Roumen Nedkov

Monitoring forest regrowth with different burn severity using aerial and Landsat data

The aim of this study is to monitor the post-fire forest recovery with different burn severity. The test area is located in southeastern Bulgaria, Haskovo region, where a significant fire took place in the summer of 2007. The recovery processes of the study area were examined for the period 2007-2014. To achieve this goal, NDVI, dNDVI, NBR, and dNBR were generated once every year during the study period. Satellite images from Landsat 5 (TM), Landsat 7 (ETM+), and Landsat 8 (OLI) were used. We calculated the average NDVI and NBR values for the test forest areas with high burn severity. Scatter diagrams of NBR and NDVI were generated and the correlation coefficient between NBR and NDVI was calculated. The approach and the results were validated on the basis of high-resolution aerial images taken before the fire and in the end of the study period.

Assessment and mapping of the current state of the landscapes/ecosystems in Haskovo region (southeastern Bulgaria) in relation to ecosystem services using remote sensing and GIS

Assessment and mapping of the ecosystems state in the context of ecosystem services that they supply are important tasks to improve human well-being, especially in regions with considerable land degradation. Haskovo region is situated in the Southeastern part of Bulgaria and is considered as an extremely sensitive to land degradation in terms of climate change and human activities in result of unappropriated land management practices. In order to improve the conservation activities and ecosystem services of the region, rapid and available technics are needed in addition to the used analytical methods. The study presents the potential of remote sensing methods (satellite data from different sensors Sentinel and Landsat) and GIS for assessment of the current state of the landscapes to supply ecosystem services and allows a comprehensive evaluation of the main indicators for assessment of ecosystem services to be performed. The proposed methodology includes application of vegetation indices (NDVI, NDWI and MSAVI2) and SAR data. The results show that the referred technics can be used for a rapid and accurate assessment of the main indicators showing the state of the terrestrial ecosystems such as: soil degradation, land use and impact of human activities, responsible for the ecosystem services supply.

Tracing dynamics of relative volumetric soil moisture content using SAR data

Soil is a dominant factor of the terrestrial geosystems in the dry sub-humid zones, particularly through its effect on biomass production. Due to the climate changes and industrial development, soil resources in these zones are prone to degradation. Mitigation of the negative effects of land degradation requires in-depth knowledge of the ongoing in the geosystems processes and application of innovative end effective methods for their investigation. The recent study aims to evaluate the relative soil moisture content in various soil differences and to trace its dynamics during growing season. In order to achieve this aim, Relative Soil Moisture Index (RSMI) based on Synthetic Aperture Radar (SAR) data was calculated. The index estimates the relative variation of volumetric soil moisture content in a given time period and enables determination of its change in relative values. The generated results show very high level of correlation for the investigated pilot areas which testifies that the RSMI is applicable in different territories.

Remote sensing measurements in creating thematic spectral library

In Earth observations the reference spectra of well-described objects are required for better object-oriented interpretation of remotely sensed data from laboratory, field, airborne, and satellite sensors. For this purpose measurements of spectra using laboratory and field spectrometers are performed. The acquired spectra are used in creating a thematic spectral library. The used spectral instruments work in the wavelengths (0.4 to 2.5 microns) covering the spectral ranges from the visible /VIS/ to the shortwave infrared /SWIR/. Two different spectrometers are used to measure spectra included in the library: (1) Thematically oriented multichannel spectrometer covering the spectral range 0.4 to 0.9 microns and (2) high resolution NIRQuest spectrometer covering the range from 0.9 to 2.5 microns, both models of Ocean Optics Inc. Spectrometric measurements of representative samples of minerals, rocks, related soils, vegetation, and their natural mixtures are made in laboratory and field conditions. In some cases, samples were purified, so that the unique spectral characteristics of the studied objects could be related to their typical structure. The relations between the spectra and the structures are important for interpreting remotely sensed data acquired in the field or from an air- or space-borne platform. In some cases for making easy wide use of the spectra in the library the obtained spectra have to resample to selected broadband multispectral sensors for example those based on the satellites Landsat and Sentinel. The obtained spectral data with the metadata and additional information are planned for including in files for better interpretation of images with different spatial resolution.

Application of remote sensing data for a wetland ecosystem services assessment in the area of Negovan village

Nowadays, the ecosystem service framework can be accepted for designing and completion of different management strategies to preserve and restore ecosystems. The present study will contribute to increase the stakeholders’ interest to wetlands condition and possibilities for better management aiming at improving the ecosystems services they provide. For the research of the wetland in the area of quarry lakes in Negovan village interim ecological monitoring (IEM) using remote sensing data after restoration measures have been implemented. The aim of IEM is to obtain results for the wetland actual condition and restoration process efficiency for ecosystems services assessment. Based on the generated data an interim ecological monitoring methodology (MIEM) implying different remote sensing data (different temporal intervals, spectral and spatial resolution) has been designed. The model functions entirely within Geographical Information System (GIS). It generates data for the actual environmental condition of the wetland in different temporal intervals. The obtained results for the wetland actual condition have been used for defining the values of Disturbance Index (DI), which in turn is defined based on orthogonalization of multispectral satellite data from Sentinel 2 - Multi Spectral Instrument (MSI) and Landsat for different temporal intervals. DI rates are determined through Wetness component and Greenness component. Ecosystem services are assigned based on the correlation between vegetation and water surface area that is connected to water balance/budget. The space distribution of vegetation is specified on the base of Normalized Differential Vegetation Index (NDVI), Normalized Differential Greenness Index (NDGI) for different temporal intervals of the research. This paper presents results for evaluation the potential for delivery of ecosystem services taking into consideration the environmental and ecological processes behind the services that have been assessed at a relevant scale generated.

MODIS satellite data for estimating actual evapotranspiration in Bulgaria (2000-2014)

In the present paper, the actual evapotranspiration for the territory of Bulgaria on an annual basis for the period 2000- 2014 has been modeled, using satellite data MOD16A3. The data was received by means of remote sensing from a MODIS sensor. Raw evapotranspiration (ET) data were integrated and processed in GIS environment in order to obtain the final goal of finding 2D distribution of the qualitative values of the actual evapotranspiration (АET) for the territory of Bulgaria. In order to generate the relevant values for the annual АET in the area, a model was developed using the MOD16A3 evapotranspiration dataset. In the present paper, the actual evapotranspiration was estimated as a function of the land cover and a digital elevation model. The results obtained show the relationship between the actual evapotranspiration, the land cover and a DEM. In the process of research, some trends for the annual quantity of АET were estimated. The model for the quantitative area estimation of the evapotranspiration developed in the study has already been applied to the catchment area of Lefedzha River (located in northern Bulgaria). It was established that the satellite data give a more representative and reliable information on the spatial distribution of the AET on a regional scale. These methods have less human interference in obtaining information about the individual physical parameters on which the process of evaporation depends. In the MOD16 product the temperature of the spreading surface that influences the evaporation processes was recorded.

Using SAR and optical data from Sentinel satellites for precise modeling of seasonal floating reed islands dynamics in Srebarna Lake

The present study is a continuation of the previous monitoring studies on floating reed islands based on remote sensing methods, but this time the study is much more precise in order to create a sustainable operating model for subsequent monitoring studies on this specific type of habitats. The aim of this study is to create a precise model for the movement and dynamic of the floating reed islands in Srebarna Lake. This was done by creating a hybrid model (based on optical and SAR data), assessing the actually condition of floating reed islands, and applying it to quantify of the movement of floating reed islands to perform an actual and seasonal habitats monitoring. To create the hybrid model, the advantages of SAR data – Sentinel-1 for the hydrological dynamics monitoring of Srebarna Lake were used. The SAR data used were obtained for different time periods, within the observed seasons. Multispectral satellite data from Sentinel-2 was also used in order to apply an orthogonal transformation model called Tasselled Cap Transformation (TCT). The Tasselled Cap model is a very effective method for classifying and analyzing processes related to the dynamics of changes affecting the main components of the Earths surface: soil, water, and vegetation. This model proved to be very effective in recognizing specific types of vegetation and habitats, such as floating reed islands and their transformation over a period of time. The results for the reconciliation of TCT images and SAR data define very well the precise boundaries of both the central water body in Srebarna Lake, and the floating reed islands. The results obtained by means of comparative analysis confirm both methods as being equally effective to determine the floating reed islands dynamics in the hybrid model proposed in this study.

Modeling of forest ecosystems recovery after fire based on orthogonalization of multispectral satellite data

The aim of this study is to monitor the post-fire recovery of forest ecosystems on the basis of remote aerospace methods and data. To achieve this goal, a hybrid model for styding the dynamics of recovery processes of forest ecosystems after fire was developed. Based on the Greenness Tasseled cap component, Normalized Differential Greenness Index (NDGI) was obtained and used as input data in combination with vegetation indices (NDVI, MCARI2). NDGI is an index for vegetation dynamic assessment based on orthogonal transformation of satellite images from Sentinel-2. NDGI shows the vegetation dynamic change depending on temporal periods. The values of this index range from +1 to -1. Using NDGI assessment can be made of negative and positive changes of the vegetation. This study uses a new approach for forest ecosystems assessment, based on this index using the Greenness component obtained from orthogonalization of satellite images in combination with generated vegetation indices (NDVI and MCARI2). Optimization of model performance and automatization of Sentinel-2 MSI data processing were conducted. Sentinel-2 MSI model for orthogonalization of multispectral data was used for Tasseled cap transformation. Results obtained by implementation of the proposed approach show that the integrated composite images of NDGI, NDVI and MCARI2 represent the condition of forest ecosystems.

Modification in landscape horizontal structure, induced by changing environmental conditions: a case study of Haskovo region (Southeastern Bulgaria)

Land cover changes (LCC) in Mediterranean lands are generally connected with anthropogenization and climate changes. The territory of Haskovo region is located in south-eastern part of Bulgaria, where, in the last years, intensification of degradation processes in landscapes, induced by drought is occurred. There is a real threat from intensification of desertification processes in these landscapes in the next decades. The precise investigation of degradation processes requires in-depth knowledge of landscape components, of the ongoing processes that take place in them and functions that ensures existence and maintenance of ecosystems. In the case study, we have determined the LCC that have occurred in the last 18 years. Remote sensing methods and GIS have been applied. The LCC have been determined by using supervised classification, as for the basis of the classification, vector layers of Land cover and vegetation have been used. Two landscape maps were created. The first is valid to 2000 and the second is a map of the modern landscapes. In order type of the change and its magnitude to be determined, Tasseled Cap Transform (TCT) and modified Change Vector Analysis (mCVA) techniques were applied. The application of this approach allows differentiation of the most affected by the LCC landscapes, determination of the type and direction of change, and assessment of the potential of the landscape to deliver ecosystem services in changing environmental conditions.

Application of remote sensing data for forest fires severity assessment

Forest fires continue to burn large territories, both within and outside Europe. It is suitably to assess fire-induced changes in the vegetation, which in turn affects infiltration, runoff, and erosion potential. Therefore it is important to identify potential areas of concern and prioritize field reconnaissance. The development of a burn severity map will facilitate quantifying of the post-fire assessment phase. In this study the potential of Normalized Burn Index (NBR), Normalized Difference Vegetation Index (NDVI) and normalized difference greenness indices (NDGI) derived from remote sensing methods (satellite data from different sensors Sentinel and Landsat) and Geographical Information System (GIS) have been analyzed for forest fire severity assessment. For more accurate assessment of the fire severity, a hybrid model was developed, using satellite data from different sensors - Sentinel and Landsat. For this purpose, the area, affected by fires occurred in august 2017 on the northwest slopes of the Ajtovska Mountain (East part of the Stara planina mountain) in the Eastern part of Bulgaria was studied. The forest fire events were spread on the area of (508.5 ha) and the affected vegetation was composed by deciduous forests (309.4ha), coniferous (62.4ha), mixed forests (61.4 ha) and grass and shrubs (75.3ha). Through the model developed, results applicable to the actual forest ecosystem conditions for different time intervals have been obtained. These results provide quantitative information about fire severity for distinct forest types, thus allowing for designing relevant fire severity maps.