ИСТИНА

https://www.youtube.com/watch?v=-C5DYue8KGs&list=PLvT7fd9OiI9WlB_c77EictmSco7Xl1fE5&index=225 Arctic region is attracting increasing attention of researchers due to rapid changes. An important prerequisite for tracking multi-year changes is to consider the seasonal rhythm. Regular surveys of Arctic region by Sentinel-1 provide an opportunity to detailed study of the region seasonal changes over the one season, as well as differences over several years. SAR data is of primary importance for this region due to SAR independence of natural illumination and clouds. Coherence is one of the parameters calculated during interferometric processing of synthetic aperture radar (SAR) remote sensing data on elevation and subsidence modelling. As the coherence is calculated for each element of the radar data, thus forming a map of coherence, it can be used as an additional source of thematic information about the state and properties of a surface. The Kotelny island (The New Siberian Islands archipelago, Russia) is one of the largest Arctic islands and its landscapes diversity is rather well-defined for these high latitudes. As an area of interest two test sites located near the meteorological stations «Ostrov Kotelny» and «Proliv Sannikova» were selected to more accurately relate coherence to real changes in the surface state. The test sites are located within the ice complex lowland covered by tundra vegetation. Seasonal changes of coherence calculated using 2-year (May 2017 – June 2019, revisit time – 12 days) VV-polarization Sentinel 1B/C-band SAR data set were investigated. Coherence values varied within 0,13…0,8 during the period on study. During the cold (with stable negative air temperature, and steady snow cover) and warm (mainly with positive air temperatures, absence of stable snow cover) periods coherence oscillations were in the range of 0,4 (rarely – 0,3)…0,8. During the transition period (when air temperature crosses 0ºC, snow cover forms or melts down) a sharp decrease in coherence to 0.2 or less was observed. The report presents the detailed comparison of coherence values for the sites with available additional information (vegetation indices obtained using optical data, meteorological data i.e. air temperature, snow height and other). Normalized radar cross-section (NRCS) values across the test sites were also analyzed in the study. It is shown that NRCS values are subjected to less variability compared with coherence, i.e. during the cold period it varies within 13… 14 dB and during the warm period – within 7… 9 dB. Significant NRCS values changes (up to 5…7 dB) are observed just during the interim periods. Generally this fact makes the coherence an important additional feature characterizing the condition of the surface of Arctic region.