LEE- Geomatik Mühendisliği-Doktora

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  • Öge
    Assessment of global gravity models in coastal zones: A case study using astrogeodetic vertical deflections in İstanbul
    (Fen Bilimleri Enstitüsü, 2020) Albayrak, Müge ; Özlüdemir, Mustafa Tevfik ; 619803 ; Geomatik Mühendisliği Ana Bilim Dalı
    Astrogeodetic vertical deflections (VDs) provide valuable information about the structure of Earth's gravity field. For this reason, astrogeodetic VD observations are essential gravity field observables. Several types of astrogeodetic observational instruments have been used to obtain astrogeodetic VD components. Currently, modern imaging instruments such as the Digital Zenith Camera System (DZCS) or the total station (TS)-based QDaedalus system, which are operated at field stations at night, are used to observe astronomical coordinates (astronomical latitude [] and longitude []). Global Navigation Satellite System (GNSS) receivers located at the same benchmark (BM) provide geocentric geodetic coordinates (geodetic latitude [] and longitude []). From these, the North-South (=  - ) and East-West (= (-) cos ) components of VDs can be calculated. This thesis aims to introduce a new astrogeodetic VDs data set, which was collected using the QDaedalus system in Istanbul, Turkey to investigate the quality of the Global Gravity Model plus (GGMplus) gravity functional maps and Earth Gravitational Model 2008 (EGM2008). To establish the Istanbul Astrogeodetic Network (IAN), 30 BMs were selected out of 1183 BMs that are part of both the Istanbul GPS Triangulation Network (IGTN) and the Istanbul Levelling Network (ILN). While IGTN provides geodetic coordinates and ellipsoidal heights, ILN provides orthometric heights. Before establishing the IAN, the ellipsoidal heights from the IGTN, the orthometric heights from ILN, and the newly-collected valley cross levelling (VCL) data were used to calculate a new geoid model in Istanbul using soft computing techniques, including the adaptive-network-based fuzzy inference system (ANFIS) and the artificial neural networks (ANNs). The aim of this calculation is to show the current status of the Istanbul geodetic geoid. After the calculation of the Istanbul geoid, which is very weak in coastal and mountainous areas, the IAN was established. The first astrogeodetic VD observations campaign taken in Istanbul were made using the Leica TCRM1101 TS integrated QDaedalus system. The measured VDs are unique in that, not only were they measured for the first time in Istanbul, but they also form Turkey's first dense astrogeodetic network. A total of 21 out of 30 BMs are located in the coastal zone allowing us to investigate the quality of global gravity models along the coast of Istanbul. Preliminary steps are required before the QDaedalus system can be used in the IAN to investigate the precision and accuracy of the system. One such activity is to test the QDaedalus system at the same BM several nights in a row to determine the precision of the system. For this thesis, these test observations were carried out at a control site at Technical University of Munich (TUM) test station, the Istanbul Technical University (ITU) test station, and at six densely-spaced pillars of the geodetic control network at the Geodetic Observatory Wettzell (GOW). The accuracy should also be established, and in this thesis was determined by comparing the Hannover DZCS TZK2-D VDs results at 10 field stations located in the Munich region to independently observed VDs data from the QDaedalus. The ITU test station was also used by the Turkish DZCS's—Astrogeodetic Camera System 2 (ACSYS2)—test station to determine the precision of this DZCS by repeated observations. The VDs results comparison of the QDaedalus and ACSYS2 at the ITU test station provide us to determine the accuracy of the ACSYS2. The initial test observations with the Leica TCRM1101 TS integrated QDaedalus system showed that it is capable of producing highly accurate VDs data (~0.20"). After establishing these satisfactory results, the astrogeodetic VDs in the IAN were measured for follow-on campaigns. The standard deviations (SDs) for the IAN are approximately 0.20" for both the North-South () and East-West () components. This new VD data set was compared with modelled VDs from the GGMplus gravity functional maps and EGM2008. The differences between the VDs from QDaedalus and those from GGMplus and EGM2008 tend to increase towards the coastlines, where discrepancies of several arcseconds amplitude between the observed and modelled values are encountered. We interpret these spurious differences as weaknesses in the modelled VDs along the Istanbul coastlines, most likely reflecting increased errors in the altimetry-derived marine gravity field the GGMplus model depends on (via EGM2008 and Danish National Space Center [DNSC2007]). The central finding of this thesis is that astrogeodetic VDs are valuable tools for independently investigating the quality of coastal-zone gravity data sets and gravity field products. The new VD data set is useful for the quality assessment of future EGMs, such as the EGM2020. The results and findings presented in this thesis were supported by grants and scholarships from several fundings and research support sources. The Turkish DZCS modernization process, determination of the precision and accuracy of the system, and the IAN's fieldwork by the QDaedalus system were supported by the Scientific and Technological Research Council of Turkey (TUBITAK) Project (grant number 115Y237). The Leica TDA5005 TS integrated QDaedalus system test observations at TUM were supported by the German Academic Research Council Scholarship (DAAD) short-term grant. The Leica TCRM1101 TS integrated QDaedalus system's test observations at TUM and the Munich region observations were supported by a TUBITAK BIDEB 2214-A scholarship. The GOW observations were supported by the Institute of Astronomical and Physical Geodesy (IAPG) at TUM and GOW. Finally, the data analysis of the IAN was supported by the Fulbright Foundation.
  • Öge
    Exploring the cognitive processes of map users employing eye tracking and EEG
    (Fen Bilimleri Enstitüsü, 2020) Keskin, Merve ; Doğru, Ahmet Özgür ; De Maeyer, Philippe ; 656904 ; Geomatik Mühendisliği Ana Bilim Dalı
    Understanding how our brain copes with complex visual information is a challenge for both cognitive psychology and cartography. If we pursue to design better and usable maps, we require building a better knowledge on the cognitive processes of map users. This thesis aims to contribute to the understanding of the cognitive processes of a group of map users in learning, acquiring and remembering information presented via digital 2D static maps. To be able to gain insight into the users' behaviors while they interact with maps, eye tracking (ET) and electroencephalogram (EEG) are enabled as synchronized data collection methods due to them being non-invasive and capturing direct responses of cognitive activities. Therefore, the preliminary goal of the research is to evaluate the use of ET and EEG for cartographic usability and spatial cognition research considering the technical and methodological aspects of this synchronization, also the limitations, possibilities and the contribution of EEG in the domain of cartography. The technical concerns refer to (i) the synchronization of ET and EEG recording systems, their accuracy and quality, and (ii) numerous processing steps (i.e. preprocessing, the alignment of the collected ET and EEG data, removal of non-cerebral activities from EEG data, segmentation and re-referencing). The methodological issues are situated in many aspects of the experimental design and its set-up, which includes identifying the research goals, participants, task and stimuli, psychological measures to use, evaluation methods and possible analyses of the collected data. These issues are pinpointed with respect to the existing literature, knowledge obtained from domain experts and hands-on experience in the neuro-lab. The fundamental object of the thesis is to investigate on the traditional expert-novice paradigm as expertise being one of the individual characteristics that influences the users' performance on map-learning tasks. Since maps are widely used by both experts and novices, to study their differences in spatial cognition enables us to determine how to use this input to enhance the map design leveraging the map users' cognitive abilities. Therefore, our main research questions are: 'Do map learning strategies of experts and novices differ? How does the cognitive load vary between expert and novices?' In this context, we conducted two mixed-methods user experiments focusing on the cognitive strategies of a group of expert and novice map users and investigated their spatial memory capabilities through cognitive load measurements. First experiment had a simple design and an exploratory characteristic, since we would initially assure that the eye tracking and EEG synchronization is of sufficient quality to explore users' cognitive behaviors towards map stimuli. Accordingly, it consisted of single trials and participants were instructed to study the main structuring elements of a map stimulus (i.e. roads, settlements, hydrography, and green areas) without any time constraints in order to draw a sketch map afterwards. On the one hand, the performance of the participants was assessed based on the order with which the objects were drawn on the digital sketch maps and the influence of a subset of visual variables (i.e. presence & location, size, shape, color). On the other hand, trial durations and eye tracking statistics such as the average duration of fixations, and number of fixations per seconds were compared. Moreover, selected AoIs, which represent the main structuring elements of the map stimulus, were explored to gain a deeper insight on visual behavior of map users. Based on the evaluation of the drawing order, we observed that experts and males drew roads first whereas; novices and females focused more on hydrographic object. According to the assessment of drawn elements, no significant differences emerged between neither experts and novices, nor females and males for the retrieval of spatial information presented on 2D maps with a simple design and content. The differences in trial durations between novices and experts were not statistically significant while both studying and drawing. Similarly, no significant difference occurred between female and male participants for either studying or drawing. Eye tracking metrics also supported these findings. For average duration of fixation, there was found no significant difference between experts and novices, as well as between females and males. Similarly, no significant differences were found for the mean number of fixation. Furthermore, based on results of time to first fixation, dwell time, fixation count, the number of fixations per second, average fixation duration for selected AoIs, the larger AoIs were gazed at earliest and the dwell times for such objects were much longer compared to those for other AoIs. The linear features were easier to learn and remember, although the viewer did not pay much attention. Longer average fixation durations for a specific AoI indicated that the chances were higher to remember that object. The objects that were absent on the sketch map received the shortest fixation durations during the study phase. However, longer fixation durations may also indicate participants' difficulty to recognize the information in the map stimulus. Regarding to the EEG Frontal Alpha Asymmetry calculations, both user groups showed greater relative right frontal activation, which is in association with the less attentional, and focus performance. The difference between experts and novices was not significant, similar to the eye tracking results. On the contrary, alpha power averaged across all electrodes demonstrated that the novices exhibited significantly lower alpha power, indicating a higher cognitive load. On the contrary, in Experiment 2, a complex and more structured approach was followed as a result of learning from the previous experiment and collaborating with the domain experts. This experiment contained a larger number of stimuli were used to study the effect of task difficulty (i.e. easy, moderate, hard) on the retrieval of map-related information. Next to the reaction time and success rate, we used fixation and saccade related eye tracking metrics (i.e., average fixation duration, the number of fixations per second, saccade amplitude and saccade velocity), and the event-related changes in EEG power spectral density (PSD) for alpha and theta frequency bands to identify the cognitive load. While fixation metrics and the qualitative analysis of the randomly selected focus/heat maps summarizing the participants' fixation behaviors indicated no statistically significant difference between experts and novices, saccade metrics proved the otherwise. EEG power spectrum analysis, on the other side, suggested an increase in theta power (i.e. event-related synchronization) and a decrease in alpha power (except moderate tasks) (i.e. event-related desynchronization) at all difficulty levels of the task for both experts and novices, which is an indicator of cognitive load. Although no significant difference emerged between two groups, we found a significant difference in their overall performances when the participants were classified as good and relatively bad learners. Triangulating EEG results with the recorded eye tracking data and the qualitative analysis of randomly selected focus maps indeed provided a detailed insight on the differences of the individuals' cognitive processes during this spatial memory task. The qualitative analysis with the 10 randomly selected focus/heat maps provided a general overview of the participants' attentional behavior towards the map elements of interest and the similarities related to their map learning strategies. However, for measurable results, we selected one map stimulus and drew AoIs around key elements of maps (i.e. green areas, water bodies, major rivers and roads, road junctions) to analyze the attention distribution of the participants using average fixation duration, time to first fixation and the number of map objects covered within AoIs. Although the results are preliminary, we found out that the eye scans through linear objects and fixates/focuses on the polygon objects. The location of the map elements is more influential on the participants' gaze behavior compared to its size. The fixation durations within the (relevant) AoIs did not depend on the task difficulty. Additionally, our analysis showed that the GL experienced the least cognitive and this finding supports the evaluation of the participants by classifying them as "good learners and bad learners" during the usability tests of maps designed for general users with basic map learning tasks. In order to increase the understandability and usability of cartographic products, the results of this research can be used as guiding experiences in production processes where design methods that minimize the factors that negatively affect user perception (e.g. exaggeration, reduction of emphasis, utilizing the visualization elements to increase visual extraction such as grids).
  • Öge
    Yerel jeodezik GNSS CORS ağları ve bilimsel çalışmalara katkıları: İSKİ UKBS örneği
    (Fen Bilimleri Enstitüsü, 2020) Gökdaş, Ömer ; Özlüdemir, Mustafa Tevfik ; 652824 ; Geomatik Mühendisliği Ana Bilim Dalı
    İstanbul Su ve Kanalizasyon İdaresi (İSKİ), dünyadaki teknolojik gelişmeleri takip ederek ve kurumun ihtiyaçlarını göz önünde bulundurarak tüm İstanbul metropoliten alanını kapsayan ve ağ RTK (NRTK) prensibi ile çalışan Sürekli Çalışan Referans İstasyonları (Continuously Operating Reference Stations-CORS) ağını 2008 yılı sonunda kurmuş, ağ 'Uydulardan Konum Belirleme Sistemi (UKBS)' olarak isimlendirilmiştir. İSKİ UKBS Ağı ilk olarak 8 istasyon ile kurulmuş olup daha sonra ağın baz mesafeleri kısaltılarak geometrisi değiştirilmiştir. Mevcut durumda 10 istasyonu bulunmaktadır. Tez kapsamında, İSKİ UKBS Ağı'nın ülkemize ve bilime olan katkıları ifade edilerek, ağın sağladığı 10 yılı aşkın süredir devam eden statik veri ve düzeltme yayımı değerlendirilerek dört adet farklı senaryo ile uygulamalar gerçekleştirilmiştir. Birinci bölümde İSKİ UKBS Ağı hakkında genel bir bilgi verilerek, tezin amaçlarını ifade eden araştırma soruları, kullanılan yöntem ve materyaller ve literatür çalışması başlıklarına yer verilmiştir. İkinci bölümde İSKİ UKBS Ağı'nın kuruluş aşamasında gerçekleştirilen faaliyetler ele alınmıştır (Kurulum aşaması, istasyonların hassas konumlarının belirlenmesi, test yayım aşamaları, istatistik veriler). Ayrıca, İSKİ UKBS Ağı'nın kullanıcılara yayımlamış olduğu düzeltme modellerinin hesaplandığı iki sunucuda var olan, biri 2009-2015 yılları arası kullanılan ve şu an pasif olan GnSmart CORS yazılımı, diğeri 2015 yılından itibaren aktif olarak kullanılan Topnet Live CORS yazılımı incelenip analiz edilmiştir. Bu aşamada kullanıcıların sistemde kayıtlı tutulan logları, sistemin ürettiği düzeltme modelleri, çalışma saatleri ve ölçü kalitesi gibi farklı parametreler irdelenmiştir. Üçüncü bölümde, tezin amaçları doğrultusunda gerçekleştirilen, İSKİ UKBS Ağı düzeltme yayımı ve statik veri seti kullanılarak gerçekleştirilen dört farklı senaryoya ilişkin uygulamalar mevcuttur. Yapılan ilk uygulamada, istasyon hızları araştırılmıştır. Tektonik plaka ile uyumluluğu irdelenmiştir. İstasyon hızlarında yıllık trend dışında, mevsimsel, yarıyıllık ve yıllık salınım hareketinin varlığı araştırılmıştır. İstasyon hızlarının karşılaştırması yapılmıştır. Ayrıca, Global Navigasyon Uydu Sistemleri (Global Navigation Satellite System-GNSS) online değerlendirme servislerinin (Automatic Precise Positioning Service-APPS ve Australia Positioning Service-AUSPOS) konum belirleme performansı ve istasyon hızlarının belirlenmesinde kullanılabilirlikleri İSKİ UKBS Ağı istasyonları kullanılarak araştırılmıştır. İkinci çalışmada, İSKİ UKBS Ağı ve CORS-Türkiye (TR) Ağı baz mesafelerinin Sanal Referans İstasyonları (Virtual Reference Stations-VRS) çözümlerindeki belirsizlik çözüm süresi (Time to Fix Ambiguity-TTFA), tamsayı belirsizlik çözüm oranı (Fix rate), presizyon ve konum belirleme doğruluklarında ürettiği sonuçlar karşılaştırılmıştır. Üçüncü çalışmada, NRTK gözlemlerinde baz mesafesinin doğruluk ve presizyona etkisi araştırılmış ve yeni bir matematiksel model ile ifade edilmiştir. Ayrıca bu çalışma ile, Alan Düzeltme Parametreleri (Flaechen Korrektur Parameter-FKP) ve VRS yöntemlerinin farklı baz mesafelerindeki performansları analiz edilmiştir. Son çalışmada ise, İSKİ UKBS Ağı'nın Toplam Zenit Gecikmesi (Zenith Tropospheric Delay-ZTD) ve Bütünleşik Su Buharı (Integrated Water Vapour-IWV) kestiriminde kullanılabilirliği araştırılmıştır. ZTD ve IWV'nin lokal İSKİ UKBS Ağı'nda yükseklik ve mesafe farkına göre değişiminin incelendiği bu çalışmada, ayrıca IWV kestiriminde GNSS Analiz ve Konum Belirleme Yazılımı (GNSS Analysis and Positioning Software-GAPS) online servisinin performansı İSKİ UKBS Ağı istasyonları kullanılarak araştırılmıştır.
  • Öge
    Social media data valuation model for disaster incidence mapping
    (Graduate School, 2020-10-16) Gülnerman Genç, Ayşe Giz ; Karaman, Himmet ; 501142609 ; Geomathic Engineering ; Geomatik Mühendisliği
    Social Media is a new age of data sources that emerged in the last decade. Users who have diverse different motivations (such as; entertainment, communicating or promoting) sign up the platforms worldwide. Currently, there is 3.5 billion active social media account worldwide. This growing number of account holders are accepted as human sensors that provide information about their environment. Unlike the traditional sensors, these human sensors have no certainty in their capacity to sense and share the information. In addition, the data provided by human sensors is unstructured. Still, social media is an invaluable data source for studies, especially that require continuous and real-time data widely. Currently, the data is widely used for politics, marketing, and most importantly in crisis management. In this thesis, social media data is assessed for incidence mapping during or shortly after a disaster with the motivation of increasing resilience to the expected major earthquake in Istanbul. The disaster management cycle has four phases as response, recovery, mitigation, and preparation. In the response phase, having real-time data from the affected area is important to properly allocate the resources. The conventional mapping technologies such as remote sensing and photogrammetry have the capacity of detecting the occurrence of a natural hazard however they are not eligible for information retrieval about the impacts of the natural hazards on human life such as emotions, opinions, and emergency situations. At this point, social media become forward as an immediate data source for incidence mapping during the response time of a disaster. Incidence mapping for resources management requires fine-grained data analyses. However, the uncertainty in data capacity, questions in the reliability of chosen techniques for pre-processing, and data bias are the key obstacles to the fine-grained analyses with the use of social media data. In this thesis, social media data is evaluated in terms of these key obstacles for Istanbul City since the data varies to the area that belongs to depending on its own human sensors. The main objective of this thesis is the determination of social media data potential for its use during the response phase of disaster management. There are three sub-objectives in order to reach the main objective; revealing the adequacy of the data for incidence mapping, adapting the pre-processing steps to Turkish language and questioning the reliability of the used filtering and classifying techniques with the quantification of its impacts on mapping, and investigating the intrinsic quality of the data (such as anomalies, trends, and biases) for the further interpretation of the incidence maps. The thesis is composed of three papers tackling these three objectives. Istanbul City is determined as the case area of each paper. In the first paper, the capacity of social media data to detect incidences in a fine-grained spatiotemporal perspective is investigated. For the case, the coup attempt data georeferenced within Istanbul city boundary is used and a series of incidences by the hour is mapped with the hotspots. According to that study, it is revealed that social media data has the capacity to identify an incidence with a fine-grain spatiotemporal resolution. In the second paper, the reliability of the chosen techniques for pre-processing and filtering social media data is researched with its effects on incidence mapping. Two terror attacks data that is georeferenced within Istanbul City is used for the case of this study. The study is not also testing the adaptation of the current pre-processing and filtering techniques to the Turkish language and also proposes a quantitative comparative index for quantifying the spatial reliability of each filtering process. This index named Giz Index which can be replicated for the similarity searches between two incidence maps. It is found in this study, with the proposed methodology for pre-processing and filtering, over 80% of spatial reliability can be achieved for incidence mapping based on social media data. In the third paper, the intrinsic quality of data is researched for the right interpretation of the incidence maps. The study overviews the weekly sampled social media data from each month during a year that is georeferenced within the Istanbul City. The data is assessed from the perspective of data anomaly, trend, and bias with the spatial statistical tests. The study infers that the data has spatial representation bias, anomaly tendency in some parts of the city, the spatiotemporal bias in terms of the time of day and day of the week. The results of the study contribute to the incidence mapping with the reference maps to avoid biased hot spot occurrences or missing information due to less amount of data.