New technologies to reduce stray light for measuring solar UV with array spectroradiometers

Abstract

Measurements of solar UV irradiance with array spectroradiometers (ASRM) are susceptible to errors in particular in the wavelength regions with low irradiance levels. This is due to the impact of stray light in the often compact single grating configuration of ASRMs. However, a significant advantage of ASRMs, in contrast to traditional scanning spectroradiometers, is their ability to detect one entire solar UV spectrum quasi instantaneously. This study aims to evaluate three different concepts and respective technologies to physically reduce the impact of stray light in conjunction with ASRM. 1. The concept of modulating the incoming solar radiation to reduce the dynamic range of the solar UV spectrum using the Digital Light Processing (DLP ®) technology. 2. The concept of pre-selecting a range of wavelength before guiding the incoming radiation to an ASRM. The corresponding technologies for this pre-dispersing instrument are based on tunable MEMS gratings. 3. The high dynamic range of the solar UV light covering 6 orders of magnitude can be adjusted with static filters, either placed in front of the detector array or in the light path between the entrance optics and the ASRM. The evaluation of the concepts and technologies according to 6 different criteria reveals that the concept of level the dynamic range using the DLP® technology is the most promising approach to construct a prototype device of a novel ARSM.