|  1.
Maintenance of Global Geodetic Networks, Terrestrial Reference Frame,
and Earth Orientation Parameters
The
accuracy of global geodetic networks advances by about a factor
10 per decade, with submillimeter-scale reference-frame accuracy
likely in the near future. Continued improvements in accuracy are
critical to a number of the recommendations of this report, from
the study of sea-level change and improved gravity-field measurements
to the detection and characterization of land surface change. The
Internet and high-speed computing have recently been harnessed to
provide near-real-time global GPS positioning and time transfer,
of significant potential benefit to onboard satellite and airborne
data reduction and natural hazards disaster management.
2. Precise Orbit Determination (POD)
As
is well-recognized by its international partners, NASA's Solid
Earth Science Program supports the development, maintenance, and
continuing refinement and enhancement of computer software for modeling
and computing satellite orbits. This precise orbit
determination (POD) capability is essential for the global space
geodesy enterprise. GPS observations have documented that deformation
across the Cacadia subduction zone in the Pacific northwest is governed
by two processes acting on very different time scales.
3
. Coordination, Validation, and Calibration
While
space-based measurements are inherently global in coverage, in many
instances they are limited in their temporal or spatial sensitivity.
For example, the spatial resolution of quantities derived from potential
field measurements or their gradients will always be limited by
the distance of a satellite from Earth's surface. In many
instances, gaps in spatial and temporal coverage can be filled by
utilizing
other measurement platforms. Fine spatial resolution is often best
achieved with land or seafloor arrays installed either semi-permanently
or on a campaign basis.
In
the past, these supporting measurements have often been neglected
or eliminated to accommodate budget shortfalls. Lack of such supporting
data, however, reduces confidence in space-based measurements and
in some instances can lead to incorrect inferences due to inherent
measurement inaccuracy. Greater attention to validation and calibration
is urged for all future mission planning.
|
