Abstract
PICARD SOL is the ground component of the PICARD mission and is operational since March 2011. A set of instruments including the replica of the space instrument and several atmospheric monitors was set up at Calern observatory in order to compare solar radius measured in space and on ground and to better understand and calibrate atmospheric effects on ground based measurements. SODISMII provides full disk images of the chromosphere and photosphere of the Sun in five narrow pass bands ranging from the near ultraviolet to the near infrared. Our preliminary results show a very good instrumental stability. After plate scale calibration using star doublet observations and corrections for atmospheric refraction, first estimates of the mean solar radius at the five wavelengths (393.37, 535.7, 607.1, 782.2, and 1025.0nm) are deduced from measurements recorded between May 2011 and December 2012.
Highlights
The PICARD program [1] owes its name to Jean Picard (1620-1682), considered as a pioneer of precise modern astrometry who measured the solar radius
PICARD SOL is a new ground-based facility for long-term solar radius measurements, which include a multi-wavelengths full disk solar imager stabilized in temperature and a set of atmospheric monitors working simultaneously
It has been operated for 20 months since May 2011 and shows good instrumental stability
Summary
The PICARD program [1] owes its name to Jean Picard (1620-1682), considered as a pioneer of precise modern astrometry who measured the solar radius. An evolution of the solar radius estimated this way from SODISM II images is shown on Figure 1 as a function of time for different wavelengths. The Fried parameter on the other hand varies as λ6/5 and the bias induced by turbulence on radius estimates will tend to decrease as wavelength increase.
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