Selecting an optimal configuration for the Soil Moisture and Ocean Salinity mission

Abstract

The Soil Moisture and Ocean Salinity (SMOS) mission is aimed at monitoring, globally, surface soil moisture and sea surface salinity from radiometric L‐band observations. The SMOS radiometer relies upon a two‐dimensional (2‐D) synthetic aperture concept in order to achieve satisfactory spatial resolution performances for a minimal cost in terms of payload mass and volume. Counterparts of this advantage are reduced radiometric sensitivity and increased complexity. The performances expected from SMOS, in terms of measurement accuracy, spatial resolution, and revisit time, depend on many parameters, among which several are crucial for assessing the payload and mission configurations. Most prominent among those configuration parameters are the flight altitude, the length of the interferometer arms, the spacing between radiating elements, and the tilt angle of the antenna plane. Their selection has to be optimized, so as to satisfy both scientific requirements and main technical constraints. This paper describes the way the optimization was carried out during the SMOS phase A. After assessing the main drivers on instrument configuration from the science requirements, the goal was to find an optimal trade‐off, minimizing technical challenges while fulfilling the science objectives. It was found that, even though salinity retrievals are the most challenging, soil moisture retrievals were the most demanding in terms of mission definition and that a configuration exists to satisfy the required retrieval accuracies. The obtained configuration was then checked against ocean salinity retrievals and found satisfactory.

Improved Image Reconstruction Algorithms for Aperture Synthesis Radiometers

“…• C, and 4 m/s, although their choice is not critical since the brightness temperature of the sea changes very little with respect to them, and in addition, the variations of T B over land are much larger) and a constant T B over land and over the iced sea [to be determined, see (8)] that will be subtracted from the calibrated visibilities prior to inversion.…”

“…However, in MIRAS, after an optimization process of the swath width, the revisit time, the angular resolution, and the range of incidence angles over the Earth that are imaged, it was decided first to increase even more the antenna spacing from d = λ 0 / √ 3 to d = 0.89λ 0 , and it was modified later to d = 0.875λ 0 , which is the current value (Fig. 2) [8].…”

About the effects of instrument errors in interferometric radiometry

“…[48] Finally, a rigorous assessment will have to reproduce the aggregation of individual retrievals, for which brightness temperature data are selected along dwell lines within the geographical FOV [Waldteufel et al, 2003]. All these steps need further developments.…”

“…While random salinity uncertainties, mostly due to radiometric sensitivity, are quite large when considering a single measurement, it is foreseen that independent retrieved estimates will be averaged over a sizable space/time domain: e.g., 200 Â 200 km 2 , 10 days, according to Global Ocean Data Assimilation Experiment (GODAE) requirements. This should bring this type of error down, enabling to achieve retrieval uncertainties better than 0.1 on the Practical Salinity Scale (PSS) [Waldteufel et al, 2003].…”

Preface to special section: Remote Sensing of the Earth's Environment by Microwave Radiometers and Radar

“…Rotbøll et al [2003] describe a fully polarimetric radiometer of the correlation type intended for L-band airborne measurements of polarimetric sea signatures. Waldteufel et al [2003] describe the accuracy and resolution of a two-dimensional (2-D) synthetic aperture radiometer designed for global monitoring of soil moisture and salinity. Tanner and Riley [2003] describe the design of two new high-stability microwave water vapor radiometers along with a performance evaluation.…”