The atmosphere above Llano de Chajnantor

At the APEX site on Llano de Chajnantor the amount of precipitable water vapour (PWV) is typically 0.5 mm but can in exceptional cases fall below 0.1 mm. The image below shows the atmospheric transmission between 250 GHz and 1 THz for different PWV values.

In order to prepare the observations and make time estimates for different atmospheric conditions the following atmospheric transmission calculator can be used. It is based on the am program developed by the Submillimeter Receiver Lab at the Smithsonian Astrophysical Observatory. The calculator covers the frequency range 212 to 1588 GHz.

Links

• The am transmission model
• ALMA Memo Series
• See in particular memos 521, 512, 382, and 187