Vicarious calibration methods have been developed to calibrate radiometric sensors in-flight. One such method, the irradiance-based method, requires the measurement of the diffuse-to-global (diffuse-to-total) irradiance ratio. Diffuse/global irradiance measurements may also be used to deduce atmospheric descriptors and provide a comparison with atmospheric modeling predictions. I describe the design, construction, calibration, and application of a spectral diffuse/global irradiance meter that can accomplish these objectives in this dissertation. I develop general integrating sphere theory, modeling methods, and describe the resultant computer model. The model results agreed with theory to better than 1% for a simple unbaffled integrating sphere. I applied the model to design an interior baffled integrating sphere-based cosine collector. I developed a method of tolerating the thermal expansion of Spectralon® and the collector was constructed. Measurements of the collector angular response agreed with the model predictions to better than 4% for input zenith angles from 0° to 70°. The resulting instrument is automated and collects diffuse and global irradiance from 300 nm to 1100 nm. It has a nominal 12 nm full-width at half-maximum bandpass and has a minimum sampling interval of 1 nm. I estimate the uncertainty of the measurements to be 3.2%. The largest contributor to the total uncertainty is the measurement uncertainty of the diffuse irradiance at 2.5%. The instrument was used in a field experiment. Optical depths derived from the diffuse/global irradiance measurements agreed with those derived from a solar radiometer to within 0.008. Diffuse-to-global irradiance measurements made by the instrument were compared with an independent method and found to generally agree within 6%. The measurements were consistently lower than radiative transfer modeling estimates. Top of the atmosphere relative radiances computed from the two independent diffuse-to-global irradiance data sets generally agreed to better than the 2.9% uncertainty associated with the diffuse/global irradiance meter data set. The relative radiances of the diffuse/global data set collected with the instrument were within the 4.9% uncertainty estimate of the reflectance-based method.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/288767 |
| Date | January 1997 |
| Creators | Crowther, Blake Glenn, 1965- |
| Contributors | Biggar, Stuart F., Slater, Philip N. |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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