Skip to main content

A. Irbah

Centre National de la Recherche Scientifique / French National Centre for Scientific Research, Experimental Physics Laboratory, Graduate Student

Followers

20

Following

11

Co-authors

11

Public Views

Armando Salvatore

McGill University

Princeton University

Stockholm University

National University of Ireland, Maynooth

University of St Andrews

Richard Gauthier

Santa Rosa Junior College

Mahmoud Abd El-Baky

Minia University

Prof BN Dwivedi

IIT BHU

Dimitris Poulos

National Technical University of Athens

Università degli Studi di Padova

Interests

Uploads

Papers by A. Irbah

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. ... more 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.

Sun from the middle ultraviolet to the near infrared

The Solar Diameter Imager and Surface Mapper (SODISM) onboard the PICARD space mission provides w... more 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 success-fully 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

Sun from the middle ultraviolet to the near infrared

The Solar Diameter Imager and Surface Mapper (SODISM) onboard the PICARD space mission provides w... more 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 success-fully 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

On-Orbit Degradation of Solar Instruments

We present the lessons learned about the degradation observed in several space solar missions, ba... more We present the lessons learned about the degradation observed in several space solar missions, based on contributions at the Workshop about On-Orbit Degradation of Solar and Space Weather Instruments that took place at the Solar Terrestrial Centre of Excellence (Royal Observatory of Belgium) in Brussels on 3 May 2012. The aim of this workshop was to open discussions related to the degradation observed in Sun-observing instruments exposed to the effects of the space environment. This article summarizes the various lessons learned and offers recommendations to reduce or correct expected degradation with the goal of increasing the useful lifespan of future and ongoing space missions.

New values of gravitational moments J2 and J4 deduced

By applying the theory of slowly rotating stars to the Sun, the solar quadrupole and octopole mom... more By applying the theory of slowly rotating stars to the Sun, the solar quadrupole and octopole moments J2 and J4 were computed using a solar model obtained from CESAM stellar evolution code (Morel (1997)) combined with a recent model of solar differential rotation deduced from helioseismology (Corbard et al. (2002)). This model takes into account a near-surface radial gradient of rotation which was inferred and quantified from MDI f-modes observations by Corbard and Thompson (2002). The effect of this observational near-surface gradient on the theoretical values of the surface parameters J2, J4 is investigated. The results show that the octopole moment J4 is much more sensitive than the quadrupole moment J2 to the subsurface radial gradient of rotation.

Adaptive Mask Coronagraph

Abstract. In this paper, the new coronagraph that will be mounted at the Pic du Midi Ob-servatory... more Abstract. In this paper, the new coronagraph that will be mounted at the Pic du Midi Ob-servatory (IMCCE- T1m telescope) is presented. To optimize the occulting process of a Lyot coronagraph, a compressed mercury (Hg) drop is used as an occulting disk and its size control offers an adaptation to the seeing conditions or to the Airy diameter fraction needed. In addition to the Hg-mask, a variation on the theme is proposed by a diameter and wavelength adaptive phase mask made of a gas bubble in immersion oil between two optical windows. The instrument concept offers a good versatility to test other mask type and pupil apodization techniques.

Operation of the Airborne 355-nm High Spectral Resolution and Doppler Lidar LNG

EPJ Web of Conferences, 2020

High spectral resolution lidar (HSRL) are known to offer capabilities of separating attenuated ae... more High spectral resolution lidar (HSRL) are known to offer capabilities of separating attenuated aerosol and molecular backscattering so that particle extinction and backscattering can be separately retrieved. UV operation provides high energy in eye-safety conditions. Further to that, it could be important for most meteorological or environmental studies to get wind measurements at the same time. LNG is now the only HSR Doppler Lidar (HSRDL) system capable of this. Results obtained during ground-based and airborne measurements show that the backscatter and extinction coefficients at 355 nm can be measured with a relative precision better than 10% (adjusting altitude and time resolution from 60 m to 240 m and 30s to 2mn, respectively) in aerosol layers of 0.5 10−6 m−1 sr−1 backscatter coefficient from ground and aircraft. The same relative precision is obtained in cirrus clouds of a 10−5 m−1 sr−1 backscatter coefficient. The capacity of the system to perform wind velocity measurements...

A new solar reference spectrum from 165 to 3088 nm

The EGU General Assembly, 2017

Since April 5, 2008 and until February 15, 2017 the SOLAR/SOLSPEC spectro-radiometer on the Inter... more Since April 5, 2008 and until February 15, 2017 the SOLAR/SOLSPEC spectro-radiometer on the International Space Station performed accurate measurements of Solar Spectral Irradiance (SSI) from the far ultraviolet to the infrared (165 nm to 3088 nm). These measurements are of primary importance for a better understanding of solar physics and of the impact of solar variability on climate (via Earth's atmospheric photochemistry). In particular, a new reference solar spectrum is established covering most of the unusual solar cycle 24 from minimum in 2008 to maximum. Temporal variability in the UV (165 to 400 nm) is presented in several wavelengths bands. These results are possible thanks to revised engineering corrections, improved calibrations and new procedures to account for thermal and aging advanced corrections. Uncertainties on these measurements are evaluated and compare favorably with other instruments.

SOLAR-ISS: A new reference spectrum based on SOLAR/SOLSPEC observations

Astronomy & Astrophysics, 2018

Context. Since April 5, 2008 and up to February 15, 2017, the SOLar SPECtrometer (SOLSPEC) instru... more Context. Since April 5, 2008 and up to February 15, 2017, the SOLar SPECtrometer (SOLSPEC) instrument of the SOLAR payload on board the International Space Station (ISS) has performed accurate measurements of solar spectral irradiance (SSI) from the middle ultraviolet to the infrared (165 to 3088 nm). These measurements are of primary importance for a better understanding of solar physics and the impact of solar variability on climate. In particular, a new reference solar spectrum (SOLAR-ISS) is established in April 2008 during the solar minima of cycles 23–24 thanks to revised engineering corrections, improved calibrations, and advanced procedures to account for thermal and aging corrections of the SOLAR/SOLSPEC instrument. Aims. The main objective of this article is to present a new high-resolution solar spectrum with a mean absolute uncertainty of 1.26% at 1σ from 165 to 3000 nm. This solar spectrum is based on solar observations of the SOLAR/SOLSPEC space-based instrument.Method...

A New Solar Spectrum from 656 to 3088 nm

Solar Physics, 2017

Multicast routing in wireless networking is the latest technology for network groups. Multicast r... more Multicast routing in wireless networking is the latest technology for network groups. Multicast routing is part of point-to-point/multipoint-to-multipoint communications. Multicast routing ensures efficient, reliable and secure for wireless networks than unicast routing due to protocols and techniques speed which are combined on multicast routing for wireless technology. Due to redundancy lack in multipath/multicast structures, multicast routing protocols are vulnerable to the ad hoc networks component failure. Some techniques to overcome this are optimizing routing which increases packet delivery minimizing overhead. Particle swarm optimization (PSO) is a network optimizing tool. This paper proposes new PSO based Multicast Ad-hoc On-demand Distance Vector (MAODV) Protocol for MANETs to improve link break prediction accuracy and congestion occurrence. The proposed technique improves routing packages packet delivery ratio. PSO based MAODV allows each network node to forward multicast data packets which are broadcast when propagated along a multicast group tree.

Solar Irradiance from 165 to 400 nm in 2008 and UV Variations in Three Spectral Bands During Solar Cycle 24

Solar Physics, 2016

Accurate measurements of solar spectral irradiance (SSI) and its temporal variations are of prima... more Accurate measurements of solar spectral irradiance (SSI) and its temporal variations are of primary interest to better understand solar mechanisms, and the links between solar variability and Earth's atmosphere and climate. The SOLar SPECtrum (SOLSPEC) instrument of the Solar Monitoring Observatory (SOLAR) payload onboard the International Space Station (ISS) has been built to carry out SSI measurements from 165 to 3088 nm. We focus here on the ultraviolet (UV) part of the measured solar spectrum (wavelengths less than 400 nm) because the UV part is potentially important for understanding the solar forcing of Earth's atmosphere and climate. We present here SOLAR/SOLSPEC UV data obtained since 2008, and their variations in three spectral bands during Solar Cycle 24. They are compared with previously reported UV measurements and model reconstructions, and differences are discussed.

$Figure 3. The red curve represents the UV PM temperature evolution during a calibration test. The SOLAR/SOLSPEC signal (S;,(t) at 210.2nm) evolves during a short time period (the blue curve). This instability effect should be corrected. wavelength (210.2nm). This test highlights that the instrument is unstable during short-time period (~6% of variation). It was repeated several times (Figure 3), which shows the reversibility of the instrumental effect (Ig(\,t)). SOLAR/SOLSPEC measurements during 20 minutes show SSI variations that are above the expected values during a solar cycle. The thermo-mechanical sta- bility of the instrument is questionable and requires an opto-thermo-mechanical analysis. One can notice that during SOLAR/SOLSPEC switch-on, the signature of the signal is slightly different. Currently, we try to understand the link between the SOLAR/SOLSPEC UV photo-multiplier (UV PM) temperature and the measured signal.$

Identification of clear days from solar irradiance observations using a new method based on the wavelet transform

Renewable Energy, 2017

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

On HMI solar oblateness during solar cycle 24 and impact of the space environment on results

Advances in Space Research, 2016

Solar oblateness is a fundamental parameter of the Sun, which provides indirect information on th... more Solar oblateness is a fundamental parameter of the Sun, which provides indirect information on the inner rotation profile and on the distribution of matter. It also puts constraints on General Relativity. But this quantity is difficult to measure due to its very small value where the solar equator-to-pole radius difference is less than 10 milli-arcsecond (mas). Indeed, the measurements can be affected by magnetic activity and by instrumental effects linked to the space environment. The Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO) has produced accurate determinations of the solar oblateness from 2010 to 2015. The HMI measurements of the solar shape are obtained during special roll maneuvers of the spacecraft by 11.25 degrees steps around the spacecraft to the Sun line. HMI roll maneuver has been repeated ten times after the commissioning phase from October 2010 to July 2015. From HMI data, we observed a slight anti-correlation between solar oblateness and solar activity. From a new correction method, we found a mean solar equator-to-pole radius difference of 8.36 ± 0.49 mas (i.e. 6.06 ± 0.35 km at one σ ) at 617.3 nm during the period 2010-2015.

How mission requirements affect observations: case of the PICARD mission

Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, 2016

The scientific objectives of a space mission result into instrumental developments and specific s... more The scientific objectives of a space mission result into instrumental developments and specific satellite operations to observe astronomical objects of interest. The payload in its space environment is however subject to important thermal variations that affect observations. This is well observed when images of the Sun are recorded with the constraint of keeping the solar rotational axis in a constant direction relatively to the camera reference frame. Consequences are clearly observed on image positions that follow the thermal variations induced by the satellite orbit. This is, in particular, the case for the space mission PICARD. This phenomenon is similar to defocus and motions of images recorded with ground-based telescopes. We first present some simulations showing these effects. We then compare our results with real data obtained from the space mission PICARD.

The Space Weather and Ultraviolet Solar Variability (SWUSV) Microsatellite Mission

We present the ambitions of the SWUSV (Space Weather and Ultraviolet Solar Variability) Microsate... more We present the ambitions of the SWUSV (Space Weather and Ultraviolet Solar Variability) Microsatellite Mission that encompasses three major scientific objectives: (1) Space Weather including the prediction and detection of major eruptions and coronal mass ejections (Lyman-Alpha and Herzberg continuum imaging); (2) solar forcing on the climate through radiation and their interactions with the local stratosphere (UV spectral irradiance from 180 to 400 nm by bands of 20 nm, plus Lyman-Alpha and the CN bandhead); (3) simultaneous radiative budget of the Earth, UV to IR, with an accuracy better than 1% in differential. The paper briefly outlines the mission and describes the five proposed instruments of the model payload: SUAVE (Solar Ultraviolet Advanced Variability Experiment), an optimized telescope for FUV (Lyman-Alpha) and MUV (200-220 nm Herzberg continuum) imaging (sources of variability); UPR (Ultraviolet Passband Radiometers), with 64 UV filter radiometers; a vector magnetometer; thermal plasma measurements and Langmuir probes; and a total and spectral solar irradiance and Earth radiative budget ensemble

the Bolometric Oscillation Sensor (BOS)

The Bolometric Oscillation Sensor (BOS) is a broadband radiation measurement instrument onboard t... more The Bolometric Oscillation Sensor (BOS) is a broadband radiation measurement instrument onboard the PICARD satellite that was active between 2010 and 2014. The main detector is a thermistor attached black coated surface, which was permanently exposed to space without any optical and aperture accessories. The temperature measurements are used within a transfer function to determine variations in incoming solar irradiance as well as the terrestrial radiation. In the present article, the measurement principle of the BOS and its transfer function are presented. The performance of the instrument is discussed based on laboratory experiments and space observations from the PICARD satellite. The comparison of the short-term variation of total solar irradiance (TSI) with absolute radiometers such as VIRGO/SOHO and TIM/SORCE over the same period of time suggests that the BOS is a relatively much simpler but very effective sensor for monitoring electromagnetic radiation variations from visible to infrared wavelengths.

Supplement Series

Error due to atmospheric turbulence eects on solar diameter measurements performed with an astrolabe

Solar radius determination from SODISM/PICARD and HMI/SDO observations of the decrease of the spectral solar radiance during the June 2012 Venus transit

On 5 to 6 June, 2012 the transit of Venus provided a rare opportunity to determine the radius of ... more On 5 to 6 June, 2012 the transit of Venus provided a rare opportunity to determine the radius of the Sun using solar imagers observing a well-defined object, namely the planet and its atmosphere, occulting partially the Sun. A new method has been developed to estimate the solar radius during a planetary transit. It is based on the estimation of the spectral solar radiance decrease in a region around the contact between the planet and the Sun at the beginning of the ingress and at the end of the egress. The extrapolation to zero of the radiance decrease versus the Sun-to-Venus apparent angular distance allows estimating the solar radius at the time of 1st and 4th contacts. This method presents the advantage of being almost independent on the plate scale, the distortion, the refraction by the planetary atmosphere, and on the point-spread function of the imager. It has been applied to two space solar visible imagers, SODISM/PICARD and HMI/SDO. The found results are mutually consistent,...

On solar radius measurements with PICARD

Solar diameter measurements performed from the ground for several decades seem to indicate a rela... more Solar diameter measurements performed from the ground for several decades seem to indicate a relation between the solar diameter and the solar activity. If this relationship is confirmed, it would be possible to use measurements of solar diameter as a proxy of solar activity in the past since the 1715 solar eclipses, and to use this input for the reconstruction of solar irradiance in climate models. However the interpretation of ground observations is controversial, ground-based measurements being affected by refraction, by atmospheric turbulence, and perhaps by atmospheric aerosols scattering. The only way to be free from atmospheric effects is to measure from space. This is the reason why, since the beginning, the PICARD program included a space and a ground component set up at the Calern site of the Observatoire de la Cote dAzur. During the last 4 years, the PICARD space mission has been used for observing the apparent solar diameter. First results of the astrometry program inclu...

MISOLFA solar monitor for the ground PICARD program

arXiv: Instrumentation and Methods for Astrophysics, 2006

Developed at the Observatoire de la C\^ote d'Azur (OCA) within the framework of the PICARD sp... more Developed at the Observatoire de la C\^ote d'Azur (OCA) within the framework of the PICARD space mission (Thuillier et al., 2006) and with support from the french spatial agency (CNES), MISOLFA (Moniteur d'Images Solaires Franco-Alg\'erien) is a new generation of daytime turbulence monitor. Its objective is to measure both the spatial and temporal turbulence parameters in order to quantify their effects on the solar diameter measurements that will be made from ground using the qualification model of the SODISM (SOlar Diameter Imager and Surface Mapper) instrument onboard PICARD. The comparison of simultaneous images from ground and space should allow us, with the help of the solar monitor, to find the best procedure possible to measure solar diameter variations from ground on the long term. MISOLFA is now installed at the Calern facility of OCA and PICARD is scheduled to be launched in 2010. We present here the principles of the instrument and the first results obtained ...

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. ... more 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.

Sun from the middle ultraviolet to the near infrared

The Solar Diameter Imager and Surface Mapper (SODISM) onboard the PICARD space mission provides w... more 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 success-fully 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

Sun from the middle ultraviolet to the near infrared

The Solar Diameter Imager and Surface Mapper (SODISM) onboard the PICARD space mission provides w... more 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 success-fully 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

On-Orbit Degradation of Solar Instruments

We present the lessons learned about the degradation observed in several space solar missions, ba... more We present the lessons learned about the degradation observed in several space solar missions, based on contributions at the Workshop about On-Orbit Degradation of Solar and Space Weather Instruments that took place at the Solar Terrestrial Centre of Excellence (Royal Observatory of Belgium) in Brussels on 3 May 2012. The aim of this workshop was to open discussions related to the degradation observed in Sun-observing instruments exposed to the effects of the space environment. This article summarizes the various lessons learned and offers recommendations to reduce or correct expected degradation with the goal of increasing the useful lifespan of future and ongoing space missions.

New values of gravitational moments J2 and J4 deduced

By applying the theory of slowly rotating stars to the Sun, the solar quadrupole and octopole mom... more By applying the theory of slowly rotating stars to the Sun, the solar quadrupole and octopole moments J2 and J4 were computed using a solar model obtained from CESAM stellar evolution code (Morel (1997)) combined with a recent model of solar differential rotation deduced from helioseismology (Corbard et al. (2002)). This model takes into account a near-surface radial gradient of rotation which was inferred and quantified from MDI f-modes observations by Corbard and Thompson (2002). The effect of this observational near-surface gradient on the theoretical values of the surface parameters J2, J4 is investigated. The results show that the octopole moment J4 is much more sensitive than the quadrupole moment J2 to the subsurface radial gradient of rotation.

Adaptive Mask Coronagraph

Abstract. In this paper, the new coronagraph that will be mounted at the Pic du Midi Ob-servatory... more Abstract. In this paper, the new coronagraph that will be mounted at the Pic du Midi Ob-servatory (IMCCE- T1m telescope) is presented. To optimize the occulting process of a Lyot coronagraph, a compressed mercury (Hg) drop is used as an occulting disk and its size control offers an adaptation to the seeing conditions or to the Airy diameter fraction needed. In addition to the Hg-mask, a variation on the theme is proposed by a diameter and wavelength adaptive phase mask made of a gas bubble in immersion oil between two optical windows. The instrument concept offers a good versatility to test other mask type and pupil apodization techniques.

Operation of the Airborne 355-nm High Spectral Resolution and Doppler Lidar LNG

EPJ Web of Conferences, 2020

High spectral resolution lidar (HSRL) are known to offer capabilities of separating attenuated ae... more High spectral resolution lidar (HSRL) are known to offer capabilities of separating attenuated aerosol and molecular backscattering so that particle extinction and backscattering can be separately retrieved. UV operation provides high energy in eye-safety conditions. Further to that, it could be important for most meteorological or environmental studies to get wind measurements at the same time. LNG is now the only HSR Doppler Lidar (HSRDL) system capable of this. Results obtained during ground-based and airborne measurements show that the backscatter and extinction coefficients at 355 nm can be measured with a relative precision better than 10% (adjusting altitude and time resolution from 60 m to 240 m and 30s to 2mn, respectively) in aerosol layers of 0.5 10−6 m−1 sr−1 backscatter coefficient from ground and aircraft. The same relative precision is obtained in cirrus clouds of a 10−5 m−1 sr−1 backscatter coefficient. The capacity of the system to perform wind velocity measurements...

A new solar reference spectrum from 165 to 3088 nm

The EGU General Assembly, 2017

Since April 5, 2008 and until February 15, 2017 the SOLAR/SOLSPEC spectro-radiometer on the Inter... more Since April 5, 2008 and until February 15, 2017 the SOLAR/SOLSPEC spectro-radiometer on the International Space Station performed accurate measurements of Solar Spectral Irradiance (SSI) from the far ultraviolet to the infrared (165 nm to 3088 nm). These measurements are of primary importance for a better understanding of solar physics and of the impact of solar variability on climate (via Earth's atmospheric photochemistry). In particular, a new reference solar spectrum is established covering most of the unusual solar cycle 24 from minimum in 2008 to maximum. Temporal variability in the UV (165 to 400 nm) is presented in several wavelengths bands. These results are possible thanks to revised engineering corrections, improved calibrations and new procedures to account for thermal and aging advanced corrections. Uncertainties on these measurements are evaluated and compare favorably with other instruments.

SOLAR-ISS: A new reference spectrum based on SOLAR/SOLSPEC observations

Astronomy & Astrophysics, 2018

Context. Since April 5, 2008 and up to February 15, 2017, the SOLar SPECtrometer (SOLSPEC) instru... more Context. Since April 5, 2008 and up to February 15, 2017, the SOLar SPECtrometer (SOLSPEC) instrument of the SOLAR payload on board the International Space Station (ISS) has performed accurate measurements of solar spectral irradiance (SSI) from the middle ultraviolet to the infrared (165 to 3088 nm). These measurements are of primary importance for a better understanding of solar physics and the impact of solar variability on climate. In particular, a new reference solar spectrum (SOLAR-ISS) is established in April 2008 during the solar minima of cycles 23–24 thanks to revised engineering corrections, improved calibrations, and advanced procedures to account for thermal and aging corrections of the SOLAR/SOLSPEC instrument. Aims. The main objective of this article is to present a new high-resolution solar spectrum with a mean absolute uncertainty of 1.26% at 1σ from 165 to 3000 nm. This solar spectrum is based on solar observations of the SOLAR/SOLSPEC space-based instrument.Method...

A New Solar Spectrum from 656 to 3088 nm

Solar Physics, 2017

Multicast routing in wireless networking is the latest technology for network groups. Multicast r... more Multicast routing in wireless networking is the latest technology for network groups. Multicast routing is part of point-to-point/multipoint-to-multipoint communications. Multicast routing ensures efficient, reliable and secure for wireless networks than unicast routing due to protocols and techniques speed which are combined on multicast routing for wireless technology. Due to redundancy lack in multipath/multicast structures, multicast routing protocols are vulnerable to the ad hoc networks component failure. Some techniques to overcome this are optimizing routing which increases packet delivery minimizing overhead. Particle swarm optimization (PSO) is a network optimizing tool. This paper proposes new PSO based Multicast Ad-hoc On-demand Distance Vector (MAODV) Protocol for MANETs to improve link break prediction accuracy and congestion occurrence. The proposed technique improves routing packages packet delivery ratio. PSO based MAODV allows each network node to forward multicast data packets which are broadcast when propagated along a multicast group tree.

Solar Irradiance from 165 to 400 nm in 2008 and UV Variations in Three Spectral Bands During Solar Cycle 24

Solar Physics, 2016

Accurate measurements of solar spectral irradiance (SSI) and its temporal variations are of prima... more Accurate measurements of solar spectral irradiance (SSI) and its temporal variations are of primary interest to better understand solar mechanisms, and the links between solar variability and Earth's atmosphere and climate. The SOLar SPECtrum (SOLSPEC) instrument of the Solar Monitoring Observatory (SOLAR) payload onboard the International Space Station (ISS) has been built to carry out SSI measurements from 165 to 3088 nm. We focus here on the ultraviolet (UV) part of the measured solar spectrum (wavelengths less than 400 nm) because the UV part is potentially important for understanding the solar forcing of Earth's atmosphere and climate. We present here SOLAR/SOLSPEC UV data obtained since 2008, and their variations in three spectral bands during Solar Cycle 24. They are compared with previously reported UV measurements and model reconstructions, and differences are discussed.

$Figure 3. The red curve represents the UV PM temperature evolution during a calibration test. The SOLAR/SOLSPEC signal (S;,(t) at 210.2nm) evolves during a short time period (the blue curve). This instability effect should be corrected. wavelength (210.2nm). This test highlights that the instrument is unstable during short-time period (~6% of variation). It was repeated several times (Figure 3), which shows the reversibility of the instrumental effect (Ig(\,t)). SOLAR/SOLSPEC measurements during 20 minutes show SSI variations that are above the expected values during a solar cycle. The thermo-mechanical sta- bility of the instrument is questionable and requires an opto-thermo-mechanical analysis. One can notice that during SOLAR/SOLSPEC switch-on, the signature of the signal is slightly different. Currently, we try to understand the link between the SOLAR/SOLSPEC UV photo-multiplier (UV PM) temperature and the measured signal.$

Identification of clear days from solar irradiance observations using a new method based on the wavelet transform

Renewable Energy, 2017

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

On HMI solar oblateness during solar cycle 24 and impact of the space environment on results

Advances in Space Research, 2016

Solar oblateness is a fundamental parameter of the Sun, which provides indirect information on th... more Solar oblateness is a fundamental parameter of the Sun, which provides indirect information on the inner rotation profile and on the distribution of matter. It also puts constraints on General Relativity. But this quantity is difficult to measure due to its very small value where the solar equator-to-pole radius difference is less than 10 milli-arcsecond (mas). Indeed, the measurements can be affected by magnetic activity and by instrumental effects linked to the space environment. The Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO) has produced accurate determinations of the solar oblateness from 2010 to 2015. The HMI measurements of the solar shape are obtained during special roll maneuvers of the spacecraft by 11.25 degrees steps around the spacecraft to the Sun line. HMI roll maneuver has been repeated ten times after the commissioning phase from October 2010 to July 2015. From HMI data, we observed a slight anti-correlation between solar oblateness and solar activity. From a new correction method, we found a mean solar equator-to-pole radius difference of 8.36 ± 0.49 mas (i.e. 6.06 ± 0.35 km at one σ ) at 617.3 nm during the period 2010-2015.

How mission requirements affect observations: case of the PICARD mission

Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, 2016

The scientific objectives of a space mission result into instrumental developments and specific s... more The scientific objectives of a space mission result into instrumental developments and specific satellite operations to observe astronomical objects of interest. The payload in its space environment is however subject to important thermal variations that affect observations. This is well observed when images of the Sun are recorded with the constraint of keeping the solar rotational axis in a constant direction relatively to the camera reference frame. Consequences are clearly observed on image positions that follow the thermal variations induced by the satellite orbit. This is, in particular, the case for the space mission PICARD. This phenomenon is similar to defocus and motions of images recorded with ground-based telescopes. We first present some simulations showing these effects. We then compare our results with real data obtained from the space mission PICARD.

The Space Weather and Ultraviolet Solar Variability (SWUSV) Microsatellite Mission

We present the ambitions of the SWUSV (Space Weather and Ultraviolet Solar Variability) Microsate... more We present the ambitions of the SWUSV (Space Weather and Ultraviolet Solar Variability) Microsatellite Mission that encompasses three major scientific objectives: (1) Space Weather including the prediction and detection of major eruptions and coronal mass ejections (Lyman-Alpha and Herzberg continuum imaging); (2) solar forcing on the climate through radiation and their interactions with the local stratosphere (UV spectral irradiance from 180 to 400 nm by bands of 20 nm, plus Lyman-Alpha and the CN bandhead); (3) simultaneous radiative budget of the Earth, UV to IR, with an accuracy better than 1% in differential. The paper briefly outlines the mission and describes the five proposed instruments of the model payload: SUAVE (Solar Ultraviolet Advanced Variability Experiment), an optimized telescope for FUV (Lyman-Alpha) and MUV (200-220 nm Herzberg continuum) imaging (sources of variability); UPR (Ultraviolet Passband Radiometers), with 64 UV filter radiometers; a vector magnetometer; thermal plasma measurements and Langmuir probes; and a total and spectral solar irradiance and Earth radiative budget ensemble

the Bolometric Oscillation Sensor (BOS)

The Bolometric Oscillation Sensor (BOS) is a broadband radiation measurement instrument onboard t... more The Bolometric Oscillation Sensor (BOS) is a broadband radiation measurement instrument onboard the PICARD satellite that was active between 2010 and 2014. The main detector is a thermistor attached black coated surface, which was permanently exposed to space without any optical and aperture accessories. The temperature measurements are used within a transfer function to determine variations in incoming solar irradiance as well as the terrestrial radiation. In the present article, the measurement principle of the BOS and its transfer function are presented. The performance of the instrument is discussed based on laboratory experiments and space observations from the PICARD satellite. The comparison of the short-term variation of total solar irradiance (TSI) with absolute radiometers such as VIRGO/SOHO and TIM/SORCE over the same period of time suggests that the BOS is a relatively much simpler but very effective sensor for monitoring electromagnetic radiation variations from visible to infrared wavelengths.

Supplement Series

Error due to atmospheric turbulence eects on solar diameter measurements performed with an astrolabe

Solar radius determination from SODISM/PICARD and HMI/SDO observations of the decrease of the spectral solar radiance during the June 2012 Venus transit

On 5 to 6 June, 2012 the transit of Venus provided a rare opportunity to determine the radius of ... more On 5 to 6 June, 2012 the transit of Venus provided a rare opportunity to determine the radius of the Sun using solar imagers observing a well-defined object, namely the planet and its atmosphere, occulting partially the Sun. A new method has been developed to estimate the solar radius during a planetary transit. It is based on the estimation of the spectral solar radiance decrease in a region around the contact between the planet and the Sun at the beginning of the ingress and at the end of the egress. The extrapolation to zero of the radiance decrease versus the Sun-to-Venus apparent angular distance allows estimating the solar radius at the time of 1st and 4th contacts. This method presents the advantage of being almost independent on the plate scale, the distortion, the refraction by the planetary atmosphere, and on the point-spread function of the imager. It has been applied to two space solar visible imagers, SODISM/PICARD and HMI/SDO. The found results are mutually consistent,...

On solar radius measurements with PICARD

Solar diameter measurements performed from the ground for several decades seem to indicate a rela... more Solar diameter measurements performed from the ground for several decades seem to indicate a relation between the solar diameter and the solar activity. If this relationship is confirmed, it would be possible to use measurements of solar diameter as a proxy of solar activity in the past since the 1715 solar eclipses, and to use this input for the reconstruction of solar irradiance in climate models. However the interpretation of ground observations is controversial, ground-based measurements being affected by refraction, by atmospheric turbulence, and perhaps by atmospheric aerosols scattering. The only way to be free from atmospheric effects is to measure from space. This is the reason why, since the beginning, the PICARD program included a space and a ground component set up at the Calern site of the Observatoire de la Cote dAzur. During the last 4 years, the PICARD space mission has been used for observing the apparent solar diameter. First results of the astrometry program inclu...

MISOLFA solar monitor for the ground PICARD program

arXiv: Instrumentation and Methods for Astrophysics, 2006

Developed at the Observatoire de la C\^ote d'Azur (OCA) within the framework of the PICARD sp... more Developed at the Observatoire de la C\^ote d'Azur (OCA) within the framework of the PICARD space mission (Thuillier et al., 2006) and with support from the french spatial agency (CNES), MISOLFA (Moniteur d'Images Solaires Franco-Alg\'erien) is a new generation of daytime turbulence monitor. Its objective is to measure both the spatial and temporal turbulence parameters in order to quantify their effects on the solar diameter measurements that will be made from ground using the qualification model of the SODISM (SOlar Diameter Imager and Surface Mapper) instrument onboard PICARD. The comparison of simultaneous images from ground and space should allow us, with the help of the solar monitor, to find the best procedure possible to measure solar diameter variations from ground on the long term. MISOLFA is now installed at the Calern facility of OCA and PICARD is scheduled to be launched in 2010. We present here the principles of the instrument and the first results obtained ...