Impulse response analysis of 5577Å emissions

A method of time series analysis termed impulse response estimation is described. The method is applied to simultaneous ground based photometry measurements of the N₂⁺ ING band at 4278Å and the 5577Å line emission in order to estimate the response in 5577Å to a discrete impulse in excitation rate.From these impulse response estimates the contribution from indirect excitation processes to the O(¹S) state is estimated to be of the order of 80% and the lifetime of the associated intermediate species to be approximately 0.1 s. Effective lifetimes for the O(¹S) excited state are obtained in the range 0.49–0.86 s with a distribution showing a sharp cut-off at 0.8 s and a mean of 0.71 s.