# A generalized differential image motion monitor

## TL;DR

The paper introduces the GDIMM, a compact, automatic instrument that continuously measures key atmospheric turbulence parameters for astronomical observations, based on a small telescope with a specialized mask.

## Contribution

It presents the design, data processing, and long-term monitoring results of the GDIMM instrument for measuring optical turbulence parameters.

## Key findings

- 3.5 years of turbulence data collected at Calern Observatory
- GDIMM accurately measures seeing, isoplanatic angle, coherence time, and outer scale
- Instrument operates fully automatically with continuous monitoring

## Abstract

We present the Generalised Differential Image Motion Monitor. It is a compact instrument dedicated to measure 4 parameters of the optical turbulence: seeing, isoplanatic angle, coherence time and wavefront coherence outer scale. GDIMM is based on a small telescope (28cm diameter) equipped with a 3-holes mask at its entrance pupil. The instrument is fully automatic, and performs continuous monitoring of turbulence parameters at the Calern Observatory (France). This paper gives a description of the instrument, data processing and error budget. We present also statistics of 3.5 years of monitoring of turbulence parameters above the Calern Observatory.