a monitor of the vertical turbulence distribution MASS: Victor Kornilov a, Andrei Tokovinin b, Olga Vozyakova a, Andrei Zaitsev a, Nicolai Shatsky a, Serguei Potatin a, and Marc Sarazin c a Sternberg Astronomical Institute, Moscow; b CTIO, Chile; c ESO, Garching MASS (Multi-Aperture Scintillation Sensor) measures light fluxes from a bright single star in 4 concentric-ring apertures A, B, C, and D with 1 ms time resolution. For each aperture, a variance of normalized light flux, scintillation index, is computed. For each pair of apertures, a differential scintillation index is computed as well. These 4+6 indices with 1 minute accumulation time are used to restore the turbulence profile with a vertical resolution of dh/h = 0.5. Restoration with 6 fixed layers: the resulting “response functions” of the layers and their sum (dashed) Restoration with 6 fixed layers: the resulting “response functions” of the layers and their sum (dashed) Weighting functions: the dependence of the 4 normal (A,B,C,D) and 6 differential (AB,AC,…) scintillation indices on the distance to the turbulent layer Weighting functions: the dependence of the 4 normal (A,B,C,D) and 6 differential (AB,AC,…) scintillation indices on the distance to the turbulent layer Feeding telescope: off-axis elliptic primary, 14 cm diameter. Spherical secondary, equivalent focal distance 3 m. The detector box : (length 21 cm) contains optics, photo-multipliers, and electronics The detector box : (length 21 cm) contains optics, photo-multipliers, and electronics Optics: the light from telescope is reflected by the folding mirror 1 and passes through a focal aperture on the disk 2 (controlled by a stepper motor). The Fabry lens 4 forms an image of the telescope pupil on the segmentator 7 with a de-magnification of 20. The segmentator consists of 4 concentric mirrors with different tilts, the diameter of the smallest mirror is 1 mm (2 cm as projected on the pupil). The 4 reflected beams fall on the spherical mirrors 3A-3D which re-image the pupil on the photo-cathodes of the PMTs A,B,C,D. A dichroic beam-splitter 5 reflects red light to the viewer (mirror 8, lens 9, eyepiece 10’ or a TV camera 10). The spectral bandpass of 90 nm centered on 480 nm is defined by the glass filter 6. Feeding telescope: off-axis elliptic primary, 14 cm diameter. Spherical secondary, equivalent focal distance 3 m. Electronics: seven microprocessor modules on RS-485 common line interfaced to a PC computer. Software: under RT-Linux, the program Turbina controls MASS through GUI. Features: real-time data reduction, instrument self-tests, automatic operation. Example of real-time display is shown. Software: under RT-Linux, the program Turbina controls MASS through Graphical User Interface and menus. Features: real-time data reduction, instrument self-tests, automatic operation. Example of real-time display is shown. One night: July 14-15, 2002 at Cerro Tololo. The C n 2 profiles restored with fixed-layer method (top left) and as three floating layers (bottom left) and the comparison of the full seeing measured by DIMM with integrated- profile seeing from MASS which excludes the lower 500m (top). SCIDAR: comparison with MASS at La Silla on July , The normalilzation was adjusted between MASS (full line) and SCIDAR (dash), SCIDAR was convolved with the MASS vertical response. CONCLUSION MASS, a simple and robust instrument for low- resolution monitoring of turbulence profile, passed its first tests successfully. More information and the full text of this paper at: CONCLUSION MASS, a simple and robust instrument for low- resolution monitoring of turbulence profile, passed its first tests successfully. More information and the full text of this paper at: