Comparative Plots of CNA and Auroral Emission
Described below are the comparative plots of cosmic noise absorption (CNA) observed by an imaging riometer of the National Institute of Information and Communications Technology and panchromatic auroral emission observed simultaneously by an all-sky camera of the University of Alaska.
1. Observation/Data Processing
The NICT imaging riometer observes the spatial distribution of the cosmic noise absorption (CNA) every second with high spatial resolution by receiving the cosmic radio noise at 38.2MHz, using a 256-element array antenna as well as a phasing system to change the antenna beam directions successively. The following figure shows the horizontal projection of -3dB contours of the main beams at the 90 km altitude.
The Geophysical Institute, University of Alaska Fairbanks (GI/UAF) observes auroras using a filterless all-sky camera at the Poker Flat Research Range of the University of Alaska, where the imaging riometer is located. The observed panchromatic all-sky auroral image data are compiled to JPEG auroral image data per minute and released to the public on the internet (http://gedds.pfrr.alaska.edu/).
The comparative plots use the above JPEG images after the following adjustments are made. The SIT camera used for the all-sky camera has a function to compress the observed brightness (gamma correction) to increase the dynamic range of the measurement. Therefore, we first remove the gamma correction to recover the brightness that would be proportional to the actual auroral intensities, then adjust the spatial resolution and coverage of the image to match the CNA image by rebinning process. The reformatted auroral images are compared with the CNA images observed simultaneously.
Auroral emission data per minute and corresponding CNA data can be compared by the following two display methods.
2. Time-trend (UT 1 - 18 hours )
The following panel shows (beginning at the top):
- Temporal variation in the east-west row of auroral optical intensity.
- Temporal variation in the east-west row of CNA.
- Temporal variation in the south-north column of auroral optical intensity.
- Temporal variation in the south-north column of CNA.
The east-west row and the south-north column mean the east-west row of 16 beams (open triangles) and the south-north column of 16 beams (open circles) marked in the figure of antenna beam patterns, respectively. The auroral optical intensity is displayed by the square root of the intensity using arbitrary scale color codes.
The following figure compares the two-dimensional auroral optical intensity images with CNA images per minute. Each panel shows an all-sky (fish-eye) image. Images are aligned according to observation time, with images for more recent data at the bottom. Three columns show (starting from the left):
- Filterless panchromatic auroral images for a range 90 degrees from the zenith.
- The auroral images reformatted from the above auroral images to the same spatial resolution and coverage as those of CNA for a range 70 degrees from the zenith.
- Two-dimensional CNA images for a range 70 degrees from the zenith.
These comparative plots were developed as part of the cooperative research project between the National Institute of Information and Communications Technology (NICT) and the Geophysical Institute, University of Alaska Fairbanks (GI/UAF).
The filterless panchromatic all-sky camera data were provided by Prof. Hans C. Stenbaek-Nielsen of GI/UAF.
If you would like to use the comparative plots for research, publication, or presentation, or if you have any comments or questions, please contact:
International Arctic Environment Research Project Group
Applied Research and Standards Division
Independent Administrative Institution
National Institute of Information and Communications Technology
4-2-1 Nukui-kita, Koganei, Tokyo 184-8795, Japan.
[Comparative Plots of CNA and Auroral Emission]
[About Imaging Riometer]