This document describes the full set of BARREL Balloon Optical Photometer instruments and allows for search aggregation of Optical Photometer information from all balloons.

Objective: To detect the flux of visible Light at wavelengths near 486.1 nm during a relativistic electron precipitation event. This will determine whether there are protons accompanying the precipitating electrons. Emissions near 486.1 nm are a signature of precipitating protons. Correlated proton and relativistic electron precipitation would support scattering by electromagnetic ion cyclotron, EMIC, waves as the precipitation mechanism. How it works: The photons are collected through a collimator tube that restricts the field of view to a cone approximately 5° full-width angle, tilted at 35° from the zenith. A 2.5 nm wide Hβ filter is mounted near the base of the collimator. Each photon incident on the 5 cm diameter photomultiplier tube results in the generation of a charge pulse. These pulses then go into a charge-sensitive pre-amplifier, discriminator, and shaping electronics, producing a TTL pulse for each incident photon. By counting the number of pulses, the flux of the precipitating protons can be determined. This paragraph was adapted in part from the Millan et al. (2013) Spase Sci. Rev. publication listed in the fifth Information URL below.