GPR surveys and RPA aerial photography using in conducting geocryological studies on the Oka plateau in the Eastern Sayan ridge

The results of ground-penetrating radar (GPR) studies of permafrost and aerial photography, carried out at key sites in the Sentsa River valley (Oka Plateau, Eastern Sayan Ridge), are presented.For geophysical studies, an OKO-2 GPR completed with an AB-90 shielded antenna unit was used with a maximum sounding depth of up to 20 m and a resolution of 0.5 m. To account for the landscape elevation, the Trimble TS635 tacheometer and the Leiсa DISTO D 510 rangefinder performed hypsometric measurements with a step of 1.0 m. Aerial photography was carried out by a remotely piloted aircraft (RPA) DJI Inspire 1 Pro, equipped with a Zenmuse 3X camera (a resolution of 3840×2160 pixels) with a spatial resolution of 5.7–7.8 cm/pixel (in different years).In the structure of frozen lacustrine-alluvial sediments, three GPR complexes are distinguished, corresponding to the active layer and frozen rocks with different amounts of schlieren, lenses and layers of texture-forming ice. The orthophoto map and tacheometric survey analysis showed that the destruction of frost mounds occurs from the second half of April to the first half of October. The most significant relief change is due to the thawing of icy pulverescent clayey silts. It leads to subsidence blocks in the ledge of the Sentsa River terrace. Lateral river thermoerosion also contributes to the frost mounds destruction.