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IR Transmission Spectra

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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.

Mauna Kea Sky Transmission (0.9-5.6 microns)
air mass water vapor column
1.0mm 1.6mm 3.0mm 5.0mm
1.0 mktrans_zm_10_10.dat mktrans_zm_16_10.dat mktrans_zm_30_10.dat mktrans_zm_50_10.dat
1.5 mktrans_zm_10_15.dat mktrans_zm_16_15.dat mktrans_zm_30_15.dat mktrans_zm_50_15.dat
2.0 mktrans_zm_10_20.dat mktrans_zm_16_20.dat mktrans_zm_30_20.dat mktrans_zm_50_20.dat

 

Cerro Pachon Sky Transmission (0.9-5.6 microns)
air mass water vapor column
2.3mm 4.3mm 7.6mm 10.0mm
1.0 cptrans_zm_23_10.dat cptrans_zm_43_10.dat cptrans_zm_76_10.dat cptrans_zm_100_10.dat
1.5 cptrans_zm_23_15.dat cptrans_zm_43_15.dat cptrans_zm_76_15.dat cptrans_zm_100_15.dat
2.0 cptrans_zm_23_20.dat cptrans_zm_43_20.dat cptrans_zm_76_20.dat cptrans_zm_100_20.dat

 


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.

Mauna Kea Sky Transmission (7-26 microns)
air mass water vapor column
1.0mm 1.6mm 3.0mm 5.0mm
1.0 mktrans_nq_10_10.dat mktrans_nq_16_10.dat mktrans_nq_30_10.dat mktrans_nq_50_10.dat
1.5 mktrans_nq_10_15.dat mktrans_nq_16_15.dat mktrans_nq_30_15.dat mktrans_nq_50_15.dat
2.0 mktrans_nq_10_20.dat mktrans_nq_16_20.dat mktrans_nq_30_20.dat mktrans_nq_50_20.dat

 

Cerro Pachon Sky Transmission (7-26 microns)
air mass water vapor column
2.3mm 4.3mm 7.6mm 10.0mm
1.0 cptrans_nq_23_10.dat cptrans_nq_43_10.dat cptrans_nq_76_10.dat cptrans_nq_100_10.dat
1.5 cptrans_nq_23_15.dat cptrans_nq_43_15.dat cptrans_nq_76_15.dat cptrans_nq_100_15.dat
2.0 cptrans_nq_23_20.dat cptrans_nq_43_20.dat cptrans_nq_76_20.dat cptrans_nq_100_20.dat

 

changing AM changing AM changing AM changing AM changing H2O changing H2O changing H2O changing H2O changing AM changing AM changing AM changing AM changing H2O changing H2O changing H2O changing H2O