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- Interobserver variability of hand-held SQM-L measurements.Publication . Bará, Salvador; C. Lima, Raúl; Arós, Ángel R.; Giráldez, LucíaUnder stable luminance conditions the uncertainty of the brightness measurements obtained with hand-held SQM-L detectors arises from the combination of their intrinsic precision and the random pointing errors incurred by the observers. Based on the observations performed by 13 independent observers without previous training in SQM-L use, we got an estimate of 0.074 mag/arcsec 2 for the observer-induced uncertainty (standard deviation of the sample) under 20.83 mag/arcsec 2 skies.
- Are SQM-L measurements polarization dependent?Publication . Bará, Salvador; C. Lima, RaúlSeveral observers informed that slightly different SQM-L zenithal brightness readings can be obtained depending on the azimuthal orientation of the device. Since the light scattered by the atmosphere generally has some degree of polarization, depending on the relative position of the source, the observation direction, the light spectrum, and the atmospheric molecular and aerosol constituents, we wanted to check whether the measurements made with these devices show any intrinsic dependence on the polarization of the incoming light. Although the SQM detectors do not purposely include any polarizing optical element, some polarization dependent effects could potentially arise from the presence of anisotropic materials (e.g. some kinds of plastics) producing differential Fresnel losses in the orthogonal vibration components of the incoming field.