BDS GNSS for Earth Observation

For millennia, human communities have wondered about the possibility of observing phenomena in their surroundings, and in particular those affecting the Earth on which they live. More generally, it can be conceptually defined as Earth observation (EO) and is the collection of information about the biological, chemical and physical systems of planet Earth. It can be undertaken through sensors in direct contact with the ground or airborne platforms (such as weather balloons and stations) or remote-sensing technologies. However, the definition of EO has only become significant in the last 50 years, since it has been possible to send artificial satellites out of Earth’s orbit. Referring strictly to civil applications, satellites of this type were initially designed to provide satellite images; later, their purpose expanded to include the study of information on land characteristics, growing vegetation, crops, and environmental pollution. The data collected are used for several purposes, including the identification of natural resources and the production of accurate cartography. Satellite observations can cover the land, the atmosphere, and the oceans. Remote-sensing satellites may be equipped with passive instrumentation such as infrared or cameras for imaging the visible or active instrumentation such as radar. Generally, such satellites are non-geostationary satellites, i.e., they move at a certain speed along orbits inclined with respect to the Earth’s equatorial plane, often in polar orbit, at low or medium altitude, Low Earth Orbit (LEO) and Medium Earth Orbit (MEO), thus covering the entire Earth’s surface in a certain scan time (properly called ’temporal resolution’), i.e., in a certain number of orbits around the Earth. The first remote-sensing satellites were the American NASA/USGS Landsat Program; subsequently, the European: ENVISAT (ENVironmental SATellite), ERS (European Remote-Sensing satellite), RapidEye, the French SPOT (Satellite Pour l’Observation de laTerre), and the Canadian RADARSAT satellites were launched. The IKONOS, QuickBird, and GeoEye-1 satellites were dedicated to cartography. The WorldView-1 and WorldView-2 satellites and the COSMO-SkyMed system are more recent. The latest generation are the low payloads called Small Satellites, e.g., the Chinese BuFeng-1 and Fengyun-3 series. Also, Global Navigation Satellite Systems (GNSSs) have captured the attention of researchers worldwide for a multitude of Earth monitoring and exploration applications. On the other hand, over the past 40 years, GNSSs have become an essential part of many human activities. As is widely noted, there are currently four fully operational GNSSs; two of these were developed for military purposes (American NAVstar GPS and Russian GLONASS), whilst two others were developed for civil purposes such as the Chinese BeiDou satellite navigation system (BDS) and the European Galileo. In addition, many other regional GNSSs, such as the South Korean Regional Positioning System (KPS), the Japanese quasi-zenital satellite system (QZSS), and the Indian Regional Navigation Satellite System (IRNSS/NavIC), will become available in the next few years, which will have enormous potential for scientific applications and geomatics professionals. In addition to their traditional role of providing global positioning, navigation, and timing (PNT) information, GNSS navigation signals are now being used in new and innovative ways. Across the globe, new fields of scientific study are opening up to examine how signals can provide information about the characteristics of the atmosphere and even the surfaces from which they are reflected before being collected by a receiver. EO researchers monitor global environmental systems using in situ and remote monitoring tools. Their findings provide tools to support decision makers in various areas of interest, from security to the natural environment. GNSS signals are considered an important new source of information because they are a free, real-time, and globally available resource for the EO community

Retrieval of sea level and surface loading variations from geodetic observations and model simulations : an integrated approach

The mass distribution in the system Earth changes dynamically over time. Time-variable mass transport mainly arises from the interplay between the terrestrial hydrological water cycle, the ocean and atmosphere, and the Earth’s cryosphere. To understand the dynamics of the system Earth and its climate, it is of paramount importance to establish and maintain an accurate observational basis of these surface processes, against which models and theories can be tested. A variety of observational techniques are used today. The time-variable gravity is measured from space by the Gravity Recovery and Climate Experiment (GRACE), Earth deformation processes are monitored by a permanent global network of GPS stations, and sea surface changes are detected by a family of satellite altimeters. The underlying motivation of this work is that the combination of the different observation types allows the mitigation of some of the technique-specific limitations. In the framework of this dissertation, several types of geodetic observations have been combined in a least-squares sense to estimate present-day changes of surface mass storage in the Earth system, using dynamically consistent surface loading theory. Two types of inversion schemes have been designed and implemented. In the first scheme, time variable gravity from GRACE, deformations of a permanent GPS station network, and simulated ocean bottom pressure changes from an ocean model, are used to estimate weekly surface loading changes covering the entire globe. In the second inversion scheme, (inter-)annual changes of the Earth’s cryosphere, ocean and terrestrial water cycle, are parameterized by a predefined set of standing waves, whose time variations are estimated by combining GRACE gravimetry with satellite altimetry from Jason-1 and Jason-2.Ein kombinierter Ansatz zur Bestimmung von Meeresspiegelschwankungen und Auflastsveränderungen aus geodätischen Beobachtungen und Modellsimulationen Die Verteilung der Massen im System Erde verändert sich dynamisch über die Zeit. Zeitvariable Massentransporte entstehen vor allem durch das Zusammenspiel von terrestrischem hydrologischem Wasserkreislauf, Cryosphäre, sowie Ozeanen und Atmosphäre. Das Verständis der Dynamik des Systems Erde sowie damit im Zusammenhang stehender Klimaveränderungen erfordert ein umfassendes Beobachtungssystem dieser Oberflächenprozesse, gegen welches Modelle und Theorien getestet werden können. Heutzutage gibt es eine Vielzahl von Erdbeobachtungstechniken. Das zeitvariable Gravitationsfeld wird aus dem Weltall durch die GRACE-Mission (Gravity Recovery and Climate Experiment) vermessen. Deformationsprozesse der Erdoberfläche können mit Hilfe eines globalen Netzwerkes permanenter GPS-Stationen überwacht und Änderungen der Meeresoberfläche von Altimetersatelliten detektiert werden. Dieser Arbeit liegt die Motivation zugrunde, dass die Kombination verschiedener Beobachtungstypen die technisch-spezifischen Einschränkungen einzelner Beobachtungstechniken verringern kann. Im Rahmen der vorliegenden Dissertation werden verschiedene geodätische Beobachtungen in einem Kleinste-Quadrate Ansatz kombiniert, um unter Ausnutzung einer dynamisch konsistenten Auflasttheorie die heutigen Veränderungen der Oberflächenspeicher im Erdsystem zu bestimmen. Zwei verschiedene Inversionsschemata wurden dazu entworfen und implementiert. In einem ersten Schema werden zeitvariable Schwerefelder von GRACE, Deformationen eines Netzwerkes permanenter GPS-Stationen und durch ein Ozeanmodell simulierte Ozeanbodendruckvariationen verwendet, um wöchentliche Auflastveränderungen für die gesamte Erde zu bestimmen. Im zweiten Inversionsschema werden (inter-)annuale Veränderungen von Cryosphäre, Ozean und terrestrischem Wasserkreislauf durch einen vordefinierten Satz stehender Wellen parametrisiert, deren Zeitvariationen aus einer Kombination von GRACE und Altimetriebeobachtungen der Satelliten Jason-1 und Jason-2 geschätzt werden

The Deep Space Network. An instrument for radio navigation of deep space probes

The Deep Space Network (DSN) network configurations used to generate the navigation observables and the basic process of deep space spacecraft navigation, from data generation through flight path determination and correction are described. Special emphasis is placed on the DSN Systems which generate the navigation data: the DSN Tracking and VLBI Systems. In addition, auxiliary navigational support functions are described

Applications of Geodesy to Geodynamics, an International Symposium

Geodetic techniques in detecting and monitoring geodynamic phenomena are reviewed. Specific areas covered include: rotation of the earth and polar motion; tectonic plate movements and crustal deformations (space techniques); horizontal crustal movements (terrestrial techniques); vertical crustal movements (terrestrial techniques); gravity field, geoid, and ocean surface by space techniques; surface gravity and new techniques for the geophysical interpretation of gravity and geoid undulation; and earth tides and geodesy

Conference on Spacecraft Reconnaissance of Asteroid and Comet Interiors : January 8-10, 2015, Tempe, Arizona

The goal of AstroRecon is to identify and evaluate the best technologies for spacecraft robotic reconnaissance of comets, asteroids, and small moons--paving the way for advanced science missions, exploration, sample return, in situ resource utilization, hazard mitigation, and human visitation.Shell GameChanger, ASU NewSpace, The Johns Hopkins University Applied Physics Laboratoryinstitutional support Arizona State University, Lunar and Planetary Institute, National Aeronautics and Space Administration, Universities Space Research Association Arizona State University's Students for the Exploration and Development of Space ; sponsors Shell GameChanger, ASU NewSpace, The Johns Hopkins University Applied Physics Laboratory ; conveners Erik Asphaug Arizona State University, Tempe, Jekan Thangavelautham Arizona State University, Tempe ; program committee Erik Asphaug (Co-chair Science) Arizona State University, Tempe [and 6 others].PARTIAL CONTENTS: Human Exploration / P. A. Abell and A. S. Rivkin--Comet Radar Explorer / E. Asphaug--Development of Communication Technologies and Architectural Concepts for Interplanetary Small Satellite Communications / A. B. Babuscia and K. C. Cheung--Numerical Simulations of Spacecraft-Regolith Interactions on Asteroids / R.-L. Ballouz, D. C. Richardson, P. Michel, and S. R. Schwartz--Kuiper: A Discover, Class Observatory for Outer Solar System Giant Planets, Satellites, and Small Bodies / J. F. Bell, N. M. Schneider, M. E. Brown, J. T. Clarke, B. T. Greenhagen, R. M.C. Lopes, A. R. Hendrix, and M. H. Wong--Landing on Small Bodies: From the Rosetta Lander to MASCOT and Beyond / J. Biele, S. Ulamec, P.-W. Bousquet, P. Gaudon, K. Geurts, T.-M. Ho, C. Krause, R. Willnecker, and M. Deleuze--High-Resolution Bistatic Radar Imaging in Support of Asteroid and Comet Spacecraft Missions / M. W. Busch, L. A. M. Benner, M. A. Slade, L. Teitelbaum, M. Brozovic, M. C. Nolan, P. A. Taylor, F. Ghigo, and J. Ford--Asteroid Comet and Surface Gravimetric Surveying can Reveal Interior Structural Details / K. A. Carroll

Beyond 100: The Next Century in Geodesy

This open access book contains 30 peer-reviewed papers based on presentations at the 27th General Assembly of the International Union of Geodesy and Geophysics (IUGG). The meeting was held from July 8 to 18, 2019 in Montreal, Canada, with the theme being the celebration of the centennial of the establishment of the IUGG. The centennial was also a good opportunity to look forward to the next century, as reflected in the title of this volume. The papers in this volume represent a cross-section of present activity in geodesy, and highlight the future directions in the field as we begin the second century of the IUGG. During the meeting, the International Association of Geodesy (IAG) organized one Union Symposium, 6 IAG Symposia, 7 Joint Symposia with other associations, and 20 business meetings. In addition, IAG co-sponsored 8 Union Symposia and 15 Joint Symposia. In total, 3952 participants registered, 437 of them with IAG priority. In total, there were 234 symposia and 18 Workshops with 4580 presentations, of which 469 were in IAG-associated symposia. ; This volume will publish papers based on International Association of Geodesy (IAG) -related presentations made at the International Association of Geodesy at the 27th IUGG General Assembly, Montreal, July 2019. It will include papers associated with all of the IAG and joint symposia from the meeting, which span all aspects of modern geodesy, and linkages to earth and environmental sciences. It continues the long-running IAG Symposia Series

GPS displacement dataset for the study of elastic surface mass variations

Quantification of uncertainty in surface mass change signals derived from Global Positioning System (GPS) measurements poses challenges, especially when dealing with large datasets with continental or global coverage. We present a new GPS station displacement dataset that reflects surface mass load signals and their uncertainties. We assess the structure and quantify the uncertainty of vertical land displacement derived from 3045 GPS stations distributed across the continental US. Monthly means of daily positions are available for 15 years. We list the required corrections to isolate surface mass signals in GPS estimates and screen the data using GRACE(-FO) as external validation. Evaluation of GPS time series is a critical step, which identifies (a) corrections that were missed, (b) sites that contain non-elastic signals (e.g., close to aquifers), and (c) sites affected by background modeling errors (e.g., errors in the glacial isostatic model). Finally, we quantify uncertainty of GPS vertical displacement estimates through stochastic modeling and quantification of spatially correlated errors. Our aim is to assign weights to GPS estimates of vertical displacements, which will be used in a joint solution with GRACE(-FO). We prescribe white, colored, and spatially correlated noise. To quantify spatially correlated noise, we build on the common mode imaging approach by adding a geophysical constraint (i.e., surface hydrology) to derive an error estimate for the surface mass signal. We study the uncertainty of the GPS displacement time series and find an average noise level between 2 and 3 mm when white noise, flicker noise, and the root mean square (rms) of residuals about a seasonality and trend fit are used to describe uncertainty. Prescribing random walk noise increases the error level such that half of the stations have noise &gt; 4 mm, which is systematic with the noise level derived through modeling of spatially correlated noise. The new dataset is available at https://doi.org/10.5281/zenodo.8184285 (Peidou et al., 2023) and is suitable for use in a future joint solution with GRACE(-FO)-like observations.</p

Understanding seismic velocity structure and its time-varying process beneath the Mississippi embayment through ambient noise analysis

We apply ambient noise analysis to image shear wave velocity from near surface to uppermost mantle beneath the Mississippi embayment, and investigate the crustal response to climatological loadings. To further understand the generation mechanism of microseisms, we explore the azimuthal distribution of the signal-to-noise ratio and amplitude difference of crustal surface waves and estimate possible source locations in the ocean through back- projections.A shear wave velocity model with 0.5 0.5 resolution for the crust and uppermost mantle has been determined. We take advantage of the dense coverage and long-term deployments of 277 3-component broadband stations installed from 1990 to 2018 to image the shear wave velocity. Rayleigh group velocity dispersion curves extracted from ambient noise are inverted to obtain shear wave velocity at 5, 12, 24, and 43 km. We find that low velocity features characterize the Reelfoot Graben, Rough Creek Graben, Black Warrior basin, and southern Mississippi embayment in the upper 5 km of crust. High velocity features characterize the Ozark plateau, Ouachita mountains and Nashville dome. From 5 to 12 km, a low velocity anomaly is associated with the Missouri batholith. From 12 to 24 km, high velocity features characterize the Reelfoot-Rough Creek graben, and along the Appalachian-Ouachita thrust front. From 24 to 43 km, high velocity anomalies are commonly observed in the Mississippi embayment, and spatially correlated with the crustal thickness.Cross-correlation of the ambient seismic field is also used to estimate seasonal seismic velocity variations and to determine the underlying physical mechanisms. We process continuously recorded broadband data from 53 stations in 2014 to obtain daily and yearly cross- correlations and measure the Rayleigh wave phase velocity change over 4 frequency bands, 0.3-1, 0.5-1.2, 0.7-1.5, and 1-2 Hz. We then calculate the correlation coefficients between the velocity variations and the precipitation, water table fluctuation, temperature, atmospheric pressure and wind speed to find which external variable correlates most strongly with the observed changes. We observe high t/t (a proxy for velocity variation), the slowest velocity relative to annual average, from May to July and low t/t in September/October, and find the t/t variations correlate primarily with water table fluctuation. The correlation coefficients between water table fluctuation and t/t are independent of the interstation distance and frequency, but high coefficients are observed more often in the 0.3-1 Hz than 1-2 Hz band probably because high-frequency coherent signals attenuate faster than low-frequency ones. The t/t variations lag behind the water table fluctuation by about 20 days, which suggests the velocity changes can be attributed to the pore pressure diffusion effect. The maximum t/t variations decrease with frequency from 0.03% at 0.3-1 Hz to 0.02% at 1-2 Hz, and the differences between them might be related to different local sources or incident angles. The seasonal variations of t/t are azimuthally independent, and a large increase of noise amplitude only introduces a small increase to the t/t variation. The maximum t/t variations non-linearly decrease with the distance, which could be associated with the attenuation of coherent noise. At close distances, the maximum t/t holds a wide range of values, which is likely related to local structure. At larger distances, velocity variations sample a larger region so that it stabilizes to a more uniform value. We find that the observed changes in wave speed are in agreement with the prediction of a poroelastic model.The source distribution of ambient noise is of fundamental importance to understanding the generation mechanism of microseisms. Cross-correlations of ambient seismic noise from 277 broadband stations with at least 1-month recording between 1990 and 2018 are used to estimate source locations of primary and secondary microseisms inside the Mississippi embayment. We investigate source locations by analyzing the azimuthal distribution of the signal-to-noise ratio (SNR) and amplitude difference of crustal surface wave arrivals and by 2D F-K analysis. We also use 84 stations with continuous 1-year recording to explore seasonal variations of SNRs of the surface wave, which could be used to locate active sources in different seasons. We observe that (1) four azimuths could be identified in the azimuthal distribution of SNRs and reflect four different energy sources. Two energy sources are active in the Pacific and Atlantic ocean of northern hemisphere during winter and two relatively weak sources are active near Australia and South America in the southern hemisphere during summer. (2) Primary microseisms originate along the coastlines of southern Australia, Canada and Alaska, Newfoundland, and northeast South America. (3) Secondary microseisms could be generated in the deep water of northern and southern Pacific ocean, along coastlines of Canada and Alaska associated with reflections, and in the deep water of south of Greenland. (4) Azimuthal distribution of SNRs of sediment surface waves observed at 1-5s is negatively correlated with the geometry of the edge of the Mississippi embayment. The sediment surface waves could be induced by the basin-edge

TOPEX/POSEIDON Science Investigations Plan

TOPEX/POSEIDON is a satellite mission that will use the technique of radar altimetry to make precise measurement of sea level with a primary goal of studying the global ocean circulation. The mission represents the culmination of the development of satellite altimetry over the past two decades. The major thrust of the mission is a commitment to measuring seal level with an unprecedented accuracy such that the small-amplitude, basinwide sea level changes that bear significant effects on global change can be detected. The mission will be conducted jointly by the United States National Aeronautics and Space Administration and the French space agency, Centre National d'Etudes Spatiales. The 3- to 5-year mission will study the long-term mean and variability of ocean circulation. This document provides brief descriptions of the planned investigations as well as a summary of the major elements of the mission