Detecting and measuring tree decay is essential part of urban forest management and tree risk assessment in public safety. Invasive and moderately invasive decay-detecting devices, such as constant feed drills, are accurate for locating wood decay in a tree. In contrast, tomography devices are either less damaging to tree tissues (the case of acoustic tomography) or even non-invasive (GPR tomography) but may represent difficulties in processing and interpretation. This paper considers detecting and characterizing the geometry of decay and cavities in live trees using Ground Penetrating Radar (GPR). Combined multi-offset ray-based GPR tomography and zero-offset GPR techniques were validated on five trees selected in the urban environment in the Central Park of Culture and Recreation named after Maxim Gorky (Gorky Park, Moscow). The zero-offset measurements were carried out at three different heights, 60 cm, 140 cm, and 180 cm, while GPR tomography of trunks was done at 140 cm. Consequently, these trees were felled and sectioned, and decay/void measurements were conducted for tree sections at 140 cm height. We demonstrated that the combination of multi-offset GPR tomography with zero-offset GPR allows accurately differentiating between rot /void and healthy wood layers and identifying the position of cavities and decay in tree trunks. There were no false positive or false negative results in void detection, while the error in determining the area was no more than 10 % of the trunk's area. We recommend combining these approaches to produce accurate contours of internal wood defects and consider the result obtained as a basis to build a three-dimensional model of a trunk in situations where conventional invasive forestry approaches are not applicable.

The data of ground-based high-frequency radar survey on the Western Elbrus plateau (Central Caucasus) in the summer of 2017 showed that snow accumulation in the summit area is characterized by great variability and also has seasonal differences. Analysis of the accumulation fields showed that less snow accumulates in the middle part of the plateau than in the eastern and western parts, and that its distribution over the plateau area is similar. In the warm period of the year, snow accumulation is on average higher than in the cold period, occurs more uniformly over the plateau area, and its distribution is more stable from year to year.

Ground penetrating radar is non-invasive technology suitable for mapping moisture content variations since it shows high sensitivity to changes in water saturation. In this work we used a GPR tomography approach to estimate moisture content within two small-leaved lime (Tilia cordata) and two Scots pine (Pinus sylvestris) trunks. Additional information was derived using the method of GPR zero-offset. GPR data was collected in Moscow (diurnal monitoring in September 2021) using a shielded GPR antenna working at 1500 MHz. Moisture values derived from GPR data were compared with the values obtained directly by measuring sampled wood cores gravimetrically. A good agreement was observed between GPR-derived moisture content and core sample-derived values. Notwithstanding GPR-derived moisture content is about two times higher than core sample-derived values, a strong linear relation with a determination coefficient more than 0.8 is observed. Diurnal monitoring did not reveal any significant changes in moisture content inside the trunks. It can be concluded that the period of early autumn in the Moscow region is characterized by a constant moisture content of the small-leaved lime trunk during the day.

This paper substantiates the necessity of using geophysical methods in geocryological monitoring to study the conditions of permafrost rock occurrence, search for taliks and cryopegs, and determine the physical and mechanical properties of frozen rocks. The advantages and disadvantages of these methods and examples of their use for solving geocryological problems are described both in natural conditions and in the impact zone of buildings and engineering structures.

Climate warming in the Russian Arctic over the past 40 years shows a variety of patterns at different locations and time periods. In the second half of the 20th century, the maximum rates of warming were characteristic of the subarctic permafrost regions of Russia. But in the 21st century, the locations of the greatest rates of climate warming moved to the Arctic zone of Russia. It was one of the reasons for a sharp increase in permafrost temperatures, an increase in the depth of seasonal thaw, and the formation of closed taliks. It was found that as a result of climate change, the differences in permafrost temperatures between different cryogenic landscapes in the area of continuous and discontinuous permafrost distribution have decreased, and in the area of sporadic permafrost distribution are now practically absent. The thermal regime of the ground shows dramatic changes everywhere with a pronounced reduction in the depth of zero annual amplitude.

The results of the application of geo-radar profiling for the study of soils and underlying rocks of polygonal bogs of the Pur-Taz interfluve (North of Western Siberia), functioning in natural and anthropogenic disturbed conditions, are presented. The research area belongs to the southern tundra with a predominantly continuous distribution of permafrost rocks. The construction of highways in the North of Russia is one of the main factors of anthropogenic impact on the tundra geosystems of the cryolithozone, affecting the temperature regimes of soils and the depth of permafrost. The features of spatial differentiation of the depth of occurrence of permafrost rocks on the site of polygonal swamps intersected by a federal highway were determined by the methods of geo-radar profiling. Georadiolactic profiling made it possible to determine the configuration of the depth of the permafrost roof both in natural and anthropogenic disturbed areas of polygonal swamps. The maximum lowering of the permafrost roof is determined at the base of the road embankment and does not exceed a depth of three meters. Despite the deep occurrence of the MMP roof under the road embankment, the thickness of the thawed buried peat horizons here is similar to that of the seasonally shallow layer of undisturbed peat polygons. The features of spatial differentiation of the depth of the permafrost roof in the polygonal swamps intersected by the bulk highway in the North of Western Siberia are similar to those characteristic of regions with a continuous low-temperature cryolithozone. The method of manual probing of the permafrost roof was used to verify the results of geo-radar profiling within undisturbed areas.

В 2020 году на территории музейного комплекса Обдорский острога в Салехарде был выполнен комплекс инженерно-геокриологических и геофизических исследований с целью изучения геокриологических условий и пространственной локализации мерзлотника, расположенного в его пределах. В результате исследований показано, что в остроге кровля многолетнемерзлых пород расположена на глубине 4-6м. Уточнено плановое положение мерзлотника, определена его глубина. По результатам исследований установлена мощность сезонно-мерзлого слоя на момент проведения работ и выявлены особенности напряжено-деформированного состояния грунтового массива на территории острога и прилегающем склоне.

The report describes the use of the method of ground penetrating radar (GPR) ray tomography, applied to non-living objects , as a tool for studying the internal structure of trunk of living trees. Due to the lack of mechanical impact on the object of study and high resolution, GPR has an advantage in comparison with other methods of examining the state of trees , such as micro-drilling or acoustic tomography. Field experiments were conducted on different tree species in different states. The results obtained on healthy oak, dry spruce and chestnut with a cavity inside are described. Observations were made in summer of 2017. A two-channel GPR “Zond 12e” (“RadarSystems”, Latvia) with two 2 GHz antennas was used in experiment. GPR tomography is used to determine the distribution of permittivity in the trunk, which is directly related to the moisture of wood. Different parts of the trunk (bark, core, sapwood), as well as healthy and affected areas differ in humidity, so the method of GPR tomography allowed us to see both the structure of the trunk of a healthy tree, and the presence and dimensions of defects.

Summary Climate changes occurring in the Arctic regions cause the transformation of permafrost conditions, including thawing of permafrost. In the last decade, cryogenic processes have been intensifying in the Arctic, including the southern tundra of Western Siberia. In the peat bogs of the khasyreys of the Pur-Taz interfluve, thermokarst processes along polygonal-wedge ice and thermal erosion are especially widespread. However, there is a significant lack of research related to the impact of transport infrastructure on polygonal peatlands. The Ground Penetrating Radar (GPR) method has shown itself to be effective in solving geocryological problems associated with areas of development of peatlands. This work is devoted to the use of GPR for assessing the warming effect of a road in a complex of geocryological works. All profiles crossed the road, the main emphasis was on the warming effect of the road and roadside depressions on the permafrost roof. The anthropogenic impact on the permafrost roof is clearly reflected in its position on the ground penetrating radar data.

Summary Non-destructive Ground Penetrating Radar (GPR) technique can provide a diagnostic tool for assessing the moisture content of live tree trunks based on internal dielectric permittivity distribution. In the current work we discuss the GPR tomography as a powerful tool of imaging the interval structure of a healthy tree and producing quantitative estimation of moisture content (MC) based on distribution of dielectric permittivity, directly related to MC. The measurement described in the work were made on the trunks of live trees of different species in different visible health status, even with rot inside. The results of suggested approach were assessed by resistography. Different parts of the trunk (bark, core, sapwood), as well as healthy and affected areas differ in moisture content, so the GPR tomography allows identifying both the structure of the trunk of a healthy tree, and the presence and dimensions of defects.

В 2021 г. продолжен мониторинг глубины сезонного протаивания, температуры многолетнемерзлых пород, активности криогенных процессов, связанных с вытаиванием подземных льдов, и изменений, происходящих с полигональными торфяниками на полуострове Ямал, севере Пур-Тазовского междуречья и Гыданского полуострова. Представлены основные результаты исследований.

This paper describes the results of ground penetrating radar (GPR) research combined with geocryological data collected from the Circumpolar Active Layer Monitoring (CALM) testing sites in Kashin and Kumzha in August 2015, 2016, and 2017. The study area was located on the Pechora River delta. Both sites were composed of sandy ground and the permafrost depth at the different sites ranged from 20 cm to 8–9 m. The combination of optimum offset and multifold GPR methods showed promising results in these investigations of sandy permafrost geological profiles. According to direct and indirect observations after the abnormally warm conditions in 2016, the thickness and water content of the active layer in 2017 almost returned to the values in 2015 in the Kashin area. In contrast, the lowering of the permafrost table continued at Kumzha, and lenses of thin frozen rocks that were observed in the thawed layer in August of 2015 and 2017 were absent in 2016. According to recent geocryological and geophysical observations, increasing permafrost degradation might be occurring in the Pechora River delta due to the instability of the thermal state of the permafrost.

Typical tree health assessment methods are destructive. Non-destructive Ground Penetrating Radar (GPR) technique can provide a diagnostic tool for assessing the health status of live tree trunks based on internal dielectric permittivity distribution. Typical GPR acquisition technique—common-offset—is not helpful in providing robust and high-resolution quantitative results. In the current work we evaluate the capabilities of GPR tomography on locating tree-decays in a number of different tree species, imaging the interval structure of a healthy tree and quantitative estimation of moisture content (MC) based on distribution of dielectric permittivity, directly related to MC. The measurements described in this work were made on the trunks of live trees of different species in different conditions: a "healthy" English oak (Quercus robur), a "dry" Siberian fir (Picea obovata), a Horse chestnut (Castanea dentata) and a European aspen (Populus tremula) with rot inside. The results of the suggested approach were confirmed by resistography. Different parts of the trunk (bark, core, sapwood), as well as healthy and affected areas differ in moisture content, so the method of GPR tomography allowed us to see both the structure of the trunk of a healthy tree, and the presence and dimensions of defects.

In this article we discuss the results of ultrasonic measurements using p and s waves on a sample of full water–saturated sand in the temperature range –20 ᵒC — + 20 ᵒC. The results are: dependence of kinematic and dynamic parameters of the ultrasonic signal on temperature and elastic waves attenuation parameter. We propose method to calculate the attenuation parameter of p and s waves at ultrasonic frequencies for a wide temperature range. The values of the attenuation parameter at negative and positive temperatures differ by 40–50 times for p waves and by 2 orders of magnitude for s waves. A smooth change in the attenuation parameter from –5 ᵒC (–10 C) to 0 ᵒC for p (s) waves was observed. The attenuation affecting the dynamic parameters reacts faster to the thawing of frozen ground than the waves velocity, which is most relevant in the case of plastic–frozen rocks and at temperatures close to 0.

—Ground-penetrating radar (GPR) profiling is applicable to study peatlands and swampy areas in permafrost but have some limitations in summer time. Theoretical calculations and field experiments show that estimating attenuation of electromagnetic waves is required for planning GPR survey. GPR data acquired with a 300 MHz antenna fail to resolve reflections from below the permafrost if the thaw/permafrost boundary is deeper than 1.5 m and the attenuation coefficient is 0.7, as in water-saturated peat. GPR data allow high-resolution lithological division of permafrost and provide reliable constraints on the depths to interfaces and physical properties of the ground. Thus, GPR can fully or partly substitute for the time- and labor-consuming direct measurements. The inferences have been confirmed by field results.

В 2018 году продолжены комплексные исследования криолитозоны, начатые в 2016 г. в северо- восточной части Пур-Тазовского междуречья. Проводится мониторинг глубины сезонного протаивания в различных ландшафтных условиях от дренированных водоразделов до полигональных торфяников. На одном из торфяников отслеживаются изменения рельефа за счет вытаивания полигонально-жильного льда, изучается морфология льда и криолитологическогостроениявмещающихотложений. Вовремяполевойкампании 2018 г. заложеныдополнительные площадки мониторинга глубины протаивания. Для изучения детальной пространственной дифференциации глубины протаиванияиопределениятехногенногоиестественноговоздействиянаучасткахсполигонально-жильнымильдами выполнены георадиолокационные исследования. Продолжено сопоставление ботанического состава современной растительности и многолетнемерзлого торфа, изучение почв пятен-медальонов в контуре торфяника. Начаты работы по оценке дефляционного влияния на осадконакопление минеральных пород в пределах торфяника. Started in 2016 complex studies of the cryolithozone in northeastern part of the Pur-Taz interfluve continue in 2018. Seasonal thaw depth in different landscapes from drained watersheds to polygonal peatlands is monitored. On one of the peatlands, the relief changes due to the melting of polygonal-wedge ice are observed, the morphology of ice and the cryolithological structure of the enclosing sediments are studied. During the field campaign of 2018 additional sites for thaw depth monitoring were established. To study the detailed spatial differentiation of thaw depth and to determine technogenic and natural impacts in the areas with polygonal-wedge ice georadar survey was performed. We continued the comparison of modern vegetation botanical composition with a permafrost peat and the study of spot-medallions soil in the peatland was carried on. We carried out the first stage assessment of the deflation impact on the mineral sedimentation within the peatland.

Summary The results of the application of ground penetrating radar (GPR) in a complex of geocryological studies at CALM (Circumpolar Active Layer Monitoring) sites in 2015–2018 are shown. Sites located in the North of the Nenets District in the delta of the Pechora River. Geological cross-sections consist of twaw and frozen sands which are a favorable media for the GPR signal. At both CALM sites, a correlation is observed between annual temperatures and the thawing depth and the moisture content in the Kashin site. At the Kumzha site in 2015, 2017 and 2018 thin lenses of frozen rocks in the active layer were observed and there weren’t any in 2016.

Summary Water phase transition divides the areas of soil approximation from the point of view of its elastic properties. It is interesting to study changing of acoustic characteristics, both kinematic and dynamic, in the process of freezing and thawing, since they can be indicators of various inelastic characteristics of the transition from one state to another. In the report we present results of attenuation parameter (a.p. ) estimation in ultrasonic p- and s- waves measurements on water-saturated sand sample. We used two methods to calculate a.p.: spectral ratio method and reference method. We used spectral ratio method in cases when spectra of signals measured at two bases overlapped. Otherwise we used sample with known a.p. as the reference sample.