20 research outputs found
Millimeter-accuracy SLR bias determination using independent multi-LEO DORIS and GNSS-based orbits
The Maintenance of the Relative Humidity of the Subtropical Free Troposphere
The relative importance of different processes in the water vapor balance of the troposphere is assessed, using high-resolution hindcast data from the ECMWF Integrated Forecast System (IFS) for DecemberâFebruary 1998/99 interpolated to isentropic coordinates. The focus is on elucidating the processes that maintain the relative humidity of the subtropical free troposphere. The dominant drying process in the subtropical free troposphere is cross-isentropic subsidence driven by radiative cooling. In some subtropical regions [e.g., over continents in the Southern (summer) Hemisphere and over western portions of ocean basins in the Northern (winter) Hemisphere], drying by radiative subsidence is partially offset or overcompensated by moistening by cross-isentropic dynamic transport of water vapor from the surface upward (e.g., in convection). Any resultant net drying or moistening of the subtropical free troposphere by cross-isentropic motions is regionally primarily balanced by isentropic mean and eddy transport of water vapor from moister into drier regions. Isentropic transport redistributes water vapor within the subtropics and moderates relative humidity contrasts; however, it does not consistently lead to a substantial net import or export of water vapor into or out of the subtropics
SLR station range bias and coordinate determination using independent multi-LEO DORIS- and GNSS-based precise orbits
GENESIS: Co-location of Geodetic Techniques in Space
Improving and homogenizing time and space reference systems on Earth and,
more directly, realizing the Terrestrial Reference Frame (TRF) with an accuracy
of 1mm and a long-term stability of 0.1mm/year are relevant for many scientific
and societal endeavors. The knowledge of the TRF is fundamental for Earth and
navigation sciences. For instance, quantifying sea level change strongly
depends on an accurate determination of the geocenter motion but also of the
positions of continental and island reference stations, as well as the ground
stations of tracking networks. Also, numerous applications in geophysics
require absolute millimeter precision from the reference frame, as for example
monitoring tectonic motion or crustal deformation for predicting natural
hazards. The TRF accuracy to be achieved represents the consensus of various
authorities which has enunciated geodesy requirements for Earth sciences.
Today we are still far from these ambitious accuracy and stability goals for
the realization of the TRF. However, a combination and co-location of all four
space geodetic techniques on one satellite platform can significantly
contribute to achieving these goals. This is the purpose of the GENESIS
mission, proposed as a component of the FutureNAV program of the European Space
Agency. The GENESIS platform will be a dynamic space geodetic observatory
carrying all the geodetic instruments referenced to one another through
carefully calibrated space ties. The co-location of the techniques in space
will solve the inconsistencies and biases between the different geodetic
techniques in order to reach the TRF accuracy and stability goals endorsed by
the various international authorities and the scientific community. The purpose
of this white paper is to review the state-of-the-art and explain the benefits
of the GENESIS mission in Earth sciences, navigation sciences and metrology.Comment: 31 pages, 9 figures, submitted to Earth, Planets and Space (EPS
Altimetry for the future: Building on 25 years of progress
In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ââGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
Altimetry for the future: building on 25 years of progress
In 2018 we celebrated 25âŻyears of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology.
The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the âGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
AmĂ©lioration des rĂ©fĂ©rences massiques de la Terre par synergie entre diffĂ©rentes mesures de gĂ©odĂ©sie spatiale. Application Ă lâocĂ©anographie par altimĂ©trie spatiale
In the context of the overall climate change and the need to analyze the implications of the record ice-sheet melting for the sea level and global fluid mass redistribution budgets, our PhD work focuses on large-scale phenomena impacting the shape of the Earth, its gravity field, and the stability of its rotation pole. We explore strategies for the observation and modeling of subtle variations in geodynamic parameters (lowermost degree coefficients), which are still poorly constrained, despite their importance in determining fundamental terrestrial references. The first part of this PhD is dedicated to the observation of the geocenter motion, using different geodetic technics. The outcomes of this work provided explanations, through a correct handling of the dominant error sources, for the discrepancies between the reference laser-based LAGEOS geocenter time series (defining the origin of the international frame, ITRF) and independent solutions using DORIS/laser/GPS observations from the Jason-2 altimeter satellite. The second part of this PhD presents a self-consistent determination of the degrees 0 (gravitational coefficient GM), 1 (geocenter motion), and 2 (Earthâs figure axis orientation) of the geopotential. To this end, we use the available laser data since the 1970s (e.g., the first geodetic satellite Starlette launched by CNES in 1975), as they are the only absolute measurements making possible the monitoring of the first three degree terms. Based on 35 years of satellite laser tracking, an updated value of the geocentric gravitational coefficient was obtained, and a viscoelastic behavior of the Earthâs mantle manifesting at decadal time scales was exhibited, combining the derived figure axis variations of the Earth and polar motion observations with the Euler-Liouville equations.Dans le contexte du changement climatique mondial et la nĂ©cessitĂ© dâĂ©tudier les consĂ©quences de lâampleur de la fonte des glaces continentales sur le niveau des mers ainsi que sur la rĂ©partition des masses fluides Ă lâĂ©chelle du globe, notre travail de thĂšse sâintĂ©resse aux phĂ©nomĂšnes Ă trĂšs grande Ă©chelle qui modifient la forme de la Terre, son champ de gravitĂ© et lâĂ©quilibre de sa rotation. Il se focalise sur la stratĂ©gie Ă mettre en place pour observer et modĂ©liser des variations trĂšs fines sur des termes gĂ©odynamiques (coefficients de bas degrĂ©s) qui sont encore aujourdâhui mal connus, et pourtant dĂ©terminants dans lâĂ©tablissement des rĂ©fĂ©rences terrestres fondamentales. La premiĂšre partie de la thĂšse concerne lâobservation du mouvement du gĂ©ocentre par diffĂ©rentes techniques de mesures gĂ©odĂ©siques. Ces travaux dĂ©bouchent, par une meilleure maĂźtrise des sources dâerreurs, sur une explication des Ă©carts entre les sĂ©ries de mesures laser du mouvement du gĂ©ocentre obtenues sur les satellites LAGEOS (rĂ©fĂ©rence actuelle pour lâorigine du repĂšre international, ITRF) et celles obtenues indĂ©pendamment sur le satellite altimĂ©trique Jason-2 Ă partir dâobservations DORIS/laser/GPS. La deuxiĂšme partie de la thĂšse sâintĂ©resse Ă la dĂ©termination cohĂ©rente des coefficients de degrĂ©s 0 (coefficient gravitationnel GM), 1 (gĂ©ocentre), et 2 (inertie/orientation) du champ de pesanteur terrestre. Nous utilisons pour cela les mesures de tĂ©lĂ©mĂ©trie laser disponibles depuis les annĂ©es 1970 (par exemple, Starlette lancĂ© en prĂ©curseur par le CNES dĂšs 1975), car ce sont les seules mesures Ă caractĂšre absolu qui donnent accĂšs Ă ces trois premiers degrĂ©s. Nos analyses menĂ©es sur prĂšs de 35 ans aboutissent Ă une nouvelle valeur de la constante gravitationnelle gĂ©ocentrique et la dĂ©tection dâune rĂ©ponse viscoĂ©lastique du manteau de notre planĂšte aux Ă©chelles de temps dĂ©cennales, par combinaison des termes de degrĂ© 2 et paramĂštres dâorientation de la Terre avec les Ă©quations dâEuler-Liouville
Improved determination of Earthâs mass references combining measurements from different satellite geodetic techniques : Applications in oceanography using satellite altimetry
Dans le contexte du changement climatique mondial et la nécessité d'étudier les conséquences de l'ampleur de la fonte des glaces continentales sur le niveau des mers ainsi que sur la répartition des masses fluides à l'échelle du globe, notre travail de thÚse s'intéresse aux phénomÚnes à trÚs grande échelle qui modifient la forme de la Terre, son champ de gravité et l'équilibre de sa rotation. Il se focalise sur la stratégie à mettre en place pour observer et modéliser des variations trÚs fines sur des termes géodynamiques (coefficients de bas degrés) qui sont encore aujourd'hui mal connus, et pourtant déterminants dans l'établissement des références terrestres fondamentales. La premiÚre partie de la thÚse concerne l'observation du mouvement du géocentre par différentes techniques de mesures géodésiques. Ces travaux débouchent, par une meilleure maßtrise des sources d'erreurs, sur une explication des écarts entre les séries de mesures laser du mouvement du géocentre obtenues sur les satellites LAGEOS (référence actuelle pour l'origine du repÚre international, ITRF) et celles obtenues indépendamment sur le satellite altimétrique Jason-2 à partir d'observations DORIS/laser/GPS. La deuxiÚme partie de la thÚse s'intéresse à la détermination cohérente des coefficients de degrés 0 (coefficient gravitationnel GM), 1 (géocentre), et 2 (inertie/orientation) du champ de pesanteur terrestre. Nous utilisons pour cela les mesures de télémétrie laser disponibles depuis les années 1970 (par exemple, Starlette lancé en précurseur par le CNES dÚs 1975), car ce sont les seules mesures à caractÚre absolu qui donnent accÚs à ces trois premiers degrés. Nos analyses menées sur prÚs de 35 ans aboutissent à une nouvelle valeur de la constante gravitationnelle géocentrique et la détection d'une réponse viscoélastique du manteau de notre planÚte aux échelles de temps décennales, par combinaison des termes de degré 2 et paramÚtres d'orientation de la Terre avec les équations d'Euler-Liouville.In the context of the overall climate change and the need to analyze the implications of the record ice-sheet melting for the sea level and global fluid mass redistribution budgets, our PhD work focuses on large-scale phenomena impacting the shape of the Earth, its gravity field, and the stability of its rotation pole. We explore strategies for the observation and modeling of subtle variations in geodynamic parameters (lowermost degree coefficients), which are still poorly constrained, despite their importance in determining fundamental terrestrial references. The first part of this PhD is dedicated to the observation of the geocenter motion, using different geodetic technics. The outcomes of this work provided explanations, through a correct handling of the dominant error sources, for the discrepancies between the reference laser-based LAGEOS geocenter time series (defining the origin of the international frame, ITRF) and independent solutions using DORIS/laser/GPS observations from the Jason-2 altimeter satellite. The second part of this PhD presents a self-consistent determination of the degrees 0 (gravitational coefficient GM), 1 (geocenter motion), and 2 (Earth's figure axis orientation) of the geopotential. To this end, we use the available laser data since the 1970s (e.g., the first geodetic satellite Starlette launched by CNES in 1975), as they are the only absolute measurements making possible the monitoring of the first three degree terms. Based on 35 years of satellite laser tracking, an updated value of the geocentric gravitational coefficient was obtained, and a viscoelastic behavior of the Earth's mantle manifesting at decadal time scales was exhibited, combining the derived figure axis variations of the Earth and polar motion observations with the Euler-Liouville equations
Millimeter accuracy SLR bias determination using independent multi-LEO DORIS and GPS-based precise orbits
Satellite Laser Ranging (SLR) has become an invaluable core technique in numerous geodetic applications. SLR measurements to passive spherical satellites essentially contribute to the determination of geocenter coordinates and global scale in the International Terrestrial Reference Frame (ITRF) realizations. In addition, SLR measurements to active satellites in Low Earth Orbit (LEO) are up to now mostly used for an independent validation of orbit solutions, usually derived by microwave tracking techniques based on Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) or Global Navigation Satellite Systems (GNSS). This allows for the analysis of systematic orbit errors (e.g., originating from poorly known non-gravitational perturbations or sensor offsets) not only in the radial direction (key to satellite altimetry missions), but in three dimensions.
Major obstacles to reach the millimeter accuracy and stability goals of
(at decadal time scales) of the Global Geodetic Observing System (GGOS) are station-satellite measurement biases and on-ground/board coordinate offsets. Among the observatories of the International Laser Ranging Service (ILRS) a large diversity of measurement qualities exists, and the calibration of station-dependent errors is now necessary to further exploit SLR data for present and future climate-driven needs.
We demonstrate that the analysis of SLR data to active LEO satellites equipped with DORIS or GNSS receivers is a promising means to characterize SLR biases and their stability. Using two independent selections of Earth observation missions in LEOs (consisting of six altimetry, three magnetic field and two gravity field satellites) with three different analysis software packages (Bernese, ZOOM, Napeos), we estimate SLR range biases for all involved tracking stations on a yearly basis. We find that for many of the stations independently estimated sets of biases agree on a few-mm level and that the inclusion of satellites from multiple missions allows rendering the bias estimation more robust and in particular less prone to geographically correlated orbit errors. This shows that microwave-derived orbits of active LEO satellites, nowadays of very high quality due to numerous advances in modeling and analysis techniques, can serve as interesting sources for SLR station calibration in demanding climate applications
Interannual variations of degree 2 from geodetic observations and surface processes
International audienc