Electromagnetic ion cyclotron (EMIC) waves potentially cause precipitation loss of relativistic electrons from the outer radiation belt to the atmosphere through pitch angle scattering. However, the direct evidence of each EMIC wave element and burst of precipitation has not yet been reported. Here we show the temporal and spatial correspondence of the EMIC waves with relativistic electron precipitation (REP) during the geomagnetic storm of 27 March 2017. EMIC waves were observed at several stations in North America. REP was detected as a decrease of subionospheric radio amplitudes observed at Athabasca, Canada. When isolated proton aurora, observed at Athabasca, appeared on the radio propagation path, we found a good correspondence between the temporal variations of REP and EMIC waves, and REP preceded EMIC waves by 24 s. This time lag is consistent with the travel time difference between relativistic electrons and EMIC waves from the magnetospheric equatorial plane to the ionosphere.

A hyperspectral (HS) imager is more effective than a multispectral (MS) imager in mineral discrimination, but spatial coverage of HS images is limited in comparison to that of MS images. Thus Kruse and Perry have proposed a method that uses coincident HS imaging and MS imaging data to extend mineral mapping to larger areas. We propose a method modified from the Kruse and Perry's (K&P) method. Though the K&P method derives the MS-based endmember spectra by weighting the HS-based endmember spectra with the response functions of the MS sensor bands, the proposed method obtains the MS-based endmember spectra from surface reflectance spectra of the MS pixels at the same positions with the HS pixels selected as the HS-based endmembers in the overlapping area. The validation study using airborne visible/infrared imaging spectrometer and advanced spaceborne thermal emission and reflection radiometer images over Cuprite and Goldfield areas, Nevada, USA, demonstrates that the proposed method is more robust against spectral inconsistency between the HS-and the MS-images caused by calibration and/or atmospheric correction errors than the K&P method, though the proposed method is more sensitive to co-registration errors between the HS-and the MS-images than the K&P method. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Recent studies suggest that electrons with energies up to several hundred keV precipitate into the atmosphere associated with pulsating aurora (PsA). It is debated the highest energy of precipitating electrons associated with PsA. Here we report for the first time that the energy extends to relativistic energies. PsA was observed by THEMIS all‐sky imagers during a substorm that occurred on 27 March 2017. Energetic electron precipitation was detected by very low frequency subionospheric propagation. We found similar time variations between the auroral intensity and perturbation of the received radio signal intensity when the PsA occurred on the radio path. The perturbation showed a short recovery time of ~2 s. The recovery time indicates relaxation from ionospheric modification due to energetic electron precipitation and depends on the stopping altitude of the electrons. The recovery time required a stopping altitude of 50–60 km and indicates that the PsA is accompanied by relativistic electron precipitation.

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We investigated the modulation of D-region signatures due to ultra-low-frequency (ULF) waves using very-lowfrequency/low-frequency (VLF/LF) radio propagation. Three transmitters from the United States (NLK, NDK, and WWVB) were received at Athabasca (ATHA), Canada. We observed oscillations in intensities and phases on the NDK-ATHA and WWVB-ATHA paths with a period of 3 to 4 minutes, associated with ULF waves during a substorm at 05:25-05:45 UT on 4 June, 2017. This is the fi rst observational report showing clear VLF/LF oscillations in the ULF range. The ground-based H-component magneticfi eld variations and Doppler velocity observed by the SuperDARN HF radars showed the same periodic changes as seen in the VLF/LF oscillations, suggesting that energetic electron precipitation (EEP) over the WWVB-ATHA and NDK-ATHA paths was modulated by the ULF waves. Based on ground-based magnetic-fi eld data, we concluded that the ULF wave corresponded to the Pi2 pulsations associated with the substorm, because the propagation direction of the wave was westward (66.4 km/s) from the pre-midnight sector, the magnetic variations at low latitudes were inphase over wide longitudes, and the magnetic variations at ATHA slightly preceded those at low latitudes. A rising-tone chorus emission was observed in the frequency range of 5 kHz to 6 kHz at ATHA during the VLF/LF oscillations. Pitch-angle diff usion by the whistler-mode chorus wave is one possible mechanism accounting for the energetic electron precipitation.