Non-parametric and least squares Langley plot methods

[摘要] Langley plots are used to calibrate sun radiometers primarily for themeasurement of the aerosol component of the atmosphere that attenuates(scatters and absorbs) incoming direct solar radiation. In principle, thecalibration of a sun radiometer is a straightforward application of theBouguer–Lambert–Beer law V = V₀e^{−τ ⋅ m}, where a plot of ln(V)voltage vs. m air mass yields a straight line with intercept ln(V₀). Thisln(V₀) subsequently can be used to solve for τ for anymeasurement of V and calculation of m. This calibration works well on some highmountain sites, but the application of the Langley plot calibrationtechnique is more complicated at other, more interesting, locales. Thispaper is concerned with ferreting out calibrations at difficult sites andexamining and comparing a number of conventional and non-conventionalmethods for obtaining successful Langley plots. The 11 techniquesdiscussed indicate that both least squares and various non-parametrictechniques produce satisfactory calibrations with no significant differencesamong them when the time series of ln(V₀)'s are smoothed and interpolated withmedian and mean moving window filters.

[学科分类] 几何与拓扑