Telluric Absorption

Telluric contamination occurs to astronomical spectra due to the Earth's Atmosphere. Telluric (syn. terrestrial) absorption is simply the absorption of electromagnetic wavelengths by atmospheric molecules. The primary causes of telluric absorption are O₂ and O₃ which absorb strongly in the near-UV region and H₂O which absorbs strongly in IR frequencies. As such, it's an important factor to consider in IR astronomy.

Obviously, absorption and emission spectra from the atmosphere (particularly in the visible and near-IR regions) interferes with astronomical spectra. Thus such spectra must be corrected for any telluric contamination using a Telluric Correction Function. This is made by dividing a model spectrum by an observation of an astronomical photometric standard star. Observations at each wavelength point are then multiplied by this function.

Unfortunately, while this method can restore the correct shape of a spectrum, it can result in high levels of noise in affected areas.

The Earth's atmosphere is opaque to many wavelengths outside the IR region too. The broad spectrum transmission of the atmosphere is shown in this diagram.