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IR Transmission Spectra

The infrared spectra of the atmospheric transmission above Mauna Kea and Cerro Pachon that are used in the Integration Time Calculators have been generated using the ATRAN modelling software (Lord, S.D. 1992, NASA Technical Memor. 103957) and are presented separately for the near-IR and mid-IR. Ascii data files of these spectra are available below.

Near-IR

Overview spectra for Mauna Kea are presented below for the wavelength ranges 0.9 - 2.7 and 2.7 - 5.6µm with a water vapour column of 1.6mm and an air mass of 1.0. To assess appropriate observing condition constraints, the effects of water vapour and air mass can be examined on an expanded wavelength scale by clicking on the upper (red) or lower (blue) bars in the images. Doing so will show examples corresponding to (blue bar) 1.0 and 3.0mm precipitable water vapour at AM=1.0 and (red bar) AM=1.0 and 2.0 at 1.0mm H2O.

0.9 - 2.7um transmission

2.7 - 5.6um transmission

If image maps are not supported by your browser the expanded spectra may be displayed by selecting the appropriate wavelength range:

AM=1.0 and 2.0 at 1.0mm precipitable water vapour: 0.9 - 1.4, 1.4 - 1.9, 1.9 - 2.3, 2.3 - 2.7, 2.7 - 3.3, 3.3 - 4.3, 4.3 - 5.0 and 5.0 - 5.6µm
1.0 and 3.0mm H2O at AM=1.0: 0.9 - 1.4, 1.4 - 1.9, 1.9 - 2.3, 2.3 - 2.7, 2.7 - 3.3, 3.3 - 4.3, 4.3 - 5.0 and 5.0 - 5.6µm

The raw data files generated by ATRAN for 0.9-5.6 microns are available via the following table. Any use of these data should reference Lord, S. D., 1992, NASA Technical Memorandum 103957, and acknowledge Gemini Observatory. The models are in ASCII two-column format: (a) wavelength with a sampling of 0.00002µm and a resolution of 0.0004µm (0.04nm) and (b) transmission.(In most browsers, hold down the shift key when clicking to save the data to a file). The numbers in the titles of the files are 10X the water vapor in mm and 10X the airmass.

 

 


Mid-IR

The atmospheric absorption in the 10µm-window is affected mainly by CO2, CH4, H2O and O3. The principal effect of an increase in the water vapour column above the site is an overall reduction of transmission, and consequent increase in the sky background, as shown by the curves for 1.0 and 3.0mm of H2O in the following figure:

10um transmission

The far greater atmospheric absorption in the 20µm window is dominated by water vapour, as shown by the curves for 1.0 and 3.0mm of H2O in the following figure:

10um transmission

The raw data files generated by ATRAN for 7-26 microns are available via the following tables. Use of these data should reference Lord (1992) and acknowledge Gemini Observatory. The models are in ASCII two-column format: (a) wavelength with a sampling of 0.0001µm and a resolution of 0.0002µm (0.2nm) for Mauna Kea and 0.002µm and 0.004µm (4nm) for Cerro Pachon and (b) transmission.(In most browsers, hold down the shift key when clicking to save the data to a file). The numbers in the titles of the files are 10X the water vapor in mm and 10X the airmass.

 

 

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