Gravity wave modulated airglow observation from spacecraft

During the STS-75 shuttle mission a special purpose electronic imager viewed the atmosphere below the shuttle orbiter in the wake direction with the objective of imaging gravity wave induced airglow modulation. A continuous sequence of images was taken with a picture repetition rate of 4 per second. A narrow band (3nm) filter was used to select the O 2 atmospheric 0,0 band at 762 nm. The effectiveness of the filter was demonstrated by comparing images of tropospheric clouds with and without filter under full moon conditions. The test showed that the atmospheric O 2 absorption combined with the filter was effective in suppressing intensity variations of the bright full moon illuminated clouds and any other earth albedo. Therefore under conditions of low moonlight the filtered images truly represented the modulation of the airglow intensity uncontaminated by earthshine. Longer sequences of airglow data were processed to compensate for spacecraft motion and to dynamically integrate the signal into a latitude and longitude map of airglow modulations. Because of the intrinsic low pass filtering of the slant view observation geometry preferential enhancement of the higher frequencies was needed to bring out waves in the wavelength range of <200 km. Although the shuttle based limited operation of the imager did not permit to make large area global surveys, the results demonstrated that spacecraft based imaging of the airglow on a long duration flight would produce a global data set much needed for the understanding of Mesosphere Lower Thermosphere dynamics.