Sensitivity calibration of digital colour cameras for auroral imaging

Abstract

A method to sensitivity calibrate Digital Single Lens Reflective (DSLR) cameras is outlined. A low intensity calibrated light source tunable in wavelength is described. 31 monochromatic lines from 4000 to 7000 A with a bandpass of approximately 12 A were used to find the spectral responses for the D70 and the D200 cameras manufactured by Nikon. The source radiance ranged from about 300 to 1.6k R/A. The cameras were operated in manual mode with 4 seconds exposure time at ISO 1600, which are typical settings required for night time photography of the aurora. For the Nikon D200 camera, the blue, green and red spectral responsivities peak at 4600, 5300 and 5900 A, respectively. The response was high for the blue colour channel with a clear cut-off at 4100 A for the UV part of the spectrum. The red channel response indicates low sensitivity above 6600 A. The D70 shows similar spectral responsivity, except that it peaks in the green colour channel and it is more sensitive to both UV and NIR radiation. Both cameras are capable of detecting night- and dayside auroral at 4 second exposure time. For optimal auroral imaging capability, the green and red spectral responsivities need to be shifted up by about 300 and 400 A in wavelength.

Imaging-based observations of low-latitude auroras during 2001–2004 at Nayoro, Japan

“…It is possible to infer the absolute brightness of auroral events from color image data if spectral sensitivity data for the total optics (i.e., an objective lens and a CCD camera) obtained by pre-calibration are available (Sigernes et al 2008). Unfortunately, no calibration data were available for the total optics used in the present study (see Table 1).…”

“…This implies that even a familiar imaging device, such as a commercial digital camera, can be used for detecting low-latitude auroral events, if a fast lens and a long exposure are employed. In some recent studies, color digital cameras have already been applied to the scientific observations of auroras in the polar region (Sigernes et al 2008;Kataoka et al 2015). It is even possible to construct a network of automated digital cameras with a data logging system for monitoring low-latitude auroras in a wide area, at a low cost of running.…”

Auroral spectral estimation with wide-band color mosaic CCDs

“…This means that, in contrast to Sigernes et al (2008Sigernes et al ( , 2009, our results cannot be used for absolute sensitivity (i.e., counts/Rayleigh) comparisons between different cameras. They do, however, provide simultaneous self-consistent results for all color channels on each CCD.…”

“…Partamies et al (2007) present a comparison of wide-band color mosaic imager and narrowband photometer observations, Sigernes et al (2008Sigernes et al ( , 2009 provide absolute spectral calibration of several different DSLR (digital single-lens reflex) cameras, and Partamies et al (2012) apply tomography to color mosaic images.…”

A new method of measuring aerosol optical properties from digital twilight photographs

“…This paper briefly describes the methods. The experiment setup is described in detail in Sigernes et al (2008). The camera and spectroradiometer detect narrowband (i) light in visible wavelengths of 380-740 nm at intervals of 5 nm, which are separated by a grating monochromator, obtaining camera RAW counts u k,i and the corresponding spectral radiance I i (λ).…”