Access to Solar Orbiter Low Latency Data

 

The Solar Orbiter teams are making public the Low Latency data from the four in-situ instruments (EPD, MAG, RPW, SWA), available via the ESA Solar Orbiter Archive.

Low Latency data are a limited subset of each instrument's data, downlinked in full during every communications pass. They are primarily an operational product, designed to provide situational awareness to the Solar Orbiter team, while the spacecraft is far from Earth, and it takes several weeks to months for science data to be returned to Earth. Within the team, low latency data will be used to perform high-level instrument health checks, to help choose the best targets for the high-resolution imagers, and, for some instruments, to help us select the most interesting events to downlink at the best resolution. 

These data will be immediately available to the whole community from now on and for the entire duration of the mission. However they should be used with caution: they are not of a sufficient quality to undertake science analysis and results derived from them should not be submitted for publication. Full science-quality level 2 data products will be released later this year. 

Data are currently available from:

  • EPD: Energetic Particle Detector (PI: Javier Rodríguez-Pacheco, University of Alcalá, Spain, fsrodriguez@uah.es)
  • MAG: Magnetometer (PI: Tim Horbury, Imperial College London, UK, t.horbury@imperial.ac.uk)
  • RPW: Radio and Plasma Waves (PI: Milan Maksimovic, LESIA, Observatoire de Paris, France, milan.maksimovic@obspm.fr)
  • SWA: Solar Wind Analyser (PI: Chris Owen, MSSL, University College London, c.owen@ucl.ac.uk)

Instrument papers are available from here: https://www.cosmos.esa.int/web/solar-orbiter/a-a-solar-orbiter-special-issue

Questions about each instrument's low latency data can be addressed to the relevant PI.

For mission-level questions, please contact the ESA Project Scientists:

Daniel Müller: Daniel.Mueller@esa.int

Yannis Zouganelis: Yannis.Zouganelis@esa.int

For questions about the Solar Orbiter Archive, please contact the Archive Scientist, Pedro Osuna (Pedro.Osuna@esa.int).

 

Low Latency data are not suitable for publication. Furthermore, instruments' data come with a set of caveats, listed below.

 

EPD Low Latency Data Caveats

The EPD Low Latency data are not to be used in any publication, they are used to identify possible interesting particles activity.

 

MAG Low Latency Data Caveats

V1 20 July 2020

The MAG Low Latency data are a useful resource but should be used with caution: they contain many artificial signals, are not of a high enough quality to undertake science analysis and results derived from them should not submitted for publication.

Routine processing of the MAG data on the ground removes the vast majority of these signals but the automated nature of the pipeline at ESA/ESAC means that this cannot be applied to the Low Latency data stream. The MAG team intends to provide a cleaned version of the MAG data in the near future which should be used in preference to the Low Latency data. We also expect to release full science-quality level 2 data products to the ESA archive from September 2020.

List of known issues in MAG Low Latency data

The MAG team has not had the opportunity to assess the reliability of the data processing pipeline for Low Latency flight data, so we cannot vouch for the reliability or accuracy of this processing.

In addition, the MAG data contain artificial signals covering a wide range of timescales and magnitudes, none of which are predictable at this time:

  1. MAG heater signal – up to 1nT in amplitude, typically lasts one minute and occurs every 10-20 minutes. This is the most visible signature in the data.
  2. Varying spacecraft offsets – spacecraft fields can vary over long timescales (weeks or more) by up to several nT. Since these can only be determined after the fact, that are not corrected in the Low Latency data. Some changes can also be rapid, such as those due to solar array movements.
  3. Spacecraft-operated heaters – over 50 heaters operate on the spacecraft and switch off and on unpredictably to keep various components within their required temperature range. Their total contribution to the field at the sensor location is around 0.5 nT but variations due to the total field are more common at around the 0.1 nT level.
  4. Thruster firings – these occur up to once a day, last up to several minutes, and have amplitudes up to 0.2 nT.
  5. Operation of other instruments – fields due to the currents from other instruments, and sharper variations due to mechanism movements, can also be present in the data. The MAG team are still quantifying these fields but the total field due to the operation of the payload is around 0.5 nT. Note that the majority of the power is consumed by remote sensing instruments, which are not operated continuously, so these fields can vary.
  6. Operation of SWA/EAS – we have evidence that operation of the electron sensor at the end of the instrument boom introduces signals into the MAG data at the 0.1 nT level but these have not yet been quantified in detail.

 

RPW Low Latency Data Caveats

RPW low latency data are not for scientific publication. RPW low latency data are currently dominated by the EMC signature of the spacecraft's Power Control and Distribution Unit. An RPW onboard software update is required to mitigate these perturbations. At this stage the RPW low latency data are useless, whatever the purpose.
 

 

SWA Low Latency Data Caveats

The SWA suite of instruments provides a number of low latency (LL) data products from each of the 3 sensors.  These were originally designed and intended for the purposes of supporting short-term operations planning and instrument health/performance monitoring.  In common with the rest of the SO payload, the SWA team subsequently agreed to release these data products as potential beacon or quick-look data.  However, the SWA LL data products are rapidly produced by an automated process hosted by a virtual machine (VM) at the SOC, and the SWA team is unable to support in depth analysis and calibration activities on them.  A number of products are in any case quickly superseded by ground-processed products.  The SWA LL data should in all cases be used with extreme caution regarding their accuracy as products for support of valid scientific analyses.

SWA PAS Low Latency data product:

SWA-PAS provides just one LL product set namely “Quick Look Ion Moments”

This product set contains parameters as follows:

  • Solar wind ion number density expressed in cm-3
  • Solar wind ion velocity vector in the spacecraft frame expressed in km s-1
  • Solar wind ion pressure tensor containing Pxx, Pyy, Pzz, Pxy, Pxz, Pyz, expressed in J cm-3
  • Solar wind ion common temperature (averaged over the degrees of freedom ) expressed in eV

The PAS Quick Look Ion Moments cadence is one sampling per 4 s.

Important notes:

  1. We consider these parameters as an “Instrument health quick indicator” and should only be used as solar wind plasma moments with a serious caution.
  2. The parameters are calculated as a moments of all measured ions without separation of H+ and He++ We consider He++ ions as protons in this calcultion. Thus the ion velocity vector can deviate a little from its real direction and temperature might be higher than the real proton temperature.
  3. Since PAS ion detector efficiency is varying with time, the number density (and, correspondingly, the pressure tensor) might include an important systematic error. We cannot consider these parameters as absolute measurements. Researchers should obtain the ground calculated SWA-PAS moments, once they are available, for the absolute calibrated values.

SWA HIS Low Latency data product:

HIS low-latency data contains 2 ion charge state ratios and two 64-element rate spectra, in raw and physical units, as well as rough moments of the spectra (density, speed and temperature). 

The primary function for this data is to provide information on HIS end-to-end operation, as well as physical quantities useful to help assess the state of the solar wind for mission planning purposes.  The source data for these four items is configurable via parameter upload.  Later in the mission, these charge state ratios will be assigned to scientifically meaningful species, such as O7+/O6+ and C6+/C4+.  One of the rate spectra will then be dedicated to scientifically interesting species such as He2+ or O6+.  However, at this early stage in the mission, the rate spectra are configured to provide maximum information about the proper end-to-end operation of HIS.  They are currently defined as the rate on the start detector and the rate of triple coincidences. These data provide detailed information about the overall count rate and performance of the event detection logic.   The two ion charge state ratios remain undefined until there is sufficient data on the ground to do so.  In their current state, HIS Low Latency data are not useable for even for quick-look science, though they are highly valuable for understanding HIS performance.

SWA EAS Low Latency data product:

The 2 EAS sensors measure electrons distributed over a spectrum of energies and over a range of azimuths and elevations.  Together they are capable of providing a full, 3D phase space distribution covering the 4π space.  In normal mode, EAS will measure one full 3D distribution every second.  However, telemetry restrictions mean only every 100th second distribution is sent to the SSMM as the full 3D data product.  

For the LL EAS data product, the SWA DPU will extract a reduced measurement from the intervening 50th second distribution, namely those counts corresponding to a single given energy bin, but from each azimuth and elevation angle sampled by both sensors.   The combined LL EAS data product is thus a 3D shell, containing measurements from a single energy bin. The selected energy bin is configurable by ground command, and we expect to generally select an energy in the solar wind  ‘strahl’ population energy range, such that the product can provide an indication of the presence of strahl beams within the data.  This LL product is thus termed the ‘single-energy-strahl’ measurement by the EAS sensor.

The product is decompressed and calibration factors automatically applied by the SWA VM at the SOC.  The accuracy of the calibration factors at any given point in time is not guaranteed by the SWA team.   In addition, no corrections for any possible spacecraft-related effects are assessed or applied.  Thus the absolute values of fluxes in this LL data product are not assured, but the product is supplied as a means of examining relative electron fluxes at strahl energies, and thus a possible early indication of the connectivity of the magnetic field at the spacecraft. All other uses are caveat utilitor.

 

Data Access

The Low Latency data can be accessed via the Solar Orbiter Archive at https://soar.esac.esa.int