would give a direct reading and with a simple switching
system you could use more than one probe -- maybe one on the surface, one
maybe about 2 cm beneath the surface, and another maybe 10 cm below the
surface. For a few more dollars you could set up a timer system to take
readings continuously or at variable time intervals. This would provide you
with data that you could correlate with air temperature, rain fall,
cloudiness, and more data. A problem you should anticipate is being buried
by the amount data you will gather. Careful planning is a bigger issue. The
'hardware' will probably be the least of your problems. I suspect you would
be able to find temperature recording
systems fairly reasonably, since multiple site temperature measuring devices
are a common laboratory issue.
How would you calculate the temperature change "over time" assuming the sun
is directly overhead?
The sun would be directly overhead only for a very short period of time,
depending on your latitude.
Perhaps your question needs further definition.
The temperature change would depend a great deal on where your 10 square
meters (3.162277 meters on a side) of asphalt laid and during which parts of
the day you are taking your measurements.
Asphalt is a lot colder in Alaska than in Florida and the temperature change
is not as much near sunrise/sunset than it is during the mid-day hours.
So for your local problem, lay a thermometer on the asphalt and take
readings at whatever time interval you choose and chart it to derive
temperature change rates.
Most long range temperature measurements (like satellite measurements of
earth's surface) is done using infrared instruments.
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Update: June 2012