# Experimentally diminishing random errors for low wavelength UV observations

Part of the work that I do involves observations of solar low wavelength UV observations, specifically UV-B and UV-A II (up to 340nm). I have noticed that when I observe responses on a CCD or CMOS based sensor, that the lower the wavelength observed the greater the random fluctuations in the pixel responses. This is also noted in the paper Evaluating UVA Aerosol Optical Depth using a Smartphone Camera (abstract only), that suggests reason as being

The greater relative error occurs at lower wavelengths (340 nm) due to increased atmospheric scattering effects, particularly at higher air masses and due to lower signal to noise ratio in the image sensor.

So, the question is how is it possible to experimentally diminish the random noise from low wavelength UV observations, while preserving as much of the signal as possible?

• Woot! This is a really well posed and interesting experimental question. Arise, ye experimentalists of the 'net! Bring forth relevant information. – DanielSank Sep 29 '14 at 1:37
• When you say there is greater fluctuations, do you mean that the CCD counts fluctuate more at lower wavelengths, or something else? Do you use a laser to calibrate atmospheric density fluctuations? – DanielSank Sep 29 '14 at 1:57
• @DanielSank, yes, the CCD/CMOS pixel counts/responses fluctuate. We use sunphotometers (e.g. Microtops II) for calibration – user60063 Sep 29 '14 at 1:59
• Follow up: It looks like the direct gap of silicon is 3.4 eV. So $\lambda = hc/E = 1240 \text{ eV}\,\text{nm} / 3.4 \text{eV} = 365 \text{nm}$. Maybe this is unrelated though. What material is your CMOS CCD? – CuriousKev Sep 29 '14 at 3:18
• Are you focusing the UV with lenses on your detectors? ( I am thinking on the lines of seeing stars in the noise with telescopes) – anna v Oct 12 '14 at 6:25