Constantin Mavrocordatos

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.

Development of ASIRAS (Airborne SAR/Interferometric Altimeter System)

ASIRAS is an airborne system designed for sea-ice and ice sheet monitoring. It has been developed by ESA under a Technology Research Program contract. The main sensor of this system is a high resolution Ku-band radar altimeter with 1GHz bandwidth. The observation concept is based on a scaled configuration of SIRAL sensor on board CryoSat. The principle of the measurements is based on a combination of ranging, SAR and Interferometric techniques. The development and the validation of ASIRAS are now completed. The system will be extensively used during the Calibration and Validation campaigns of CryoSat mission. This paper describes the key design drivers and the main features of the system. The key operational parameters of the instrument are discussed, with particular focus on the link between the space-based and the airborne configuration. Finally, the performance of the instrument is presented, based on the results obtained from technical flights and a validation campaign.

SRAL SAR radar altimeter for sentinel-3 mission

The SRAL SAR radar altimeter is the core instrument of the topography mission carried on board the Sentinel-3 satellite which is planned to be launched in 2012. A detailed overview of this instrument is given in this paper in terms of architecture, functions, modes and performances.

Concept and realization of an Airborne SAR/Interferometric Radar Altimeter System (ASIRAS)

Cryosat is an approved ESA mission. Its objective is to determine fluctuations in the Earths land mass and marine ice fields. The mission utilizes a completely new SAR/interferometric altimeter concept, which combines a nadir-looking configuration with pulse-limited altimetry. The concept has been verified by simulations, but no dedicated experimental validation has been performed so far. For this reason, an Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) is currently under development in the frame of an ESA contract. Due to the large bandwidth of the system, several components, i.e. the chirp generator, are critical and therefore require innovative solutions. A dedicated software performs SAR- and interferometric radar data processing and, in addition, supports internal instrument calibration. ASIRAS is intended to be tested, verified and optimized on a DO 228/100 aircraft carrier during a measurement campaign scheduled fall 2002 in the area of Fram Street north of Greenland. The paper presents mission objectives, the instrument concept of ASIRAS, and critical building blocks.

The Ocean and Land Colour Imager (OLCI) for the Sentinel 3 GMES Mission: status and first test results

The Ocean and Land Colour Imager (OLCI) is a high accuracy visible spectral imager selected as optical payload for the Sentinel 3 component of the GMES mission, to provide climatological data continuity with the previous ESA Envisat missions. OLCI is based on the very successful opto-mechanical and imaging design of MERIS. The instrument is a quasi-autonomous, self contained, visible-NIR push-broom imaging spectrometer and incorporates significant improvements when compared to MERIS. The paper highlights the technical and programmatic challenges of the project, first results from the EM test activities and a projected flight model performance summary.

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.

High spatial resolution radar altimeter for ocean and ice-sheet monitoring

The monitoring of the ice-sheet height over Antarctica and Greenland is of primary importance for climate studies. The required height accuracy is of the order of a few centimetres. Current spaceborne altimeters are pulse-limited and therefore fail to deliver high accuracy surface height measurements over land and ice because of pulse spreading and slope induced errors. Moreover, sudden changes in the topography often result in a loss of track. Several techniques have been investigated during the past ten years in order to improve the spatial resolution of radar altimeters and therefore the accuracy of elevation estimates over terrains. Most of these techniques result in a significant increase in cost and complexity compared to a conventional altimeter. This paper presents the results of a recent feasibility study for a spaceborne high-spatial resolution radar altimeter (HSRRA) performed by Alcatel and the University College of London for the European Spatial Agency (ESA). This paper gives an overview of the concept and of the processing scheme. The theoretical altimeter waveforms derived for a flat tilted surface are also presented and discussed.

SRAL, a radar altimeter designed to measure a wide range of surface types

The SRAL (Sar Radar ALtimeter) instrument is the core instrument of the topography mission carried on -board the Sentinel-3 satellite which is to be launched in 2013. A detailed overview of this instrument (on -going C/D phase) is given in terms of mission requirements, architecture and modes, budgets/performa nces and equipments.

SRAL, a radar altimeter designed to measure several surface types

In the frame of the Global Monitoring for Environment and Security (GMES) program ESA is currently implementing the Sentinel-3 mission [1], [2]. It is designed as a constellation of two identical polar orbiting satellites, separated by 180 deg, for the provision of longterm operational marine and land monitoring services. As such, the Sentinel-3 satellite carries a topography mission including mainly RF instruments and an ocean and land colour mission composed of optical instruments. The aim of this paper is to first provide a brief overview of the Sentinel-3 mission and then focus on the core instrument of the topography mission [3], the SRAL radar altimeter [4], and its latest development steps.

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.