Limb-tangent measurements

Fig. 8.2.4 Geometry for limb-tangent measurements. A ray is depicted with tangent height Zo for a planet with radius R. Distance from the tangent point to an arbitrary point along the ray path is denoted by s, and z is the height of the point above the planetary surface.

Figure Bl.4.1. Top schematic illustration of the observing geometry used for limb sounding of the Earth s atmosphere. Bottom illustrative stratospheric OH emission spectra acquired by the SAO FIRS-2 far-infiared balloon-borne FTS in autumn 1989. The spectra are from a range of tangent heights h = tangent height in the drawing), increasing toward the bottom, where the data are represented by solid curves nonlinear least-square fits to the measurements, based on a combination of laboratory data, the physical structure of the stratosphere and a detailed radiative transfer calculation, are included as dashed curves. The OH lines are Fj 7/2 ...

Thermal emission data acquired in the limb viewing mode have also been used to obtain composition measurements in the terrestrial atmosphere. The geometry is the same as that given in Fig. 8.2.4, only in this case thermal emission from the atmosphere itself is observed rather than transmitted solar radiation. The radiance measured by the spacecraft sensor along a ray path with tangent height h can be written... 

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