Turbulence level (or seeing) is a great concern when recording images of objects the sky, because this is simply jeopardizing astronomical telescope resolution. Recording images during best seeing is really a big advantage. In order to achieve this goal, continuous seeing measurement is required to optimize image recording time. To get seeing / turbulence measurements, the DIMM method is mostly used by professional observatories in order to measure atmospheric seeing (or turbulence) and allowing to optimize targets and observation programs.
Nevertheless, DIMM method requires a telescope with enough focal length (>3000mm) and enough aperture (>250mm), and to track bright stars the whole night. This is quite stringent and can be a quite costly approach. The telescope needs a shelter, and automatically jump from a star to another to get not so far away from zenith.
ALCOR-SYSTEM provides a method to overcome some of the drawbacks of the DIMM system.
In the northern hemisphere, a bright star called "polaris" that does not move so much in the sky and is bright enough.
The fixed seeing monitor uses the Polaris star, and ALCOR-SYSTEM is proud to present this new product : micro-CYCLOPE seeing monitor
To compare this product with the Cyclope, is simple. Both are totally identical, but the micro-cyclope does not have any sub system to measure external and internal temperature and humidity, and has no front entrance window automatic heating system to remove dew (if any).
The goal of this product is to measure atmospheric seeing condition in a continuous fashion, so this setup stays outdoors all the time 24h a day, and is aimed at the polaris star in a fixed fashion.
This system can only work in the northern hemisphere, at latitudes above 15° North, for southern hemisphere please contact us for solutions.
The fixed seeing monitor is a totally sealed system that can overcome all extreme weather conditions, and is not sensitive to wind gust due to its strong design. The software starts measurements automatically when the Sun is below the horizon and only when the stars are visible.
The added value of this product compared to competitors are :
- better measurement accuracy because of more and smaller pixels
- ethernet link to the host
- ability to measure very low seeing figure, whereas other systems are not reliable under 1.5 arcsec seeing.
- strong and robust construction, that avoid measurements to be jeopardized by wind gust
This system offers watertight connectors, for continuous outdoor operation.
The line of sight can be adjusted accurately to aim at polaris star. Once this is performed, there is no need to carry out any further adjustements. The system is made of high quality alloy colorless anodized aluminum.
The weight of this item is 4.8 kg, and size is 200 mm x 150 mm (base) Height is 260 mm
The software is embedded to this system (Windows 7/10 versions only).
The field of view of the system is 3.6° x 2.5° and perfectly accomodates the polaris star path throughout the whole night / whole year, so that continuous measurements can be performed.
Since the image recording is performed continuously, it can provide a figure of seeing expressed in arcsec (or Fried's Ro) in a continuous matter, if weather conditions allows. 0.55µm wavelength is used, but also 1.55µm figure can be provided by the software.
The next plot shows seeing measurement over the course of a night. The data is coming from this product (vertical axis is seeing, horizontal axis is time)
In order to validate this concept is working in reliable fashion, it has been compared with other systems, at the same time and the same place, twice.
Comparison with DIMM
Another test consisted in using a Ritchey Chretien 250 mm F8 telescope, with a standard scientific sony ccd camera, and a pixel scale of 0.35 arcsec per pixel. The exposure time was 5 sec, and unsaturated star FWHM was measured on both star axis. The selected star was always close to zenith.
The red dots are the star FWHM over the time from the RC telescope. The black dots are from the cyclop apparatus, and shows very good agreement with the telescope measurements.
Here are the results, the blue line is from the DIMM and the red line from the fixed seeing monitor.The agreement between these two plots is very good, so the data coming out from the fixed seeing monitor can be regarded as reliable.
A last comparison with 10" DIMM system, carried out in July 2016. This is very close, and some difference is visible because polaris star and a star in cygnus constellation has been used, so the optical atmospheric path is not exactly the same.