Two instruments use the skydip technique to measure the atmospheric transparency at the CSO. Both instruments were originally developed at the NRAO.
One is a narrowband heterodyne radiometer tuned to 225 GHz. This has been operating almost continuously since it was installed in 1989. Versions of this instrument have been operated at other astronomical sites including the South Pole and the Chajnantor Plateau in Chile.
The other is a broadband instrument with a filter matching the 350 μm atmospheric window. This was installed at the CSO in late 1998. Identical copies of this instrument remain in operation at the South Pole (2835 m) and in Chile at APEX on the Chajnantor Plateau (5100 m) and at the CCAT site on Cerro Chajnantor (5612 m).
This article summarizes the measurements.
Observing Conditions for Submillimeter Astronomy, Radford, S. J. E., 2011, in Astronomical Site Testing Data in Chile, ed. Curé, M., Otárola, A., Marín, J., & Sarazin, M., RevMexAA (SC) 41, 87 [ ADS, arXiv/1107.5633 ]
If the 225 GHz optical depth has stopped updating on the antenna monitor screen:
If the 225 GHz optical depth updates on the antenna monitor screen but not on the web page, remove any orphan lock files:
lapakahi> ls /srv/www/htdocs/tau_plot/LOCK.*
lapakahi> sudo rm /srv/www/htdocs/tau_plot/LOCK.*
Please notify the staff if any of these remedies are necessary.