Kronometrik nivelman yöntemi ile yüksekliklerin belirlenmesi
Determination of heights with chronometric levelling
Yazar: HASAN ONUR IŞIK
Danışman: DOÇ. DR. MUSTAFA TEVFİK ÖZLÜDEMİR ; DR. KEREM HALICIOĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Geomatik Mühendisliği Ana Bilim Dalı / Geomatik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Jeodezi ve Fotogrametri = Geodesy and Photogrammetry

Özet:
Genel Görelilik teorisinin bir sonucu olarak, kütleçkimsel alanlar gözlemci zaman akışını etkilemektedir. Zaman akışının aynı hıza sahip olduğu yüzeyler, Newton potansiyeli ile tariflenen eşpotansiyel yüzey kavramı ile aynı yüzeyleri tarif etmektedir. Eşpotansiyel yüzeyler klasik anlamda uzun yıllardır gravite ve yükseklik ölçmelerine bağlı olarak belirleniyordu. 
Yükseklik belirleme için kullanılan geleneksel yöntemler bütünsel açıdan bakıldığında ölçme sonuçlarını etkileyebilecek önemli hata kaynakları barındırmaktadır. Bunlardan biri nokta üzerindeki potansiyel değerlerin doğrudan ölçülememesi nedeni ile yükseklik taşınması ile artan derecelerde hata birikmesidir. Ortalama deniz seviyeleri farklı olarak belirlenen karasal kütleler arasındaki yükseklik entegrasyonunun zorluğu da ayrı bir sorun oluşturmaktadır. Gözlemlerin yatay düzlemde gerçekleşmesi ve arazi zorlukları nedeniyle engebeli arazilerde işgücü, ekipman gücü ve yol uzunluğunun artması ile klasik yöntemlerde büyük zorluklar yaşanabilmektedir. Bu ciddi olumsuzlukları aşabilmek açısından, son yıllarda uydu teknolojileri önde gelen çözümlerden birisi olarak kullanılmaktadır. Fakat son 10 yıldır, temelleri 20. yüzyılın ikinci yarısına dayanan bir yöntem olan kronometrik nivelman, doğrulukları artan saatler ve ağ teknolojilerinin kullanıldığı test gözlemleri sonucunda önemli sonuçlar ortaya koymaya başlamıştır. 
Zaman bilgisi atomik saat teknolojilerindeki gelişmeler ile birlikte atomik frekans standardında optik spektrumda yüksek frekansta gözlemler yapılarak artan ölçüde doğruluklarla belirlenebilmektedir. Bugüne kadar kullanılan mikrodalga atom saatlerinin daha düşük düzeydeki doğruluk ve kararlılıklarına karşı 100 kat daha iyileştirilmiş olan optik atomik saatler yükseklik belirlenmesinde yeni bir yöntem olarak kronometrik nivelman yönteminin önünü açmaktadır. Ayrıca fiber iletim teknolojileri ile birlikte optik atomik saat karşılaştırmaları 〖10〗^(-19) mertebelerinde bir hassasiyetle yapılabilmektedir. Yerçekimi ivmesi g≈10 m/s2 ve c≈ 300 000 000 m/s olmak üzere; 1 santimetrelik yükseklik değişimlerinde ∆v/v≈〖10〗^(-18) frekans kayması oranı elde edilebilmektedir. Böylece optik atomik saatlerin 1 santimetrelik yükseklik farklarını belirleyebilecek hassasiyette olduğu söylenebilir. 
Bu kapsamda, bu tez çalışmasında atom saatleri arasında yapılan frekans karşılaştırmaları neticesinde kütle-çekimsel Doppler etkisi ile ortaya çıkan farktan yararlanılarak potansiyel farkların belirlenmesi konusundaki teorik temellere, yöntemin genel çerçevesine ve güncel atomik saat test ağlarına değinilmektedir. 
Bu bağlamda kronometrik nivelman yönteminin teorik temelleri ve güncel çalışmalar incelenmekte, uluslararası yükseklik referans sistemine olabilecek katkıları, sistemin çalışma mekanizmaları ve geoit belirleme yöntemlerine katkıları tartışılmaktadır.

Abstract:
Height determination as the subject of Modern Geodesy is based on theoretical foundations of Newtonian physics. After Einstein introduced Special Relativity in 1905 and General Relativity in 1915, the concept of absolute space in Newtonian mechanics was altered.
With this revolutionary development in physics, the content of classical mechanics has changed. This development, which created a great transformation in applied sciences, caused an important transformation in Geodesy. Over the last decades, serious effects of relativity are discussed in Geodesy.
As a result of the general theory of relativity, gravitational fields affect the observer time flow. Surfaces where the time flow has the same velocity describe the same surfaces as the equipotential surface described by the Newtonian potential. The equipotential surfaces have been determined in the classical measurement methods for many years due to gravity and height measurements.
Conventional methods used to determine heights have important error sources that affect the measurement results. One of these is the fact that the potential values at the point cannot be measured directly, and that the error propagation increases with increasing height. The difficulty of height integration between terrestrial masses with differing sea levels is another problem. Great difficulties can be experienced in classical methods with increasing road path due to the occuring observations in the horizontal plane and difficulties of working in mountainous terrain. In order to overcome these serious problems, satellite technologies have been used as one of the leading solutions in recent years. But for the last 10 years, chronometric levelling, which had been introduced in the second half of the twentieth century, has started to produce important results as a result of test observations with improvements of clock accuracy and network technologies.
In addition, the concept of time has been one of the most widely considered concepts in science, philosophy, mythology, art and many other fields throughout history. The concept of time continues to deepen with practical applications. In addition, many discussions about the content of the concept continue to be up to date.
The time measurement principles of clocks are formed by repetitive movements of objects or particles. Thus, they become time scale determination equipment. However, the frequencies of repetition, ie frequencies, may vary according to the frame of reference. Astronomical measurements based on the repetitive motion of large bodies in space as a traditional method of time determination, yielded accurate results at the beginning and near future. But in recent years, motion of objects in space can decrease the measurement reliability due to getting involved of several parameters to the models that will vary according to reference frames and propagation of the error by taking into account the reference frame where the object is located.
Thanks to advances in atomic clock technologies, time is determined with increasing accuracy by observing high frequency in the optical spectrum in the atomic frequency standard. Optical atomic clocks, which are 100 times superior to the lower accuracy and stability of microwave atomic clocks used to date, pave the way for chronometric levelling as a new method for determining heights. In addition, optical atomic clock comparisons with fiber transmission technologies can be performed with an accuracy 〖10〗^(-19). Assuming the gravitational acceleration is g≈10 m/s2 and c≈ 300 000 000 m/s; 1 centimeter height changes, we obtain the frequency shift ratio ∆v/v≈〖10〗^(-18). Thus, we can say that optical atomic clocks are accurate enough to detect height differences of 1 centimeter.
Therefore, atomic clock comparison networks can be seen as systems that will make a significant contribution in the near future in order to obtain a global geoid model with centimeter accuracy.
However, there are current problems due to the method is new. One of these problems is being of the insufficient number of trained personnel. Also, since the method is multidisciplinary, training of new qualified people requires time and cost. In addition, the cost of measuring instruments is too high. It also requires high-precision measuring processes and high attention. Another problem is that it is difficult to carry measuring instruments.
Today, many test steps are carried out on the measurement method. In this context, optical atomic clock measurements and fiber frequency transfer applications made by institutions such as Max-Planck-Institut für Quantenoptik (MPQ), Physikalisch-Technische Bundesanstalt (PTB) and Laboratoire national de métrologie et d'essais - Système de Références Temps-Espace (LNE-SYRTE) in Paris were examined within the scope of the thesis. These applications can be seen as the early stages of the continental atomic clock network in Europe. 
TUBITAK UME's Time-Frequency Laboratory in Gebze, Turkey has contributed to the establishment of a universal time unit in the TAI club membership with 5 Cs atomic clocks and 2 GPS receivers since 1994. As of 2018, the work on the optical atomic clock has been started and it has been announced that the project will start in 2019. After the implementation of the project, connection using with fiber frequency transfer technologies to an optical atomic clock network to be established at European continent will be able to provide determination of the unified height reference system. It will also be able to associate Turkey Geodetic Systems with unified height reference system. An international optical atomic clock network is important not only in terms of spatial parameter but also in determining the international precise time parameter. In addition, a relative geoid to be determined in centimeter precision will make the ellipsoidal heights obtained by GPS useful due to the high accuracy model.
Within the scope of this thesis, the theoretical basis for identifying potential differences using the gravitational Doppler effect, the general framework of the method and the current atomic clock test networks as a result of frequency comparisons between optical atomic clocks are discussed.
In the first chapter, Newtonian concepts used to determine the height are studied and the need for a high-precision global height system is examined. 
In Chapter 2, height systems and accuracies in Turkey were researched and studies were examined. 
In Chapter 3, the mathematical and physical conceptual foundations of General Relativity Theory are examined. 
In Chapter 4, the theoretical foundations of the Chronometric Levelling Method are discussed, and the applications, systems and methods are examined.