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- Output:
The NSGF delivers
accurate laser and microwave range measurements of selected
Earth-orbiting satellites to global data banks. The Satellite Laser
Range (SLR) normal points are precise at the mm level, and accurate to
better than 1 cm. In terms of quality and quantity of tracking data,
the Facility is ranked in the top five of more than 30 stations
worldwide. The GPS and GLONASS receivers are state-of-the art, and
operate autonomously and continuously.
The
Satellites
The principal
satellites
that are tracked are the series of Earth Observation satellites
(including ENVISAT, JASON-1, ERS-2 and GEOSAT-follow-on) that carry
microwave instruments for measuring distances to sea, ice and land.
Full exploitation of the satellite information is achieved by observing
the geodetic satellites (including LAGEOS'), and gravity-field missions
(the GRACE satellites, CHAMP, STELLA). SLR also regularly observes two
of the constellation of GPS satellites and all of the campaign-GLONASS
satellites.
- The
Science
The work of the Space
Geodesy Facility provides the raw material to underpin many areas of
science in which the UK is a stakeholder.
Observations of the geodetic satellites by SLR, collocated with a
Continuously Operating GPS receiver, contribute to the definition of a
global geocentric reference frame: Herstmonceux is one of the ten key
global reference stations that define the scale and origin. Ranging to
Earth Observation satellites allows accurate computation of their
orbits within this same, well-defined reference frame. In turn, the
satellite altimetry and SAR measurements to the oceans, ice caps and
land areas can be accurately calibrated using this precise knowledge of
the positions of the satellites. Examples of the resulting UK science
based on altimetry and SAR include computations of Antarctic ice
mass-balance, multi-year sea level variations, accurate global digital
elevation models, ocean-passage flow monitoring, radar remote sensing
of forests. Microwave and laser tracking of the GLONASS satellites is
used, through analyses carried out by NSGF, to check on orbital
anomalies and on the accuracy of broadcast ephemerides.
The
Future.
New
Earth-observation
satellites continue to be
launched; recent successful launches include ENVISAT
(ESA; altimetry and SAR) and JASON-1 (NASA, CNES; altimetry).
SLR tracking and GPS data for orbit
determination and altimeter calibration will continue to be important.
NERC thematic programme COEPEC (Ocean-atmosphere processes) includes
use of altimetry data to study Atlantic dynamics; altimetry is
particularly well suited to study processes such as Gulf-stream
dynamics. The EO Centre for Polar Observation and Modelling will use
data from current and future satellites such as IceSat (NASA) and
CRYOSAT-2 (ESA); both these missions will require GPS or DORIS and SLR
support for orbit determination and calibration/validation.
The same is true for
the new
generation gravity field missions CHAMP and GRACE.
On-board GPS systems provide continuous tracking data for rapid orbit
determination, the SLR data again being used for validation. These
satellites provide detailed information on the high-frequency
terms in models of the Earth's gravity field and the more traditional
laser-tracked
spherical geodetic satellites provide the static and temporal
long-wavelength
terms.
For these reasons the
work of
the NSGF provides an essential underpinning of current and future
science in the broad area of monitoring climate change.
 NERC
Space Geodesy Facility
Background
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