Activities of the Czech group within the CTA Consorcium
The Czech team brings to the Consortium a large volume of experience gathered over years by participation in many high-energy particle physics project, in particular the Pierre Auger Observatory, which is currently the largest cosmic ray detector in the world. The two large fields in which the expertise of the group is particularly valuable in the current preparatory
- optics - design, manufacture, maintenance and measurements of optical systems, in particular large segmented mirrors
- atmospheric monitoring - collection and analysis of data on atmospheric properties using astronomical, satellite and other methods.
These two topics collided during the site search campaign when all the locations considered were equipped by Czech optical devices to monitor cloudiness and background light in situ - the All-Sky Cameras (ASC).
The Joint Laboratory of Optics of the Institute of Physics ASCR and the Palacky Universiry, located in Olomouc is the primary venue for all our activities related to optics. Recently the Laboratory has obtained several new machines that allow fast and reliable production of glass mirror segments with quality and capacity that fit very well with the needs of the Small Scale Telescopes of Davies-Cotton design (SST-DC) which are one of the two possibilities for the highest-energy part of the Observatory currently under consideration. Each of the (potentially many dozens of) telescopes requires 18 hexagonal mirror segments of the size of 80 cm face-to-face with radius of curvature of ca 11 meters. This possibility offers a significant in-kind (material) contribution from the Czech Republic and discussions with the CTA management and especially with Polish colleagues are now very frequent.
For successful realization of the project, it is vital to identify the best location, based on many different criteria, such as infrastructure, costs, safety and, with high priority, atmospheric conditions that determine the fraction of useful uptime and the volume of scientifically valuable data produced within the lifetime of the detector. Nine such locations have been extensively studied across both hemisphere and 8 of them were, among other instrumentation, equipped by the All-Sky Cameras (ASC) (the ninth location already had a similar camera).
The ASC is a simple, autonomous and reliable device which observes the stars during every night and from their visibility deduces the cloud coverage . At the same time, it allows the determination of light levels of the night-sky background. The data from these cameras are being used as an anchor point for interpretation of other sources of meteorological information, in particular the satellite data. The cameras have been designed, produced and installed on all the sites by the Czech group, which is also responsible for data collection, storage and analysis. The ASCs have been originally developed for the Pierre Auger Observatory and tested there thoroughly, so they were ready for the application for the CTA on extremely short notice.
The Czech group has been also involved in processing satellite data on cloud coverage at the sites. This task encompasses obtaining the data for the relevant agencies, transfer and storage of huge amount of data and the development of tools to process such volumes of data. The result is a series of cloudiness values for each site which is then compared with other observations for clearer interpretation.
Atmospheric monitoring at the Observatory
Atmospheric monitoring will be also crucial during the operation of the Observatory - it will serve to guarantee the quality of data and to adapt the scheduling of observations in real time according to the changes of conditions. It is planned that one or more ASCs will monitor continuously the sky above the CTA sites and provide real-time data to the central control, where decisions may be taken to change observed targets if clouds are coming into the field of view of the telescopes.
Another device, also already well tested at Auger, is the FRAM robotic telescope. This instrument employs the same mode of operation, as an ASC - it observes the light of stars as it passes trough the atmosphere. In comparison with the ASC, FRAM has a much smaller field of view (that will just cover the FoV of the CTA itself) but much larger sensitivity to small absorbing layers, aerosols etc. Thus these two devices will ideally complement each other. The CTA version of FRAM is now being developed and it will likely be funded and donated to the Observatory by the Institute of Physics.