Noel Suinot

Pulse compression with -65 dB sidelobe level for a spaceborne meteorological radar

With a breadboard activity, funded by ESA, ALCATEL ESPACE associated with four other European companies, demonstrates the feasibility of an all digital generation and compression system, operating in real time and meeting range sidelobes of the compressed pulse lower than -65 dB despite a low pulse bandwidth x pulse duration product. The chosen pulse compression technique consists in a frequency domain processing taking into account distortions due mainly to IF filters and non linear behavior of the HPA by the implementation of an automatic compensation procedure. After a complete description of the processing technique and the breadboard, this paper presents achieved performances in particular in presence of severe non linear distortions, sinusoidal amplitude and phase ripples.

CLIMACS: design of a high radiometric resolution SAR for land and sea ice applications

CLIMACS (Climate studies of Land surfaces and Ice using Microwave ACtive Sensing) is a synthetic aperture radar and is intended to be an element of a mission dedicated to global observation of land surfaces and ice. CLIMACS will provide relevant information for the studies related to climate change. In addition further expected applications are in the areas of disaster monitoring, ice reconnaissance and forest monitoring. In order to obtain valuable geophysical products for these applications, SAR images with modest spatial resolution but very high radiometric accuracy and high temporal sampling are desirable.

High performance digital pulse compression and generation

The European Space Agency (ESA) with an industrial team led by Alcatel Espace, has developed an all digital pulse generation and compression system for spaceborne rain radar application. The particular and most challenging constraint for this system was the capability to achieve a compressed pulse shape with very low range side-lobe level (<-60 dB). This objective was met and the results were published in a recent paper. More recently and as a continuation of this breadboarding activity, possible implementation in a real system was investigated taking into account different configurations, such as centralized amplification instruments or active array antennas. Performance improvement was also investigated and all factors limiting the actual performance were identified. Hardware integration using space qualified technologies was also assessed. Encouraged by the overall positive results of these activities, ESA is now planning to adapt this technique-or elements of this technique-to next generation spaceborne radars, such as topographic radar altimeters or future SARs.

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.

Very low side-lobe level pulse compression for rain radar

In a 2-year breadboarding activity funded by ESA, ALCATEL ESPACE lead the design, manufacturing, and test of an all digital pulse generation and compression sub-system for a rain radar, capable of real time processing. Despite the low time/bandwidth product waveforms (BT equals 270), the breadboard meets -60 dB side-lobe level which prevents contamination of the rain echo by the surface return. The compression principle is a frequent product of samples with a replica, the result of an automatic error compensation procedure that takes into account affects of distortions representative of the radar hardware (such as filters, phase/amplitude ripple, saturation effects of high power amplifier).

Design of MACSIM Cloud Radar for Earth observation Radiation Mission

Based upon results of a pre-phase A study, this paper presents the design of MACSIM Cloud Radar, which is one of the two active instruments of the Radiation Mission. This radar is a 95 or 79 GHz non-scanning instrument which collects echoes reflected by cloud particles. Its main measurement objectives are the altitudes of the cloud top and base with an accuracy of /spl plusmn/250 m and the ice/liquid water content as a function of the altitude of the different cloud layers. As a result of several trade-offs, a nadir looking radar transmitting unmodulated pulses of about 3 /spl mu/s is designed with a primary design objective of improving the sensitivity. In the last section, detection results for a set of typical clouds are summarised which demonstrates the feasibility of a light instrument in compliance with the user requirements.

Spaceborne rain radar mission and instrument analysis

The main objective of this paper, based upon a Pre-phase A study founded by ESA, is to define a preliminary design of a spaceborne rain radar from a precise review of user requirements proposed for climate research and operational meteorology purpose. A mission analysis defines the most suitable space segment, taking into account the instrument related aspects and mission constraints. As a result of several trade-off, the dual frequency rain radar design is described presenting in particular the way pulse compression is implemented to achieve a pulse response with a side-lobe level lower than -60 dB. Finally simulated performances shows this feasible spaceborne rain radar is in compliance with the user requirements.

CLIMACS prephase A: design of a medium-resolution SAR for land applications

This paper gives the current status of a medium resolution SAR definition prephase A study. The objective of such a novel SAR instrument is the global monitoring of land surfaces and polar region. The study was conducted in order to analyze all the possible concepts that could be compliant with this mission definition. Several trade-offs were performed in order to select an instrument concept compatible with large coverage, medium spatial resolution, good absolute radiometric accuracy, low mass and low power consumption.

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.

Rain radar instrument definition

As a result of a pre-phase a study, founded by ESA, this paper presents the definition of a spaceborne Rain Radar, candidate instrument for earth explorer precipitation mission. Based upon the description of user requirements for such a dedicated mission, a mission analysis defines the most suitable space segment. At system level, a parametric analysis compares pros and cons of instrument concepts associated with rain rate retrieval algorithms in order to select the most performing one. Several trade-off analysis at subsystem level leads then to the definition of the proposed design. In particular, as pulse compression is implemented in order to increase the radar sensitivity, the selected method to achieve a pulse response with a side-lobe level below--60 dB is presented. Antenna is another critical rain radar subsystem and several designs are com pared: direct radiating array, single or dual reflector illuminated by single or dual feed arrays. At least, feasibility of centralized amplification using TWTA is compared with criticality of Tx/Rx modules for distributed amplification. Mass and power budgets of the designed instrument are summarized as well as standard deviations and bias of simulated rain rate retrieval profiles. The feasibility of a compliant rain radar instrument is therefore demonstrated.