Symbol z

The passage around this formula

where $I_0(\lambda)$ is the incident spectrum, $\tau(\lambda)$ the wavelength-dependent optical depth, n(z) the number density of an absorbing species at altitude z , and $\sigma(\lambda, z)$ its absorption cross-section, which itself depends on temperature and pressure. The instrument records I($\lambda$) ; the abundance profile n(z) is recovered by inverting this relation against a model atmosphere, which means every composition result carries the assumptions of that model — cloud and haze opacity, temperature structure, and the line-list data used for $\sigma(\lambda,z)$ — bundled in with the raw spectral measurement.

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