Author
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COBOS, DOUG - UNIVERSITY OF MINNESOTA |
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Baker, John |
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Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/10/2002 Publication Date: N/A Citation: N/A Interpretive Summary: Incoming radiation (light and heat) from the sun and sky minus reflected and emitted radiation from the earth's surface is known as net radiation. Net radiation has a profound impact on heat, moisture, and biological processes at the earth's surface. For this reason, researchers have been developing methods and instruments for the measurement of net radiation for rover half a century. Despite the considerable resources that have been invested in net radiometry, highly accurate measurement apparatus are prohibitively expensive. There are, however, several commercially available instruments that are much less expensive than the most accurate measurement devices. This project involved the evaluation of a newly introduced, inexpensive instrument using the more widely accepted, expensive technique as a standard of comparison. The inexpensive instrument performed well under most circumstances, surpassing expectations. It was concluded that with some slight modifications, the instrument that was evaluated could be useful for research applications. This simple comparison and the suggested modifications could be of value to researchers who need to measure net radiation in many locations, and can accept slightly less accurate measurements than are available using the high priced methods. Technical Abstract: The use of net radiation as a critical variable in models of surface- atmosphere exchange is routine. However, its measurement is not. The discrete measurement of incoming and outgoing solar radiation with pyranometers and long-wave radiation with pyrgeometers is widely thought to be the most accurate method for estimating net radiation, but is cost prohibitive. A recently developed single-sensor net radiometer differs from other commonly used net radiometers in that it has no domes covering the thermopile sensor. Long term field data from this net radiometer were compared to reference net radiation calculated as the sum of the four independently measured components. The domeless net radiometer agreed well with the reference measurements, out-performing a similarly priced, widely used, domed net radiometer under most conditions. However, our analyses suggest that the domeless net radiometer has differing sensitivities to short and long-wave radiation, which is not accounted for in the calibration. Additionally, precipitation affected the domeless net radiometer much more severely than the domed model, which could be a significant limitation in areas with frequent rainfall. |
