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Monitoring Nighttime Cloud Amount at Muztagh-ata Site

Jun 08, 2023

For optical astronomical observatories, the cloud coverage during nighttime directly determines the available observing time (AOT) of a telescope, the most basic parameter in astronomical observations.
Using the ground-based all-sky cloud camera to monitor cloud amount is the fundamental step for astronomical observation site selection. Since the beginning of site testing in January 2017, the ground-based cloud detection has been carried out at the Muztagh-ata site.
XU Jing, a senior engineer from Xinjiang Astronomical Observatory of the Chinese Academy of Sciences, and his collaborators have processed and analyzed the night-time ground-based cloud detection data collected at the Muztagh-ata site from 2017 to 2021. The results showed that the site could provide 175 clear nights in a year, in which 169 nights are with at least four hours of continuous observing time.

The study was published in Research in Astronomy and Astrophysics.

Statistical results of processed images showed 65% annual available observing nighttime, 66% observing nighttime with AOT more than 50%, and 51% of clear nights with AOT more than 75%. The amount of continuous observing time more than six hours during the night accounted for 31.1% of the total nighttime.

Moreover, the researchers found discrepancies between the CM SAF cLoud, Albedo and surface RAdiation (CLARA) data and ground-based statistical results in the months with average cloud top heights lower than 3,500m from the ground. This might be caused by the limitation of the capability of ground-based all-sky cameras to recognize high clouds.

According to the researchers, these results could be applied to a wide range of cloud coverage analyzes.

Contact

XU Jing

Xinjiang Astronomical Observatory

E-mail:

Site-testing at the Muztagh-ata Site V. Nighttime Cloud Amount during the Last Five Years

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