ENVISAT RA-2 advanced radar altimeter: Instrument design and pre-launch performance assessment review.

RA-2 is a second generation spaceborne radar altimeter designed and develop ed by ALENIA AEROSPAZIO (ALS) in the frame of the European Space Agency (ES A) ENVISAT programme. The project, started at beginning of 1990, reached it s completion in October 1998 with the delivery of the Instrument Flight Mod el to Daimler-Benz Aerospace, Dornier (the mission prime contractor of ENVI SAT) for its integration on the platform. ionospheric bias correction of th e range measurements, enhanced precision range measurements over oceans, ca pability of including in the instrument telemetry data down linked to groun d In-phase and Quadrature samples of individual Ku band radar echoes, resol ution adaptivity and robust tracking algorithms to allow range measurements and radar echoes collection not only over open oceans but also at land-oce an boundaries, ice and land regions with the real objective of continuous g lobal Earth topography mapping. RA-2 only partly resembles in its characteristics those of ERS-1 / ERS-2 fi rst generation Radar Altimeters, designed by ALS. Principal innovative feat ures of the RA-2 are: dual frequency operation (Ku and S band) for ionosphe ric bias correction of the range measurements, Aim of this paper is to provide an overview of the instrument key design ch aracteristics and to present instrument pre-launch performance results deri ved from the evaluation of the test results gathered during the instrument integration and characterisation campaign of the Flight Model(FM). (C) 1998 International Astronautical Federation Published by Elsevier Science Ltd. Ail rights reserved.