Below we're measuring temperature without really knowing what we're doing. * Why read the manuals, why study detailed physics beforehand? Theory is more fun with practical results in your hands; no matter how crappy they are. Start bottom-up and learn by failing. This is just a game of (re-)discovery, nothing is at stake here.
Differences between the sunny and the shadow side of street objects measured with different devices on different dates:
a) Measurements with an infra-red thermometer on 4 february 2012 near noon. Air temperature (digital electronic thermometer) was -4 degrees Celsius. Temperature of snow surface (infra-red thermometer) was -10.4 degrees. Official measurements by the KNMI: Mean -8.1 Max -3.6 Min -14.2 °C.
b) Measurements with an infra-red thermometer on 11 february 2012 near noon. Air temperature (digital electronic thermometer) was -2.6 degrees Celsius. Official measurements by the KNMI: Mean -7.6 Max -2.8 Min -13.2 °C.
c) Measurements with the thermocouple on 11 february 2012. Air temperature (thermocouple) was +3 +4 degrees Celsius.
* Somehow I cannot avoid using the scientific convention of talking about "we" - "I" feels unnatural in this context.
* And in the meantime I've discovered that I've made serious errors in my measurement method. The infrared thermometer should be used differently.
The results
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Plane tree - emissivity 0.98 - sunny side : a) -0.24 b) -2.8 -0.5 +2.2 c) +10 +11 |
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Plane tree - shadow side : a) -9.7 b) -6.7 -9.1 -9.2 -10.1 c) +8 +9 |
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Brick wall - emissivity 0.93 Sunny side - sun perpendicular to wall a) -3.5 b) +4.0 c) +18 |
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Brick wall - semi sunny side - sun parallel to wall : a) -5.4 b) -6.8 c) +11 |
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Brick wall - shadow side : a) -10.5 b) -12.1 c) +6 |
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Painted iron lamppost - sunny side: a) -4.1 b) -3.6 -5.1 c) +8 |
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Painted iron lamppost - shadow side: a) -5.7 -6.1 b) -7.4 -7.8 c) +7 |
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Enameled steel dustbin - sunny side: a) +1.7 b) -1.8 +0.7 c) +13 |
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Enameled steel dustbin - shadow side: a) -7.3 b) -8.6 -10.1 c) +11 |
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Concrete street curb - emissivity 0.94 Sunny side - sun perpendicular to surface: a) +0.4 b) -2.1 c) +14 |
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Concrete street curb - semi sunny side sun parallel to surface : a) -8.7 |
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Concrete street curb - shadow side a) -10.4 -11.2 b) -12.4 c) +9 |
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Concrete street pylon - sunny side : a) +1.1 |
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Concrete street pylon - shadow side : a) -7.4 -7.3 -7.2 |
Sources:
Official weather measurements by the KNMI
Introduction to infrared thermometers - it's more complicated than you would think - and I've made serious measurement errors - see the illustration
Infrared Thermometer Emissivity Tables - this does not change the results very much
Emissivity measurements - extremely detailed and interesting
Tree Thermography + tree emissivity
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