The WIVERN (WInd VElocity Radar Nephoscope) mission, now in Phase 0 of the ESA Earth Explorer program, promises to complement Doppler wind lidar by globally observing, for the first time, the vertical profiles of winds in cloudy areas. This work describes an initial assessment of the performances of the WIVERN conically scanning 94 GHz Doppler radar, the only payload of the mission. The analysis is based on an end-to-end simulator characterized by the following novel features tailored to the WIVERN radar: the conically scanning geometry, the inclusion of cross-polarization effects and the simulation of a radiometric mode, the applicability to global cloud model outputs via an orbital model, the incorporation of a mispointing model accounting for thermoelastic distortions, microvibrations, star-tracker uncertainties, etc., and the inclusion of the surface clutter. Some of the simulator capabilities are showcased for a case study involving a full rotational scan of the instrument. Preliminary findings show that mispointing errors associated with the antenna's azimuthal mispointing are expected to be lower than 0.3 m s−1 (and strongly dependent on the antenna's azimuthal scanning angle), wind shear and non-uniform beam-filling errors have generally negligible biases when full antenna revolutions are considered, non-uniform beam filling causes random errors strongly dependent on the antenna azimuthal scanning angle, but typically lower than 1 m s−1, and cross-talk effects are easily predictable so that areas affected by strong cross-talk noise can be flagged. Overall, the quality of the Doppler velocities appears to strongly depend on several factors, such as the strength of the cloud reflectivity, the antenna-pointing direction relative to the satellite motion, the presence of strong reflectivity and/or wind gradients, and the strength of the surface clutter. The end-to-end simulations suggest that total wind errors meet the mission requirements in a good portion of the clouds detected by the WIVERN radar. The simulator will be used for studying tradeoffs for the different WIVERN configurations under consideration during Phase 0 (e.g., different antenna sizes, pulse lengths, and antenna patterns). Thanks to its modular structure, the simulator can be easily adapted to different orbits, different scanning geometries, and different frequencies.

This paper presents the design of two spaceborne Doppler radar for 3D winds mapping inside cloud at 94 GHz : first one corresponds to radar with high quality of the retrieved 3D components of the wind field without scanning capability (fixed antenna with two reflectors) ; second one corresponds to scanning Doppler radar with swath width capability thanks to conical scanning antenna (rotation of all the instrument).

EarthCARE, a candidate Earth Explorer Core mission of ESA, aims to improve our knowledge of the impact of clouds and aerosols on the Earth's radiative budget. The satellite will carry two nadir sounding active instruments: a Cloud Profiling Radar (CPR) and a backscatter lidar. In addition, a multispectral cloud-imager, a Fourier transform spectrometer and a broadband radiometer complement the payload. The objective of the present study was to optimise the parameters of the CPR for retrieving accurate radiative profiles for highly layered cloud structures. Realistic cloud scenarios taken from ground-based experiments have been used for simulating the radar response to cloud layers. A radar simulator was developed initially for one-dimensional simulation of the radar echos. The cloud microphysical properties were retrieved using a model as a function of the reflectivity factor and temperature, based on information from in-situ measurements. An extensive parametric analysis was performed for various vertical resolutions and sensitivities which have direct impacts on the radar design and necessary resources on-board the satellite. The analysis demonstrated that the proposed radar characteristics will meet the top-of-the-atinosphere radiative flux density estimation accuracy of 10 W/m(2) as recommended by WCRP.

The goal of the NASA/NASDA GLobal Precipitation Mission (GPM) is to provide frequent global rainfall observations, using a satellite cluster based on a 'core' platform and a number of 'drone' satellites large enough to provide a repeat observation cycle of about 3 hours. ESA has proposed a contribution to GPM in the form of a drone satellite, with a scheduled launch foreseen by 2007. The 'E-GPM' Drone satellite is currently studied within the frame of the ESA Earth Opporutnity Missions Program, and involves many innovative aspects, among which are: (i) a 5 band, 13 channel conical scan radiometer, operating at 18.7, 23.8, 36.5, 89 and 157 GHz for rainfall water content and ice content estimation of the atmosphere; (ii) a Nadir pointing Precipitation Radar embarked in order to enhance the overall accuracy of precipitation estimates, operating at 35.6 GHz. The radar will provide high quality estimates of vertical profile precipitation; (iii) an implementation on a small satellite based on Alcatel's multi-mission PROTEUS Platform, already flying with the JASON altimetry satellite launched in 2001. This presentation summarizes the definition of the E-GPM satellite, from the scientific requirements to the satellite and instrument design, performance, and budget.

CNES is studying in partnership with scientific laboratories and industry the feasibility of a high-resolution ocean topography mission based upon a new class of wide-band, Ka-band altimeter. This paper presents the altimeter/radiometer design and performance as well as results from the breadboard activities. The accommodation on a microsatellite is also shown.

The paper presents the current status of the AltiKa3 mission and performance analysis. It mainly focuses on satellite and instrumental studies as phase B of the payload is currently going on. Apart from the combined altimeter and radiometer, this payload also consists of a DORIS plus LRA (Laser Retroreflector Array) orbitography system that will ensure a high level of accuracy in terms of orbitography and that will ease the connection of historical altimetry series within a common well surveyed geodetic reference frame. Feasibility of accommodating such a payload aboard a microsatellite platform has been shown and will be shortly introduced in the paper.

Ka-band altimetry has been proposed by Verron et al. (2001) to complement the altimetry reference missions of the Jason class. The goal of this paper is to provide information on the so-called “AltiKa” proposal in terms of science requirements, responsive technical specifications, and a priori performances. Besides the fact that the feasibility of embarking an AltiKa payload on a microsatellite has already been assessed, there is also the information that a small launcher may have the capability of launching several microsatellites simultaneously (up to three) in a number of configurations that may be adapted to the space time requirements of high resolution altimetry.

In preparation of the post ENVISAT and Jason-2 altimetry missions, Alcatel has completed a phase A study for CNES on a new class of altimeter. A major objective is to propose a combined altimeter and radiometer at minimum cost, size and power consumption compatible with a micro satellite (<100 kg class). The micro-satellite(s) would be used to improve the spatial/temporal sampling of the ocean which is not sufficient for current and future oceanographic missions. The Ka-band (35 GHz) is more interesting than the Ku-band for the altimeter since it improves the link budget and allows larger bandwidth (500 MHz) and pulse repetition frequency (4 kHz). From the scientific point of view, Ka-band altimeter data would give access to a different part of the sea surface roughness spectrum and thus would complement the C+Ku measurements available from other altimeters. The microwave radiometer, used for wet path delay correction, is a dual-frequency instrument (23.8 & 36.8 GHz). The proposed architecture for the Ka-band altimeter is based on the classical deramp technique for pulse compression and it takes benefits of Alcatel and CNES experience from the realisations of Poseidon 1 & 2. The radiometer is of the total power type and is based on direct detection. The altimeter and the radiometer share the same antenna. In parallel of the phase A, breadboarding activities have been started under development in Alcatel on CNES contracts: the transmit power module (2W SSPA) composed of a medium level amplifier, a divider, two high power amplifiers and a combiner. - the signal generator unit (500 MHz bandwidth chirp)

In preparation of the post ENVISAT and Jason-2 altimetry missions, Alcatel is currently studying in phase A for CNES a new class of altimeter. A major objective is to propose a combined altimeter and radiometer at minimum cost, size and power consumption compatible with a micro-satellite (<100 kg class). The micro-satellite(s) would be used to improve the spatial/temporal sampling of the ocean which is not sufficient for current and future oceanographic missions. For a given antenna size, the Ka band (35 GHz) is more interesting than the Ku band for the altimeter since it improves the link budget and allows larger bandwidth (500 MHz). From the scientific point of view, Ka-band altimeter data would give access to a different part of sea surface roughness spectrum and thus would complement the C+Ku measurements available from other altimeters. The microwave radiometer, used for wet path delay correction, is a dual-frequency instrument (23.8 and 36.8 GHz). This paper presents the altimeter and radiometer required performances and the overall instruments design. Preliminary results from the breadboarding activities are also reported.

In preparation of the post ENVISAT and Jason-2 altimetry missions, CNES and Alcatel are currently investigating the feasibility of a new class of altimeter. A major objective is to propose an instrument at a minimum cost and size which can be accommodated equally on micro satellites (~50 kg) and on larger satellites such as Jason. The micro-satellite(s) would be used to improve the spatial/temporal sampling of the ocean which is not sufficient for current and future oceanographic missions. Although the C+Ku-band Poseidon-2 altimeter to be flown on Jason-1 has a moderate mass and power consumption, it is not directly compatible with a micro-satellite limited resources. For a given antenna size, limited to about 60 cm for a micro satellite, the Ka band (~35 GHz) is a more interesting candidate than the Ku band in order to improve the link budget. From the scientific point of view, Ka-altimeter data would give access to a different part of the sea surface roughness spectrum and thus would complement the C+Ku measurements available from other altimeters on board the same or a different platform. This paper presents the altimeter concept and the required performances. The proposed concept is a Ka-band altimeter with a high vertical accuracy (0.3 m) based on the classical deramp technique for pulse compression. A particular attention is given to the analysis of the propagation losses due to atmospheric gazes, clouds and rain. The preliminary design of the altimeter is described and mass and power consumption budgets are given. A preliminary assessment of the elevation accuracy over ocean is discussed