Realizing ITRF-Consistent Continental-Scale Geodetic Reference Frames

<p>To achieve a regional or continental-scale reference frame that is a densification of the International Terrestrial Reference Frame (ITRF), one can use a set of fiducial GPS / GNSS stations in the ITRF and regional frames.  Predicting coordinates in the realization epoch using the fiducial stations’ trajectory parameters in the ITRF and applying a Helmert transformation aligns the regional solution’s polyhedron onto the ITRF.  This paper shows inconsistencies in the regional realization of ITRF when the fiducial stations’ trajectory model ignores the periodic terms, resulting in a periodic coordinate bias in the regional frame.  We describe a generalized procedure to minimize this inconsistency when realizing any regional frame aligned to ITRF or any other ‘primary’ frame. We show the method used to realize the Argentine Geodetic Positions (Posiciones Geodésicas Argentinas, POSGAR) reference frame and discuss its results. Inconsistencies in the vertical were reduced from 4 mm to less than 1 mm for multiple stations after applying our technique.  We also propose adopting object-oriented programming terminology to describe the relationship between different reference frames, such as a regional and a global frame. This terminology assists in describing and understanding the hierarchy in geodetic reference frames.</p>

Sistemas Geodésicos de Referência: Rumo ao GGRS/GGRF

O estabelecimento de Sistemas Geodésicos de Referência globais integrando características geométricas e físicas é um dos desafios atuais da Geodésia, principalmente devido às demandas de diversas áreas do conhecimento de que as informações relacionadas aos Sistemas de Observação da Terra (EOS – Earth Observation Systems), sejam integradas em Redes Geodésicas de Referência (RGRs) com uma acurácia de 10-9 ou melhor. O surgimento das técnicas de posicionamento espacial trouxe melhora significativa na qualidade posicional e possibilitou a substituição das RGRs clássicas por redes modernas com características globais. Hoje, a questão das coordenadas de caráter geométrico, está bem resolvida com o ITRS/ITRF (International Terrestrial Reference System/International Terrestrial Reference Frame). Todavia, aspectos associados a diversos processos físicos, tais como os reflexos das redistribuições de massa, não são atendidos por referenciais puramente geométricos. A aprovação da resolução para o GGRS/GGRF (Global Geodetic Reference System/Global Geodetic Reference Frame) surge com a visão da integração entre o referencial terrestre, o celeste, um referencial com características físicas para as altitudes e a nova rede global de gravidade absoluta. Esforços têm sido feitos para definição e realização deste referencial global para as altitudes. É uma tarefa complexa em vista das características clássicas dos referenciais verticais, heterogeneidade em termos de qualidade e distribuição espacial de dados necessários, principalmente os relacionados ao campo de gravidade da Terra. Apresentam-se como grandes desafios para o futuro a necessidade de estabelecimento de procedimentos padrão para a integração ao referencial altimétrico global e a precisão necessária para o estabelecimento dos EOS.

Twenty-Five Years of the International GNSS Service

<p>For over twenty-five years, the <strong>International Global Navigation Satellite System (GNSS) Service (IGS)</strong> has carried out its mission to advocate for and provide freely and openly available high-precision GNSS data and products.</p><p>The IGS is an essential component of the <strong>IAG’s Global Geodetic Observing System (GGOS)</strong>, where it facilitates cost-effective geometrical linkages with and among other precise geodetic observing techniques, including: Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS). These linkages are fundamental to generating and accessing the International Terrestrial Reference Frame (ITRF).  As it enters its second quarter-century, the IGS is evolving into a truly multi-GNSS service, and at its heart is a strong culture of sharing expertise, infrastructure, and other resources for the purpose of encouraging global best practices for developing and delivering GNSS data and products all over the world.</p><p>This poster will present an update on current IGS products and operations, as well as highlights on recent organizational developments and community activities. The impacts and benefits of global cooperation and openly available data will be emphasized, and information about the IGS stations and network, contributions to the International Terrestrial Reference Frame solutions, and product applications will be presented. A summary of IGS products, with emphasis on analysis, coordination, applications, and their availability will be described. Information about efforts to form new groups supporting product generation within IGS open data and product policies will be included. Information about the themes and topics of discussion for the upcoming 2020 IGS Workshop in Boulder, Colorado, USA will also be provided.</p>

Aplikasi Satellite GEOSAT dan ERS sebagai Metode Alternatif Pengukuran Gravity Ground pada Cekungan Hidrokarbon di Pulau Timur

Graviti merupakan metode awal yang digunakan untuk mempelajari basement pada area potensial hidrokarbon. Pada umumnya metode graviti diukur melalui darat dengan peralatan Scientrex maupun LaCoste & Romberg, teknik ini membutuhkan waktu dan financial yang relative banyak. Padahal secara prinsip pengukuran, metode ini tidak membutuhkan kontak langsung dengan tanah, sehingga dimungkinkan untuk diukur melalui airborne dan satelit. Oleh karena itu untuk mempelajari akurasi data graviti satelit, maka pada penelitian ini data satelit akan dibandingkan dengan pengukuran darat yang telah diakuisisi pada area hidrokarbon di Pulau Timor. Data graviti pengukuran darat telah diakuisisi sejak tahun 1948-1989 oleh beberapa perusahaan minyak, sedangkan graviti satelit yang digunakan berupa Geodetic Satelit (GeoSat) dan European Remote Sensing (ERS) tahun 2011 dengan resolusi 1.85 km/px. Perbedaan waktu pengukuran yang relative jauh dari kedua data tersebut, maka data graviti darat ditransformasikan ke model standar ellipsoid baru dari International Terrestrial Reference Frame ITRF (WGS84). Data bouger anomali dari kedua data tersebut menunjukkan pola yang relative sama, disisi utara didominasi oleh anomali yang tinggi (90 s/d 185 mGal), sedangkan sisi selatan anomali yang rendah (-75 s/d 90 mGal). Pada beberapa tempat yang diduga terdapat hidrokarbon; ditunjukkan oleh syncline, anticline, rembesan oil dan gas maka data graviti satelit dapat menunjukkan anomali yang kontras dibandingkan dengan graviti pengukuran didarat. Hal ini diakibatkan oleh resolusi data satelit yang bersifat regional dibandingkan dengan graviti darat Gravity is the frontier method used for mapping the basements in hidrokarbon areas. In general, the method is measured from the ground surface using the Scintrex or LaCoste & Romberg instrument, but for a large area the ground gravity is highly cost and financial resources in data observation. In principle, the gravity method does not require direct contact with the ground that will be possible to measure from airborne and satellite. Therefore, we study the accuracy of satellite data that potential used for hidrokarbon investigation. In this research, we compare the satellite data with the ground surveys that have been acquired on the island of Timor. The Ground survey data was acquired from 1948-1989 by several oil companies, while the satellites used is Geodetic Satellites (GeoSat) and European Remote Sensing in 2011 with a resolution of 1.85 km/px. The Ground survey data is transformed into a new ellipsoid standard model from the International Terrestrial Reference Frame ITRF (WGS84), this is due to the difference in measurement time that is relatively far from the two data. Based on the results, it can be shown that the anomaly bouger from both data shows a very similar pattern, where the north side is dominated by high anomalies (90 to 185 mGal) while the southern side of the anomaly is low (-75 to 90 mGal). In some places that are suspected to have hidrokarbons; indicated by syncline, anticline, oil and gas seepage, satellite gravity data can show contrast anomalies compared to ground surveys. This is caused by satellite data resolution which is regional compared to ground survey.

THE IMPLEMENTATION OF MODERN GEOCENTRIC DATUM: A REVIEW

A dynamic datum denotes a coordinate datum in real-time linked with the International Terrestrial Reference Frame (ITRF) in order to provide a dynamic ITRF-like datum to the users. The ITRF is dynamic and updating every few years as its stations’ coordinates consider the motion of earth’s tectonic plate and other deformations. This paper is an effort to review the implementation of dynamic geocentric datum techniques from a few countries. An overview of dynamic geocentric datum implements Malaysia, Australia, New Zealand, Uzbekistan, Israel and Brunei will be summarized to support the future application. Thus, a review consists of a type of datum; datum parameters, reference frame and epoch will be discussed and outlined. This initiative is the significance for the advancement of the future datum development.

IDENTIFIKASI MEKANISME SESAR DI BAGIAN TIMUR PULAU JAWA DENGAN MENGGUNAKAN DATA GNSS KONTINYU 2010-2016

Pulau Jawa terletak tepat di utara zona subduksi jawa yang merupakan zona pertemuan Lempeng Indo-Australia dengan Lempeng Sunda. Beberapa Sesar terbentuk di Pulau Jawa mengakomodasi stress yang dihasilkan oleh subduksi jawa yang berada di selatan Pulau Jawa. Studi deformasi dengan menggunakan data GNSS telah dilakukan untuk mengestimasi laju geser dari sesar-sesar utama di Pulau Jawa. Koulali dkk (2016) mengestimasi laju geser untuk Sesar Baribis dan Sesar Kendeng sebesar 2.3 – 5.6 mm/tahun dan dinyatakan sebagai sesar-sesar aktif. Pada studi ini, 15 data GNSS kontinyu dari tahun 2010 hingga 2016 di bagian timur Pulau Jawa digunakan untuk mengidentifikasi mekanisme sesar yang berada di wilayah ini meliputi Sesar Kendeng dan ekstensinya. Data fase GPS dari setiap stasiun GNSS diolah dengan menggunakan GAMIT/GLOBK 10.6 untuk mendapatkan koordinat di dalam sistem koordinat kartesian 3D di dalam kerangka referensi International Terrestrial Reference Frame 2008 (ITRF2008). Sebanyak 15 vektor kecepatan GNSS digunakan untuk menghitung strain rate dan laju geser untuk setiap segmen sesar yang dilalui oleh 3 profil. Ketiga profil tersebut menunjukkan adanya kompresi sebagai akomodasi stress dari subduksi Jawa dan laju geser untuk segmen barat Sesar Kendeng, segmen timur Sesar Kendeng, dan ekstensinya sebesar 1.93 mm/tahun, 0.90 mm/tahun, dan 0.60 mm/tahun secara berurutan dengan mekanisme sesar mengiri. Mekanisme yang sama yang terjadi pada ekstensi Sesar Kendeng menunjukkan adanya potensi sumber gempa yang baru di sekitar Selat Madura. Hal ini merupakan informasi penting untuk mengidentifikasi potensi sumber gempa dari Sesar Kendeng dan ekstensinya mengingat zona dari sesar aktif ini merupakan zona yang berpenduduk cukup padat.