Precise Geodetic Infrastructure National Requirements for a Shared Resource (2010) / Chapter Skim
Currently Skimming:
3 Geodesy Requirements for Earth Science
3 Geodesy Requirements for Earth Science
Pages 37-66
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 37... ...
Given the breadth of scientific and societal applications, this chapter is not intended to be comprehensive, but rather to highlight only a sampling of the benefits that high-precision geodetic infrastructure provides for Earth science and the nation. SOLID EARTH DyNAMICS Geodynamics Plate Motion and Tectonics Nothing on Earth's surface is fixed, and enormous pieces of the crust are being ripped apart or forced into collisions with each other by the movement of the mantle below, causing earthquakes, volcanoes, and mountain building.
|
From page 38... ...
Consistency in connecting the longest to the shortest time scales requires an accurate and stable global terrestrial reference frame, which drives the most stringent requirements on the geodetic infrastructure.
|
From page 39... ...
The amount of ice locked up in the ice sheets at the time was enough to cause global sea levels to lie 100–150 meters below their pres ent levels (Peltier, 2004)
|
From page 40... ...
. These space-based gravity measurement techniques use the geodetic infrastructure to determine an accurate reference against which to measure the small post-glacial rebound motions; the geodetic techniques also provide the data containing important geophysical signals.
|
From page 41... ...
In addition, knowledge of the static component of Earth's gravity field has been improved by orders of magnitude, providing a global geoid model accurate to the centimeter level at 200-kilometer resolution. The twin GRACE satellites using a dual one-way K-band (20–40 GHz)
|
From page 42... ...
discovery that volcanoes once thought to be dormant are actually undergoing gradual deformation and may eventually erupt. Because volcanic deformation tends to be a slow process taking decades to centuries between eruptions, InSAR and GNSS/GPS measurements must be tied to decades of data from a stable terrestrial reference frame with better than 5 millimeter precision.
|
From page 43... ...
, a phenomenon of short-term transient slow slip behavior at a subduction zone. Each blue circle in the plot indicates the daily change of the east-west position of the Victoria GPS station relative to the interior of the North American Plate.
|
From page 44... ...
over multiple time scales. InSAR is a highly complementary and synergetic technique to the Plate Boundary Observatory's GPS network, because it can generate continuous high-resolution maps of surface strain over large areas in any weather condition day or night, typically on monthly times cales.
|
From page 45... ...
GEODESY REquiREMENTS FOR EARTh SCiENCE FIGuRE 3.6 Ground deformation from ALOS L-band interferometry (each concentric color "fringe" corresponds to approximately 10 centimeters of displacement) due to the 7.9-magnitude Wenchuan earthquake, which occurred on May 12, 2008, along the western edge of the Sichuan Basin in China.
|
From page 46... ...
FIGuRE 3.7 These false-color geodetic images of a landslide near Flathead Lake, Montana, were made from airborne LiDAR data collected by the NSF National Center for Airborne Laser Mapping (NCALM)
|
From page 47... ...
report Elevation Data for Floodplain Mapping (2007b) , "…elevation data of at least 1-foot equivalent contour accuracy should be acquired in these very flat areas, rather than the 2-foot equivalent contour accuracy data that the FEMA floodplain map ping standards presently require for flat areas." Achieving this 1-foot accuracy actually requires two geodetic measurements -- the terrain elevation and the geoid height (see Chapter 1)
|
From page 48... ...
, it is possible to predict how much energy is imparted to the ocean, and thus FIGuRE 3.9 The largest tsunamis are generated by earthquakes occurring at ocean trenches, known as subduction zones, where tectonic plates converge. If the rapid horizontal displacement of a GNSS/GPS receiver near the coast of a subduction zone was measured and immediately available, it would be possible to infer how much slip had taken place and predict the likely size of the resulting tsunami.
|
From page 49... ...
. The key to this method is to be able to accurately measure the rapid horizontal displacement of GNSS/GPS receivers at the time of the earthquake.
|
From page 50... ...
. A number of error sources have to be considered when interpreting the apparent global mean sea level rise, either from tide gauges or altimeter missions.
|
From page 51... ...
Table 3.1 provides an estimate of the systematic errors in measuring the global mean sea level rise from altimeter data (adapted from Nerem, 2009)
|
From page 52... ...
The rate at which fresh water from ice melt is entering the oceans is a critical component of understanding what is causing the apparent acceleration of global mean sea level rise. There also is evidence that Greenland and Antarctica are losing ice mass at an accelerating rate (Chen et al., 2009; Jiang et al., 2010; Shum et al., 2008; Velicogna, 2009)
|
From page 53... ...
Only through careful monitoring of the ice sheets -- using tech niques that rely heavily on geodetic infrastructure -- was the acceleration noticed and quantified. The continued application of current and future geodetic techniques is required for the scientific community to be able to monitor the ice sheet mass balance at the accuracy needed to understand what is happening today and to develop models for predicting future ice sheet mass changes.
|
From page 54... ...
Traditional hydrological observations do not typically employ geodetic techniques, but with the advent of high-precision geodetic measurement systems, most of which depend heavily on the geodetic infrastructure, new and innovative methods for probing hydrological processes are providing valuable new information and hold great promise for the future. FIGuRE 3.13 Mass changes in the Greenland ice sheets observed by GRACE.
|
From page 55... ...
The GRACE results also will help to determine the role of con tinental water variability in global mean sea level change and to better understand the transfer of water between the land and the atmosphere (precipitation and evaporation) at regional scales (see Frappart et al., 2006; Rodell et al., 2007; Swenson and Milly, 2006; Swenson et al., 2006; Zaitchik et al., 2008)
|
From page 56... ...
FIGuRE 3.14 Major groundwater loss in the Sacramentro–San Joaquin River Basins in California (left) (Strassberg et al., 2009)
|
From page 57... ...
Negative values for the uplift rates indicate subsidence. Most of New Orleans is subsiding relative to the global mean sea level, at an average rate of about 8 millimeters per year.
|
From page 58... ...
Thus, improvements in the geodetic infrastructure benefit both fields of science. Ground-based Measurements Atmospheric refraction effects have long been recognized as an important error source in geodesy.
|
From page 59... ...
Well-designed sites with low multipath errors are also valuable as they will produce more accurate estimates of PWV. For weather prediction, however, there is the additional requirement that accurate orbits must be available in real time, whereas for climate studies, orbits can be made available in days to weeks.
|
From page 60... ...
and European weather forecast models. In order to operate properly, however, they have requirements similar to those of ground-based GNSS/GPS networks, including accurate orbits and reference frame (which require a global GNSS/GPS tracking network providing near-real-time data)
|
From page 61... ...
. PRECISION SPACECRAFT NAVIGATION Precision Orbit Determination for Near-Earth Satellites Over the past several decades, the requirements for highly accurate determination of the orbits of near-Earth satellites have been driven by the evolution of the fields of satellite geodesy, includ ing reference frame and gravity field determination, satellite radar and laser altimetry, and InSAR.
|
From page 62... ...
These same tracking measurements, along with satellite-to-satellite measurements, are providing unparalleled views of Earth's gravity field and the gravity signals associated with temporal variations in the distribution of mass within Earth. These advances are intimately tied to the advances in precision orbit determination of Earth-orbiting satellites.
|
From page 63... ...
DECADAL MISSIONS The NRC's Earth Science and Applications From Space: National imperatives for the Next Decade and Beyond (known as the "Decadal Survey," NRC, 2007a) recommended a number of efforts and missions to address a wide range of scientific and societal challenges, from scientific questions related to melting ice sheets and sea level change to the occurrence of extreme events like earthquakes and volcanic eruptions.
|
From page 64... ...
Of these factors, changes in the volume of ice sheets in response to climate change is the least understood. The laser altimeter on ICESat-2 would quantify polar ice sheet contributions to recent sea level change and illuminate the linkages to climate conditions.
|
From page 65... ...
This not only will enable scientists to gather valuable data about climate, but also will provide the public with images that will enable them to visualize the dynamic Earth system and to understand the connection and interaction among the global water cycle, climate, and the solid Earth. The Decadal Survey missions also will benefit greatly from the global geodetic infrastructure.
|
Key Terms
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.