Monitoring the structure parameters and damage to trees plays an important role in forest management. Remote-sensing data collected by an unmanned aerial vehicle (UAV) provides valuable resources to improve the efficiency of decision making. In this work, we propose an approach to enhance algorithms for species classification and assessment of the vital status of forest stands by using automated individual tree crowns delineation (ITCD). The approach can be potentially used for inventory and identifying the health status of trees in regional-scale forest areas. The proposed ITCD algorithm goes through three stages: preprocessing (contrast enhancement), crown segmentation based on wavelet transformation and morphological operations, and boundaries detection. The performance of the ITCD algorithm was demonstrated for different test plots containing homogeneous and complex structured forest stands. For typical scenes, the crown contouring accuracy is about 95%. The pixel-by-pixel classification is based on the ensemble supervised classification method error correcting output codes with the Gaussian kernel support vector machine chosen as a binary learner. We demonstrated that pixel-by-pixel species classification of multi-spectral images can be performed with a total error of about 1%, which is significantly less than by processing RGB images. The advantage of the proposed approach lies in the combined processing of multispectral and RGB photo images.

The knowledge about urban green infrastructure (UGI) is important for maintaining the quality of life in cities, suburbs and the fringes of metropolitan areas. The perspective of rapid urban sprawl generates the need for establishment and use of adequate systems for monitoring the condition of the urban ecosystems and green spaces. This triggers the search for a stronger link between the condition of urban green infrastructure and its capacity to supply ecosystem services (ES). In this paper are presented the results of the assessment of the health status of tree and shrub vegetation in UGI of Karlovo through an integrated application of in-situ observation and remote sensing using Unmanned Aerial Vehicle (UAV) technology. The study showed that the implementation of this flexible approach provides rapid and low-cost results, with good quality of the generated information. This makes the approach appropriate as a basis for monitoring of green systems in urbanised areas, with subsequent detailed investigation of solitary trees for cataclysms and epiphytotics of native species and rapid detection for the population of invasive insect and pathogen’s in order to prevent their distribution in new areas.

This article presents the results of the thermal survey of the capital of Bulgaria (Sofia) carried out in August 2019, with the application of an unmanned aerial system (UAS). The study is based on the concept of local climate zones (LCZs), taking into account the influence of the features of land use/land cover and urban morphology on the urban climate. The basic spatial units used in the study are presented in the form of a regular grid consisting of 3299 cells with sides of 250 × 250 m. A total of 13 types of LCZs were identified, of which LCZs 6, 5, 8, 4, D, and A form the largest share. In the thermal imaging of the surface, a stratified sampling scheme was applied, which allowed us to select 74 cells, which are interpreted as representative of all cells belonging to the corresponding LCZ in the urban space. The performed statistical analysis of the thermal data allowed us to identify both the most thermally loaded zones (LCZs 9, 4, and 5) and the cells forming Urban Cool Islands (mainly in LCZs D and C). The average surface temperature in Sofia during the study period (in the time interval between 8:00 p.m. and 10:00 p.m.) was estimated at 20.9 °C, and between the different zones it varied in the range 17.2–25.1 °C. The highest maximum values of LST (27.9–30.6 °C) were registered in LCZ 4 and LCZ 5. The relation between the spatial structure of the urban thermal patterns and urban surface characteristics was also analyzed. Regression analysis confirmed the hypothesis that as the proportion of green areas increases, surface temperatures decrease, and, vice versa, as the proportion of built-up and impermeable areas increases, surface temperatures increase. A heat load map (via applying a z-transformation to standardize the temperature values), a map of the average surface temperature, and a map of the average intensity of the heat island on the surface were generated in the GIS environment. The results of the study adequately reflect the complex spatial model of the studied phenomenon, which gives grounds to conclude that the research approach used is applicable to similar studies in other cities.

Urban ecosystems are the areas where built infrastructure covers a large proportion of the land surface but the main source of ecosystem services provision is the green infrastructure. This provision is very much dependent on the particular combination of green spaces such as parks or vegetation belts and paved areas such as buildings and streets. The spatial arrangement of these elements is an important parameter which could be used for the assessment of the ecosystem condition in the urban areas. An integrated index of spatial structure is proposed which incorporates built types and land cover from the Local Climate Zones (LCZ) concept with urban ecosystems' classes developed on the basis of MAES typology. An algorithm has been developed for index generation using an urban ecosystems' database and remote sensing data. The index is used to define vegetation cover in urban ecosystems and assess their condition as a part of the assessment framework. It is also applied in the assessment of several ecosystem services through quantification of ecosystem services' indicators or as an indicator in a complex assessment. The results show that, although most urban ecosystems in Bulgaria are assessed as moderate and good condition, very few of them have very good condition and about 3.5% have very bad condition. The highest scores are defined for urban green areas while the lowest are for transport networks. The use of an integrated index in urban ecosystem services' assessment is represented by examples for global and local climate regulation. The results are used to develop maps of ecosystem services supply capacity for selected cities. The overall analysis indicates that the urban ecosystems in Bulgaria have a moderate to good capacity for local climate regulation and moderate to low capacity for global climate regulation. The integrated index of spatial structure provides an appropriate basis for characterisation and assessment of the urban ecosystems condition and ecosystem services following the requirements of the EU Biodiversity Strategy and the MAES process. The proposed approach enables the internal heterogeneity of the urban ecosystems at national level to be defined, this being one of the main challenges in studying urban ecological systems.

The urban heat island effect (UHI) is among the major challenges of urban climate, which is continuously intensifying its impact on urban life and functioning. Against the backdrop of increasingly prolonged heatwaves observed in recent years, practical questions about adaptation measures in cities are growing—questions that traditional meteorological monitoring can hardly answer adequately. On the other hand, UHI has long been the focus of research interest, but due to the technological complexity of providing accurate spatially referenced data at high spatial resolution and the requirement to survey at strictly defined parts of the day, information provision is becoming a major challenge. This is one of the main reasons why UHI research results are less often used directly in urban spatial planning. However, advances in geospatial technologies, including unmanned aerial systems (UASs), are providing more and more reliable tools that can be applied to achieve better and higher-quality information resources that adequately characterize the UHI phenomenon. This paper presents a developed and tested methodology for the rapid and efficient assessment and mapping of the effects of surface urban heat island (SUHI). It is entirely based on the integrated use of data from unmanned aerial systems (UAS)-based remote sensing methods, including thermal photogrammetry and GIS-based analysis methods. The study follows the understanding that correct SUHI research depends on a proper understanding of the urban geosystem, its spatial and structural heterogeneity, and its functional systems, which in turn can only be achieved by supporting the research process with accurate and reliable information resources. In this regard, the possibilities offered by the proposed methodological scheme for efficient geospatial registration of SUHI variations at the microscale, including the calculation of intra-urban SUHI intensity, are discussed in detail. The methodology builds on classical approaches for using local climate zoning (LCZ), adding capabilities for precise delineation of individual zone types and for geostatistical characterization of the urban surface heat island (SUHI). Finally, the proposed scheme is based on state-of-the-art technological tools that provide flexible and automated capabilities to investigate the phenomenon at microscales, including by enabling flexible observation of its dynamics in terms of heat wave manifestation and evolution. Results are presented from a series of sequential tests conducted on the largest residential area in Bulgaria’s capital city, Sofia, in terms of area and population, over a relatively long period from 2021 to 2024.

Natural heritage (NH) includes natural features that can be described as outstanding universal value at a national level. It refers to the importance of ecosystems, biodiversity, and geodiversity for their existence value, and the ecosystems can be considered as the spatial units for its mapping and assessment. The ecosystem services (ES) concept provides an appropriate basis in the form of assessment and mapping methods that enable linking the state of ecosystems with human well-being. Thus, it can be used as a platform to find solutions to the problems related to the conflicts between conservation and the use of the NH. In this paper, we aim to present the process of developing a methodological framework for mapping and assessment of ecosystem services provided by the natural heritage in Bulgaria for recreation and tourism. The conceptual framework of the ecosystem-based assessment of NH in Bulgaria is based on the assumption that the generation of NH for the needs of tourism can be presented as the linkages between the natural systems and tourism in the form of ES potential, flow, and demand. The results demonstrate that the NH can be presented as a spatial phenomenon conceptualized by the flows of benefits from ecosystems to people which contribute to human well-being. The mapping and assessment procedures are fully developed for application at a national level, while for the regional and local level, few pilot studies mark some basic foundations for further development.