Geodesy is the science of accurately measuring and understanding three fundamental properties of Earth: its geometric shape, its orientation in space, and its gravity field, as well as the changes of these properties with time. Over the past half century, the United States, in cooperation with international partners, has led the development of geodetic techniques and instrumentation. Geodetic observing systems provide a significant benefit to society in a wide array of military, research, civil, and commercial areas, including sea level change monitoring, autonomous navigation, tighter low flying routes for strategic aircraft, precision agriculture, civil surveying, earthquake monitoring, forest structural mapping and biomass estimation, and improved floodplain mapping. Recognizing the growing reliance of a wide range of scientific and societal endeavors on infrastructure for precise geodesy, and recognizing geodetic infrastructure as a shared national resource, this book provides an independent assessment of the benefits provided by geodetic observations and networks, as well as a plan for the future development and support of the infrastructure needed to meet the demand for increasingly greater precision. Precise Geodetic Infrastructure makes a series of focused recommendations for upgrading and improving specific elements of the infrastructure, for enhancing the role of the United States in international geodetic services, for evaluating the requirements for a geodetic workforce for the coming decades, and for providing national coordination and advocacy for the various agencies and organizations that contribute to the geodetic infrastructure.

Geodetic datum (including coordinate datum, height datum, depth datum, gravimetry datum) and geodetic systems (including geodetic coordinate system, plane coordinate system, height system, gravimetry system) are the common foundations for every aspect of geomatics. This course book focuses on geodetic datum and geodetic systems, and describes the basic theories, techniques, methods of geodesy. The main themes include: the various techniques of geodetic data acquisition, geodetic datum and geodetic control networks, geoid and height systems, reference ellipsoid and geodetic coordinate systems, Gaussian projection and Gaussian plan coordinates and the establishment of geodetic coordinate systems. The framework of this book is based on several decades of lecture noted and the contents are developed systematically for a complete introduction to the geodetic foundations of geomatics.

The Global Geodetic Observing System (GGOS) has been established by the Int- national Association of Geodesy (IAG) in order to integrate the three fundamental areas of geodesy, so as to monitor geodetic parameters and their temporal varia- ?9 tions, in a global reference frame with a target relative accuracy of 10 or b- ter. These areas, often called ‘pillars’, deal with the determination and evolution of (a) the Earth’s geometry (topography, bathymetry, ice surface, sea level), (b) the Earth’s rotation and orientation (polar motion, rotation rate, nutation, etc. ), and (c) the Earth’s gravity eld (gravity, geoid). Therefore, Earth Observation on a global scale is at the heart of GGOS’s activities, which contributes to Global Change - search through the monitoring, as well as the modeling, of dynamic Earth processes such as, for example, mass and angular momentum exchanges, mass transport and ocean circulation, and changes in sea, land and ice surfaces. To achieve such an - bitious goal, GGOS relies on an integrated network of current and future terrestrial, airborne and satellite systems and technologies. These include: various positioning, navigation, remote sensing and dedicated gravity and altimetry satellite missions; global ground networks of VLBI, SLR, DORIS, GNSS and absolute and relative gravity stations; and airborne gravity, mapping and remote sensing systems.

Various effects of the atmosphere have to be considered in space geodesy and all of them are described and treated consistently in this textbook. Two chapters are concerned with ionospheric and tropospheric path delays of microwave and optical signals used by space geodetic techniques, such as the Global Navigation Satellite Systems (GNSS), Very Long Baseline Interferometry (VLBI), or Satellite Laser Ranging (SLR). It is explained how these effects are best reduced and modelled to improve the accuracy of space geodetic measurements. Other chapters are on the deformation of the Earth’s crust due to atmospheric loading, on atmospheric excitation of Earth rotation, and on atmospheric effects on gravity field measurements from special satellite missions such as CHAMP, GRACE, and GOCE. All chapters have been written by staff members of the Department of Geodesy and Geoinformation at TU Wien who are experts in the particular fields.