09:00 〜 10:30
[PPS04-P14] Exploration of planetary lightning with two-band simultaneous observing by a ground-based telescope
キーワード：金星、雷、地上望遠鏡
The solar system's explorations have revealed lightning's existence on Earth and Jupiter. Many night-side optical imaging and radio wave observation by spacecraft has detected jovian lightning. LAC on board AKATSUKI detected compelling evidence of Venusian lightning existence (Takahashi et al., 2020). The monitoring of lightning is one of the methods for understanding atmospheric dynamics. Many small-scale eddies driving the zonal jet receive their energy from moist convection that generates jovian lightning (Gierash et al., 2000; Ingersoll et al., 2000). The moist convection would correlate with planetary lightning the same as on Earth. Observing global planetary lightning activity and distribution can provide information on atmospheric activity to understand the dynamics.
We have developed the two-band simultaneous photometer, Planetary lightning Detector (PLD). PLD is mounted on a 1.6-m Pirka ground-based telescope. It observes the optical Jovian and Venusian lightning flashes using two high-speed photon-counting sensors simultaneously to obtain the light curve of lightning optical flashes. The sampling rate is over 20 s-1. We use a beamsplitter to separate the incident light from the telescope into two photomultiplier tubes. One sensor observes the background level simultaneously with another photomultiplier tube with a broadband filter to distinguish between the lightning and variation of the planet disk's dayside brightness or sky. The first sensor observes the wavelength of Jovian or Venusian lightning. The PLD is equipped with narrowband filters of 777 nm (FWHM = 1nm) for Venusian lightning and 656 nm (FWHM = 1nm) for Jovian lightning (Borucki et al., 1996). The wavelength of the second sensor is 700 nm (FWHM = 10 nm). We have observed Venus and Jupiter since 2021. We analyze the data with wavelet denoising to remove the pulses caused by cosmic rays and shot noise. The triggered waveform recorded by the first sensor, which peak count is larger than four sigmas of the noise, is compared with the second PMT's waveform. If the correlate coefficient is small, we consider that the candidate signal has been detected. We compare the distribution of triggered candidate signals' peak value on a lightning wavelength with the distribution in background wavelength to exclude the false signal generated by noise. In the case of Venus, several possible pulses are found. We need to discuss statistically and precisely, such as signal-to-noise ratio, to conclude the detection of the lightning by increasing the total observation time and comparing the other observation or simulation results.
We have developed the two-band simultaneous photometer, Planetary lightning Detector (PLD). PLD is mounted on a 1.6-m Pirka ground-based telescope. It observes the optical Jovian and Venusian lightning flashes using two high-speed photon-counting sensors simultaneously to obtain the light curve of lightning optical flashes. The sampling rate is over 20 s-1. We use a beamsplitter to separate the incident light from the telescope into two photomultiplier tubes. One sensor observes the background level simultaneously with another photomultiplier tube with a broadband filter to distinguish between the lightning and variation of the planet disk's dayside brightness or sky. The first sensor observes the wavelength of Jovian or Venusian lightning. The PLD is equipped with narrowband filters of 777 nm (FWHM = 1nm) for Venusian lightning and 656 nm (FWHM = 1nm) for Jovian lightning (Borucki et al., 1996). The wavelength of the second sensor is 700 nm (FWHM = 10 nm). We have observed Venus and Jupiter since 2021. We analyze the data with wavelet denoising to remove the pulses caused by cosmic rays and shot noise. The triggered waveform recorded by the first sensor, which peak count is larger than four sigmas of the noise, is compared with the second PMT's waveform. If the correlate coefficient is small, we consider that the candidate signal has been detected. We compare the distribution of triggered candidate signals' peak value on a lightning wavelength with the distribution in background wavelength to exclude the false signal generated by noise. In the case of Venus, several possible pulses are found. We need to discuss statistically and precisely, such as signal-to-noise ratio, to conclude the detection of the lightning by increasing the total observation time and comparing the other observation or simulation results.