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Instrument: PRARE : Precise Range and Range-Rate Equipment
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Description
The Precise RAnge and Range-Rate Equipment (PRARE) was developed and
maintained as a national German experiment by the Institute for
Navigation (INS) of the University of Stuttgart, the
GeoForschungsZentrum Potsdam, Time Tech GmbH Stuttgart, and
Kayser-Threde GmbH Munich. Development is funded by BMFT (Germany's
Federal Ministry for Research and Technology).

PRARE was flown on the European Space Agency (ESA) European Remote
Sensing Satellites ERS-1 and ERS-2 and will be flown on the ESA
ENVISAT.

PRARE is a highly accurate microwave ranging system, supported by a
network of mobile ground stations, which are used for orbit
determination at decimeter level of accuracy as well as for various
geodetic applications.

The PRARE is designed to:

- provide, in all weather conditions, precise
satellite-to-ground or ground-to-satellite
range and range-rate information
- guarantee very reliable measurements through
cross-checks and calibration procedures
- ensure highly effective operation of the ground
segment through data collection and dissemination
via the satellite itself and control of the global
network via one central ground station
- allow fast product generation at an archiving,
processing and distribution centre.

In this two-way microwave ranging system, the on-board equipment
performs the measurements in X-band (8.5 GHz), with some additional
functions in S-band (2.2 GHz) for ionospheric correction purposes.

The PRARE measures range and Doppler (range rate) between the
satellite's antenna and up to four ground stations simultaneously. It
is an autonomous system for precise satellite orbit observation. It
consists of the space segment with its own computer and data storage
medium, and the ground segment, the unattended user ground stations, a
dedicated command station and a master station for receiving the data
dumps. PRARE operates in X-band and, in the downlink, also in
S-band. Thus, the ionospheric total electron content (TEC) can be
determined along the line-of-sight from the ground station to the
satellite.

The applications of PRARE are:

- precise satellite orbit determination
(e.g. of altimeter and geodynamic satellites)
- earth gravity field
recovery
- precise point positioning (tectonics)
- earth rotation
parameter determination and measurement of the ionospheric total
electron content (TEC).

In the measurement process the space segment is the active part,
i.e. the satellite is the start and end point of the two-way line and
the Range and Doppler correlations take place on-board. A ground
station only turns the signal around after amplification and after
modulating the S/X-band travel time difference and meteorological data
on the carrier. All data are collected on-board and dumped during
contact with the master station. The space segment also provides
updated orbit and schedule data to the ground stations in the
downlink. With this design it is possible to operate a global ground
station network without external data transmission
facilities. Especially important is that even the host satellite is
not encumbered by the PRARE data flow.

Related URL:


http://op.gfz-potsdam.de/prare/general/general.html


http://earth.esa.int/ers/prare



Reference online documentation:


http://earth.esa.int/services/esa_doc/doc_pra.html

For any query, please refer to:

ESA/ESRIN Earth Observation Help Desk

http://earth.esa.int

E-mail: eohelp@esa.int

Phone: +39 06 94180777

Fax: +39 06 94180292

Address:

ESA/ESRIN

Via G.Galilei

00044 Frascati

Italy