Sub-mm Atmospheric Issues
• Opacity vs. frequency is a function of
PWV, “dry air” and temperature
– Compared to Mauna Kea and Chajnantor, South Pole
has lowest PWV and temperature, but highest
pressure
• Sky noise is mostly caused by variations
in the abundance and temperature of
water vapor, in time and across sky
– Small, constant water vapor at Pole results in low sky
noise
– Sky noise at Pole is 10 to 50× smaller than
Chajnantor (Lay and Halverson 1999)
• Sky noise causes systematic errors in
submillimeter-wave astronomical
measurements, and is often the
dominant effect limiting the flux levels
which can be reached with any
particular instrument and technique
– Sky noise in signal decreases more slowly than t–½