Atmospheric Seeing at ING

ING provides seeing measurements online and updated throughout the night, taken by its Robotic Differential Image Motion Monitor (known as RoboDIMM). RoboDIMM is intended foremost to provide observers at ING telescopes with a real-time guide to seeing conditions, and its function as a site testing instrument is always subject to results from the campaigns undertaken for that purpose at ORM.

Accuracy and comparability of RoboDIMM data

Seeing FWHM estimates from RoboDIMM are considered by ING to be reliable in almost all atmospheric conditions. Nevertheless, measurements smaller than about 0.6 arcseconds are less frequent than would be expected.

Shortly after it started operating in August 2002, RoboDIMM seeing was shown to agree with the IAC's DIMM seeing monitor to within better than 10%, using samples of typically a few hour's length. RoboDIMM also shows a similar level of agreement with SloDAR and JKT-SCIDAR monitors in summer 2004 and January 2005. More detail here.

RoboDIMM description

The Monitor: a Meade 12" telescope with an SBIG CCD detector at Cassegrain focus, controlled via serial link by a PC running custom software. Instrumental focus is also under PC control.

The telescope forms four separate images of the same star on the CCD thanks to a pupil mask with 4 subapertures covered by small-deviation glass prisms. This allows four independent differential motions to be measured, from which the monitor program derives four simultaneous estimates of seeing.

Tower: The telescope is mounted 5m above ground, thus escaping much of the ground level turbulence, on a tower that also provides a high degree of vibrational stability, thanks to its serrurier truss-type structure.

Dome: The monitor and PC are housed inside a fibreglass clamshell dome (from Astrohaven, Canada) which is mounted on an access platform at approximately 4.5m above ground.

More detail here.