Abstract

The rocketborne SPIRE (SPectral InfraRed Experiment) probe was launched from Poker Flat Research Range, Alaska, on Sept 28, 1977 to measure infrared atmospheric emission from the earth’s limb.¹ The payload included two coaligned, telescoped, circular-variable-filter (CVF) spectrometers. The short-wavelength spectrometer, cooled to 77° K, covered the spectral region between 1.4μm and 7.0μm while the long-wavelength instrument, cooled to 4° K, made measurements between 9.0μm and 16.5μm. The payload reached an altitude of 285 km. The earthlimb was continuously spatially scanned from hard earth to local horizontal at 0.5 deg/sec while taking a spectrum at 2 scans/sec. The spectrometers measured the earthlimb emission during 12 vertical spatial scans at different azimuths. In doing so the emission was measured from the night (scan 8), terminator (scans 1 through 7), and daylit (scans 9 through 12) sectors of the earthlimb. For a given tangent height day scans correspond to different solar elevation angles. The emission from the a ¹Δ_g (v′=0) --> x³Σ_g (v″=1) transition of O₂ at 1.58μm is observed during the day scans only and increases in radiance with solar elevation angle (Figure 1). This shows that the only important process lending to the production of O₂(¹Δ_g) is the photodissociation of ozone. The emissions from ozone at 9.8μm (ν₃ band), as well as the 4.8μm v₁ + v₃ combination band, are measured during both day and night (Figure 2). Around 80 km tangent height, the daytime 9.6μm emission is smaller than the nighttime value by a factor of about 5, because of the decreased daytime ozone density due to photodissociation. Below 50 km tangent height the daytime and nighttime emissions do not show a significant variation, in spite of the fact that some daytime ozone is photodissociated to O₂(¹Δ_g) which is observed at 1.58μm. The observed emissions from ozone and O₂(¹Δg) state are discussed in terms of modelled time-dependent ozone concentrations along the line-of-sight.

© 1983 Optical Society of America