2:45 PM - 3:00 PM
[PEM12-15] Spectroscopic and imaging observations of short-wavelength infrared (1.1-1.2 µm) aurora and airglow at Longyearbyen (78.2°N, 16.0°E) coordinated with EISCAT Svalbard radar
Keywords:Aurora, Short-wavelength infrared, Spectroscopic observation, EISCAT Svalbard radar, OH airglow, twilight
Dayside aurora and polar patch are the key phenomena for understanding of the dayside magnetosphere-ionosphere coupling process. These phenomena are being monitored by ground-based optical instruments in high latitude region corresponding to polar cap and cusp, although the observations are done at limited geographic location and in limited season for avoiding strong photon intensity of sky background. Alternatively, active/passive radio remote sensing such as HF/VHF/UHF radar, GNSS and LF wave receiver are effective, but spatial and temporal resolutions by those measurements are not sufficient generally in comparison to optical measurements.
We have developed a 2-D imaging spectrograph with a fast optical system and high spectral resolutions to challenge twilight/daytime aurora measurements from the ground. It is designed for short-wavelength infrared (SWIR) wavelength from 1.1 to 1.3 microns in which sky background intensity is weaker than in visible. It covers strong auroral emissions in N2+ Meinel band (0-0) and N21st Positive bands (1-2, and 0-1). Its field-of-view (FOV) and angular resolution are 55 degrees and 0.11 degrees per pixel, respectively. If a 30-microns slit is used, spectral bandpass around 1.1 microns are 0.52 nm and 0.22 nm with two different gratings (950 lpmm and 1500 lpmm).
In a test observation, we successfully measured airglow emissions of OH (5-2), (6-3), and (7-4) bands in 1.07-1.23 microns (shown in an attached figure), and O2 IR band at 1.27 µm. With the 1500-lpmm grating and the 60-µm slit, each line in OH (5,2) band was spectrally resolved well. Rotational temperature can be estimated with 10-min resolutions and errors up to 15 K. It should be noted that peak intensity of N2+(0,0) band is about 10 times greater than that of OH (5,2) P1(3) line, and therefore we concluded that the spectrograph can detect aurora activities with sufficient time resolutions shorter than 30 seconds and allows us to investigate spatial and temporal variations associated with magnetosphere-ionosphere coupling and particle precipitations both in nightside and in dayside.
In addition to the spectrograph, we have been developing a brand-new SWIR imager focusing on aurora emissions in N2+ (0-0) band. The imager consists of a few commercial SWIR lenses for security/defense purposes, plano-convex lenses, a custom optical filter (center: 1112.76 nm, FWHM: 13.8 nm) and an InGaAs FPA (640 x 512 pixels). Total optical system is fast (F-number 1.5) and we examined that the point spread function is less than 5 pixels in full width at half maximum even near the end of the FPA. The FOV is 115 x 92 degrees and slightly wider than that of the spectrograph. The more detailed specification of the imager will be shown in this presentation.
Both the instruments are going to be installed at The Kjell Henriksen Observatory/The University Centre in Svalbard (KHO/UNIS), Longyearbyen (78.2°N, 15.6°E) by the end of 2022. Taking geographical advantage of the observatory, 24-hours continuous observations can be expected near the winter solstice. Coordinated studies with active/passive radio remote sensing, such as EISCAT Svalbard radar and VLF/LF radio wave receivers, are also planned to precisely estimate energy flux of precipitating particles associated with aurora and sub-sequent changes in electron density and neutral/ion temperatures. Possible scientific targets are as follows: dayside reconnections and wave-particle interactions monitored by aurora emissions, ion upflow seen as resonant scattering of N2+ ions, energetic particle precipitations impact on OH chemistry in the mesosphere, one-to-one correspondence between PMSE and background mesopause temperature, and atmospheric waves variability. We will also discuss the observational strategies and future collaborations.
We have developed a 2-D imaging spectrograph with a fast optical system and high spectral resolutions to challenge twilight/daytime aurora measurements from the ground. It is designed for short-wavelength infrared (SWIR) wavelength from 1.1 to 1.3 microns in which sky background intensity is weaker than in visible. It covers strong auroral emissions in N2+ Meinel band (0-0) and N21st Positive bands (1-2, and 0-1). Its field-of-view (FOV) and angular resolution are 55 degrees and 0.11 degrees per pixel, respectively. If a 30-microns slit is used, spectral bandpass around 1.1 microns are 0.52 nm and 0.22 nm with two different gratings (950 lpmm and 1500 lpmm).
In a test observation, we successfully measured airglow emissions of OH (5-2), (6-3), and (7-4) bands in 1.07-1.23 microns (shown in an attached figure), and O2 IR band at 1.27 µm. With the 1500-lpmm grating and the 60-µm slit, each line in OH (5,2) band was spectrally resolved well. Rotational temperature can be estimated with 10-min resolutions and errors up to 15 K. It should be noted that peak intensity of N2+(0,0) band is about 10 times greater than that of OH (5,2) P1(3) line, and therefore we concluded that the spectrograph can detect aurora activities with sufficient time resolutions shorter than 30 seconds and allows us to investigate spatial and temporal variations associated with magnetosphere-ionosphere coupling and particle precipitations both in nightside and in dayside.
In addition to the spectrograph, we have been developing a brand-new SWIR imager focusing on aurora emissions in N2+ (0-0) band. The imager consists of a few commercial SWIR lenses for security/defense purposes, plano-convex lenses, a custom optical filter (center: 1112.76 nm, FWHM: 13.8 nm) and an InGaAs FPA (640 x 512 pixels). Total optical system is fast (F-number 1.5) and we examined that the point spread function is less than 5 pixels in full width at half maximum even near the end of the FPA. The FOV is 115 x 92 degrees and slightly wider than that of the spectrograph. The more detailed specification of the imager will be shown in this presentation.
Both the instruments are going to be installed at The Kjell Henriksen Observatory/The University Centre in Svalbard (KHO/UNIS), Longyearbyen (78.2°N, 15.6°E) by the end of 2022. Taking geographical advantage of the observatory, 24-hours continuous observations can be expected near the winter solstice. Coordinated studies with active/passive radio remote sensing, such as EISCAT Svalbard radar and VLF/LF radio wave receivers, are also planned to precisely estimate energy flux of precipitating particles associated with aurora and sub-sequent changes in electron density and neutral/ion temperatures. Possible scientific targets are as follows: dayside reconnections and wave-particle interactions monitored by aurora emissions, ion upflow seen as resonant scattering of N2+ ions, energetic particle precipitations impact on OH chemistry in the mesosphere, one-to-one correspondence between PMSE and background mesopause temperature, and atmospheric waves variability. We will also discuss the observational strategies and future collaborations.