Martin Iliev
@martin@gea.uni-sofia.bg
Sofia University St. Kliment Ohridski, Faculty of Geology and Geography
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Stelian Dimitrov, Martin Iliev, Bilyana Borisova, Lidiya Semerdzhieva, and Stefan Petrov
MDPI AG
The urban heat island (UHI) and its intensity is one of the phenomena that are of determining importance for the comfort of living in cities and their sustainable development in the face of deepening climate change. The study is objectively difficult due to the large dynamics like land cover and the considerable diversity of land use patterns in urban areas. Most of the frequently used research practice approaches provide information with problematic spatial and temporal resolution, making them difficult to apply for sustainable urban planning purposes. This paper proposes to calculate SUHI intensity as the difference between the temperature of a given point within a city and the average minimum temperature of the land cover class with the lowest surface temperatures within the same urban area. The study presents the results of the application of thermal photogrammetry based on the use of unmanned aerial systems (UAS), combined with geographic information systems (GIS), in the study of surface urban heat island intensity (SUHI), at the local level for the largest housing complex in Bulgaria–Lyulin district of the capital of Sofia city. The studies were carried out during a heat wave in July 2023. A difference of 16.5 °C was found between locations with SUHI occurrence and of the peripheral non-build and natural land cover types within the urbanized area. The information benefits of locally addressed data and their direct applicability are discussed to support decision-making processes in the planning and management of urban areas, including their climate adaptation and sustainable development.
Bilyana Borisova, Stelian Dimitrov, Ivo Ihtimanski, Lidiya Semerdzhieva, Stoyan Valchev, and Martin Iliev
SPIE
This study presents a methodological approach and the results of a geospatial localization analysis of selected residential areas of the Sofia Municipality, which are highly vulnerable in terms of Ambient air Quality (AQ). The objective is a scientifically sound selection of locations for the construction of additional Green Infrastructure (GI) elements. A targeted selection of 13 indicators was carried out on urban morphology, demography, geo-ecological conditions, and an annual average concentration of pollutants. The output data are organized in a spatial grid (250/250 m). A weighted overlay was performed to identify cells with a high need for the construction of GI as additional measures to regulate microclimatic conditions and the associated AQ. Additional prioritization has been carried out for units with largest number of schools, kindergartens, hospitals. They have been surveyed with unmanned aerial systems (E-BeeX SenseFly). A digital surface model in 3D point cloud and an orthophoto map were generated in Pix4D environment. As a result, 401 specific land properties have been identified for the construction of new GI or upgrading of existing GI elements to increase the potential for effective regulation of the urban microclimate and mitigation of the negative effects of air pollution. The study was conducted in 2022 by the National University Center for Geospatial Research and Technology on behalf of Sofia Municipality. The results will be used for the expansion of parks and gardens, the afforestation of inter-block spaces ("mud patches"), the greening of schoolyards and kindergartens, busy transport arteries, or other innovative green solutions.
Stelian Dimitrov, Bilyana Borisova, Martin Iliev, and Lidiya Semerdzhieva
SPIE
The aim of this study is to present the possibilities of thermal photogrammetry, carried out by an Unmanned Aerial System (UAS) in determining the Local Climate Zones (LCZ) in the city of Burgas, Bulgaria. This LCZ-based methodological approach has been used as one of the major standards in the research practices of mapping and assessment of the effects of the Urban Heat Island phenomenon (UHI). А complex methodological approach specifically designed for the purpose of the study was applied, which includes the use of a flying wing type UAS and a specialized integrated sensor with a thermal calibrated camera and a photogrammetric one, as well as a developed scheme for the collection, processing, and modeling of the data. As a result, the thermal characteristics of the surface of the individual types of LCZ on the territory of the city of Burgas were determined and specified. The latter was used as an information basis for modeling and mapping the effect of the UHI and determining its intensity. The data were collected according to a predetermined sampling scheme within a two-year period (2021-2022) during the hottest months of the year for the city (July and August) by the National University Center for Geospatial Research and Technology. All in-situ studies were carried out after sunset, in the time interval 20:30 - 22:00, in order to eliminate the effect of direct solar radiation on the recorded temperatures of the different land cover types. Subsequently, the collected and processed data were cataloged and integrated into geographic database of the LCZ, and the potential thermal load of each individual LCZ and individual land cover types was estimated. The results have been discussed with the Municipality of Burgas and will be used in the development of a series of urban planning measures focusing on energy efficiency, human health (regulating ecosystem services from green infrastructure) and the conservation of protected areas (falling immediately within the municipality).
Alexander Gikov, Stelian Dimitrov, Martin Iliev, Leonid Todorov, and Nadezhda Nikolova
SPIE
The aim of the present study is to present an integrated approach based on the use of both classical remote sensing data and data generated by Unmanned Aerial Systems (UAS) for the purpose of precise mapping and assessment of vertical deformations of large-scale landslides structure (160 ha) located in the Eastern Rhodopes region, Bulgaria. The evaluations and the mapping itself were carried out by means of different types of generated Digital Terrain Models (DTMs), reflecting the dynamics in the development of the structure over a long period of time. The DTMSs were generated on the basis of three groups of methods – vectorized data of large-scale topographic maps from the 1980s, photogrammetric data and data from airborne laser scanning (LIDAR) based on an unmanned aerial vehicle platform. The complex geospatial analysis of the different digital terrain models shows that as a result of the landslide, significant vertical deformations occurred in the study area, with their maximum amplitude ranging from -17,2meters to more than +20 meters. The results of the present study demonstrate the enormous possibilities of modern geoinformation technologies to integrate and analyze various data, approaches and methods, which provides the necessary tools for conducting long-term precise monitoring of territories affected by risk processes, including landslides.
Martin Iliev, Stelian Dimitrov, Kliment Naydenov, Stephan Petrov, and Ivan Ivanov
SPIE
This article aims to present the developed and applied methodology for the study, mapping, and evaluation of urban mobility patterns in the city of Sofia. The research is based on the combination and integration of GIS-based spatial analysis techniques and high-resolution data obtained through sensors based on state-of-the-art Unmanned Aerial Vehicle systems (UAVs). The results obtained from this study are adapted to their use for the purpose of supporting urban planning processes in the city and could greatly assist in the establishment of more adequate models for solving some of the most pressing problems of urban mobility in the urban area of Sofia.
Margarita Georgieva, Sevdalin Belilov, Stelian Dimitrov, Martin Iliev, Vladislav Trenkin, Plamen Mirchev, and Georgi Georgiev
MDPI AG
Intensive forest afforestation with native pine species was developed in the 1960s on degraded and deforested lands in the region of the Eastern Rhodopes (south-eastern Bulgaria). Severe damage by wet snow was registered in the coniferous forests of the Rhodopes in March 2015. In the following years, bark beetle attacks were registered on the broken and felled fresh wood. As a result, bark beetle infestation spots appeared in the pine plantations. In the period 2019–2021, damage caused by bark beetles was assessed in the region of State Forestry Kirkovo (the Eastern Rhodopes, south-eastern Bulgaria). An integrated approach using the data of the information system of the Executive Forest Agency (ISEFA), remote sensing data obtained by an “eBee SQ” unmanned aerial vehicle (UAV) equipped with a “Parrot Sequoia” multispectral camera, and subsequent terrestrial observations, was applied. ISEFA data showed that there was no serious damage caused by abiotic and biotic factors in the pine forests of SF Kirkovo until 2014. Snow damage in 2015 affected 513 ha of pine plantations, and bark beetle infestations reached up to 1316 ha in 2016. In 2019, a total of 226.87 ha of pine plantations were captured in three localities—Fotinovo, Kirkovo, and Kremen. The relative share of damage caused by bark beetles was greater in P. sylvestris plantations (15.3–23.0%), compared to damage in P. nigra (2.3%). Four different categories of normalised difference vegetation index (NDVI) were separated in bark beetle infestation spots—living trees, dead trees, grass and shrub vegetation, stones and rocks. The NDVI values in locations with living trees varied between 0.500 (spaces between tree crowns) and 0.700 (central part of the crown projection) (an average of 0.617). In the locations with dead trees, the average values of NDVI of lying trees was 0.273, and in standing trees, NDVI varied between 0.275 (central part of crown projections) and 0.424 (spaces between tree crowns). In the locations with grass and shrub vegetation, stones and rocks, the average NDVI was 0.436 and 0.329, respectively. In the field study, average defoliation of 31.2–32.3% was registered in P. sylvestris plantations, and 47.4% in P. nigra plantations. Defoliations mainly were caused by pine processionary moth (Thaumetopoea pityocampa) and fungal pathogens (Dothistroma septosporum and Lecanosticta acicola). The damage was caused by Ips acuminatus (in P. sylvestris only), and I. sexdentatus, Tomicus piniperda and T. minor (in P. sylvestris and P. nigra). Infestations by other xylophages, such as Phaenops cyanea, Rhagium inquisitor, and Pissodes spp., were also found on pine stems.
Georgi Georgiev, Margarita Georgieva, Stelian Dimitrov, Martin Iliev, Vladislav Trenkin, Plamen Mirchev, and Sevdalin Belilov
MDPI AG
The Chuprene Reserve was created in 1973 to preserve the natural coniferous forests in the Western Balkan Range in Bulgaria. The first infestations by European spruce bark beetle (Ips typographus) were registered in Norway spruce (Picea abies) stands in the mid-1980s. The aim of this study is to assess the damages caused by I. typographus in the Chuprene Reserve using remote sensing techniques – unmanned aerial vehicle (UAV) images, airborne images, and satellite images of European Space Imaging (EUSI), combined with terrestrial verification. High-resolution images in four bands of the electromagnetic spectrum and in a standard RGB channel were taken in 2017 via a multispectral camera ‘Parrot Sequoia’, integrated with a specialized professional UAV system eBee ‘Flying Wing’. The health status of Norway spruce stands in the reserve was assessed with the normalized difference vegetation index, based on the digital mixing of imagery captured in the red and near infrared range. The dynamic of bark beetle attacks was studied in GIS on the basis of maps generated from photographic surveys, airborne images taken in 2011 and 2015, and satellite images from 2020. In the UAV-captured area (314.0 ha), the size of Norway spruce stands attacked by I. typographus increased from 7.6 ha (2.4%) in 2011 to 44.9 ha (14.3%) in 2020. The satellite images showed that on the entire territory of the Chuprene Reserve (1451.9 ha), I. typographus killed spruce trees on 137.4 ha, which is 9.6% of the total area.
Stelian Dimitrov, Anton Popov, and Martin Iliev
MDPI AG
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.
Anastasiia Safonova, Yousif Hamad, Egor Dmitriev, Georgi Georgiev, Vladislav Trenkin, Margarita Georgieva, Stelian Dimitrov, and Martin Iliev
MDPI AG
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.
Stelian Dimitrov, Anton Popov, and Martin Iliev
SPIE
This article aims to present the developed, adapted and applied methodology for the study, mapping, and evaluation of the effect and intensity of the urban heat island(UHI) within the urban space of the city of Sofia, while assessing its potential impact on the structure of the city and the prospects for its development and structure. For this purpose, a combination of GIS-based spatial analysis techniques is used, based both on the application of traditional satellite data sources and on the use of state-of-the-art unmanned aerial vehicle systems (UAVs), delivering highresolution information. The results obtained from the study are adapted towards their use for the purpose of supporting urban planning processes in the city and could greatly assist in the establishment of more adequate models of spatial planning in the urban area of Sofia, in the context of global climate change and the expected intensification of the UHI effects in the near future.
Stelian Dimitrov, Georgi Georgiev, Plamen Mirchev, Margarita Georgieva, Martin Iliev, Danail Doychev, Sonja Bencheva, Gergana Zaemdzhikova, and Nikolay Zaphirov
SPIE
Over the last decades, massive forest decline has occurred in many countries because of prolonged periods of drought and anomalous climatic phenomena. Studies show that in most cases this is the result of a combination of unfavourable climatic conditions and impact of harmful biotic factors, mostly insect pests and fungal pathogens. The massiveness of these unfavourable phenomena, as well as the specificities of their occurrence and spatial distribution, including mountainous and difficult to access areas, require the application of flexible, high-tech methods of collecting and processing data and information, and in recent years, modern unmanned aerial platforms and systems. This article presents the used approach, the methodology for complex assessment and the results obtained in integrated application of the potential of modern unmanned aerial platforms and traditional entomological and phytopathological methods for field investigation of sanitary status of two protected areas in West Balkan Range in Bulgaria – Gornata koria Reserve and Chuprene Biosphere Reserve.