Opacity Curves at the HHT

To get a sense of what conditions are required for a particular project, we present some atmospheric transmission plots for various tau(225 GHz) at the HHT.

  1. Tau(225 GHz) = 0.050
  2. Tau(225 GHz) = 0.075
  3. Tau(225 GHz) = 0.100
  4. Tau(225 GHz) = 0.125
  5. Tau(225 GHz) = 0.150
  6. Tau(225 GHz) = 0.200
  7. Tau(225 GHz) = 0.250
  8. Tau(225 GHz) = 0.300

To estimate the opacity in the different frequency bands accessible at the HHT, you can use the following table:

Opacity for some lines of interest
Spectral Line Frequency (GHz) opacity (tau 225 GHz)
12CO 2-1230 1 *
12CO 3-23454.4 *
12CO 4-346024.*
[C I]49236 *
12CO 6-569134 *
[C I]80940 *

Thus, a tau(225 GHz) of 0.05 corresponds to a tau(809GHz) of 2, or a tranmission of 0.14 at an airmass of 1.

These numbers are estimates only, since we have not yet calibrated the taumeter 225 GHz values with the theoretical values produced by the atmospheric transmission programs we use to produce the plots.

Last Changed: September 16, 1997 by Harold M. Butner