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  Radar Altimeter 2 (RA-2) is an instrument for determining the two-way delay of the radar echo from the Earth's surface to a very high precision: less than a nanosecond. It also measures the power and the shape of the reflected radar pulses.

It is a nadir-looking pulse-limited radar altimeter based on the heritage of ERS-1 RA functioning at the main nominal frequency of 13.575 GHz (Ku Band), which has been selected as a good compromise between the affordable antenna dimension that provides the necessary gain and the relatively low attenuation which experience the signals propagating through the troposphere.
TypeRadar altimeter
Technical Characteristics
Accuracy Altitude: better than 4.5cm, Wave height: better than 5% or 0.25m
Spatial Resolution
Swath Width
Waveband Microwave: 13.575Ghz (Ku-Band) & 3.2GHz (S-Band)
ApplicationsSnow and Ice (Sea Ice) Atmosphere (Winds) Land (Topography/Mapping) Ocean and Coast (Ocean Waves,Ocean Currents and Topography)
Latest Mission Operations     News
Envisat RA-2 IGDR product anomaly

ECMWF atmospheric model pressure grids are operationally used to derive dry troposphere and inverse barometer corrections for the ENVISAT RA-2 height measurements.

Following the upgrade of the ECMWF model to a higher spatial resolution done on 26 January 2010 for the Envisat OFL products, anomalies have been identified on the IGDR products.

The largest impact is seen in the inverse barometer correction, which has static variations of up to 2 cm amplitude at a wavelength of ~ 50 km. This effect is most noticeable in regions within 200 km of the coast, but is not negligible outside those regions. The anomalous short-wavelength variations can be detected comparing IB values before and after the model evolution. The dry tropospheric correction is affected as well (~4 times smaller amplitude), but not the wet tropospheric correction.

The IGDR products have been affected by the ECMWF model resolution change from cycle 86 (pass 404).

The solution is to retain all the model's spectral information when interpolating from the high-resolution to low-resolution grids, which is an option when creating the operational grids. This change was implemented on 02-Feb-2010, and the first FGDR and IGDR products that have reduced pressure-induced errors are from cycle 86 (pass 613).
A smaller issue remains that the interpolation of the high-resolution ECMWF surface pressure grids to a lower resolution does not allow us to fully remove spectral leakage of land features onto the ocean. The remaining errors have a smaller amplitude (~20% of the short-wavelength features seen in the first figure),is also static in time, and almost exclusively affects regions within about 100 km of the coast. Work is ongoing to solve the remaining issue as well, and users will be kept updated on the progress.

The affected IGDR products will be reprocessed. A short note will be issued when those are available. All issues related to the ECMWF model resolution change will be corrected prior to OFL Level 2 GDR production for this time period.

Latest Data Product RA-2 wind/wave product for Meteo users
Available Resources
RA-2 FAQTechnical DocumentHTML
RA2_MWR_IPF_5.03 Technical DocumentHTML
ENVISAT RA-2 and MWR Products and Algorithms User GuideTechnical DocumentHTML
The ENVISAT Radar Altimeter System (RA-2) ESA BulletinDownload
Glossary Technical DocumentHTML
RA2 Products SpecificationsProduct DocumentDownload
Annex A - Product Data ConventionsProduct DocumentDownload
Envisat in depth
Key Resources