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Instrument: VIRGO : Variability of Solar Irradiance and Gravity Oscillations
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Associated Platforms
SOHO

Spectral/Frequency Information
Wavelength Keyword: Ultraviolet
Number Channels: 1
Spectral/Frequency Coverage/Range: 335 nm

Wavelength Keyword: Visible
Number Channels: 1
Spectral/Frequency Coverage/Range: 550 nm

Wavelength Keyword: Near Infrared
Number Channels: 1
Spectral/Frequency Coverage/Range: 865 nm

Related Data Sets
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Description
The Variability of solar IRradiance and Gravity Oscillations (VIRGO) is an
international collaboration of different European countries. This is a part of
the payload of the SOHO spacecraft. SOHO is an international collaboration
programme between ESA and NASA.

The VIRGO experiment will provide the following observational and derived data:
- continuous high-precision, high-stability and high-accuracy measurements
of the solar total and spectral irradiance and spectral radiance variation;
- continuous measurements of the solar polar and equatorial diameters;
- frequencies, amplitudes and phases of oscillation modes in the frequency
range of 1 uHz to 8 mHz;

The total irradiance is measured with active cavity radiometers (PM06-V and the
Dual Irradiance Absolute Radiometer, DIARAD), the spectral irradiance by
three-channel Sunphotometers (SPM) and the radiance with 12 resolution elements
on the solar disk using the Luminosity Oscillations Imager (LOI).

These data will be utilized to achieve the main scientific objectives of VIRGO
summarized in the following list:
- detect and classify low-degree g modes of solar oscillations;
- determine the sound speed, density stratification and rotation in the
solar interior, specifically determine the physical and dynamical properties of
the solar core;
- study the solar atmosphere through comparison of amplitudes and phases of
the p modes with these from GOLF (Global Oscillations at Low Frequencies) and
SOI/MDI (Solar Oscillation Investigation/Michelson Doppler Imager);
- search for the long periodicities or quasiperiodicities that have been
found in other solar parameters;
- utilize the solar `noise' signal to develop models for the global
signature of stellar surface parameters;
- determine properties of the solar asphericity and its variation in time;
- study the relation between p-mode frequency changes and irradiance
variations;
- study the influence of solar active regions and other large-scale
structures on total and spectral irradiance;
- study the solar energy budget;
- provide accurate total and spectral irradiance data for input in
terrestrial climate modelling.

Observations of the total solar irradiance will be a continuation of previous
measurements from satellites, which have been performed by the radiometer HF of
the Earth Radiation Budget experiment (ERB) on the NIMBUS-7 satellite from
November 1978 until January 1993 (Hoyt et al 1992), by ACRIM~I on the Solar
Maximum Mission satellite (SMM) from February 14, 1980 until June 1, 1989 (e.g.
Willson and Hudson 1991), by ACRIM~II on the Upper Atmospheric Research
Satellite (UARS) since October 1991 (Willson 1992) and by SOVA (Solar
Variability) on the European Retrievable Carrier (EURECA) from August 1992
until May 1993 (Crommelynck et al 1993, Romero et al 1994).

For more information, see:
http://www.ias.u-psud.fr/virgo/virgomain.html

Online Resources
http://www.ias.u-psud.fr/virgo/

Instrument Logistics
Instrument Start Date: 1995-02-12
Instrument Owner: Institut d'Astrophysique Spatiale, Framce