Influence of the Exomars 2016 lander elements in the uncertainty of irradiance measurements for the dreams-SIS instrument

DREAMS-SIS: The Solar Irradiance Sensor on-board the ExoMars 2016 lander

“…In the case of the top detector, this was an annular-ring around the diffusing dome. Nevertheless, the analysis performed with regard to the lander interference (Álvarez Ríos, F.J., et al, 2016) showed no relevant problem for the subsequent scientific retrieval. Regarding possible reflections on the ground, the albedo, the view factor (ground/detectors) and the aforementioned below-horizon ARF percentages, guarantee that the interference remains below 0.5% even for the Top detector.…”

“…For normal incidence light, the source irradiance uniformity is still the dominant uncertainty in the NIR and Top channels. For the UV case, a technical problem that arose during the thermal calibration (described in Jiménez, J.J., et al, 2016) made the thermal uncertainty close to 2% for the worst-case temperature, becoming the dominant uncertainty for normal incidence. Thus, the final calibration accuracy including normal incidence responsivity, ARF and TRF is dominated by the source uniformity uncertainty for the NIR and Top detectors at normal incidence, leading to values around 1%.…”

“…Figure 5 Relative error in the ARF due to the 0.5 degrees pointing uncertainty during calibration (from Jiménez, J.J., et al, 2016) Regarding precision, understood as repeatability of the measurements, the main sources of uncertainty are, apart from noise itself: the precision in the measurement of the TRF (which is driven by the precision in the measurement of the resistance of the thermal sensor inside the OH), signals' offset (an offset voltage was introduced in the electronics to provide a wellknown value when in complete darkness) and ARF. The last one is the dominant one, and it is mainly due to the precision (repeatability of minimum step) of the motors that control de calibration set-up.…”

“…The resulting values when considering all these sources, range from less than 0.1% for all channels with normal incidence, to 0.4% when the incidence angle is at the edge of a detector's FoV (ARF below 10%). Detailed calculations of all the uncertainty aspects can be found in (Jiménez, J.J., et al, 2016).…”