The Fine Resolution Explorer for Salinity, Carbon and Hydrology (FRESCH) is presented. The science case and the mission objectives are discussed before presenting the mission concept. FRESCH is an L-band antenna array operated in beamforming mode providing data at a spatial resolution of 10-15 km to study the biogeochemical and physical phenomena taking place at the interfaces of ocean, land and ice. FRESCH has been submitted to the European Space Agency Earth Explorer 12 program.

This paper reports on the main results of SMOS-HR instrument technical study, a new interferometric radiometer dedicated to Soil Moisture and Ocean Salinity measurement from space. The instrument aims at providing enhanced spatial resolution with respect to SMOS and integrating robust RFI (RF Interference) mitigation technique. The instrument key performance requirements and the architecture features and trade-offs are exposed in this paper.

Recent applications of passive L-band observations from space are summarized for ocean, land surface and cryosphere applications. The main limitation of the measurements performed by the current generation of sensors is the spatial resolution. The need of a mission ensuring the continuation of L-band measurements from space with high spatial resolution (10-15 km) is discussed.

Digital Beam Forming (DBF) and Synthetic Aperture Inter-ferometry (SAI) are signal processing techniques that mixes the signals collected by an antenna array to produce high resolution images. This study aims at comparing these two approaches with the aid of simulations conducted at microwaves frequencies within the frame of the Soil Moisture and Ocean Salinity (SMOS) mission which is providing for more than a decade systematic passive L-band measurements from space. Although the two techniques are using the same signals and sharing the same goal, there are few differences that deserve attention. This is the case of the reconstruction floor error whose level and angular signature are significantly lower with the DBF paradigm than with the SAI one.

International audience

International audience

The Soil Moisture and Ocean Salinity (SMOS) satellite has provided, for the very first time, systematic passive L-band (1420 - 1427 MHz) measurements from space with a spatial resolution of ~40 Km. Preliminary results of studies conducted within the frame of a High Resolution (HR) follow-on mission are presented. The SMOS-HR project has undergone a Phase 0 study by the French space agency. The aim of this contribution is to improve the spatial resolution capabilities of SMOS-HR from ~10 Km to ~4 Km with the aid of a swarm of nano-satellites orbiting close to the connected array selected for SMOS-HR. After SMOS and SMOS-HR, this third generation named SMOS-NEXT will be the very first one to perform aperture synthesis from space with both connected and unconnected interferometric measurements.

The SMOS mission, launched in 2009, has been followed by Aquarius and SMAP, but follow-on missions are still in the preliminary phases. One of the main expected improvements is on the spatial resolution, for which a 10-fold increase is needed. Regardless of the choice on acquisition principle (real aperture or interferometry) such a massive improvement cannot be addressed with current technology. But interferometry has an advantage here in the sense that it can be distributed over multiple satellites. The mission described in this paper is the first step towards a complete system to satisfy these challenging requirements. Such a massive improvement cannot be addressed with current technology and requires a major revisit of the acquisition of interferometric measurements. Of course, technological advances targeted by this mission concept is of far wider interest than L-band interferometry. The mission described in this paper is the first step towards a complete system to satisfy these challenging requirements.

The Soil Moisture and Ocean Salinity (SMOS) satellite is performing systematic L-band observations since 2009, allowing a large number of science and operational applications. Several recent studies have shown the need of the continuity of L-band observations, in particular with an increased angular resolution. In this contribution, two instrumental concepts are presented to reach native resolutions of 5–10 km. In addition, using airborne data, it is also shown that the accuracy of downscaling coarser resolution L-band data to 5–10 km using a high resolution auxiliary data set, is significantly lower than that of native high resolution observations.