Hyperspectral all-sky imaging of auroras.

A prototype auroral hyperspectral all-sky camera has been constructed and tested. It uses electro-optical tunable filters to image the night sky as a function of wavelength throughout the visible spectrum with no moving mechanical parts. The core optical system includes a new high power all-sky lens with F-number equal to f/1.1. The camera has been tested at the Kjell Henriksen Observatory (KHO) during the auroral season of 2011/2012. It detects all sub classes of aurora above ~½ of the sub visual 1kR green intensity threshold at an exposure time of only one second. Supervised classification of the hyperspectral data shows promise as a new method to process and identify auroral forms.

The absolute sensitivity of digital colour cameras.

A new and improved method to obtain the average spectral pixel responsivity and the quantum efficiency of Digital Single Lens Reflex (DSLR) cameras is outlined. Two semi-professional cameras, the Nikon D300 and the Canon 40D, are evaluated. The cameras red, green and blue pixel responsivities and quantum efficiency are retrieved by illuminating an integrating sphere with a wavelength tunable monochromator. 31 intensity calibrated monochromatic spectral lines from 4000 to 7000 A, with a bandpass of approximately 12 A, were used as a library to solve the main equations of observation for the cameras. Both cameras have peak sensitivity in the blue and minimum sensitivity in the red. The Canon 40D has blue and green channel sensitivity close to the Nikon D300. The Canon red channel has half the sensitivity of the Nikon camera.

Sensitivity calibration of digital colour cameras for auroral imaging.

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.

Diel vertical migration of Arctic zooplankton during the polar night.

High-latitude environments show extreme seasonal variation in physical and biological variables. The classic paradigm of Arctic marine ecosystems holds that most biological processes slow down or cease during the polar night. One key process that is generally assumed to cease during winter is diel vertical migration (DVM) of zooplankton. DVM constitutes the largest synchronized movement of biomass on the planet, and is of paramount importance for marine ecosystem function and carbon cycling. Here we present acoustic data that demonstrate a synchronized DVM behaviour of zooplankton that continues throughout the Arctic winter, in both open and ice-covered waters. We argue that even during the polar night, DVM is regulated by diel variations in solar and lunar illumination, which are at intensities far below the threshold of human perception. We also demonstrate that winter DVM is stronger in open waters compared with ice-covered waters. This suggests that the biologically mediated vertical flux of carbon will increase if there is a continued retreat of the Arctic winter sea ice cover.