The Boltzmann Vibrational Temperature of N₂ (B³Π_g) Derived From ISUAL Imager Multiband Measurements of Transient Luminous Events

One of the main challenges for the observation of a transient luminous event (TLE) is to observe TLEs in different emission bands. Here, we show TLEs recorded using the ISUAL 427.8 nm, 630 nm, N₂ 1P (623–750 nm) and 762-nm-filtered imager, and we analyze the 630-nm-filtered, N₂ 1P-filtered, and 762-nm-filtered images of TLEs for estimating the N₂ (B³Π_g) Boltzmann vibrational temperature in comparison with the theoretical N₂ 1P spectrum. For ISUAL recorded sprites, the average brightness of N₂ 1P (I_1p), 762 nm (I₇₆₂), and 630 nm (I₆₃₀) emission was 2.3, 0.6, and 0.02 MR. The N₂ (B³Π_g) vibrational temperatures (T_v) was estimated to be 2800 K, 3200 K, and 4300 K for multiband emission ratios of I₆₃₀/I_1p, I₆₃₀/I₇₆₂, and I₇₆₂/I_1p. For observed elves, the average brightness I_1p, I₇₆₂, and I₆₃₀ were 170, 50, and 3 kR. The estimated T_v values were 3700 K, 3700 K, and 3800 K for ratios I₆₃₀/I_1p, I₆₃₀/I₇₆₂, and I₇₆₂/I_1p. For observed gigantic jets, the derived T_v values were 3000–5000 K for a ratio I₇₆₂/I_1p. Through N₂ (B³Π_g) T_v analyses from emission ratios of ISUAL multiband observation, we derived the N₂ (B³Π_g) vibrational temperature that ranges between 3000 and 5000 K or higher in TLEs. Accuracy and variations of derived N₂ (B³Π_g) T_v are also discussed while relative population of vibrational levels in the Boltzmann equilibrium are also compared with past spectra observation.