The BOLT system records the electromagnetic waveforms in atmospheric electricity sign convention, which means that positive electric field changes deflect upward. The recorded waveforms allow detailed analysis of lightning discharge processes. Once a detected signal exceeds a threshold, the E field change waveforms are continuously recorded for 200 ms with a 100 ms pretrigger. The electric field antenna bandwidth is broad from 500 Hz to 500 kHz. The mean distance between stations is approximately 20 km. The system provides the 3-D location of lightning discharges using the time-of-arrival location technique. The BOLT network, which consists of 13 LF sensors installed in the Kansai area in Japan as shown in Figure 1, was established in 2013. The maximum duration is 512 ms for each triggered event. The optical waveform is recorded with a temporal resolution of 50 µs and digitalized on 12 bits per sample. Consequently, the observation range of PH4 is 400 km from the nadir point at the ground level when the altitude of the ISS is assumed to be 410 km.
The PH4 has a conical field of view (FOV) of 86.8°.
Compared to other photometers, PH4 data are immune to the effect of atmospheric transmission. When the light source is located at 8 km altitude, the atmospheric transmittance is more than 90% in the wavelength band of the PH4 optical filters. The PH4 has a wide band wavelength filter from 599 to 900 nm. In this paper, to discuss the relationship between the lightning discharge process and light curve data, PH4 data are used. The PHs consist of six spectrophotometers with six different wavelengths, called PH1–PH6, that obtain light curve data for measuring the absolute intensity of lightning and TLE emissions. 2 Instrumentation 2.1 Spectrophotometer on GLIMS In addition, the relationship between the absolute optical intensity and the peak current of return strokes of natural lightning is discussed. Particularly, the relationship between the optical intensity of lightning discharges recorded by the PHs and the lightning discharge process is defined. In this paper, we compare optical lightning data collected with PHs on the ISS with electromagnetic waveforms in the LF band acquired with the ground-based BOLT LF lightning locating system and discuss the detailed characteristics of different types of lightning discharges. It consists of 13 sites in the Osaka area in Japan and has been operational since June 2013. indicated a correlation between the current moment waveform and charge moment change, when a sprite is generated by lightning from optical measurements.īOLT (Broadband Observation network for Lightning and Thunderstorms) is capable of locating lightning discharges three-dimensional (3D) with a low-frequency (LF) band. The system detects TLEs in the Earth's limb direction. The Imager of Sprites and Upper Atmospheric Lightning (ISUAL) on the FORMOSAT-2 satellite has also been used to observe TLEs and lightning emissions. showed that the pulse widths for return strokes, detected by the National Lightning Detection Network, are inversely proportional to pulse peak power. Using space- and ground-based measurements, Kirkland et al. The photodiode and VHF radio receiver on the Fast On-orbit Recording of Transient Events (FORTE) satellite has simultaneously observed optical emissions and VHF radiation, respectively. One way of obtaining optical lightning observations is by satellite. These studies mainly focused on the lightning discharge process of the return strokes. investigated the relationship between rise times of current and light using laboratory experiments or rocket-triggered lightning observations. Based on rocket-triggered lightning observations, there is a correlation between peak current and peak optical intensity in the return strokes. Several ground-based studies have focused on the relationship between optical and electrical observations of lightning. reported observation results for optical lightning and TLEs using optical sensors (e.g., PHs and LSI). The PHs work as a trigger system for the other observation instruments, because they provide light emission timing from lightning discharges at high temporal resolution.
A very low frequency receiver and a very high frequency (VHF) interferometer are used to detect the whistler signals and a VHF band radiation from lightning. The lightning and sprite imager (LSI) and six photometers (PHs) provide us the optical intensity and the location of the optical lightning emission, respectively. Four types of instruments installed on the International Space Station (ISS) are used to achieve the mission. The Global Lightning and Sprite Measurements (GLIMS) mission for observations of lightning and transient luminous events (TLEs) was carried out from 2012 to 2015.
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