MISOLFA: a generalized monitor for daytime spatio-temporal turbulence characterization (original) (raw)

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.

Atmospheric Turbulence Profiles C 2 n (h) deduced from Solar Limb Observations

Publications of the Astronomical Society of the Pacific

Atmospheric turbulence is responsible of the spatio-temporal fluctuations in astronomical object images obtained by means of ground-based telescopes. They are due to wave-front degradations present at the entrance of the instrument pupil plane. We first establish in this paper the formulation of the angle-of-arrival angular structure function d(θ) of image fluctuations which is linked to the turbulence "optical strength" C 2 n (h). We use this property to propose an optical method to estimate atmospheric turbulence profiles. This is based on the inversion of the d(θ) integral equation using the Marquardt-Levenberg method. Application to synthetic data shows the efficiency and the stability of the developed method. We applied then this method to estimate optical turbulence profiles from the analysis of solar limb images.

Estimation of turbulence parameters from solar observations

Optics in Atmospheric Propagation and Adaptive Systems IV, 2002

The one-dimensional point spread function for long-exposure frames of the whole system atmosphere-instrument is calculated from solar limb observations using data recorded at OCA Observatory (France). It is then compared to the theoretical one deduced from the Von Karman model and various wave-front structure functions. Good agreement is found allowing to deduce the spatial coherence outer scale L 0 and the Fried parameter r 0 .

Temporal Variations of the Turbulence Profiles at the Sayan Solar Observatory Site

Atmosphere, 2019

The paper focuses on the development of the method to estimate the mean characteristics of the atmospheric turbulence. Using an approach based on the shape of the energy spectrum of atmospheric turbulence over a wide range of spatial and temporal scales, the vertical profiles of optical turbulence are calculated. The temporal variability of the vertical profiles of turbulence under different low-frequency atmospheric disturbances is considered.

Atmospheric seeing measurements obtained with MISOLFA

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.

Two campaigns to compare three turbulence profiling techniques at Las Campanas Observatory

2008

In preparation to characterize the Giant Magellan Telescope site and guide the development of its adaptive optics system, two campaigns to systematically compare the turbulence profiles obtained independently with three different instruments were conducted at Las Campanas Observatory in September, 2007 and January 2008. Slope detection and ranging (SLODAR) was used on the 2.5-m duPont telescope. SLODAR measures the C2n profile as a function of altitude through observations of double stars. The separation of the observed double star sets the maximum altitude and height resolution. Ground layer (altitudes < 1 km) and free atmosphere turbulence profiles are compared with those obtained with a lunar scintillometer (LuSci) and a multi-aperture scintillation sensor (MASS), respectively. In addition, the total atmospheric seeing was measured by both SLODAR and a differential image motion monitor (DIMM).

3D optical turbulence characterization at San Pedro Mártir

Muchos instrumentos son capaces de proporcionar estimaciones locales (en espacio y tiempo) de todos los parámetros astroclimáticos que dependen de la turbulenciaóptica. Actualmente, la técnica numérica es eĺ unico método que puede proporcionar una caracterización en 3D de la turbulenciaóptica. Desde hace algunos años, grandes esfuerzos han sido dedicados a incrementar la confiabilidad del modelo atmosférico de meso-escala llamado Meso-Nh para simular perfiles de C 2 N arriba de sitios astronómicos. Los resultados más recientes y más prometedores han sido obtenidos en el sitio de San Pedro Mártir. En este artículo, se presenta un resumen de dichos resultados.

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.

Turbulence Profiles with Generalized Scidar at San Pedro Mártir Observatory and Isoplanatism Studies

Publications of the Astronomical Society of the Pacific, 1998

The results obtained from 3398 vertical pro les of atmospheric turbulence measured during 11 nights at the Observatorio Astron omico Nacional in San Pedro M artir (Baja California, M exico) are presented. The observations were carried out with the generalized scidar (GS) installed at the 1.5 m and the 2.1 m telescopes of that site, in March and April 1997. The open air seeing was measured with a di erential image motion monitor (DIMM). The GS can detect turbulence pro les along the whole optical path, unlike the classical scidar which is insensitive to low altitude turbulence. For the rst time, to our knowledge, pro les including turbulence near the ground are monitored and statistically analyzed. Isoplanatic angles for speckle interferometry and adaptive optics (AO) in either full or partial compensation are deduced, as well as the focus anisoplanatism parameter for sodium laser guide stars. The advantage of minimizing the distance between the turbulent layers and the conjugated plane of the deformable mirror of an AO system is studied. The comparison of GS pro les obtained at both telescopes, together with DIMM measurements, show that the turbulence near the ground is more strongly dominant at the 1.5 m telescope than at the 2.1 m telescope, where the median values of the seeing near the ground, in the free atmosphere and in the whole optical path are 0.56, 0.44 and 0.77 arcsec, respectively. These values are comparable to or better than those of the major astronomical observatories, although a larger data sample is needed for a de nitive comparison.