Skip to main content

Currently Skimming:

1 Where on Earth Am I Now?
Pages 11-26

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 11...
... The geodetic infrastructure in place today allows us to measure sea-level rise of a couple of millimeters a year; a shift in the center of the Earth by a tenth of a millimeter per year; changes in the length of the day of microseconds per day; and shifts in the position of the pole by fractions of a centimeter. Such highly precise measurements are critical to applications that monitor milli meter-scale deformation in the Earth's crust in earthquake-prone or active volcano areas; real-time navigation systems that position vehicles, ships, and airplanes to an accuracy of a few centimeters; systems that enable farmers to reliably plant two different crop seeds centimeters apart on the same field; mining machinery that operates automatically to an accuracy of a few centimeters; and unmanned aircraft that can fly anywhere on the planet to survey natural disaster areas, erupting volcanoes, or combat theaters.
From page 12...
... For example, the depletion of underground aquifers or oil and gas reserves can cause local subsidence, or sinking of the land, disrupting sew ers and other underground utilities. On a much larger scale, geodesy enables us to monitor global climate change as it is reflected in ice sheet melting and sea level change.
From page 13...
... The combined measurements obtained from three geodetic observing systems -- altimetry and gravity satellite missions, and tide gauge networks -- allow us to estimate the contributions of these sources. Recent measurements indicate that melting of glaciers and polar ice sheets contribute approximately 2 millimeters per year to sea level rise.
From page 14...
... gives us unique and essential limits on climate dynamics models. Although ice sheet melting causes global sea level rise -- seven meters for a hypothetical total melting of Greenland and 3–5 meters for total collapse of West Antarctica -- it also leads to significant regional variability.
From page 15...
... Degradation of the geodetic infrastructure could lead to gaps in critical observations that are needed to test the validity of models for ice dynamics, sea level rise, and climate change. This report assesses the scientific and societal requirements for precise geodetic observations and offers options for the support of a sustainable national geodetic infrastructure capable of serving the full range of existing and future users.
From page 16...
... , and Global Geodetic Observing System: Meeting the Requirements of a Global Society on a Changing Planet in 00 (Plag and Pearlman, 2009) .3 Building on these prior studies, this report assesses the scientific and societal benefits of precise geodetic observations and networks to the nation, discusses the associated requirements, explores opportunities for technological innovation, and suggests ways to improve national coordination and implementation of the geodetic infrastructure (Box S.1)
From page 17...
... FuNDAMENTAL GEODETIC PARAMETERS The fundamental parameters of geodesy include the Earth's shape (land and sea surface topography, bathymetry, and ice sheet thickness) , rotation and orientation in space, and gravity field.
From page 18...
... is required, known as the geoid height. This calls for densely sampled maps of the gravity field, which can be greatly improved nowadays by airborne surveys using GPS/GNSS navigation.
From page 19...
... in the Earth's solid and fluid interior, atmosphere, oceans, hydrosphere, and cryosphere -- such as seasonal snowpack and groundwater changes or post-glacial rebound -- can be detected as corre sponding variations in the Earth's gravity. Gravity measurements also can distinguish the underlying mechanisms behind mass redistribution, such as thermal expansion of the ocean or the addition of water from the melting of continental ice sheets, which are both contributing to global sea level rise.
From page 20...
... , it refers to systems that are designed to address specific goals (such as measuring sea level changes) and may be used for a finite period of time.
From page 21...
... • Gravity field theory. Mathematical approach for describing the gravitational field of a planet, including, in the case of the Earth, such geometric constructs as mean sea level.
From page 22...
... Gravimetry Gravity Tide Gauges Geocenter Air-/Shipborne Gravity Field Temporal variations Observation Influence/ Modeling Modelling FIGuRE 1.3 Precision geodetic techniques, supported by the geodetic infrastructure, determine the time-dependent geometry, rotation, and gravity field of the Earth. SOURCE: Adapted from Plag and Pearlman (2009)
From page 23...
... In the 1990s, civilian networks of permanent GPS stations were developed and deployed, first in southern California and Japan, and later globally, thereby permitting the production of detailed, time-dependent deformation maps in seismic and volcanic areas. Further advances led to precise satellite orbits derived from onboard GPS receivers, and more recently ultra-precise (to an accuracy of 10 centimeters)
From page 24...
... geodetic infrastructure components of global ground-based networks; supports fundamental geodetic research; supports development of the Global Geodetic Observing System; supports geodetic infrastructure critical to many satellite missions. DoD Yes Yes Operates the Global Positioning System (GPS)
From page 25...
... The CORS system is operated in partnership with many local, state, and federal agencies, and contains CORS stations that are located at sites of varying positional stability and with various models of receivers, antennas, and documentation. In cooperation with the USGS, NOAA also has responsibilities for supporting the geodetic infrastructure to provide ocean bathymetry, coastline and sea surface topography, which are critical for understanding tsunamis and predicting where they might come ashore, as well as for determin ing local or regional changes in sea level.
From page 26...
... Although data from some GPS stations operated by USGS are processed by the International GNSS Service, they are not used to to maintain the International Terrestrial Reference Frame. USGS depends on geodetic infrastructure to cary out its earthquake and volcano monitoring mission, and that infrastructure is crucial to development and production of data products, such as hazard maps and real-time ShakeMaps.


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.