Stoyan Valchev

Prof. Stoyan Valchev

orcid

Research Focus & Metrics

Academic Career Length

3Years (2024-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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13 September 2024 in Land
Verified
Journal Article
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BBBilyana Bogomilova Borisova
Bilyana Bogomilova Borisova
LSLidiya Nikolaeva Semerdzhieva
Lidiya Nikolaeva Semerdzhieva
SDStelian Dimitrov
Stelian Dimitrov
SVStoyan Valchev
Stoyan Valchev
MIMartin Iliev
Martin Iliev
Kristian Angelov GeorgievKristian Angelov Georgiev
Kristian Angelov Georgiev
This study aims to scientifically justify the identification of suitable urban properties for urban green infrastructure (UGI) interventions to optimize its natural regulating functions for long-term pollution mitigation and secondary dust reduction. This study adheres to the perception that planning urban transformations to improve ambient air quality (AQ) requires a thorough understanding of urban structural heterogeneity and its interrelationship with the local microclimate. We apply an approach in which UGI and its potential multifunctionality are explored as a structural–functional element of urban local climatic zones. The same (100 × 100 m) spatial framework is used to develop place-based adapted solutions for intervention in UGI. A complex geospatial analysis of Burgas City, the second largest city (by area) in Bulgaria, was conducted by integrating 12 indicators to reveal the spatial disbalance of AQ regulation’ demand and UGI’s potential to supply ecosystem services. A total of 174 municipally owned properties have been identified, of which 79 are of priority importance, including for transport landscaping, inner-quarter spaces, and social infrastructure. Indicators of population density and location of social facilities were applied with the highest weight in the process of prioritizing sites. The study relies on public data and information from the integrated city platform of Burgas, in cooperation with the city’s government. The results have been discussed with stakeholders and implemented by the Municipality of Burgas in immediate greening measures in support of an ongoing program for Burgas Municipality AQ improvement.

14 April 2026 in Urban Science
Verified
Journal Article
Open access
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SDStelian Dimitrov
Stelian Dimitrov
MIMartin Iliev
Martin Iliev
BBBilyana Bogomilova Borisova
Bilyana Bogomilova Borisova
SPStefan Petrov
Stefan Petrov
IIIvo Stoyanov Ihtimanski
Ivo Stoyanov Ihtimanski
Kristian Angelov GeorgievKristian Angelov Georgiev
Kristian Angelov Georgiev
Urban rooftop photovoltaic systems represent a substantial yet still underutilized renewable energy resource, particularly in high-density residential environments. Accurate large-scale assessment of rooftop solar potential, however, remains challenging due to the complex geometry of urban morphology and the limited availability of high-resolution geospatial data. This study presents a large-scale methodological framework for estimating the theoretical photovoltaic potential of urban rooftop spaces using Unmanned Aerial System (UAS)-based digital photogrammetry and GIS-based spatial analysis. The approach integrates centimeter-resolution Digital Surface Models (DSMs) and orthophotos derived from fixed-wing UAS surveys with detailed rooftop vectorization and solar radiation modeling implemented in a GIS environment. The methodology accounts for rooftop geometry, surface orientation, slope, shading effects, and rooftop-mounted obstacles. The methodology consists of data collection of high-resolution RGB imagery suitable for detailed three-dimensional reconstruction. The images are captured with a UAS equipped with a S.O.D.A. 3D photogrammetric camera, creating a dense, georeferenced three-dimensional point cloud based on UAS imagery. Based on the point cloud, a high-resolution Digital Surface Model (DSM) was produced. Rooftop boundaries and rooftop-mounted structures were digitized on the basis of an orthophoto created from UAS imagery. The analysis workflow consists of solar modeling using ArcGIS Pro, including calculating the solar radiation. The next methodological step is to filter low radiation rooftops, steep slopes, and northern-oriented rooftops. Finally, we calculate the potential electricity production. The framework was applied to high-density residential districts in Sofia, Bulgaria, dominated by prefabricated panel buildings with predominantly flat rooftops. Drone applications in such studies are typically restricted to modeling individual roofs, which severely limits their scalability for district-wide evaluations. To overcome this, the study employs a specialized fixed-wing UAS uniquely certified for legal operations over densely populated urban environments. This platform rapidly maps large territories, ensuring consistent lighting and shading conditions that significantly enhance the accuracy of subsequent rooftop digitization. Furthermore, the resulting centimeter-level precision enables the exact vectorization of micro-rooftop obstacles. Capturing these intricate details is a critical innovation that effectively prevents the overestimation of solar energy potential commonly observed in conventional large-scale models. Solar radiation was modeled at the pixel level for a full annual cycle and filtered using photovoltaic suitability criteria, including minimum annual radiation thresholds, slope, and aspect constraints. Theoretical electricity production was subsequently estimated using zonal statistics and system performance parameters representative of contemporary photovoltaic installations. The results indicate a total theoretical annual electricity potential of approximately 76.7 GWh for the analyzed rooftop spaces, with an average production of about 34 MWh per rooftop and pronounced spatial variability driven by rooftop geometry and exposure conditions. The findings demonstrate the significant renewable energy potential embedded in existing urban rooftop infrastructure and highlight the applicability of UAS-based photogrammetry for high-resolution, large-area solar potential assessments. The proposed framework provides actionable information for urban energy planning, municipal solar cadaster development, and the strategic integration of photovoltaic systems into dense urban environments, particularly in regions lacking open-access high-resolution geospatial datasets.

19 August 2026 in Journal of the Bulgarian Geographical Society
Verified
Journal Article
Open access
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LTLeonid Todorov
Leonid Todorov
SHSuzana Hadzhieva
Suzana Hadzhieva
ETElena Rumenova Todorova
Elena Rumenova Todorova
SDStelian Dimitrov
Stelian Dimitrov
MIMartin Iliev
Martin Iliev
PNPetar Nikolov
Petar Nikolov
Spatial accessibility of healthcare facilities may result in substantial differences in the population’s access to medical care. This is a topic of great public importance that needs effective planning based on contemporary spatial technologies and analytical approaches. The aim of the present study is to demonstrate how the application of spatial analyses, tailored to the specific context, contributes to identifying gaps in the existing organization of emergency medical services in mountainous areas and enables a more comprehensive and robust assessment of transport accessibility. By integrating three complementary analytical approaches—Service Area, Closest Facility, and Origin–Destination Cost Matrix analyses within a single methodological framework, the present study provides a comprehensive assessment of travel times from emergency medical care branches to the settlements they serve, as well as an evaluation of branch service areas in terms of their spatial extent. The analyses identified shortcomings that could be addressed with reorganization and low-cost optimization measures, thus demonstrating their efficiency in identifying limitations in the current allocation of service areas among the emergency medical care branches. The study is based on carefully selected data and was conducted with a strong emphasis on maximizing both accuracy and practical applicability.