Fundamental Data Records (FDRs) and Thematic Data Records (TDR) from FDR4ALT project

In 2024, ESA has released the Altimetry Fundamental Data Record (FDR) derived from the ESA FDR4ALT project. This dataset is based on information gathered from the ERS-1, ERS-2 and ENVISAT missions and overcomes the individual mission datasets in various aspects.

The FDR4ALT initiative has encompassed the creation of Fundamental Data Records (Level 1 Altimeter and Radiometer data) and Thematic Data Records (Level 2 + geophysical products) within ESA's Heritage Space Programme.

The new records, available in NetCDF format, are derived from the ERS-1, ERS-2 and Envisat Altimeter and Radiometer instruments, spanning the mission archives from 1991 to 2012.

The new products, which demonstrate notable improvements (see the FDR4ALT Validation Report Document - FDR).

The records are aimed at different user communities and include the following datasets:

1. Fundamental Data Records for Altimetry
2. Fundamental Data Records for Radiometry
3. Atmospheric Thematic Data Product
4. Inland Waters Thematic Data Product
5. Land Ice Thematic Data Product
6. Ocean & Coastal Topography Thematic Data Product
7. Ocean Waves Thematic Data Product
8. Sea Ice Thematic Data Product

For more details visit the FDR4ALT project website.

Details on the operational processing of Radar Altimeter and ATSR/MW (microwave radiometer) data is provided in the RA/ATSR Products User Manual.

REAPER: REprocessing of Altimeter Products for ERS

The REAPER (REprocessing of Altimeter Products for ERS) project covers both the ERS-1 and the ERS-2 Altimetry missions. 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. However, the REAPER dataset presented some limitations (such as the use of poor MWR Wet tropospheric correction, out of range PTR corrections, etc.) that are fully described in the REAPER 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

Papers

"REAPER: Reprocessing 12 Years of ERS-1 and ERS-2 Altimeters and Microwave Radiometer Data", D. J. Brockley, S. Baker, P. Féménias, B. Martínez, F-H. Massmann, M. Otten, F. Paul, B. Picard, P. Prandi, M. Roca, S. Rudenko, R. Scharroo, and P. Visser - IEEE TGRS, June 2017, DOI: 10.1109/TGRS.2017.270934

The paper presents the REAPER data set and main results on the validation activities.

The REAPER data set presents 12 years of ERS altimetry data, cross-calibrated both within the mission and with Envisat V2.1. The data format is netCDF 3, and the data set is fully described in the accompanying REAPER product handbook.

The major improvements of the REAPER data set with respect to the previous ESA RA products were due to use of four Envisat RA-2 retrackers, RA calibration improvement, new reprocessed precise orbit solutions, ECMWF ERA-interim model, NIC09 ionospheric correction until 1998, GIM ionospheric correction up to 2003, and new sea-state bias.

The assessment of the REAPER data quality versus the ERS OPR and WAP data shows a clear improvement in terms of accuracy over the tandem periods between ERS-1, ERS-2, and Envisat missions.

Documents

Download MWR related documents:

• REAPER Product Handbook
• REAPER Calibration Monitoring
• Cal/Val evaluation of REAPER ERS altimeter data
• REAPER RA L2 Validation Report
• REAPER ERS-1 and ERS-2 ORBIT Validation report
• REAPER - Specifications for POD Products for ERS Altimetry Reprocessing

During the full-mission reprocessing of the ESA ERS Radar Altimetry (RA), a non optimal MWR inter-calibration activity resulted in a poor MWR wet tropospheric correction in the REAPER products. More details available in the REAPER Product Handbook.