Optimised data archiving for a synoptic telescope

1. Optimised data archiving for a synoptic telescope M.Klvaňa, M.Sobotka,and M.Švanda Astronomical Institute, Academyof Sciences of the Czech Republic, Ondřejov 1st SPRING Workshop, November 2013

2. Purposes of a solar synoptic telescope • Monitoring of solar atmosphere in spectral channels according to scientific requirements • Real-time visualisation of solar atmosphere and activity, including an internet access to fresh data (images, position measurement, Dopplergrams, magnetograms, etc.) • Observation of fast active processes and their evolution (pre-onset situation, dynamic phase, slow changes, end of activity) – “flare catcher” • Smart archiving of changes in fast active processes, including the scene before their onset (activity archives) • Archiving of the history of long-term solar activity (long-term archive) • Data archiving for helioseismology (helioseismology archive)

3. Requirements to a synoptic telescope • A full-automatic operation (reliability !!) • Open concept allowing modifications and improvements • Simultaneous observations of all (active) processes in the solar atmosphere • Records of transient active processes including periods before their onsets Large high-resolution solar telescopes have a small field of view, so that they cannot track simultaneously several active regions. The requirements are met by a full-disc telescope that shows the whole solar disc including near surroundings. However, the spatial resolution is limited by the resolution (number of pixels) of the used detector.

4. The full-disc telescope FOV, including an off-disc area, compared with a high-resolution telescope FOV.

5. Limiting factors of the full-disc telescope • Limited resolution of a detector chip chips currently available on the market:8000x6000 px (48 Mpx) • Digital sampling of the image is limited by the chip resolution Diameter of the solar disc and its near surroundings:3000 arcsec According to the Nyquist’s theorem: Digital image resolution = 1 arcsec • The digital image resolution constraints the optical system The sufficient aperture of the full-disc telescope (concerning the resolution) is D = 150 mmfor λ = 600 nm • The control system of the telescopemust keep the solar disc image always at the centre of the detector – otherwise we loose a part of FOV or we must make the image of the disc smaller, loosing the resolution

6. Example: Auxiliary full-disc telescope (AFDT) for the EST project Mechanical structure

7. Example: Auxiliary full-disc telescope (AFDT) for the EST project Optical scheme: D = 150 mm refractor

8. Parameters of the synoptic telescope • The AFDT-type paralactic mount may be considered. Its advantage is a very high stability; a drawback is the flat mirror that introduces a time-dependent instrumental polarisation. • The minimum aperture is 150 mm. Larger apertures should be considered, depending on photon flux required by post-focus instruments. • Optical channels and post-focus instruments according to SRD. • Equal size of the solar disc in all optical channels. • Each optical channel shall have an autonomous automatic focusing and a correction for solar-disc deformation due to the refraction.

9. The problem of a large volume of data • Data archiving in astronomy has the following problems: • The volumes of data continuously increase • The data manipulation becomes difficult • The data archiving requires huge storage capacities • The long-term maintenance of archives is laborious • For these reasons, a reduction of archived data volume is needed. • Possibilities of data volume reduction for synoptic observations: • Selection of an appropriate sampling frequency • “Smart” data archiving– selection and archiving of images containing a new useful information • Archiving of parts of images containing active phenomena instead of the whole FOV

10. Archiving of fast active processes • Continuous check for dynamic phases of active processes in all selected channels. • When a beginning of the dynamic phase is detected in any channel, start the 1st phase of digitisation in all selected channels. • Continuous check for the end of the active process in all selected channels. • The end of the active process is defined when the time-sampling interval is longer than used for the long-term archiving. • When the end of the active process is detected in all selected channels, finish the 1st phase of digitisation. • If a new active process is detected during the 1st phase of digitisation, the 1st phase of digitisation is re-launched from the beginning.

11. 1st phase of digitisation – full FOV • Frame acquisition with frequency ~ 10 fps; frame selection to obtain the sharpest image every 1 second. • Selected frames are stored into the first-in first-out register (FIFO) with capacity of 600 frames (10 minutes of observation). • Frames in FIFO are compared each to other. If a change in the solar scene (an activity) is detected, the frame is labelled. • When a new active process is detected, all the frames in FIFO are labelled – to record the scene before the activity onset. • All labelled frames are stored into the activity archive. Each active process has its own activity archive.

12. 2nd phase – final archiving of active processes • Identification of the positions of active processes in the telescope’s FOV • Division of the image according to the positions and areas of active processes By archiving of one active region of 200 x 300 arcsec instead of the full FOV we save 99.5 % of capacity.

13. Archiving of the history of long-termsolar activity • Processed full-disc data with all measured physical parameters are stored into the long-term archive. • The time-sampling is chosen to describe sufficiently in detail the long-term evolution of solar activity. For example, the best sample obtained in the interval of 15 minutes. • In this archive, the fast active processes are sampled randomly, with an insufficient frequency. • Therefore, the long-term archive will also include a chronologic list of observed active events with links to particular activity archives.

14. Data archiving for helioseismology • The helioseismology archive stores for instance: - full-disc intensities at different wavelengths in selected lines - full-disc Dopplergrams in the lines according to SRD - depths and equivalent widths of selected lines, etc. • Sampling frequency: 30 – 60 sec, equidistant in time • Spectral sampling: ~ 6 points per one line profile

15. Important hardware components • Guider – the solar disc has to be centred at the detectors. The guiding can be realised by telescope drives or a tip-tilt mirror. • Automatic focusing of all optical channels. • Automatic evaluation of meteorological conditions and protection of the telescope against bad weather. • Fast tip-tilt – depends on exposure times: for short ones, fast image motion and guiding errors can be compensated by software means. • No adaptive optics – AO is not necessary due to the relatively small aperture and it is very hard to implement due to the extremely large FOV (> 2000 arcsec).

16. Important software components • Test for clouds (false changes in images) • Test for image quality (sharpness) • Correction for image motion • Test for changes in images (activity signs) • Recognition of a new activity • Test for activity evolution and end

17. Summary The SPRING telescope should have the following functions: ● Data acquisition of solar disc and its vicinity ● Recognition and timely archiving of fast active processes ● Archiving of long-term history of solar activity ● Archiving of data for helioseismology These functions can be fully automated. The resolution of present detectors impose the following limitations: ● The solar disc must be centred on the detectors. ● The resolution of the full-disc telescope equipped with chips of 8000 x 6000 px will not be better that 1 arcsec. ● The useful aperture of the full-disc telescope is 150 mm at 600 nm. Larger apertures do not increase the resolution but collect more light.

18. References: Klvaňa M., Sobotka M., Švanda M. 2011, Solar synoptic telescope: Characteristics, possibilities, and limits of design, Contrib. Astron. Obs. Skalnaté Pleso, 41, 92 Klvaňa M., Sobotka M., Švanda M. 2012, Optimisation of solar synoptic observations, in Observatory Operations: Strategies, Processes, and Systems IV, Proc. of SPIE Vol. 8448, 84480A Thanks for attention