RoboDIMM data are written automatically to a database that can be accessed through this link.

At night, the mean of the last 5 seeing measurements is printed on the ING Weather Station Mast View. If (Solar) "Radiation" is displayed when you load this page, it probably means that RoboDIMM has not taken any data yet tonight (but try Reload). There is a plot of these average values against time of observation on the Graph View page.

Note that modifications have been made to the RoboDIMMM software that have a notable effect on the behaviour of the FWHM measurements. Only data taken after Sep 4 are corrected for the airmass of observation, and data prior to this consequently shows a trend in FWHM with respect to airmass.

The seeing estimates produced by RoboDIMM are calculated, using the Kolmogorov theory of atmospheric turbulence, from a series of 10 millisecond images. The calculated values correspond to a prediction of the Full Width at Half Maximum (FWHM) of a "long" exposure image (a few seconds or more) taken through an aperture of infinite size, i.e. there is no correction for diffraction (this is generally small anyway). The values thus represent the best atmospheric seeing obtainable at that moment, at zenith, unaffected by dome seeing, telescope tracking or optical distortion.

RoboDIMM simultaneously produces four independent estimates of the FWHM, by measuring differential image motion from the 4 images formed on the detector. Since all 4 should be in agreement, these allow a first order, internal calibration or check of data quality.

In the near future, it is hoped that the FWHM estimates from RoboDIMM can be calibrated against data from the Wave Front Sensor of NAOMI. However, comparing seeing measurements is problematic mostly due to instrinsic sources of bias in DIMM measurements (see Andrey Tokovinin's recent article in PASP, 114, p1134 ). The finite (10ms) exposure and application of a threshold before centroiding both work to decrease the seeing estimate while the presence of CCD readout noise tends to increase it. These effects will have to be taken into account in any eventual cross-calibration.