The results of the studies of astroclimatic conditions for the territory of the Altai Republic for ground-based observations of extensive air showers initiated by very high energy cosmic rays using an array of atmospheric Cherenkov telescopes are presented. Information about the fraction and spatial distribution of cloudless events for considered areas was obtained from the night data of the VIIRS sensor on board the Suomi NPP weather satellite for the period of October 2017 - March 2018. The most suitable zone for construction of an array of optical Cherenkov telescopes was identified.
The main source of information used to solve this problem is the VIIRS Cloud Mask product of algorithm for
processing VIIRS/Suomi NPP data, version 1.5.08.04 [
Data from digital terrain model SRTM (Shuttle Radar Topographic Mission) with a spatial resolution of 90x90 m
was used to determine the parameters of the underlying surface relief [
Statistical data processing and post-processing were performed using GRASS (Geographic Resources Analysis
Support System) GIS, version 7.2 [
The areas of the Altai Republic best suited for gamma ray observations were selected on the basis of the following requirements: maximum fraction of cloudless nights during the active phase of observations from October to March; area altitude (above 1500 m); angle of the terrain slope within the area(<5º); extensive transport and telecommunications infrastructure availability. 3
At the first step, the fraction of cloudless events for the Altai Republic territory was established using the night data from the VIIRS/SNPP sensor for the period October 2017–March 2018. Figure 1 shows the fraction of cloudless atmosphere nights obtained from VIIRS/SNPP data for the study period. It can be seen that the areas with the largest fraction of cloudless nights are mainly in the highland part of the Altai Republic, that mostly consists of hard-to-reach mountain ranges.
The study of astroclimatic conditions for performing night astrophysical observations on the territory of the Altai Republic is carried out. The spatial distribution of cloudless events is obtained according to the nighttime data of the VIIRS radiometer aboard the Suomi NPP satellite platform for the period October 2017 – March 2018.
As potential regions for the second stage of TAIGA observatory construction, in terms of topography and infrastructure criteria, the most suitable areas are the Kurai and Chuya Steppes. A significant part of these zones is located at altitudes of ~1000-2000 m above sea level, that meets the requirements for terrestrial gamma-ray observations. The location of these regions is distant enough from large agglomerations and industrial centers that leads to low aerosol content in the atmosphere and low light pollution.
At the same time, it was found that the fraction of cloudless nights in the Kurai steppe (average height ~1000 m) does not exceeds 35% during the study period at night. For the western part of the Chuya steppe (average height ~2000 m) it reaches ~75%, which makes this area the most suitable place for gamma-ray astronomical observations using optical Cherenkov telescopes.