Bölgesel ve küresel boyuttaki afetlerin farklı jeosensörler ile incelenmesi ve analizi
Investigation and analysis of regional and global disasters using different geosensors
Yazar: BİLAL MUTLU
Danışman: PROF. DR. SERDAR EROL
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Geomatik Mühendisliği Ana Bilim Dalı / Geomatik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2022
Konu: Jeodezi ve Fotogrametri = Geodesy and Photogrammetry
Dizin: Antarktika = Antarctica ; Jeodezi = Geodesy ; Küresel ısınma = Global warming ; Lavanta = Lavender ; Sisam Adası = Samos Island ; Yer çekimi = Gravity

Özet:
Bu tez calışması kapsamında, bölgesel ve küresel etkiye sahip doğal afetlerin gözlemlenmesi ve analizinde, farklı özelliklerdeki jeosensörlerin kullanılabilirliği araştırılmıştır. Bu amaç doğrultusunda, biri bölgesel diğeri ise küresel olan iki afetin farklı jeosensör verilerini kullanarak değerlendirilmesi yapılmıştır. Bu kapsamda, birinci uygulamada, 30.10.2020 tarihinde İzmir Sisam Adasında gerçekleşen Mw 6.9 büyüklüğündeki depremin değerlendirilmesi; ikinci uygulamada ise küresel ısınma sebebiyle Antarktika kıtasında gerçekleşen buzul erimesi kaynaklı dinamik hareketlerin izlenmesi gerçekleştirilmiştir. Tezin ilk kısmında, Küresel Konum Belirleme Sistemi (GNSS), kuvvetli yer hareket sensörü (SGMS), interferometrik yapay açıklıklı radar (InSAR) ve mareograf verileri kullanılarak deprem sonucu oluşan deformasyonların belirlenmesi amaçlanmıştır. Türkiye Ulusal Sabit GNSS Ağı – Aktif (TUSAGA-Aktif) ağına dahil olan ve deprem bölgesinde bulunan 4 farklı GNSS istasyonunun 1 saniye aralıklı (1 Hz) gözlem verileri, CSRS-PPP ve AUSPOS servisleri kullanılarak sırasıyla PPP-AR (statik ve kinematik) ve rölatif-statik yöntemlerine göre çözdürülmüş ve konum değişimleri elde edilmiştir. Afet ve Acil Durum Yönetimi Başkanlığı (AFAD) tarafından depremlerin takibi için kurulan Türkiye İvme Veri Tabanı ve Analiz Sistemi (TADAS) ağı dahilinde ve kullanılan TUSAGA-Aktif GNSS istasyonlarının yakınında bulunan SGMS istasyonlarının ham ivme verilerinden yer değiştirme ve hız değerleri türetilmiştir. GNSS gözlemlerinin PPP-AR kinematik çözümlerinden elde edilen yer değiştirme değerlerinden de hız ve ivme verileri türetilmiş, iki farklı jeosensörden elde edilmiş olan veriler karşılaştırılmıştır. Sonrasında, Avrupa Uzay Ajansı (ESA) tarafından yönetilen Sentinel-1 uydu misyonundan elde edilen deprem öncesi ve sonrası zamanlara ait olan yapay açıklıklı radar (SAR) görüntüleri yardımıyla InSAR yönteminden yararlanılarak uydu görüş hattı (LOS) üzerindeki yer değiştirme haritası üretilmiştir. Ayrıca deprem üssüne yakın konumda ve açık deniz havzasında bulunan mareograf istasyonlarının deprem anını içeren zaman serileri elde edilmiş ve deprem sebebiyle meydana gelen sapmalar olduğu gözlenmiştir. Tez çalışmasının diğer kısmında Antarktika Kıtasındaki buzul kaybının takibi ve analizi gerçekleştirilmiştir. İlk olarak, 2 farklı mareograf istasyonu ve yakınlarında yer alan GNSS istasyonlarının verilerinden yararlanılmıştır. Mareograf istasyonlarından elde edilen, rölatif deniz seviyesi (RSL) değişimi ile GNSS gözlemlerinden elde edilen düşey kara hareketi (VLM) değişimi trend değerlerinden mutlak deniz seviyesi (ASL) değişimi elde edilmiştir. Ayrıca, altimetre uydu misyonları kullanılarak üretilen deniz seviyesi anomalisinin (SLA) zamansal değişimi, ASL değişimini ifade edeceği için iki farklı yöntemle elde edilen trend değerleri birbirleriyle doğrulanmıştır. Bunlara ek olarak, GRACE ve GRACE-FO uydu gravite misyonlarından yararlanılarak türetilen eşdeğer su kalınlığı (EWT) değişimi iki mareograf istasyonunun bulunduğu bölge için de elde edilmiş fakat kullanılan ürünün mekansal çözünürlüğü düşük olduğu ve ilgili bölge kıyı şeridi olduğu için buzul kütlesinin trend değerini ifade etmek yerine, yükselen deniz seviyesi trendi ile uyuştuğu saptanmıştır. Sonrasında aynı bölgeler için, buzul izostatik denge (GIA) sonucunda gerçekleşen buzul sonrası geri-tepme (PGR) hareketinin zamansal kütle değişim oranları ile VLM trendleri karşılaştırılmış ve birbirlerini valide ettiği gözlenmiştir. Çalışmanın devamında, Antarktika Pine Adası özelinde çeşitli analizler gerçekleştirilmiştir. İlk olarak, kaya üzerinde bulunan GNSS istasyonlarının VLM trendleri ile bölgedeki PGR trend değeri karşılaştırılmış ve iki farklı veri grubundan da yükselen trend değerleri elde edildiği görülmüştür. Buzul üstünde bulunan GNSS istasyonlarına ait VLM trendi ise negatif yönde olup, CryoSat-2 ve ICESat-2 uydu misyonlarından elde edilen kara buz yüksekliği trendlerinin yönüyle ve ayrıca bölgedeki EWT değişiminin trend yönü ile birbirlerini valide etmekte olduğu ortaya konulmuştur. Pine Adası açıklarındaki ASL trendinin ise pozitif yönlü olduğu görülmüştür. Çalışmanın son aşaması olarak, Antarktika Kıtasının batı bölgesinde bulunan 9 adet GNSS istasyonunda kar kalınlığının değişimini belirlemek amacıyla reflektometri yönteminden yararlanılmış ve bölgede azalan trend olduğu ortaya konulmuştur.

Abstract:
Natural disasters can be divided into regional and global scales. Regional disasters such as earthquakes, floods, fires, volcanic eruptions, tornadoes and erosion affect smaller areas. While these disasters only affect the regions where they occur, global warming, which has a global impact, is actually one of the most important natural disasters of today. Due to global warming, the glaciers are melting, and accordingly the sea level rises, droughts occur and seasonal irregularities are experienced. In order to determine the impact of disasters, which have such important effects on our world, various observations should be made by using different methods. Within the scope of this thesis, it is aimed to investigate and analyze regional and global disasters using different geosensors. Within the scope of this thesis, two different case studies were conducted. Firstly, the Samos earthquake, and secondly, the glacial loss in Antarctica Continent were investigated with various geosensors. 
In the first stage of the thesis, a disaster with a regional effect was investigated with geosensors. In this context, data belonging to the Samos earthquake with a magnitude of Mw 6.9 (Kandilli Observatory and Earthquake Research Institute - KOERI) occurred 8 km north of Samos Island at a depth of 16 km, on 30.10.2020, at 11:51:24 UTC in the sea between Samos Island and Kusadasi Bay of Turkey, were used.  Within the scope of this study, deformations in the region were determined using Global Navigation Satellite System (GNSS), strong ground motion sensors (SGMS) and interferometric synthetic aperture radar (InSAR) methods, and in addition to these, sea level observations recorded at tide-gauges were investigated and interpreted. Observation data of GNSS stations which is included in Turkish National Permanent GNSS Network-Active (TUSAGA-Aktif) located in the earthquake zone were used. Firstly, 3 dimensional position data according to PPP-AR kinematic and static methods were generated by using the CSRS-PPP web-based service. In addition, the position calculations of the relevant data according to the relative static positioning method were performed using the AUSPOS service. Afterwards, the raw accelerometer data obtained from the SGMS stations in the Turkish Accelerometric Database and Analysis System (TADAS) network were first converted into velocity data and then displacement data. Besides, the displacement values obtained from the PPP-AR kinematic solution by using the GNSS method were first converted into velocity and then acceleration values, and compared with displacement, velocity and acceleration data obtained from SGMS stations. With the InSAR method, the line of sight (LOS) displacement map of the region was produced by processing the data obtained from the Sentinel-1 satellites of 2 different dates belonging to the earthquake region. The data of 3 tide-gauge stations located on the island of Kos, Plomari and Syros, which are the closest to the earthquake zone and in the open sea basin, were analyzed and interpreted. 
In the second stage of the thesis, it is aimed to analyze a global disaster. In recent years, with the increasing effect of global warming, a serious decrease in glacial masses has been observed in the polar regions. Due to the greater loss of mass, especially in the western parts of the Antarctic continent, various analyzes were carried out around Pine Island within the scope of this study. Continuous observations in these regions are necessary to determine the loss of glacier mass and the increase in global mean sea level (GMSL). Also, as a result of the mass loss of glaciers, an uplift occurs in the affected areas due to glacial isostatic adjustment (GIA). This uplift is called post-glacial rebound (PGR), and it is important to observe this effect as well. In this context; Geosensors such as GNSS, radar altimeters, gravity satellite missions and tide-gauges are widely used and contribute to the tracking of these dynamic phenomena. Within the scope of this study, the changes of the glacier mass in the Antarctic region in a certain time interval were investigated by using geosensors data. Firstly, temporal variation data of vertical land motions (VLM) of various GNSS stations provided to users by GNSS analysis centers, were used. In addition, the temporal variation of the snow height around the station was obtained by using the GNSS Reflectometry (GNSS-R) technique by utilizing GNSS observations. Afterwards, equivalent water thickness (EWT) data obtained from the GRACE/GRACE-FO solutions was used. GIA data which is obtained from ICE-5G globel GIA model was used to validate VLM trend derived from the GNSS data. The temporal variation of the ice mass was observed using the ice thickness data on land derived from the CryoSat-2 and ICESat-2 satellite radar altimeter data. In addition, sea level anomaly (SLA) change data between 1998 and 2019, which was presented to researchers within the scope of the US National Aeronautics and Space Administration (NASA) MeaSUREs project, was used. This dataset contains data from the satellite altimeter missions TOPEX/Poseidon, ERS-1-2, Envisat, Jason-1-2-3, CryoSat-2, AltiKa and Sentinel-3A. SLA change represents absolute sea level (ASL) change. Besides, relative sea level change trend was calculated by using tide-gauge stations data. The time series obtained from these geosensors provide information about the change in the relevant region. Thus, the mass loss in the study area has been studied from a broad perspective based on the comparative results of different geosensors data.
As a result of the first part of the study, the effects of the Samos Earthquake were determined with different geosensors. According to PPP-AR static solutions, significant deformations were found in CESM and IZMI GNSS stations and it was validated with relative static solutions. With respect to PPP-AR kinematic solutions, the maximum horizontal displacement was found to be 12 cm at the CESM station, and it was obtained that this movement was predominantly in the North direction, while values varying between 6-8 centimeters were obtained at the other stations. The effect of the earthquake cannot be understood from the changes in height values according to the daily PPP kinematics solution of CESM and IZMI GNSS stations. However, it was determined that there was an instantaneous subsidence of up to 4 cm when the kinematic change in the 1-minute time interval including the earthquake moment was examined in order to compare the SGMS and GNSS data. Afterwards, Çeşme and Konak SGMS stations were analyzed located near CESM and IZMI GNSS stations, respectively. Displacement, velocity and acceleration data obtained from GNSS and SGMS geosensors were compared. It has been observed that the results of CESM GNSS and Çeşme SGMS stations are compatible with each other, but the same situation is not true for IZMI GNSS and Konak SGMS stations. Thanks to the LOS displacement map obtained by using the InSAR technique, it has been revealed that there is a 10 cm uplift in the west of Samos Island and a 10 cm subsidence in the east. In addition, a 5 cm subsidence was observed in Çeşme province on the opposite northern coast of the island, and this value is matched with the difference values obtained from the CESM GNSS station located at that location. According to the tide-gauge stations, it was observed that there were deviations from 5 cm to 12 cm according to the current oscillation due to the effect of the earthquake and the aftershocks.
In the second part of the thesis, the glacial loss in the western parts of the Antarctic continent was revealed with different geosensors. Firstly, time series were produced from the data of 2 different tide-gauge stations located in the northwest and south of the continent and the VLM data of GNSS stations located near these stations. In addition to these, the SLA and EWT change values of the same regions were obtained. It has been revealed that the ASL trend obtained as a result of the sum of the VLM and RSL trend values and the SLA trends obtained from the satellite altimeter validate each other for both tide-guages. Since the spatial resolution of the EWT and GIA data is low, there is no significant result for these 2 points located in the coastal regions. However, it was seen that the EWT trends obtained around both tide gauges were consistent with the SLA trends. In the Pine Island part of the study; firstly, the GIA mass rate was verified with the trend values of the GNSS stations located on the rock. The trend direction obtained from the PIG2 GNSS station on the glacier was validated by CryoSat-2 and ICESat-2 land ice elevation and GRACE EWT change data. Although the trend of uplifting GNSS stations and the direction of the GIA mass rate are the same, their numerical magnitudes are different. In addition, ASL rise in the offshore areas of the island was shown with the SLA change graph and its trend was found. Finally, the snow thickness variation obtained by using the GNSS-R method has a decreasing trend of approximately -35 mm/y at the PIG1 and PIG2 stations located on the Pine Island glacier; It was found that there was a decreasing trend below a millimeter at PHIG, VNAD, FTP4 and HOWE stations, while there was no significant change in snow thickness at other stations (BERP, INMN and BRIP). 
In conclusion, investigation and analysis of regional and global disasters was carried out with the help of various geosensors with open access data. Although the data obtained from SAR and gravity satellite missions have low spatial and temporal resolution, that they are of great importance for the observation of disasters by expressing the general trend of large regions. Geosensors such as GNSS, SGMS and tide-gauge stations are higher accurate but only express the characteristics of the places where they are located. However, it has been demonstrated that they are of great importance in disaster observations due to their high accuracy and being able to validate satellite mission's results.