Browsing by Author "Altunel A.O."

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Accuracy assesment of a low-cost UAV derived digital elevation model (DEM) in a highly broken and vegetated terrain
(2019-03-01) Akturk E.; Altunel A.O.
Digital Elevation Models (DEMs) are frequently used in geology, environment, engineering and architecture related studies. Along with the technological advances, there are also improvements in the production techniques of these data. The use of low cost UAVs and what they can achieve, are therefore important for researchers. This study was designed to find answers to two main questions. Firstly, in areas of challenging conditions, if it is feasible to produce DEM with the low-cost UAV imagery, and if the obtained precision would be comparable enough to those of the proven methods. Secondly, if the addition of Ground Control Points (GCPs) would further increase the precision. As a result of this research, the uncertainty, in other words the RMSE of the DEM data obtained from the area with challenging topography, was found to be 0.57 m. In addition, the use of GCPs provided 6 cm decrease in the overall error margin.
Capturing the level of progress in vertical accuracy achieved by ASTER GDEM since the beginning: Turkish and Nigerian examples
(2022-01-01) Altunel A.O.; Okolie C.J.; Kurtipek A.
There is little information on the improvement achieved across all versions of ASTER GDEM in terms of vertical accuracy. This study assessed the vertical accuracies of all three versions in Turkey and Nigeria based on the mean error, root mean square error, mean absolute error, average relative error, residual dispersal patterns and combined error performance rankings. Although the improvements from GDEM v1 onward were obvious, they were rather marginal from GDEM v2 to GDEM v3 when five elevation classes were considered from coastal to high mountain. In the coastal, lowland and upland classes in Turkey, and lowland and upland classes in Nigeria, version 2 was superior to version 1. Compared to SRTM version 3.0, the last version produced relatively similar results, but no version outperformed it at any of the test sites. The same was also true in Nigeria. These results showed that a comprehensive vertical accuracy improvement was only partially realized through the successive development phases of the ASTER GDEM.
Determining the habitat fragmentation thru geoscience capabilities in Turkey: A case study of wildlife refuges
(2021-07-01) Altunel A.O.; Caglar S.; Altunel T.
Technical forest management started 180 years ago in Turkey, during which time there have been various approaches and policy changes. The primary objective of forestry has been considered as timber production, so the intangible benefits have never been given the proper attention they deserve. The majority of Turkey’s wildlife has prospered within the forest ecosystems. This situation has gradually led to a change of status, so some forests and land areas have been reassigned with the conservation agendas as the primary purpose; however timber production has never slowed down. Thus, operational forestry practices, such as roading, logging, etc., have kept on exploiting these lands to their full extent despite their conservation statuses. In Turkey and anywhere else, since forestry has always evolved around extracting the timber out of the forest lands, the accessibility has long been provided, building roads to take related services to forested ecosystems. The remnants of these roads, along with the more standardized new ones can be found everywhere, regardless of the land status. Such expansion has resulted in habitat fragmentation emerging as a major threat for the protected areas. In this study, the expansion of all-weather and dry-weather accessible roads and suburban spread was examined in two adjacent, Ilgaz and Gavurdagi, wildlife refuges for the years of 1960, 1993, 2010 and 2019, relying heavily on the mapping, geographic information systems (GIS) and remote sensing. It was found that 275.5 km dry-weather roads in 1960 rose to 700 km in 2019, which meant 254% increase. Additionally, when the core along with the surrounding 3000 m buffer area was considered, 51 km all-weather roads in 1960 increased almost four and a half times by 2019. Suburban expansion was relatively stable inside the core area but had almost quadrupled within the surrounding areas, exposing the refuges to more people. These findings indicated that the wildlife habitats of Turkey are fragmented and under heavy human pressure.
Effects of environmental factors and forest management on landscape-scale forest storm damage in Turkey
(2020-06-01) Torun P.; Altunel A.O.
Key message: Windstorms have recently caused noteworthy destruction across the Northern forests of Turkey. The intensive forest management practices applied for more than 60+ years may unknowingly have resulted in wind-sensitive forests in the region. After a storm, the forest service salvages the losses, but no further precaution is taken against future storms. To our knowledge, there has not been any research looking into the cumulative effects of environmental factors on storm damage in Turkish forests. Maxent, which is an ecological niche model, might help decision-makers in developing forest management strategies against storms given its ease of use, known successful performance, and flexible variable evaluation approach. This study revealed that management preferences were mainly responsible for forest storm damage in Kastamonu Province, Turkey. Context: Excessive wind cause serious damages to individual trees and forest stands. When unintentionally coupled with the forest management preferences, catastrophic levels of damage might be unavoidable. Aims: The main objective was to assess the environmental factors contributing to the impact of a strong windstorm that occurred between March 14 and 15, 2013 and resulted in 1.5-million m3 timber losses in the Kastamonu Regional Directorate of Forestry. Methods: Maximum entropy modeling (Maxent) and geographic information systems (GIS) were used to evaluate the factors contributing to the forest damage. Results: Stand type, diameter class, and elevation were the most important variables affecting the level of wind damage. The pure and mixed coniferous stands were the hardest hit when compared with the deciduous stands. The damage increased as the density of forest roads grew. Conclusion: It was concluded that windstorms pose serious threats to Turkish forests. Storm damage risks must therefore be integrated into forest management. In order to better understand the environmental factors contributing to the destructive effects of windstorms in forests, it would be best to focus on the telltale signs pointing the wrong-doing in forest management preferences at larger environmental scale rather than looking for reasons behind the occurrences of scattered small-scale damage.
Examining the PALSAR-2 Global forest/non-forest maps through Turkish afforestation practices
(2020-08-17) Altunel A.O.; Akturk E.; Altunel T.
Forests and afforestation have significant importance, given the present course of World’s climate resulting from our insensitive behaviours, policies, ambitions, etc. Turkish Forest Service has departments, sole purposes of which are to combat desertification through afforestation, flood control, and watershed rehabilitation works. Majority of the works is carried out in the semi-arid central part of the country, which is known as the Irano-Turanian phytogeographic region. Hydroelectric dam projects, which have extensively been conducted to produce energy and to harness the rivers when needed, have been at the centre of these efforts in the region. Afforestation works, which have long been used to safeguard dam reservoirs, have always been associated with such projects because they are implemented even prior to water deposition. They along with the country’s managed forests are looked after as the natural forest cover. Improvements in remote sensing at this point enabled the agencies to diversify their efforts in monitoring the natural resources and strengthening the decision makers’ hand in management preferences in both global and regional scales. There are various data produced through the classification of satellite imagery representing the existence or the percentage of forests in any location on Earth. In this study, Global Phased Arrayed L-band Synthetic Aperture Radar PALSAR-2/PALSAR mosaic and forest/non-forest maps of Japan Aerospace Exploration Agency (JAXA) and Global Forest Cover Change (GFCC) thematic image tiles of National Aeronautics and Space Administration (NASA), which are two of the widely accepted such data, were compared to one another and to our control results produced by a pixel-based classification method to assess the performance of afforestation works around seven major hydroelectric dam reservoirs situated within the central part of Turkey. The results showed that Global PALSAR-2/PALSAR forest/non-forest maps were somewhat capturing the trend, but overly exaggerating the ground facts up to 1064%. GFCC epochs, on the other hand, did not yield sound results in this semi-arid part of Turkey. Latter data could not even capture the successfully afforested sites.
How good is TanDEM-X 50 m forest/non-forest map? Product validation using temporally corrected geo-browser supplied imagery through Collect Earth
(2023-01-01) Akturk E.; Altunel A.O.; Atesoglu A.; Seki M.; Erpay S.
TanDEM-X Forest/Non-Forest (FNF) map(s) have been one such data focusing on the status of global forest coverage, which has played an essential role in combating climate change. Although the producers have carried out verification and comparison analyses, the need for accuracy assessments in a broader sense creates uncertainties for the users to approve the new data. For this purpose, TanDEM-X 50 m FNF maps were exclusively examined visually through 66,000 test grids within 30 geocells selected from temperate, boreal, and tropical forest zones. Thus, it was aimed to provide product accuracy utilizing visual inspections to the end users of TanDEM-X FNF maps. In addition, Collect Earth (CE) software was used to evaluate the dataset visually, and its advantages or disadvantages were compared with similarly designed studies. Consequently, even though the producers’ data sets were found to have an accuracy of around 85%, it was observed that there were some issues, especially in the definition of the “non-forest” class. CE software was found to be helpful in such studies. However, the dependence of the analyses on geo-browser supplied imagery had some limitations in estimating the accuracy of a new dataset.
Questioning the effects of raster-resampling and slope on the precision of TanDEM-X 90 m digital elevation model
(2021-01-01) Altunel A.O.
Defining watersheds with enough topographical features is crucial when large infrastructure projects are concerned. German Aerospace Center (DLR) recently announced the dissemination of the 90 m variant of the original global TanDEM-X 12 m Digital elevation model (DEM). It was announced as produced with a special averaging technique, which would even surpass the precision of the 12 m DEM. This study aimed to test this claim while simultaneously testing whether resolution coarsening would deteriorate the performance of a higher precision DEM. AW3D30 was used as auxiliary data in four sites. Results confirmed that the 90 m DEM was indeed highly reliable at or below 20% slopes in two investigated dam reservoir areas with gentle terrain conditions, and overestimated in other two dam reservoirs with severe topography. The resampling approach did not necessarily worsen the elevation values aggregated into a larger raster resolution as obvious from the auxiliary data analyses.
Questioning the effects of raster-resampling and slope on the precision of TanDEM-X 90 m digital elevation model
(2021-01-01) Altunel A.O.; Altunel, AO
Defining watersheds with enough topographical features is crucial when large infrastructure projects are concerned. German Aerospace Center (DLR) recently announced the dissemination of the 90 m variant of the original global TanDEM-X 12 m Digital elevation model (DEM). It was announced as produced with a special averaging technique, which would even surpass the precision of the 12 m DEM. This study aimed to test this claim while simultaneously testing whether resolution coarsening would deteriorate the performance of a higher precision DEM. AW3D30 was used as auxiliary data in four sites. Results confirmed that the 90 m DEM was indeed highly reliable at or below 20% slopes in two investigated dam reservoir areas with gentle terrain conditions, and overestimated in other two dam reservoirs with severe topography. The resampling approach did not necessarily worsen the elevation values aggregated into a larger raster resolution as obvious from the auxiliary data analyses.
Suitability of open-access elevation models for micro-scale watershed planning
(2018-09-01) Altunel A.O.
Watershed planning is a major issue in Turkey and other parts of the world. Surrounded by seawater on almost three-quarters of its international borders and by sheer mountains along the coastal regions and throughout the country, Turkey experiences a range of climatic changes, which constantly shape its topography. Recently, the occurrences of floods, landslides, and torrents have increased, forcing decision-makers to come up with solutions to manage and rehabilitate the upper watersheds in order to stop or limit the impact of disasters on downstream areas. Possible solutions should reduce flow coefficients, erosion, and sedimentation and increase reservoir capacities. It is expected that torrent volumes will decrease, drainage regimes on slopes will be better organized and adjusted, thawing snow will be better deposited and delayed, evapotranspiration will increase, surface runoffs will be delayed, and water regimes will be better managed, meaning that flood and torrent control will be achieved. For the reasons mentioned above, watershed parameters need to be firmly set. In the scope of this study, the elevation, slope acreage, and reservoir capacity of a small watershed, as extracted from open-access elevation models, were compared to a real-time kinematic (RTK) global positioning system (GPS)-generated point cloud and the resulting elevation model through various geospatial and analytical means. The Shuttle Radar Topography Mission (SRTM) C-band digital elevation model (DEM) (version 3) proved to be a satisfactory method in making residual, correlation, mean, and reservoir capacity comparisons. An L-band Advanced Land Observing Satellite (ALOS) phased-array-type synthetic aperture radar (PALSAR) and an X-band DLR_SRTM ASTER were slightly superior methods in terms of defining a greater number of slope categories than the other models. Finally, DLR_SRTM and SRTMv3 could match a greater number of slope façades than the other models. Seventeen years after its acquisition, SRTM and its derivatives have continued leading the topographic definition of the Earth.
Suitability of open-access elevation models for micro-scale watershed planning.
(2018-08-10T00:00:00Z) Altunel, Arif Oguz; Altunel, AO
Watershed planning is a major issue in Turkey and other parts of the world. Surrounded by seawater on almost three-quarters of its international borders and by sheer mountains along the coastal regions and throughout the country, Turkey experiences a range of climatic changes, which constantly shape its topography. Recently, the occurrences of floods, landslides, and torrents have increased, forcing decision-makers to come up with solutions to manage and rehabilitate the upper watersheds in order to stop or limit the impact of disasters on downstream areas. Possible solutions should reduce flow coefficients, erosion, and sedimentation and increase reservoir capacities. It is expected that torrent volumes will decrease, drainage regimes on slopes will be better organized and adjusted, thawing snow will be better deposited and delayed, evapotranspiration will increase, surface runoffs will be delayed, and water regimes will be better managed, meaning that flood and torrent control will be achieved. For the reasons mentioned above, watershed parameters need to be firmly set. In the scope of this study, the elevation, slope acreage, and reservoir capacity of a small watershed, as extracted from open-access elevation models, were compared to a real-time kinematic (RTK) global positioning system (GPS)-generated point cloud and the resulting elevation model through various geospatial and analytical means. The Shuttle Radar Topography Mission (SRTM) C-band digital elevation model (DEM) (version 3) proved to be a satisfactory method in making residual, correlation, mean, and reservoir capacity comparisons. An L-band Advanced Land Observing Satellite (ALOS) phased-array-type synthetic aperture radar (PALSAR) and an X-band DLR_SRTM ASTER were slightly superior methods in terms of defining a greater number of slope categories than the other models. Finally, DLR_SRTM and SRTMv3 could match a greater number of slope façades than the other models. Seventeen years after its acquisition, SRTM and its derivatives have continued leading the topographic definition of the Earth.
The effect of DEM resolution on topographic wetness index calculation and visualization: An insight to the hidden danger unraveled in Bozkurt in August, 2021
(2023-07-05) Altunel A.O.
Topographic Wetness Index, also known as the compound topographic index, (TWI) is a topographic indicator that calculates the potential of where water is likely to accumulate during excessive precipitation cycles resulting from abrupt atmospheric anomalies. High index values represent serious potential of water accumulation due to low slope, and the opposite for high slope. As expected from the term, slope, Digital Elevation Model (DEM) datasets play an important role in the calculation of TWI. DEMs are produced utilizing tachometry, GPS benchmarking, UAV, aerial or satellite image capture and LIDAR capabilities. However, no matter how it is generated, a DEM is as good as the actual ground sampling algorithm, on which the final resolution is based. Using six different DEM resolutions coming from three global and one national source presented in three different setting coverages, upper feeder basin of Bozkurt sub-province, Kastamonu, was analyzed emphasizing the urbanized part of the sub-province, which was devastated during the August 11th, 2021 flood. Coarser resolution missed the overall precision while the finer resolution captured it nicely. On the flip side, finer resolution excessively fragmented the questioned area while the coarser resolution formed a unity coinciding with the destructed area recorded during the event.
The effect of DEM resolution on topographic wetness index calculation and visualization: An insight to the hidden danger unraveled in Bozkurt in August, 2021
(2023-07-05) Altunel A.O.; Altunel, AO
Topographic Wetness Index, also known as the compound topographic index, (TWI) is a topographic indicator that calculates the potential of where water is likely to accumulate during excessive precipitation cycles resulting from abrupt atmospheric anomalies. High index values represent serious potential of water accumulation due to low slope, and the opposite for high slope. As expected from the term, slope, Digital Elevation Model (DEM) datasets play an important role in the calculation of TWI. DEMs are produced utilizing tachometry, GPS benchmarking, UAV, aerial or satellite image capture and LIDAR capabilities. However, no matter how it is generated, a DEM is as good as the actual ground sampling algorithm, on which the final resolution is based. Using six different DEM resolutions coming from three global and one national source presented in three different setting coverages, upper feeder basin of Bozkurt sub-province, Kastamonu, was analyzed emphasizing the urbanized part of the sub-province, which was devastated during the August 11th, 2021 flood. Coarser resolution missed the overall precision while the finer resolution captured it nicely. On the flip side, finer resolution excessively fragmented the questioned area while the coarser resolution formed a unity coinciding with the destructed area recorded during the event.
The effect of population shift on land cover change and illegal forest activities
(2021-02-01) Guloglu Y.; Bulut A.; Altunel A.O.; Bayramoglu M.M.
Interaction between humans and forests has always been strong. Wood has been at the core of all humankind’s endeavors since the discovery of fire and learning how to fabricate it out of trees. The exploitation of forests has not been limited to the procurement of wood, but the concepts of sheltering, hunting, and protection have also been matured near or within the forests. This win-win situation intuitively attracted more and more people to this type of resource. As the human population has grown in forest villages, the pressure caused by the human on the forests has increased. Without active management of the forests, the situation has become so dire that uncontrolled and irregular utilization has started jeopardizing the existence of this resource. The objective of this study was to examine the changes in forest road, forestland cover, and forest crimes in the Daday Forest Enterprise (DFE) located in Kastamonu Regional Directorate of Forestry, Turkey. The results indicated that the population in 51 forest villages was decreased from 1975 to 1990. This decrease was also apparent in all villages across the region during the 1990–2000 period and continued decreasing in 45 villages during the 2000–2016 period. The forestland cover was 57% in 1975, 44% in 2000, and 57% in 2016 while the density in the forest road kept increasing. A noticeable decrease in the forest-related crimes was also determined, and the results showed that effective forest management, consciousness, and conservation policies stopped the deterioration.
Visibility analysis of fire lookout towers in the Boyabat State Forest Enterprise in Turkey
(2017-07-01) Kucuk O.; Topaloglu O.; Altunel A.O.; Cetin M.
For a successful fire suppression, it is essential to detect and intervene forest fires as early as possible. Fire lookout towers are crucial assets in detecting forest fires, in addition to other technological advancements. In this study, we performed a visibility analysis on a network of fire lookout towers currently operating in a relatively fire-prone region in Turkey’s Western Black Sea region. Some of these towers had not been functioning properly; it was proposed that these be taken out of the grid and replaced with new ones. The percentage of visible areas under the current network of fire lookout towers was 73%; it could rise to 81% with the addition of newly proposed towers. This study was the first research to conduct a visibility analysis of current and newly proposed fire lookout towers in the Western Black Sea region and focus on its forest fire problem.