Two different methodologies for geoid determination from ground and airborne gravity data

In this study, two methodologies are investigated for geoid determination from ground and airborne gravity data. These two methodologies depend on the downward continuation method used. The first is the inverse Poisson integral; the second is the normal free-air gradient. Each of the two methods requires different treatment of the terrain effects and in turn different approaches to determine the geoid. The two geoid solutions, from ground data, are compared with existing GPS/levelling benchmarks and it is found that the second method gives a better fit due to the bias introduced from the inverse Poisson integral. The same process was applied to the airborne data, but with additional processing, that is the filtering of the terrain effects to preserve the consistency of the data due to the filtering of the airborne data. A study on the effect of filtering was also carried out in this paper and it concluded that filtering the terrain effects has no impact on the geoid. In addition, the airborne data, filtered to three different cut-off frequencies, were used to compute the geoid to investigate the possibility of using the denser data, of lower accuracy, to determine a high-resolution geoid. Even though the data filtered to small cut-off frequency have poorer agreement with the ground data, the geoids computed from the different filtered data is the nearly the sam

ESTUDIO PRELIMINAR DE GEOIDE MARINO EN EL OCÉANO ATLÁNTICO ARGENTINO

The objective of this paper is to present the studies conducted for the determinationof marine geoid model in the Atlantic coastal region of Argentina using satellitealtimetry and shipborne gravity data. The altimetry data of the satellite altimetrymission ERS1 and shipborne gravity data were used to compute a pure altimetricgeoid and a pure gravimetric geoid, respectively using the well known removerestoretechnique. The effect of the Quasi-Stationary Sea Surface Topography(QSST) and the effect of the Sea Surface Variability (SSV)were taken into accountduring the processing of the different solutions. From the results achieved it wasconcluded that the pure altimetric geoid has an accuracy of near 8 cm in someareas, while the pure gravimetric solution gives poorer results. The accuracy of thefinal geoid models was assessed through comparisons with stackedTOPEX/POSEIDON (T/P) SSHs, known for their high precision. In order toimprove the accuracy of the gravimetric geoid, a combined solution using theMultiple input –Multiple output system theory , known as MIMOST were used.MIMOST allow to combine heterogeneous data in the spectral domain. Thecombination of satellite and shipborne data with the proposed algorithm improvesthe accuracy of the gravimetric geoid model by about 2 cm.En este trabajo se presentan estudios realizados sobre la determinación de geoidesmarinos preliminares en el océano Atlántico próximo a Argentina, utilizando datosde altimetría satelital y datos de gravedad marina. Los datos correspondientes a lamisión espacial de altimetría satelital ERS1 y los datos de gravedad medidos enbarco permitieron determinar un geoide altimétrico puro y un geoide gravimétricopuro en el océano Atlántico argentino utilizando la técnica remover-restaurar. Elefecto de la componente casi estacionaria de la topografía del mar (QSST) y elefecto de la variabilidad de la superficie del mar (SSV) se tuvieron en cuentadurante el procesamiento de las diferentes soluciones. De los resultados obtenidos,se concluye que el geoide altimétrico puro tiene una exactitud de 8 centímetros enalgunas áreas mientras que los resultados de la solución gravimétrica pura son máspobres. La exactitud de los modelos de geoide finales se evalúo a través decomparaciones con datos de altura de la superficie del mar (SSHs) medidos por lamisión TOPEX/POSEIDÓN (T/P), conocidas por su gran precisión. Con el fin demejorar la exactitud del geoide gravimétrico se obtuvo una solución combinadautilizando la Teoría de Múltiple Entrada-Múltiple Salida, conocida como MIMOSTque permite la óptima combinación de datos heterogéneos en el dominio espectral.La combinación de la solución satelital pura con la solución obtenida con los datosde gravedad marina utilizando el algoritmo propuesto, mejoraron la exactitud,comparada con el geoide gravimétrico puro, en aproximadamente 2 centímetros.En este trabajo se presentan estudios realizados sobre la determinación de geoidesmarinos preliminares en el océano Atlántico próximo a Argentina, utilizando datosde altimetría satelital y datos de gravedad marina. Los datos correspondientes a lamisión espacial de altimetría satelital ERS1 y los datos de gravedad medidos enbarco permitieron determinar un geoide altimétrico puro y un geoide gravimétricopuro en el océano Atlántico argentino utilizando la técnica remover-restaurar. Elefecto de la componente casi estacionaria de la topografía del mar (QSST) y elefecto de la variabilidad de la superficie del mar (SSV) se tuvieron en cuentadurante el procesamiento de las diferentes soluciones. De los resultados obtenidos,se concluye que el geoide altimétrico puro tiene una exactitud de 8 centímetros enalgunas áreas mientras que los resultados de la solución gravimétrica pura son máspobres. La exactitud de los modelos de geoide finales se evalúo a través decomparaciones con datos de altura de la superficie del mar (SSHs) medidos por lamisión TOPEX/POSEIDÓN (T/P), conocidas por su gran precisión. Con el fin demejorar la exactitud del geoide gravimétrico se obtuvo una solución combinadautilizando la Teoría de Múltiple Entrada-Múltiple Salida, conocida como MIMOSTque permite la óptima combinación de datos heterogéneos en el dominio espectral.La combinación de la solución satelital pura con la solución obtenida con los datosde gravedad marina utilizando el algoritmo propuesto, mejoraron la exactitud,comparada con el geoide gravimétrico puro, en aproximadamente 2 centímetros

Different topographic reduction methods in practical gravimetric geoid determination

Three different topographic reduction methods in geoid determination were investigated. The first method is the classical Helmert second method of condensation yielding the geoid, the second is the Residual Terrain Model (RTM) method yielding the quasigeoid and the third is the Rudzki inversion method. The different types of indirect effects (indirect effect on gravity and indirect effect on geoid) in Helmert's method were also investigated. All three methods use the remove-restore technique and the EGM96 geopotential model as the reference gravity field. A mountainous area, ranging from 32°S to 42°S in latitude and 72°W to 68°W in longitude, was chosen as test area. The area was selected due to its high topography, with a maximum height of 6795 meters and a mean height of 1188 meters, and due to the existence of GPS/leveling points in three different networks. The topography in the test area is-represented by a digital terrain model (DTM) with a grid spacing of 1 km x 1 km. Another test was carried out in a flat area with denser data coverage. The external accuracy of the three gravimetric geoids was evaluated by comparing them to undulations derived from GPS/leveling.En el siguiente trabajo se investigan tres métodos diferentes de reducciones gravimétricas para la determinación práctica del geoide gravimétrico: el clásico segundo método de condensación de Helmert, el modelo residual de terreno y el método de inversión de Rudzki. Los tres métodos utilizan la técnica remover-restaurar y el modelo de geopotencial EGM96. Fueron seleccionadas dos áreas, una en una zona montañosa de alta topografía con una altura máxima de 6795 metros y una altura promedio de 1188 metros y otra en una zona plana con cobertura más densa. La topografía está representada por un modelo digital de terreno con un espaciamiento de grillado de un kilómetro por un kilómetro. La evaluación externa del geoide gravimétrico se realiza comparándolo con ondulaciones obtenidas a partir de puntos GPS sobre nivelación.Asociación Argentina de Geofísicos y Geodesta

Assessment of recent global potential models with terrestrial data

Bu çalışmada gravite alanı belirleme amaçlı GRACE ve CHAMP uydularının verileri ile hesaplanan güncel global potansiyel modellerin (GGM02S, EIGEN-CHAMP03S, EIGEN-CG03C ve EIGEN-GL04C) Türkiye’deki performansları test edilmekte ve Türkiye bölgesel geoidi TG03’ün hesaplanmasında referans olarak kullanılmış EGM96 global potansiyel modeli ile karşılaştırılmaktadır. TG03 geoit modeli gravimetrik yöntemle belirlenmiştir ve Türkiye’deki jeodezik çalışmalarda kullanılmaktadır. Modelin mutlak doğruluğu desimetre mertebesindedir. Bu çalışmada amaç, farklı global potansiyel modeller ile Türkiye’de gravite alanının uzun dalga boylu bileşenindeki iyileşmenin araştırılmasıdır. Bu amaçla, farklı maksimum derecelerden küresel harmonik eşitlikler ile ifade edilen potansiyel modeller kullanılarak hesaplanan gravite anomalileri ve geoit yükseklikleri sırasıyla yersel gravite verileri ile ve GPS/nivelmandan elde edilen geoit yükseklikleri ile karşılaştırılarak test edilmiştir. Bunun yanı sıra yersel gravite anomalileri ve global potansiyel modeller kullanılarak bölgesel geoit modelleri hesaplanmış, global potansiyel modellerin gravimetrik bölgesel geoit modellerinin doğruluğuna katkısı böylelikle de test edilmiştir. Bunun için hesaplanan bölgesel gravimetrik geoit modellerinden türetilen geoit yükseklikleri bağımsız GPS/nivelman verileri ile karşılaştırılarak Türkiye geoidi için en uygun global potansiyel model belirlenmeye çalışılmıştır. Çalışmanın sonuçlarının presizyonlu Türkiye bölgesel geoidinin gelecek versiyonunun hesaplanmasında referans model olarak kullanılmak üzere en uygun global potansiyel modelin seçilmesinde faydalı olması beklenmektedir. Anahtar Kelimeler: Global potansiyel model, CHAMP, GRACE, bölgesel gravimetrik geoit modeli, yersel gravite anomalileri, GPS/nivelman.CHAMP and GRACE satellites are low Earth orbiters which are used for the determination of the Earth’s gravity field. The mission of the satellites is to provide the knowledge for the gravity field that leads to observe the Earth system for geodetic and geodynamic purposes with a sufficient accuracy. The characteristics specific to the satellites such as design, orbit, measurement and processing techniques have provided new approaches for the global gravity field determination. Earth potential models are representation of the global gravity field and they are divided into three classes, namely satellite-only Global Potential Models (GPMs) (derived from the tracking of artificial satellites), combined GPMs (derived from a combination of a satellite-only model, terrestrial gravimetry, satellite altimetry and/or airborne gravimetry) and tailored GPMs (derived by refining existing satellite-only or combined GPMs using regional gravity data). Satellite-only GPMs are known to be weak at the coefficients of degrees higher than 60 or 70 due to several factors such as the power-decay of the gravitational field with altitude, modeling of atmospheric drag, non-gravitational and third-body perturbations and incomplete tracking of satellite orbits from ground stations. Although the effects of some of these limitations on the GPMs decreased after the dedicated satellite gravity missions CHAMP and GRACE, the new satellite-only GPMs still have not got full power until a certain degree, and rapidly increasing errors make their coefficients unreliable at high-degrees. In this study, the most recent satellite-only and combined global potential models from the CHAMP and GRACE satellite missions released by GFZ (GeoForschungsZentrum) and the Center for Space Research of Texas University were tested. The older combined-GPM EGM96 was also included in the tests. Although EGM96 model was not calculated using data from CHAMP and GRACE, the study includes this model since it serves as the reference model for the official regional geoid model of Turkey. The Earth potential models from CHAMP, GRACE, and other data, assessed in the tests here, are GGM02S, EIGEN-CHAMP03S, EIGEN-CG03C and EIGEN-GL04C and they were compared with the older EGM96. The aim of this study is to investigate the improvements in the modelling of the long wavelength gravity field components for the area of Turkey. With this aim gravity anomaly and geoid height grids were generated for varying maximum degrees of the spherical harmonic expansions and the global potential models were compared with terrestrial gravity data as well as GPS/levelling data in Turkey. Furthermore, regional geoid models were computed by Fast Fourier Transform techniques using terrestrial gravity data and various geopotential models, and the results were again evaluated against GPS/levelling data. The intention of the study is to provide a valuable input for the selection of “the best reference geopotential model” for a high resolution hybrid geoid model for Turkey. In the investigation steps, firstly, the GPMs derived gravity anomalies were compared with the free-air gravity anomalies from the terrestrial data over Turkey. Than the GPMs derived geoid heights were interpolated and compared with the low-pass filtered GPS/levelling derived geoid heights at the co-located benchmarks in two test areas (İzmir and İstanbul) in the West part of Turkey. The statistics from these comparisons provided preliminary results in the assessment of the GPMs. According to this, EGM96, EIGEN-CG03C and EIGEN-GL04C combined geopotential models with the maximum degree and order of 360 fit slightly better in Turkey. In the second evaluation stage, the regional geoid models were computed in Turkey using Remove-Restore technique. The computed regional models refer to each of the GPMs (with their maximum expansion) as reference models. The differences between the geoid heights derived from the gravimetric geoid models and from the GPS/levelling data were investigated in Istanbul and Izmir test networks. According to statistical results, the EIGEN-CG03C is optimal GPM for pure gravimetric geoid model in West of Turkey. Finally, the regional geoid models were fitted to the GPS/levelling with a 2nd order polynomial using the residual geoid heights at the benchmarks. The tests of the regional gravimetric geoid models after corrector surface fitting against the GPS/levelling control data shown that the fitted geoid models has the similar performance in a test area. Keywords: Global potential model, CHAMP, GRACE, regional gravimetric geoid model, terrestrial gravity anomalies, GPS/levelling

Geoide gravimétrico en Argentina : Presente y futuro

En el siguiente trabajo se presenta el estado actual del geoide gravimétrico de la República Argentina. En el mismo se discuten la metodología y los datos utilizados para su cálculo y se plantean los trabajos futuros que se realizarán con el fin de mejorar su precisión y exactitud. ARG05_EGM96 es un geoide gravimétrico puro calculado durante 2005. Las ondulaciones del geoide ARG05_EGM96 se refieren al elipsoide geocéntrico GRS80 y fueron calculadas en una grilla de 5' x 5' cubriendo toda la Argentina (tierra y mar). El cálculo se realizó utilizando la técnica clásica remover-restaurar. La componente del geoide residual así como los efectos de terreno se calcula ron utilizando la transformada rápida de Fourier. Para el tratamiento de la topografía se empleó el segundo método de compensación de Helmert. ARG05 EGM96 fue determinado en cuatro componentes. La primera componente fue calculada a partir del modelo de geopotencial EGM96, la segunda componte representa la contribución de los datos de gravedad reducidos por el modelo de geopotencial, la tercera es la derivada de las correcciones topográficas y la cuarta componente representa el efecto indirecto primario sobre el geoide. De comparaciones externas realizadas entre ARG05_EGM96 y el geoide derivado de GPS y nivelación, se estima que la exactitud absoluta de ARG05 es de 32 cm en términos de desviación standard. La exactitud relativa, para toda la Argentina, es de 1.4 a 0.2 ppm para líneas bases entre 15 km y 115 km. En el presente trabajo se presentan, otras tres soluciones, denominadas: ARGÓ5EIGEN-CG01C (Tocho et al., 2005), ARG06EIGEN-CG03CyARG06_EIGEN-GL04C calculadas utilizando otros modelos de gravedad globales recientemente distribuidos. Finalmente se enumeran trabajos futuros, por ejemplo, la evaluación de modelos digitales de terreno y sus implicancias en la determinación práctica de geoides gravimétricos.The status of the gravimetric geoid for Argentina is presented in this paper. The methodology applied for its computation as well as the data used is discussed. A high-accuracy and high-precision gravimetric geoid model (ARG05 EGM96) for Argentina has been computed during 2005. ARG05 EGM96 is a purely gravimetric geoid model. The geoid undulations refer to the geocentric ellipsoid GRS80 and they were computed on a 5' x 5' grid covering all of Argentina (both land and ocean regions) ARG05_EGM96 was computed using the classical remove-compute-restore technique. The Fast Fourier Transform technique was employed in the computation of the residual geoid and terrain effects. The treatment of the topography inARG05_EGM96 was based on Helmert’s second method of condensation. ARG05 EGM96 is developed in four components. The first component is determined from the EGM96 global geopotential model, the second component represents the contribution of the local gravity data reduced by the global field, the third component was determined from the contribution of the terrain corrections to the geoid, and the four component is the primary indirect effect on the geoid. From comparisons between Global Positioning System (GPS) and Argentinean Height Datum (GPS/levelling-derived) geoid undulations withARG05_EGM96, it is estimated that the absolute accuracy of the new geoid, after fit, is around 32 cm in terms of standard deviation. The relative agreement for the whole Argentina is 1.4 to 0.2 ppm for baselines between 15 km and 115 km. Three new solutions,ARG06EIGEN-CG01C,ARG06_EIGEN-CG03CyARG06_EIGEN-GL04C, calculated with new global gravity models are presented in this paper. Finally, futures works are mention, especially those concerning with digital terrain models and their implications in practical geoid determination.Material digitalizado en SEDICI gracias a la colaboración de la Facultad de Ciencias Astronómicas y Geofísicas (UNLP).Asociación Argentina de Geofísicos y Geodesta

EON-ROSE and the Canadian Cordillera Array – Building Bridges to Span Earth System Science in Canada

EON-ROSE (Earth-System Observing Network - Réseau d’Observation du Système terrestrE) is a new initiative for a pan-Canadian research collaboration to holistically examine Earth systems from the ionosphere into the core. The Canadian Cordillera Array (CC Array) is the pilot phase, and will extend across the Cordillera from the Beaufort Sea to the U.S. border. The vision for EON-ROSE is to install a network of telemetered observatories to monitor solid Earth, environmental and atmospheric processes. EON-ROSE is an inclusive, combined effort of Canadian universities, federal, provincial and territorial government agencies, industry, and international collaborators. Brainstorming sessions and several workshops have been held since May 2016. The first station will be installed at Kluane Lake Research Station in southwestern Yukon during the summer of 2018. The purpose of this report is to provide a framework for continued discussion and development.RÉSUMÉEON-ROSE (Earth-System Observing Network - Réseau d’Observation du Système terrestrE) est une nouvelle initiative de collaboration de recherche pancanadienne visant à étudier de manière holistique les systèmes terrestres, depuis l’ionosphère jusqu’au noyau. Le Réseau canadien de la cordillère (CC Array) en est la phase pilote, laquelle couvrira toute la Cordillère, de la mer de Beaufort jusqu’à la frontière étasunienne. L’objectif d’EON-ROSE est d’installer un réseau d’observatoires télémétriques pour suivre en continu les processusterrestres, environnementaux et atmosphériques. EON-ROSE est un effort combiné et inclusif des universités canadiennes, des organismes gouvernementaux fédéraux, provinciaux et territoriaux, de l’industrie et de collaborateurs internationaux. Des séances de remue-méninges et plusieurs ateliers ont été tenus depuis mai 2016. La première station sera installée à la station de recherche du lac Kluane, dans le sud-ouest du Yukon, au cours de l’été 2018. Le but du présent rapport est de fournir un cadre de discussion et de développement continu

One Health: The global challenge of epidemic and endemic leishmaniasis

'One Health' proposes the unification of medical and veterinary sciences with the establishment of collaborative ventures in clinical care, surveillance and control of cross-species disease, education, and research into disease pathogenesis, diagnosis, therapy and vaccination. The concept encompasses the human population, domestic animals and wildlife, and the impact that environmental changes ('environmental health') such as global warming will have on these populations. Visceral leishmaniasis is a perfect example of a small companion animal disease for which prevention and control might abolish or decrease the suffering of canine and human patients, and which aligns well with the One Health approach. In this review we discuss how surveillance for leishmaniases is undertaken globally through the control of anthroponootic visceral leishmaniasis (AVL) and zoonotic visceral leishmaniasis (ZVL). The ZVL epidemic has been managed to date by the culling of infected dogs, treatment of human cases and control of the sandfly vector by insecticidal treatment of human homes and the canine reservoir. Recently, preventive vaccination of dogs in Brazil has led to reduction in the incidence of the canine and human disease. Vaccination permits greater dog owner compliance with control measures than a culling programme. Another advance in disease control in Africa is provided by a surveillance programme that combines remote satellite sensing, ecological modelling, vector surveillance and geo-spatial mapping of the distribution of vectors and of the animal-to-animal or animal-to-human pathogen transmission. This coordinated programme generates advisory notices and alerts on emerging infectious disease outbreaks that may impede or avoid the spreading of visceral leishmaniasis to new areas of the planet as a consequence of global warming

The genetic history of the Southern Arc: a bridge between West Asia and Europe

By sequencing 727 ancient individuals from the Southern Arc (Anatolia and its neighbors in Southeastern Europe and West Asia) over 10,000 years, we contextualize its Chalcolithic period and Bronze Age (about 5000 to 1000 BCE), when extensive gene flow entangled it with the Eurasian steppe. Two streams of migration transmitted Caucasus and Anatolian/Levantine ancestry northward, and the Yamnaya pastoralists, formed on the steppe, then spread southward into the Balkans and across the Caucasus into Armenia, where they left numerous patrilineal descendants. Anatolia was transformed by intra–West Asian gene flow, with negligible impact of the later Yamnaya migrations. This contrasts with all other regions where Indo-European languages were spoken, suggesting that the homeland of the Indo-Anatolian language family was in West Asia, with only secondary dispersals of non-Anatolian Indo-Europeans from the steppe

Computation of gravimetric terrain corrections using fast fourier transform techniques

Bibliography: p. 97-100.The scope of this research is the development of a method for evaluating the terrain correction integral using Fast Fourier Transform (FFT) techniques. The FFT method presented herein is a very fast and rigorous method of computing the terrain corrections. The only data required are the elevations of the points on a plane grid with constant spacing along the x and the y direction. The terrain corrections are computed simultaneously for all grid points. This is a valuable feature of the method for use in the solution of bolll1dary value problems in physical geodesy. The method is insensitive to errors in the heights and gives results of about the same accuracy as those obtained by the conventional prism methods using the same gridded data. The main advantage of the FFT method is its computational efficiency. It requires, for the computation of the terrain corrections for all N points on a grid, a time roughly proportional to NlogN, while the prism methods require a time roughly proportional to N2. In addition to its speed, the FFT method provides the means for spectral and correlation analyses between heights and terrain corrections. The procedures for such analyses are given in this thesis together with a presentation of the main features of the two-dimensional discrete Fourier transform. A simple computer program, written in FORTRAN V, is given, which can be used as the basis for building up a complete and flexible software package on terrain correction computations

Spectral methods for the numerical solution of Molodensky's problem

Bibliography: p. 98-107