2007MNRAS.382.1268K

Several site-testing programmes and observatories currently use combined Multi-Aperture Scintillation Sensor (MASS)-Differential Image Motion Monitor (DIMM) instruments for monitoring parameters of optical turbulence. The instrument is described here. After a short recall of the measured quantities and operational principles, the optics and electronics of MASS-DIMM, interfacing to telescopes and detectors, and operation are covered in some detail. Particular attention is given to the correct measurement and control of instrumental parameters to ensure valid and well-calibrated data, to the data quality and filtering. Examples of MASS-DIMM data are given, followed by the list of present and future applications.