Microwave Interferometric Radiometer Research Articles

Helsinki University of Technology L-Band Airborne Synthetic Aperture Radiometer

An airborne L-band 2-D interferometric radiometer for Soil Moisture and Ocean Salinity (SMOS) measurements has been developed in the Helsinki University of Technology, Laboratory of Space Technology. The first successful flights were conducted in spring 2006. In this paper, the technical description, calibration, and image reconstruction philosophy and the latest results from the use of the instrument are discussed. One of the key goals of the instrument design has been to acquire L-band interferometric data to support the European Space Agency's SMOS mission that employs the L-band interferometric radiometer Microwave Interferometric Radiometer using Aperture Synthesis. Both instruments use aperture synthesis technology for the target image reconstruction in two dimensions.

The determination of surface salinity with the European SMOS space mission

The European Space Agency Soil Moisture and Ocean Salinity (SMOS) mission aims at obtaining global maps of soil moisture and sea surface salinity from space for large-scale and climatic studies. It uses an L-band (1400-1427 MHz) Microwave Interferometric Radiometer by Aperture Synthesis to measure brightness temperature of the earth's surface at horizontal and vertical polarizations (T/sub h/ and T/sub v/). These two parameters will be used together to retrieve the geophysical parameters. The retrieval of salinity is a complex process that requires the knowledge of other environmental information and an accurate processing of the radiometer measurements. Here, we present recent results obtained from several studies and field experiments that were part of the SMOS mission, and highlight the issues still to be solved.

Consequences of surface heterogeneity for parameter retrieval from 1.4-GHz multiangle SMOS observations

The L-band (1.4 GHz) two-dimensional microwave interferometric radiometer, the payload of the Soil Moisture and Ocean Salinity (SMOS) mission, will observe elements of the Earth's surface simultaneously at multiple angles. Compared to single-angle observations, this multiangle observation technology is expected to significantly improve the capability of passive microwave remote sensing to retrieve soil moisture and vegetation properties from space. Although multiangle retrieval algorithms have been developed and successfully evaluated for homogeneous surfaces on the basis of simulation studies, the inherently large footprint of microwave observations from space has serious consequences for parameter retrieval from "real-world" inhomogeneous surfaces. At the spatial scale of SMOS (/spl sim/30 km for nadir observations), the Earth's surface is inhomogeneous almost by default. This aspect has not been fully accounted for yet. This study gives some insight into the consequences of vegetation spatial heterogeneity for the retrieval of "effective" surface parameters (soil moisture, canopy microwave transmissivity, and effective surface temperature) from inhomogeneous surfaces without prior knowledge of the within-pixel canopy heterogeneity.

Two-Dimensional Microwave Interferometer Retrieval Capabilities over Land Surfaces (SMOS Mission)

This paper discusses the potential of an L-band 2-D microwave interferometric radiometer for monitoring surface variables over land surfaces. The instrument is the payload of the Soil Moisture and Ocean Salinity (SMOS) Mission recently selected for phase A studies by the European Space Agency (ESA) as the second Earth Explorer Opportunity Mission. The L-band radiometer is based on an innovative two-dimensional aperture synthesis concept. This sensor has new and significant capabilities, especially in terms of multiangular viewing configurations. The main aspects of the retrieval capabilities of SMOS for monitoring soil moisture, vegetation biomass, and surface temperature are presented in this paper. The analysis is based on model inversion. The standard errors of estimate of the surface variables are computed for various configurations as a function of both the uncertainties associated with the space measurements and those associated with the ancillary information used in the retrievals. The potential of SMOS and the possibility to retrieve one, two, or three surface variables are investigated, depending on the view angle configuration. These questions are key issues to optimize the SMOS mission scenario, to meet both the scientific requirements and the technical constraints of the mission.