Satellite Missions and Observations Dan Gershman SHINE Student Day 7/10/2011
This talk • Overview • What makes each spacecraft dataset important? • Where can you get all this data? • Summary
Overview of current missions http://science.nasa.gov/missions/
What makes each spacecraft dataset important? • Measurement time period • Spacecraft location • Types of measurements (i.e. types of instruments)
Measurement Time Period • Solar min vs. solar max • Solar min vs. solar min • Solar max vs. solar max • Conjunctions with planets, comets, etc… • It’s hard to cross-calibrate instruments on different spacecraft, so ideally we want to use the same spacecraft for all of our analysis on a given dataset! (Though this isn‘t always possible)
Spacecraft location • L1 – first Lagrangian point • Outside Earth’s magnetosphere and bow shock • Never shadowed by the Earth or the Moon • Near Earth (R=1AU) observations • solar wind monitors • Examples: • ACE, SOHO, Wind Courtesy of Wikipedia
Spacecraft location • Sun-synchronous • Inside Earth’s bow shock • Satellite orbits Earth such that its always at the same local time (i.e., constant view of the Sun!) • Examples: • Yohkoh, TRACE, Hinode, Proba 2, RHESSI
Spacecraft location • A few others: • Geo-synchronous (SDO) • Satellite orbits such that its always above the same point on Earth, i.e. continuous datastream to the ground! • Earth orbit (IBEX) • Solar orbit • wide variety of heliographic latitudes (Ulysses) • wide variety of heliographic longitudes (STEREO) • wide variety of heliographic radii (Ulysses) • Bounced around through the solar system (Voyager) • Headed towards the ISM http://helio.estec.esa.nl/ulysses/images/third_orbit_2002_rev2006_bigfont.jpg Ahh… Wikipedia
Types of Measurements • In situ (means ‘in position’ in Latin) • Particle measurements (ions, electrons, neutrals) • Magnetic field measurements • Measure what’s happening in the heliosphere • Usually used to compare the output of models • Remote Sensing/Imagers • Photon measurements • Measure what’s happening at the Sun • Usually used as input for models….
Ion instruments • These instruments give plasma velocities and plasma composition. • These typically have one or two sections: • Electrostatic analyzer (ESA) • Time-of-flight chamber (TOF) • Examples: • ACE/SWEPAM, ACE/SWICS, Ulysses/SWICS, STEREO/PLASTIC, Wind/3DP, SOHO/CELIAS, and a bunch of others…. • Instruments that measure other particles typically work in analogous ways, but can have some ionization source (for neutral measurements) and/or have the polarities of the voltages flipped (for electron measurements) Some Relevant Sessions: 3. The Role of Magnetic Geometry and Reconnection in the Origin of the Slow Solar Wind 4. Coronal mass ejections without photospheric/chromospheric signatures 5. Multi-viewpoint observations of Solar Energetic Particle (SEP) events 7. The Nature of CMEs: Heliospheric properties from remote-sensing observations and their relationship to in situ signatures. 8. Particle Acceleration and Transport in Flares and their Relation to SEP events
Electrostatic Analyzer • Makes an electric field that filters out particles based on their E/q. Too high energy 1kV Too low energy 0V Just right!
Time-of-flight -1kV • Ion punches through a thin carbon foil • Ion is usually neutralized • A secondary electron is usually created • Secondary electron is guided to hit a particle detector (start signal) • Neutralized ion, which travels a lot slower than the electron, later hits a different particle detector (stop signal). • With a known E/q and velocity of the ion, can estimate the ion’s m/q. • i.e., E/q = ½ m/q v2 • Instruments that calculate composition need a TOF to distinguish between different species, i.e., ACE/SWICS • Instruments that only care about the bulk plasma (which is usually 95% H+ only need an ESA), i.e., ACE/SWEPAM ion neutral Stop detector Carbon foil e- Start detector 0V
Magnetic Field Measurements • Measure vector magnetic fields at high (relative to plasma measurements) rates. • Typically use ‘fluxgate magnetometer’ design, which measure currents in coils of wire (an inductor) induced by changes in the ambient magnetic field. • ACE/MAG, Wind/MFI, STEREO/IMPACT Some Relevant Sessions: 3. The Role of Magnetic Geometry and Reconnection in the Origin of the Slow Solar Wind 4. Coronal mass ejections without photospheric/chromospheric signatures 7. The Nature of CMEs: Heliospheric properties from remote-sensing observations and their relationship to in situ signatures. 11. The Dissipation of Solar Wind Turbulence 12. The rise of solar cycle 24: Magnetic fields from the dynamo through the photosphere and corona and connecting to the Heliosphere
Remote Sensing/Imagers • SOHO, STEREO, Hinode, SDO • There’s a lot of different photons of interest. • Infrared/Visible • UV/EUV/X-rays • These observations are line-of-sight (LOS). They are an integrated measurement along the look direction. • Note: You don’t need to be in space to make these observations! • i.e., Kitt Peak, Mauna Loa, Mount Wilson, to name a few (http://en.wikipedia.org/wiki/List_of_solar_telescopes )
Imaging – Infrared/Visible • Zeeman-splitting – a spectral line can split into several components (wavelengths/polarizations) near a strong magnetic field • This gives measurements of the photospheric magnetic field! (But only LOS) Some Relevant Sessions: 2. Comparing and Validating Models of the Corona and Inner Heliosphere 3. The Role of Magnetic Geometry and Reconnection in the Origin of the Slow Solar Wind 9. Coronal Magnetic Fields: What are we learning from CoMP observations? 10. What IS a coronal hole? 12. The rise of solar cycle 24: Magnetic fields from the dynamo through the photosphere and corona and connecting to the Heliosphere SDO/HMI
Imaging – Infrared/Visible • Counting Sunspots • Total Solar Irradiance (TSI) • Observing CMEs with scattered white light from electrons • Some relevant sections: • Bridging the Great Divide: Linking the Solar Dynamo to the Dynamic Heliosphere • 6. Assessing the Contribution of Heliospheric Imaging in Improving Space Weather Prediction SOHO/MDI SOHO/LASCO
Imaging – UV/EUV/X-ray • Different features (coronal holes, flares, active regions, etc..) are more easily seen in different wavelengths: SDO/AIA 193nm 304nm 171nm Some relevant sections: 6. Assessing the Contribution of Heliospheric Imaging in Improving Space Weather Prediction 7. The Nature of Coronal Mass Ejections: Heliospheric properties from remote-sensing observations and their relationship to in situ signatures. 8. Particle Acceleration and Transport in Flares and their Relation to SEP events 10. What IS a coronal hole? 12. The rise of solar cycle 24: Magnetic fields from the dynamo through the photosphere and corona and connecting to the Heliosphere 13. Flare Classification in the Era of Global Coverage of the Sun 211nm 131nm 335nm 94nm 1600nm 1700nm
Imaging - UV/EUV/X-ray • Most spacecraft only see one side of the Sun so we have to wait two weeks to see the other side • STEREO A and B recently got far enough apart to see the whole Sun at once! http://stereo-ssc.nascom.nasa.gov/
Where can you get the data? • Data centers (SPDF, SDAC, VSO) http://science.nasa.gov/heliophysics/heliophysics-data-centers/ • Mission websites • ACE http://www.srl.caltech.edu/ACE/ASC/ • SOHO http://sohowww.nascom.nasa.gov/data/ • SDO http://sdo.gsfc.nasa.gov/data/ • STEREO http://stereo-ssc.nascom.nasa.gov/data.shtml • Individual instrument teams
Summary • Satellite missions give us the best (and in most cases, the only) measurements of the solar and heliospheric environment. • These measurements are vital to advancing our fields of study. • Satellite data will be mentioned in EVERY SHINE session at some point. • There are a wide variety of both spacecraft and instruments – it can be tricky to find the right dataset to use!