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Physical
Climatology: Field Methods
GEOG 5231/4231 - Fall 2001 Professor Konrad Steffen
Lab I Radiation Sensor Reaction Time Experiment If a physical system is subject to a step function input, its response (e.g., the temperature of cooling body, the angular velocity of a freely de-spinning wheel, or the current of a discharging capacitor) may often be expressed with an exponential function. This function may be concisely expresses as a = A exp(-t/t), where a is the instantaneous value, A is the amplitude, t is the time in seconds and t is a time constant. Since an exponential function exhibits an asymptotic nature, the time required for the response to achieve its final steady state value is poorly defined. Thus, by convention, the time required for a to achieve about 36.8 % of the original value (or 62.2 % of its final value if a is increasing) is described as the time constant (t) of the system, where exp (-t/t) = 1/e = 1 / 2.718 = 0.368. Measure the time constant for different radiometers (pyranometer and net-radiometer). a) Li-Core Radiation Sensor
Design the experiment using a strong lamp
(500 – 1000 W).
Measure the reaction time for each of the three instruments at least 3-5 times. Analyze the data and prepare the first lab report according to the guidelines. Use graphics to display the reaction time, and statistics to derived the true value. General reading: Pal Arya, S., Introduction to Micrometeorology, Chapter 3: Radiation balance near the surface, 21-35, 1988. Froehlich, C., and J. London, Revised instruction manual on radiation instruments and measurements, WCRP Publication Series No. 7, WMO/TD – No. 149, 1986. Coulson, K., Solar and Terrestrial Radiation, Academic Press, 1975. Lab report I is
due on Oct 11, 2001
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