The Millimeter Sky Transparency Imager (MiSTI)

TL;DR

MiSTI is a compact millimeter-wave telescope that measures atmospheric water vapor to monitor sky transparency at Atacama, providing real-time data crucial for millimeter and submillimeter astronomy observations.

Contribution

This paper introduces MiSTI, a novel small telescope operating at 183 GHz for atmospheric water vapor measurement and real-time sky transparency monitoring.

Findings

Validated 183 GHz measurements against 220 GHz tipper data.

Achieved detection of excess path length <~ 0.05 mm in 1 s.

Provided continuous real-time all-sky opacity data since 2008.

Abstract

The Millimeter Sky Transparency Imager (MiSTI) is a small millimeter-wave scanning telescope with a 25-cm diameter dish operating at 183 GHz. MiSTI is installed at Atacama, Chile, and it measures emission from atmospheric water vapor and its fluctuations to estimate atmospheric absorption in the millimeter to submillimeter. MiSTI observes the water vapor distribution at a spatial resolution of 0.5 deg, and it is sensitive enough to detect an excess path length of <~ 0.05 mm for an integration time of 1 s. By comparing the MiSTI measurements with those by a 220 GHz tipper, we validate that the 183 GHz measurements of MiSTI are correct, down to the level of any residual systematic errors in the 220 GHz measurements. Since 2008, MiSTI has provided real-time (every 1 hr) monitoring of the all-sky opacity distribution and atmospheric transmission curves in the (sub)millimeter through the internet, allowing to know the (sub)millimeter sky conditions at Atacama.