Observing time calculator
Atmospheric opacity calculator
By entering the frequency (in GHz) and the amount of precipitable water vapor (PWV) you can calculate the zenith optical depth τzenith. The PWV values vary both during the day and over the year (see the annual weather information page http://www.apex-telescope.org/weather/year_weather). Night and morning conditions are generally better, while the afternoons are worse. Conditions are best from June to November, but significantly worse from the end of December to early April. Averaged over the year, the median value is around 1 mm. Conditions better than 0.5 mm occur during 25% of the time. The entered frequency and the calculated τzenith will be transferred to the RMS and integration time calculators below. For the APEX-2a receiver the tuning range is 279-381 GHz.
This plot shows the PWV as function of month as measured by the ALMA radiometer.
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