Minimize Dataset Details
Earth Topics (Applications)
Instrument type
Date of Launch:
ERS-1 - 17 July 1991
ERS-2 - 21 April 1995
Mission Status:
ERS-1 ended on March 2000 and ERS-2 September 2011 
Orbit Height:
782 to 785 km
Orbit type:
Near-circular, polar, Sun-synchronous
Swath Width:
5 km
PRARE Precise Orbit Product
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Last update: 26 September 2009

The precise orbit results from a data reduction process in which all available tracking data (Single-Lens Reflex, radar altimeter crossovers, PRARE range and doppler data) and most accurate correction, transformation and dynamical models are taken into account and in which high level numerical procedures are applied.

These orbits are "optimal" achievable representations of the real orbital motion under the circumstances of tracking situation and the "state of the art" model situation. The precise orbit product for the ERS satellites of the satellite ephemeris (position and velocity vector) including time tag, given in a well defined reference frame, together with the nominal satellite attitude information and a radial orbit correction.

The chosen reference systems for the satellite position and velocity representation are the Conventional Inertial Time (CIS) and the Conventional Terrestrial System (CTS). The time frame used is the Terrestrial Dynamic Time (TDT). The precise orbit will be used for reduction of the radar altimeter measurements and the determination of geodetic/geophysical products.

The quality of the generated orbits is controlled formally and internally. The formal quality control includes procedures to check the correct format and to flag periods where the orbit is degraded by manoeuvres or platform anomalies. Internal quality checks are performed by: - examining the fits of the laser ranges and the altimeter crossovers to the adjusted orbit - comparing overlapping arc segments. Each product is complemented by records containing quality information like fit of the observations to the orbit, comparison of overlapping orbit segments, crossover rmr (root mean square) before and after consideration of a radial orbit correction. For the revision 1 orbits the radial accuracy is in the order of 12-15 cm, while the revision 2 provides about 8-10 cm radial accuracy.

Product characteristics
Spatial Coverage Global
Time Coverage App. 1 month or 1 35d-cycle, consisting of several continuous 5-7 day files
Time Resolution 30 seconds
Time/Rate of Generation D-PAF computed uninterrupted precise orbital subarc for about 5 to 7 days of tracking data. All subarcs of one month 1/35d-cycle are compiled into one precise orbit product.
Data Set Specifications
Spatial coverage: 82 N, 82 S, 180 W, 180 E
Temporal coverage: 1991-07-27 - 2011-07-04
Processing level
Level 1

How to access this data

Data available from ERS-1 and ERS-2 is distributed online via FTP upon Registration

Terms & Conditions applicable
Utilisation of this data is subject to ESA's Earth Observation Terms and Conditions


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