The solar seeing monitor MISOLFA: presentation and first results (original) (raw)

Ground-based solar astrometric measurements during the PICARD mission

Optics in Atmospheric Propagation and Adaptive Systems XIV, 2011

PICARD is a space mission developed mainly to study the geometry of the Sun. The satellite was launched in June 2010. The PICARD mission has a ground program which is based at the Calern Observatory (Observatoire de la Côte d'Azur). It will allow recording simultaneous solar images from ground. Astrometric observations of the Sun using ground-based telescopes need however an accurate modelling of optical effects induced by atmospheric turbulence. Previous works have revealed a dependence of the Sun radius measurements with the observation conditions (Fried's parameter, atmospheric correlation time(s) ...). The ground instruments consist mainly in SODISM II, replica of the PICARD space instrument and MISOLFA, a generalized daytime seeing monitor. They are complemented by standard sun-photometers and a pyranometer for estimating a global sky quality index. MISOLFA is founded on the observation of Angle-of-Arrival (AA) fluctuations and allows us to analyze atmospheric turbulence optical effects on measurements performed by SODISM II. It gives estimations of the coherence parameters characterizing wave-fronts degraded by the atmospheric turbulence (Fried's parameter, size of the isoplanatic patch, the spatial coherence outer scale and atmospheric correlation times). This paper presents an overview of the ground based instruments of PICARD and some results obtained from observations performed at Calern observatory in 2011.

Atmospheric seeing measurements obtained with MISOLFA in the framework of the PICARD Mission

Ground-based and Airborne Telescopes IV, 2012

PICARD is a space mission launched in June 2010 to study mainly the geometry of the Sun. The PICARD mission has a ground program consisting mostly in four instruments based at the Calern Observatory (Observatoire de la Côte d'Azur). They allow recording simultaneous solar images and various atmospheric data from ground. The ground instruments consist in the qualification model of the PICARD space instrument (SODISM II: Solar Diameter Imager and Surface Mapper), standard sun-photometers, a pyranometer for estimating a global sky quality index, and MISOLFA a generalized daytime seeing monitor. Indeed, astrometric observations of the Sun using ground-based telescopes need an accurate modeling of optical effects induced by atmospheric turbulence. MISOLFA is founded on the observation of Angle-of-Arrival (AA) fluctuations and allows us to analyze atmospheric turbulence optical effects on measurements performed by SODISM II. It gives estimations of the coherence parameters characterizing wave-fronts degraded by the atmospheric turbulence (Fried parameter r 0 , size of the isoplanatic patch, the spatial coherence outer scale L 0 and atmospheric correlation times). We present in this paper simulations showing how the Fried parameter infered from MISOLFA records can be used to interpret radius measurements extracted from SODISM II images. We show an example of daily and monthly evolution of r 0 and present its statistics over 2 years at Calern Observatory with a global mean value of 3.5cm.

Atmospheric seeing measurements obtained with MISOLFA

2012

PICARD SOL mission, a ground-based facility for long-term solar radius measurement

Ground-based and Airborne Instrumentation for Astronomy IV, 2012

For the last thirty years, ground time series of the solar radius have shown different variations according to different instruments. The origin of these variations may be found in the observer, the instrument, the atmosphere and the Sun. These time series show inconsistencies and conflicting results, which likely originate from instrumental effects and/or atmospheric effects. A survey of the solar radius was initiated in 1975 by F. Laclare, at the Calern site of the Observatoire de la Côte d'Azur (OCA). PICARD is an investigation dedicated to the simultaneous measurements of the absolute total and spectral solar irradiance, the solar radius and solar shape, and to the Sun's interior probing by the helioseismology method. The PICARD mission aims to the study of the origin of the solar variability and to the study of the relations between the Sun and the Earth's climate by using modeling. These studies will be based on measurements carried out from orbit and from the ground. PICARD SOL is the ground segment of the PICARD mission to allow a comparison of the solar radius measured in space and on ground. PICARD SOL will enable to understand the influence of the atmosphere on the measured solar radius. The PICARD Sol instrumentation consists of: SODISM II, a replica of SODISM (SOlar Diameter Imager and Surface Mapper), a high resolution imaging telescope, and MISOLFA (Moniteur d'Images SOLaires Franco-Algérien), a seeing monitor. Additional instrumentation consists in a Sun photometer, which measures atmospheric aerosol properties, a pyranometer to measure the solar irradiance, a visible camera, and a weather station. PICARD SOL is operating since March 2011. First results from the PICARD SOL mission are briefly reported in this paper.

Solar seeing monitor MISOLFA: A new method for estimating atmospheric turbulence parameters

Astronomy & Astrophysics, 2016

Aims. Daily observation conditions are needed when observing the Sun at high angular resolution. MISOLFA is a daytime seeing monitor developed for this purpose that allows the estimation of the spatial and temporal parameters of atmospheric turbulence. This information is necessary, for instance, for astrometric measurements of the solar radius performed at Calern Observatory (France) with SODISM II, the ground-based version of the SODISM instrument of the PICARD mission. Methods. We present a new way to estimate the spatial parameters of atmospheric turbulence for daily observations. This method is less sensitive to vibrations and guiding defaults of the telescope since it uses short-exposure images. It is based on the comparison of the optical transfer function obtained from solar data and the theoretical values deduced from the Kolmogorov and Von Kàrmàn models. This method, previously tested on simulated solar images, is applied to real data recorded at Calern Observatory in July 2013 with the MISOLFA monitor. Results. First, we use data recorded in the pupil plane mode of MISOLFA and evaluate the turbulence characteristic times of angle-ofarrival fluctuations: between 5 and 16 ms. Second, we use the focal plane mode of MISOLFA to simultaneously record solar images to obtain isoplanatic angles: ranging from 1 to 5 arcsec (in agreement with previously published values). These images and our new method allow Fried's parameter to be measured; it ranges from 0.5 cm to 4.7 cm with a mean value of 1.5 cm when Kolmogorov's model is considered, and from less than 0.5 to 2.6 cm with a mean value of 1.3 cm for the Von Kàrmàn model. Measurements of the spatial coherence outer scale parameter are also obtained when using the Von Kàrmàn model; it ranges from 0.25 to 13 m with a mean value of 3.4 m for the four days of observation that we analyzed. We found that its value can undergo large variations in only a few hours and that more data analysis is needed to better define its statistics.

Picard SODISM, a Space Telescope to Study the Sun from the Middle Ultraviolet to the Near Infrared

2014

The Solar Diameter Imager and Surface Mapper (SODISM) onboard the PICARD space mission provides wide-field images of the photosphere and chromosphere of the Sun in five narrow pass bands (centered at 215.0, 393.37, 535.7, 607.1, and 782.2 nm). PICARD is a space mission, which was successfully launched on 15 June 2010 into a Sun synchronous dawn-dusk orbit. It represents a European asset aiming at collecting solar observations that can serve to estimate some of the inputs to Earth climate models. The scientific payload consists of the SODISM imager and of two radiometers, SOVAP (SOlar VAriability PICARD) and PREMOS (PREcision MOnitor Sensor), which carry out measurements that allow estimating the Total Solar Irradiance (TSI) and the Solar Spectral Irradiance (SSI) from the middle ultraviolet to the red. The SODISM telescope monitors solar activity continuously. It thus produces images that can also feed SSI reconstruction models. Further, the objectives of SODISM encompass the probing of the interior of the Sun via helioseismic analysis of observations in intensity (on the solar disc and at the limb), and via astrometric investigations at the limb. The latter addresses especially the spectral dependence of the radial limb shape, and the temporal evolution of the solar diameter and asphericity. After a brief review of its original science objectives, this paper presents the detailed design of the SODISM instrument, its expected performance, and the scheme of its flight operations. Some observations with SODISM are presented and discussed.

Picard satellite for solar astrometry

The Picard solar satellite has been launched on June 15, 2010. This mission is dedicated to the measurement of the solar diameter with an expected accuracy of milliarcseconds of arc. The radiometer onboard is to measure the total solar irradiance. The final goal is the evaluation of the W, the logarithmic ratio of radius and luminosity. This parameter will help the climatologists to recover past values of the solar luminosity when the radius is available from ancient eclipses data.

PICARD SOL, a new ground-based facility for long-term solar radius measurements: first results

Journal of Physics: Conference Series, 2013

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. SODISM II 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 1025.0 nm) are deduced from measurements recorded between

Solar observations from space and from the ground

Astronomische Nachrichten, 2003

Recent results from space missions like YOHKOH, SOHO or TRACE as well as ground-based observations clearly indicate that physical processes of most solar phenomena take place on small scales, which are still below the resolution of the instruments employed. There is an urgent need for observations at higher resolution and also for their extension to multi-wavelength regimes. Space-borne as well as ground-based instruments have limitations of the present-day technology, although in a different way. In this communication, an overview of space instruments currently in operation or in the preparation phase is presented and references to more detailed information are given.

The solar seeing monitor MISOLFA: presentation and first results (original) (raw)

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