Theory
Solar radiation causes objects to be warmer than the surrounding
air. For this reason, thermometers are traditionally
shielded by a screen. For accurate measurements, forced ventilation
is necessary, which was not provided in our case
(WMO, 2010). The temperature difference between a heated
cylinder (or sphere) and the air that moves around it scales
with the square root of the diameter (White, 1988). If the diameter
of a cylinder were zero, the heat generated by solar
radiation would also be zero. Such a zero diameter cylinder
would take on the temperature of the surrounding air. One
can create a virtual cylinder with zero diameter by extrapolating
the temperatures of two cylinders with different diameters.
The fiber optic cables used by DTS can be considered
to be very long cylinders. When the temperatures of two
cables (T1 and T2) with different diameters (d1 and d2) are
measured, then the air temperature can be determined by extrapolating
to a zero diameter, which results in Eq. (1)
TheorySolar radiation causes objects to be warmer than the surroundingair. For this reason, thermometers are traditionallyshielded by a screen. For accurate measurements, forced ventilationis necessary, which was not provided in our case(WMO, 2010). The temperature difference between a heatedcylinder (or sphere) and the air that moves around it scaleswith the square root of the diameter (White, 1988). If the diameterof a cylinder were zero, the heat generated by solarradiation would also be zero. Such a zero diameter cylinderwould take on the temperature of the surrounding air. Onecan create a virtual cylinder with zero diameter by extrapolatingthe temperatures of two cylinders with different diameters.The fiber optic cables used by DTS can be consideredto be very long cylinders. When the temperatures of twocables (T1 and T2) with different diameters (d1 and d2) aremeasured, then the air temperature can be determined by extrapolatingto a zero diameter, which results in Eq. (1)
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