RA (ERS) Products Information
RA (ERS) Products Information
Reprocessed ESA ERS Altimetry (REAPER) dataset
The full-mission reprocessing of the ESA ERS Radar Altimetry (RA) Level 2 data was completed and the dataset is available online to the ESA Earth Observation user community.
The REAPER (REprocessing of Altimeter Products for ERS) project covers both the ERS-1 and the ERS-2 Altimetry missions. The reprocessed dataset spans from the start of the ERS-1 mission in July 1991 to June 2003, when the loss of the ERS-2 on-board data storage capability occurred causing the end of the ERS-2 global mission coverage. The reprocessing campaign was performed with REAPER processor version 1.08 and use of the latest reprocessed ESA precise orbit products (see ESA news "Homogeneous reprocessed ERS-1 and ERS-2 Orbit dataset"). The output products were delivered in netCDF format (version 3.6) and were based on dump orbits (i.e. not split in pole-to-pole passes).
The REAPER Product Handbook provides exhaustive information on the ERS RA product content, format and improvements. It provides also, for user's convenience, a list of passes with known data quality issues (i.e. orbital manoeuvres, telemetry problems, etc).
The ERS-1/2 REAPER Altimeter dataset is composed of the following three product types:
- Radar Altimeter REAPER Geophysical Data Record - GDR (ERS_ALT_2)
- Radar Altimeter REAPER Meteo Product - METEO (ERS_ALT_2M)
- Radar Altimeter REAPER Sensor Geophysical Data Record - SGDR (ERS_ALT_2S)
Data Processing and Quality Improvement
Major improvements with respect to the previous ESA RA products format (OPR - Ocean Product - and WAP - Waveform product) were implemented (e.g. the four Envisat RA-2 retrackers, RA calibration improvement, new reprocessed Precise Orbit Solution, ECMWF ERA-interim model, NICO09 ionospheric correction until 1998, GIM ionospheric correction up to 2003, new SSB, etc.). The assessment of the REAPER data quality versus the ERS OPR and WAP data showed a clear improvement in terms of accuracy over the tandem periods between ERS-1, ERS-2 and Envisat missions (currently assessed periods).
However, the REAPER dataset presented some limitations (such as the use of poor MWR Wet tropospheric correction, out of range PTR corrections, etc.) that were fully described in the Product Handbook.
Intercalibration between ERS-1, ERS-2 and Envisat, between all three radar altimeters and all three microwave radiometers, led to several improvements, including the incorporation of inter-mission bias corrections. Envisat style retrackers were used in the REAPER processing, allowing easier comparison. REAPER ERS-2 data was cross-calibrated to the released Envisat v2.1 product and the REAPER ERS-1 data to REAPER ERS-2.
Validation reports for all three product types (GDR/SGDR/METEO) are available to users:
- REAPER Calibration Monitoring
- Cal/Val evaluation of REAPER ERS altimeter data
- RA L2 Validation Report
- ERS REAPER Performance and QA Website
If you have any questions about this project, contact:
Dr. Philippe Goryl