Collision-induced absorption of solar radiation in the atmosphere by molecular oxygen at 1.27 μm:: Field observations and model calculations

Significant uncertainties in the spectroscopy of collision-induced absorption by oxygen have a limited knowledge of the contribution made by molecular oxygen to the shortwave radiation budget of the Earth's atmosphere. As part of a programme of high-resolution (up to 0.02 cm(-1)) studies of atmospheric short-wave transmittance under clear-sky conditions, field measurements in the region of the 1.27 mum (7874 cm(-1)) oxygen absorption are reported here. Measurements of direct solar radiation incident at the ground were made using a ground-based Fourier transform spectrometer at the Rutherford Appleton Laboratory (51.6 degreesN, 1.3 degreesW, altitude 135 m). Model calculations of the atmospheric transmittance in the region of the broad continuum feature underlying the a(1)Delta (g) <-- X(3)Sigma (-)(g) (0,0) band of oxygen were made using absorption cross sections derived from recent laboratory measurements. The agreement between the field observations and the model calculations validates a simple model developed to describe the atmospheric oxygen continuum absorption centered at 1.27 mum for atmospheric short-wave radiative transfer and remote sensing applications.