ATM Predictions for Atmospheric Opacity
Joaquín SG. 2020/10/12
We have developed an ASTRO procedure that plots the zenith opacity (Tau) at the IRAMm 30m site versus the frequency, for a given amount of precipitated water vapor (Pwv). The opacity is estimated using the ATM2009 atmospheric model included in ASTRO, the same model used for calibrating the data with MIRA and MRTCAL. So far, we use the default sea level pressure and ambient temperature, since they have not a big effect on the result under typical conditions: Hence, slight differences with the calibration results could be found. This procedure could be useful in order to plan the frequency setup strategy as a function of the weather conditions, or for interpreting baseband features related to atmospheric components.
Below we can see two output examples covering all the EMIR bands, one for 1.5 mm pwv, and the other for 7 mm pwv:
Together with the total zenith opacity (in black), we represent the contribution to the opacity of the water lines (in blue, the only component that changes with the amount of water vapor), and the oxygen and other species isotopes (in green). Overlaid we also plot the EMIR bands coverage.
For executing this program, we have to connect to the operator account (ask the operator for the passw) and run:
$ slogin -X operator@mrt-lx3 $ cd jq_astro/atmo-tau $ astro @ atmo_test.astro taumax fmin fmax pwv
taumax = maximum opacity plotted
fmin, fmax = minimum and maximum frequencies plotted (in GHz)
pwv = amount of precipitated water vapor (in mm).
Hence, as an example, there are the results for:
$ astro @ atmo_test.astro 0.5 100 125 1
... an example that we can use for explaining the frequent question "Why I have very much noise in my 3 mm band with no so much water vapor".
Or the following one:
$ astro @ atmo_test.astro 0.7 233 238 6
...where we can inspect some of the several atmospheric components that could show up in our spectra if the atmosphere effects are not well corrected, as in the example on the right.