Excede 2 Test, an artificial auroral experiment: Ground‐based optical measurements

On April 13, 1975, a rocket‐borne electron accelerator was launched from the Poker Flat Research Range near Fairbanks, Alaska. The launch, the second effort in the Excede series of artificial auroral experiments, was designated Excede 2 test. The pulsed accelerator operated for approximately 100 s in the altitude range 106–135 km, providing a 3‐kV electron beam with maximum currents of 10 A. A rocket‐borne retarding potential analyzer indicated that the charge buildup on the electron‐emitting payload never exceeded a positive potential of 200 V. Ground‐based television systems and a dual channel telephotometer recorded the optical emissions induced in the night atmosphere by the rocket‐borne accelerator. The ground‐based telephotometer measured the time dependent emission profiles of the N2+ (B²Σu+ → X²Σg+) first negative (0‐0) band at 3914 Å and the O(¹S) emission at 5577 Å produced by the pulsed rocket‐borne electron source. The fluorescent or luminous efficiency for the production of the N2+ 1 N (0‐0) band at 3914 Å by energetic electrons at altitudes of approximately 110 km was determined to be equivalent to or greater than 3.2 × 10−3. A value of 1.1 was measured for the steady state photon emission ratio of the O(¹S) 5577‐Å to N2+ 1 N (0‐0) 3914‐Å emissions induced in the atmosphere at 110 km by the rocket‐borne electron source. The ground‐based telephotometer measurements have been corrected for the effects of atmospheric extinction by measuring the apparent stellar radiance of Vega.