Precise Geodetic Infrastructure National Requirements for a Shared Resource (2010) / Chapter Skim
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4 The Geodetic Infrastructure: Current Status and Future Requirements
4 The Geodetic Infrastructure: Current Status and Future Requirements
Pages 67-88
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From page 67... ...
The VLBI infrastructure includes the radio telescopes ("VLBI observatories") and central data processing facilities called correlator centers.
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From page 68... ...
By observing radio sources in multiple directions, the VLBI network can be used to determine Earth's geometric shape and orientation in space. SOURCE: NASA, Goddard Space Flight Center.
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From page 69... ...
The optimal radio telescope parameters for geodetic applications are different than those for astronomical applications. The geodetic infrastructure must, there fore, include a dedicated network of geodetic VLBI observatories to obtain continuous measurements.
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From page 70... ...
VLBI data analysis centers should consider using products from GNSS/GPS data analyses, such as polar motion and atmospheric delay estimates, in the generation of VLBI products. The combined analysis would aid in terrestrial reference frame realization using VLBI networks with a small numbers of sites.
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From page 71... ...
The network coordinated by the International GNSS Service (IGS) , which provides the GPS component of the ITRF, consists of approximately 360 active stations (see Figure 5.1)
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From page 72... ...
On the national scale, the current GPS network to serve highprecision applications is actually a collection of networks operated by different federal agencies including NGS, NSF, USGS, and NASA. In addition, NASA contributes to the global GNSS/GPS network operated under the IGS for precision orbit determination and for reference frame realization in order to meet scientific objectives.
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From page 73... ...
With regard to data processing, there are currently several agencies and universities that rou tinely process data from the various high-precision GPS networks using custom software. Some are official analysis centers for the IGS.
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From page 74... ...
An SLR station in Matera, Italy is capable of lunar ranging but has not yet initiated a lunar observ ing program. In addition to performing LLR using two-way ranging to the retroreflector arrays on the moon, experiments have begun that are attempting one-way laser ranging to the Lunar Reconnaissance Orbiter.
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From page 75... ...
. In addition, multi-kilohertz firing rates, improved epoch timing, more stable ranging calibration, and operating in the single photon regime will reduce random and systematic errors for laser ranging.
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From page 76... ...
(DORIS) The DORIS system is a French civil precise orbit determination and positioning system.
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From page 77... ...
Measurements of the number of beat cycles can be used to determine the velocity of the satellite, which is then incorporated with satellite orbit dynamics to determine the distance between the satellite and the ground beacon. DORIS is optimized for precise orbit determination with global coverage and all-weather measurements.
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From page 78... ...
. In order to develop a geoid model that is accurate to the centimeter level and with a spatial resolution approaching the few kilometer level over the continental United States, it is necessary to record millions of ground or airborne gravity measurements that can be combined with a global satellite gravity field.
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From page 79... ...
The launch of the joint United States/Germany Gravity Recovery and Climate Experiment (GRACE) in 2002 dramatically improved the ability to measure Earth's global gravity field from space.
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From page 80... ...
Nevertheless, accurate knowledge of vertical land movements at tide gauge sites is still lacking. A significant part of the 0.4-0.6 millimeter/year uncertainty in the altimetry-derived rate of global mean sea level rise comes from reference frame errors or from the lack of any measurement of the vertical motions of the tide gauges used for calibration (Nerem and Mitchum, 2001; Beckley et al., 2007)
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From page 81... ...
Red dots represent stations for which no PSMSL data exist. SOURCE: Courtesy of the Permanent Service for Mean Sea Level and the Global Sea Level Observing System (GLOSS)
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From page 82... ...
ERS-1 C-band, VV ESA 1992-1996 Solid Earth, 780 km polarization hydrology, glaciology, oceanography, geotechnical, natural hazards ERS-2 C-band, VV ESA 1996-present 780 km polarization JERS-1 L-band, HH JAXA 1992-1998 570 km polarization
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From page 83... ...
; ASI - Italian Space Agency Abbreviations: HH (Horizontal transmit, Horizontal receive) ; HV (Horizontal transmit, Vertical receive)
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From page 84... ...
Though GNSS/GPS and DORIS are now routinely used for operational orbit determination on most geodetic satellites that require high precision orbits, SLR has proven to be vital as a backup tracking system. For example, the primary tracking aboard the European Space Agency's Earth Remote Sensing satellite (ERS-1)
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From page 85... ...
It is now common for geodetic missions to operate a GNSS/GPS receiver on board their satellites for precision orbit determination, relying upon either the IGS orbits and clock solutions or the ground data collected by the IGS network for computing their own solutions. The IGS analysis centers also now provide the dominant contribution to the determination of the Earth's polar motion.
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From page 86... ...
It does not distribute the gravity data directly, but rather functions as a unifying service for the various gravity-related IAG services. The data of the IGFS services include satellite-derived global models; terrestrial, airborne, satellite, and marine gravity observations; Earth tide data; GNSS/GPS leveling data; digital models of terrain and bathymetry; and gravity field information from satellite altimetry.
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From page 87... ...
In summary, the geodetic infrastructure, which supports myriad national and international interests in the Earth sciences, consists of geodetic networks (ground-based instruments and their attached GNSS/GPS receivers, radio telescopes, laser tracking stations, DORIS beacons, tide gauges, and gravity meters) , geodetic platforms (satellites, aircraft, and other vehicles)
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