Title: Water Vapor Radiometer for Radio Astronomy, Astrometry and Geodesy

　　Speaker: Prof. Noriyuki Kawaguchi (Visiting Professor of SHAO / Professor Emeritus of NAOJ)

　　Date: March 17，2017 (Friday)

　　Time: 14:00-15:30?

　　Location：Middle conference room, 3rd floor　

　　Abstract:

　　Water vapor in atmosphere causes absorption on a radio signal passing through the atmosphere. The absorption not only increases system noise temperature of a radio telescope but also gives large uncertainty on brightness of a radio source, which is the main cause of difficulties in radio photometry. The water vapor also makes delay on the signal propagating in the atmosphere. The delay greatly changes in time due to the non-uniform distribution of the water vapor. The change in the delay is a major source of an error in astrometric/geodetic observations by VLBI. We need to pay serious attention on these bad effects when we study radio astronomy in higher frequencies, precise astrometric/geodetic measurement, and accurate obit determination in deep space navigation.

　　Here I will review these bad effects caused by water vapor and show the ways of correction. I specially focused on a water vapor radiometer which is expected to work well in the correction but not fully utilized like as the SHAO water vapor. I will show the current state of the SHAO water vapor radiometer and suggestions to use the radiometer much better. I also show the current state of new developments of an advanced water vapor radiometer now made in Japan.