Keith L. Walker

Denman Island, British Columbia

Thermal Imaging

If you have studied my temperature recordings, you may have noticed an anomaly in the morning temperatures. Between 07:00 and 08:30 on spring and summer mornings, the recording often shows one or two sharp peaks. You may have guessed that the sun shines directly on the sensor at this time, and your guess would be correct.

A true data mining nerd, I wasn't content with that explanation. The double peak suggested that a shadow was being cast on the sensor during part of the time the sun shines on it. Knowing the site, the shadow was most likely that of a tree. So, I thought, I should be able to create an image of the tree by using the temperature recordings as scan lines in a raster scan, in much the same way as a television picture is built.

I wrote a program to extract temperature data from the relevant time each day, convert temperatures to brightness, adjust for solar elevation based on date, then draw the result on a graphic. Of course, some days are cloudy, causing a loss of data, but by combining data from three seasons (summer 2005, spring 2006, summer 2006), I was able to fill in much of the obscured data.

As you can see, the image of the tree is quite distinct. For comparison, here is a photograph of the tree, from the point-of-view of the temperature sensor. You can see the sensor just under the eave of the roof.

An approximate, but likely, superimposition of the thermal and photo images:

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