Thierry Amiot

Directional wave spectrum estimation by SWIM instrument on CFOSAT

SWIM is a Ku-band radar designed for wave directional spectrum estimation. This radar operates at six incidence angles (from 0° to 10°) with a complete azimuth scanning. SWIM is currently in Phase B (concept and design phase). In [1, 2], the preliminary design and associated performance analysis have been published taking into account the end of Phase A design. This paper is focused on the performance assessment of the SWIM instrument based on the new developments which occur during Phase B. In addition, major reviews have been carried out on the performance analysis.

Latest advances of the swim instrument

The CFOSAT mission is an innovative spatial mission for oceanography: for the very first time, both wind and wave vectors will be measured at the global ocean surface. This paper presents the wave scatterometer, SWIM and its associated scientific performances.

Estimation of wave spectra with swim on cfosat - illustration on a real case

SWIM (Surface Wave Investigation and Monitoring) is a spaceborne radar pointing at nadir and small incidence angles, scanning in azimuth. It is designed for the measurement of directional ocean wave spectra and will be embarked on the CFOSAT (China France Oceanography SATellite) mission to be launched in 2014. The CFOSAT project is now in the C/D phase (manufacturing phase). Taking into account the very last definition of the instrument, we present here the expected performances for estimates of significant wave height and spectral parameters of long ocean waves. These performances have been obtained using numerical simulations taking into account instrument specifications and realistic sea surface conditions, in particular those corresponding to the Atlantic storm of November 2002, which caused the Prestige ship sinking and its terrible oil slick.

Distributed SAR for performance improvement

Using small satellites constellations is of growing interest, because of the ability to offer low cost space systems and to push away technology constraints. Here, two SAR formations are studied, one along-track and one across-track. The alongtrack formation aims at sampling the total antenna area to improve the merit factor at a given azimuth ambiguity rate. However, for standard waveforms, such a formation requires strong positioning constraints. The across-track formation aims at improving the range resolution by combining observations of a given swath with slightly different incidence angles. The limited positioning knowledge accuracy is compensated using an autofocus-like method.

Performance status of the wave scatterometer SWIM

SWIM is a Ku-band radar designed for wave directional spectrum estimation. This radar operates at six incidence angles (from 0° to 10°) with a complete azimuth scanning covering a swath of 180 km. The phase B (addressing preliminary design) of SWIM is currently under finalization. In [3,4], the preliminary design and associated performance analysis have been published taking into account the first results of Phase B design. This paper is focused on the last performance assessment of this phase B for all the measurements performed by the SWIM instrument.

The SWIM instrument, a wave scatterometer on CFOSAT mission

SWIM is part of the CFOSAT satellite mission payload. It is designed for the measurement of directional ocean wave spectra. It is a Ku-band real-aperture radar with 6 rotating fan-beams pointing near nadir. The main characteristics of the instrument, data, products are presented in this paper, as well as performances estimated from simulations.

CFOSAT: a new Chinese-French satellite for joint observations of ocean wind vector and directional spectra of ocean waves

CFOSAT (the China France Oceanography Satellite) is a joint mission from the Chinese and French Space Agencies, devoted to the observation ocean surface wind and waves so as to improve wind and wave forecast for marine meteorology, ocean dynamics modeling and prediction, climate variability knowledge, fundamental knowledge of surface processes. Currently under Phase D (manufacturing phase), the launch is now planned for mid-2018 the later. The CFOSAT will carry two payloads, both Ku-Band radar: the wave scatterometer (SWIM) and the wind scatterometer (SCAT). Both instruments are based on new concepts with respect to existing satellite-borne wind and wave sensors. Indeed, one of the originalities of CFOSAT is that it will provide simultaneously and in the same zone, the directional spectra of ocean waves and the wind vector. The concept used to measure the directional spectra of ocean waves has never been used from space until now: it is based on a near-nadir incidence pointing, rotating fan-beam radar, used in a real-aperture mode. In this paper we present the CFOSAT mission, its objectives and main characteristics. We then focus on the SWIM instrument, the expected geophysical products and performances. Finally, we present ongoing studies based on existing satellite data of directional spectra of ocean waves (Sentinel-1, ..) and carried out in preparation to CAL/VAL activities and to future data exploitation.

Innovative focal planes in submillimeter wave radiometers for atmospheric chemistry study and ice clouds observation

This paper summarizes a study done by the EADS ASTRIUM and founded by the CNES (French spatial agency) in the field of the innovative focal planes for sub-millimetre wave radiometers. The objectives are to improve performance of space sub-millimetre wave instruments for two main applications: atmospheric chemistry study and ice clouds and precipitations observations. The areas for improvement are focused on global instrument architecture and on some specific focal plane components such as dichroïc filters and mixers.

High resolution SAR micro-satellite based on passive reflectors

In a study proposed by CNES, EADS ASTRIUM has analysed the feasibility and the design of Synthetic Aperture Radars within the stringent envelope of micro satellites. The primary mission objective is high resolution (2 metres for -17 dB.m2/m2 sensitivity) for a 5 km swath width, in X band. Two options have been analysed for this study. The first one was based on a passive reflector. Platform agility is required to achieve steering of the SAR beams in elevation. The second option was based on an active reflector antenna designed by THALES which detailed performances are currently studied under a Research and Technology study with CNES. This paper presents the definition and performances of a micro-satellite based on passive reflector antenna. This satellite design is compatible of a launch of up to three satellites at a time on low earth orbit, and offers Stripmap and ScanSAR modes capabilities. Finally, this short overview identifies the technological developments required to achieve the SAR on a micro satellite concept in the mid term