L. Rey

SWIMSAT: A Real-Aperture Radar to Measure Directional Spectra of Ocean Waves from Space—Main Characteristics and Performance Simulation

Abstract The project SWIMSAT aims to measure the directional spectra of waves from space using a real-aperture radar with a low-incidence, conical-scanning beam. This system’s design is based on airborne versions developed in France and the United States. In this paper, the authors present the satellite measurement principle and instruments. For this study, the authors developed a simulation method to analyze the sensitivity of wave spectra, taking into account radar observation conditions (spatial resolution, signal-to-noise ratio, integration time, etc.) and inversion processing parameters (noise level and range displacements during temporal integration). The simulation method and results are presented in this paper. The study enabled validation and refinement of the satellite concept. The simulations show that in the chosen configuration, SWIMSAT is capable of measuring wave spectral properties in wind–sea conditions (at dominant wavelengths over approximately 70 m) and swell conditions (at significant...

SIRAL, a high spatial resolution radar altimeter for the Cryosat mission

SIRAL (SAR Interferometer Radar Altimeter) is the new spaceborne altimeter designed for CryoSat mission. This ESA mission, planned for 2004, will be used to estimate-on a global scale- the fluctuations in mass of sea-ice and land-ice. The novelty of SIRAL concept with respect to conventional pulse-limited altimeter, is the implementation of Doppler processing for along-track resolution enhancement and also of interferometry, used to locate the echo in the across-track direction. The innovative technical features of SIRAL are presented hereafter with regards to the function requirements and also the expected performance.

Overview of the performances and tracking design of the SIRAL altimeter for the CryoSat mission

This paper presents the principle of the measurements, the main system features and the basic ground processing of SIRAL. Simulations of the main performances in the different modes are also discussed including the bidimensional impulse response (range and azimuth). A major scientific requirement is to ensure the continuity of the measurements. This is particularly challenging for the on-board tracker over the steepest parts of the Antarctica. As a consequence a new tracking algorithm has been designed for SIRAL with the expertise of CNES. The algorithm has been derived from the analysis of simulated echoes using an Antarctica DEM and a radar echo simulator. The tracking design and performance are briefly described.

Poseidon 2, the new generation altimeter for JASON mission

Poseidon 2 is the new spaceborne altimeter designed to follow the successful TOPEX Poseidon altimetry mission. The follow-on mission JASON is under preparation and is planned to be operational in early 2000. Alcatel Space Industrie, under CNES contract, completes the engineering and qualification model and 2 flight models. This paper provides a brief overview of the instrument and describes the results obtained during the flight model ground tests. Hardware, new subsystem characteristics and primary performance results are presented.

SIRAL: the radar altimeter for CryoSat mission, under development

SIRAL (SAR Interferometer Radar Altimeter) is the new spaceborne altimeter designed for CryoSat mission. The instrument is currently in the development phase, in ALCATEL SPACE, which encompasses an Engineering Model and a Flight Model. This ESA mission, planned for 2004, will be used to estimate - on a global scale - the fluctuations in mass of sea-ice and land-ice. This paper discusses the flexibility of the instrument and in particular its capability to operate in various modes (conventional altimeter, SAR and interferometer modes), and gives main results from the pre-developments and breadboard activities.

Siral the radar altimeter for the cryosat mission, pre-launch performances

The development phase of the SAR Interferometer Radar Altimeter (SIRAL) is in the final stage in Alcatel Space and during year 2004 the Engineering and the Flight Models is tested before delivery to the Mission Prime ASTRIUM GmbH. This ESA mission will be used to estimate - on a global scale - the fluctuations in mass of sea-ice and land-ice. This paper gives a detailed presentation of the microwave and processing units developed, followed by a survey of the pre-launch performances.

Phase B and breadboard results for the TOPEX POSEIDON FOLLOW-ON mission

Pursuing the successful TOPEX POSEIDON altimetry mission, activities for the follow-on program are in progress. ALCATEL ESPACE completes the phase B of the next generation altimeter funded by the French Space Agency (CNES). The main evolution with respect to the former POSEIDON-1 rely upon the dual frequency (Ku & C bands) operation, and the doubled processed range depth within the same mass and power budgets. The altimeter design and development resulting from study and breadboarding activities are presented with regards to the function requirements and also the expected altimeter performances.

New generation of RF unit for radar altimeter

Alcatel developed a new generation of dual-frequency radar altimeter (POSEIDON 2) which works in C and Ku band. This article discusses about the radiofrequency unit (RFU) which plays a major role for the stringent performances of the altimeter. The compact RF unit has been designed with a modular concept. It uses the new advanced technologies: extensively use of MMIC, pHemt LNA and hybrid HFET power amplifiers. The transmitted peak power level is greater than 23W in C band and 7W in Ku band.

Preliminary design of the VAGSAT wave scatterometer

The aim of the small satellite project VAGSAT is to provide measurement of the directional wave spectrum over the globe to improve the climatology models. The system definition is based upon the nadir beam measurement to normalize the wave spectrum, and the spectrum beam measurement to provide the directional wave spectrum. The dual beam antenna sub- system with one rotative beam and the on-board processing design with the pulse compression solution selected are presented. The first VAGSAT design is encouraging; the payload conception demonstrates the feasibility with an overall mass and power consumption compatible with a small satellite platform.