Abstract. This paper presents the three-waveband spectrally agile technique (TWST) for measuring cloud optical depth (COD). TWST is a portable field-proven sensor and retrieval method offering a unique combination of fast (1 Hz) cloudresolving (0.5 • field of view) real-time-reported COD measurements. It entails ground-based measurement of visible and near-infrared (VNIR) zenith spectral radiances much like the Aerosol Robotic Network (AERONET) cloud-mode sensors. What is novel in our approach is that we employ absorption in the oxygen A-band as a means of resolving the COD ambiguity inherent in using up-looking spectral radiances. We describe the TWST sensor and algorithm, and assess their merits by comparison to AERONET cloud-mode measurements collected during the US Department of Energy's Atmospheric Radiation Measurements (ARM) TwoColumn Aerosol Project (TCAP). Spectral radiance agreement was better than 1 %, while a linear fit of COD yielded a slope of 0.905 (TWST reporting higher COD) and offset of −2.1.
We have determined optimal minimum-conspicuity monocoat paint colors for the CH-47F Chinook helicopter, viewed photopically against forest, desert, and sky backgrounds. Our methodology combines use of a validated spectroradiometric model for rigorous 3D signature prediction with statistics of varying background fields and a CIE color difference metric. The study considered a large subset of the Federal Standard 595 (FS595) paint inventory. Each paint color was rigorously modeled with bidirectional reflectance distribution function scattering properties to match existing army paint and spectral reflectances to match spectrophotometer measurements of FS595 reference samples. We devised and validated a method to impute statistical variation in background radiances over environmental conditions consistent with the aircraft radiometric computations. Using a visual jury, we informally calibrated the CIE 1994 color difference formula (which gauges both luminance and chromaticity contrast) to gauge how each paint performed against each background, for varying range, view direction, and sun location. The statistical dispersions in performance were summarized for the CH-47F Program Manager, who selected the best overall paint for the CH-47F fleet. We found paints that were optimized to a specific background (forest, desert, etc.) yielded enhanced performance against those backgrounds, as would be expected, and that those paints were better than the paint used on CH-47s in the current US inventory.
Scattered ultraviolet radiation in the 40 to 46 km altitude range is evaluated using an analytic, single‐scattering description and results from the atmospheric ultraviolet radiance integrated code (AURIC). The calculations are compared with measurements obtained from a balloon‐borne spectrometer at 1.5‐nm resolution. The analytic approach is useful for approximating the angular and spectral dependence of scattered UV radiation; however, use of a single scale height to describe the vertical distribution of absorbers and scatterers leads to errors of 50% or greater at intermediate ozone opacities. Results from AURIC generally are compatible with the observations, particularly below 210 nm where large discrepancies have been noted in prior model/measurement comparisons.
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