Une station de mesure de la turbulence atmosphérique à Calern Calern Atmospheric Turbulence Station E. Aristidi – J.S. Lagrange – 24 May 2018 A Ziad (PI) E Aristidi M Ben Rahhal (doc) J Borgnino (Emeritus) J Chabé (Géoazur) Y Fantei (Inge) C Giordano (post-doc) C Renaud (Inge)

Optical turbulence starstation.jp

Why study atmospherical turbulence ? Support to observations on existing sites : « site-monitoring » Prospection for new astronomical sites : « site-testing » The lab. Lagrange has a long experience (40+ yrs) in the field of atmospheric turbulence Ex: ELT site characterization (Vernin et al., 2011, PASP) Ex: VLT Atmospheric Site Monitor

Optical telecommunications Turbulence Optical telecommunications: high bit rate (expected 1 GB/s ; classical telecom satellite (radio waves) : ~20 MB/s) PhD M. Ben Rahhal (CNES/PACA) Turbulence has an impact on optical/near IR laser links with satellites

The CATS station : 5 instruments GDIMMPBL Intense MeO Telescope 2 robotic instruments to measure atmospheric turbulence (GDIMM / PBL) 1 instrument to study turbulence inside the dome (Intense) 1 AllSky camera 1 Meteo station No long-term turbulence monitoring at Calern in 40 years

GDIMM: Generalized Differential Image Monitor 7ft diameter dome 4m elevation 11inch telescope 3 « sub-pupils » Observation of a bright star : 3 sub-images Turbulence moves sub-images on the camera And creates variation of flux (scintillation)

Automatic observation sequence :40:38: Start main sequence. 19:40:38: Sun presence close. 19:40:38: Waiting opening instrument at 19:56:21 19:56:21: Bad Weather : cloudy, close.. 01:24:55: Opening Instrument... ok 01:25:39: Waiting for observing. 01:25:39: Start observing sequence 01:25:39: Vega is selected for observation. 01:25:39: Goto Vega... ok 01:26:28: Centring Vega on finder... ok 01:27:20: Search Vega on cams... 01:30:41: Centering Vega on cams... ok 01:30:56: Centering Vega on cams... ok 01:30:58: Observing Vega during correct zenithal height 01:30:58: Centering Vega on cams... ok 01:31:01: Observing seq ok. 02:40:57: Centering Vega on cams... ok 02:41:00: Observing seq ok 02:42:02: === Sequence stopped Sun rising. === 02:42:02: End Sequence observing. 02:42:02: Closing Instrument... ok 02:42:47: Instrument in standby 02:46:22: Sun Rising close. 03:10:01: Waiting opening instrument at 19:56:43

Real-time publication of the data: cats.oca.eu

Results for October 2017 Aristidi et al., SPIE 2018

PBL : Profileur Bord Lunaire / PML : Profiler of Moon Limb 16inch telescope 2 sub-pupils Optical setup to reflect one of the Moon images Observation of the Moon or Sun limb Agitation of the limb position gives acces to turbulence vertical profile Pupil mask 2 apertures (6cm) Solar filters

PBL : How does it work ? Turbulence Altitude low layer high layer Principle : mesure the agitation at 2 points of the limb → 2 points far away : access to low altitude turbulent layers → 2 close points : high altitude layers PBL measures the quantity of turbulence in each atmosphere layer Estimation of the turbulence profile up to h=24km : 33 layers 1 profile every 2 minutes Resolution: 100m (low altitude) to 2km (high altitude)

Night and day profiles SunMoon Ben Rahhal et al., SPIE 2018 From PBL data: possible to calculate some parameters measured by GDIMM

PBL versus MASS Catala et al., 2017, MNRAS Simultaneous observations with a MASS, Multi Aperture Scintillation Sensor (Kornilov 2002) Sutherland Observatory (South Africa), August

Perspectives Turbulence predictions meteo models contrained by CATS (Post-doc C. Giordano + PhD CNES/OCA) Progress on the robotization (especially for PBL) Progress on the data processing (GDIMM outer scale/coherence time, PBL outer scale profile, coherence time…) GDIMM/PBL campains (ex Paranal) Comparison with other instruments

Construction : summer 2015

GDIMM number of data since Nov, 2015 Aristidi et al., SPIE 2018

Distorted images telescope Star perturbated wave turbulent layers km Perfect plane wave Atmospheric optical turbulence

The « seeing »  The seeing is the size of smallest details in long exposure images  = 0’’05 r 0 =2.5 m  = 0’’1 r 0 =1 m  = 0’’3 r 0 =30 cm  = 1’’ r 0 =10 cm Typical value: 1 arc second

Plane wavefront Sub-images Sub-pupils Tilted wavefront Lateral shift of images Distorted wavefront How to measure the turbulence ? Turbulence makes sub-images to move on the camera :