The MIRAS “all-licef” calibration mode

Since each of the individual elements of the MIRAS array is a total power radiometer, the zero-spacing visibility can be obtained by the average of all the corresponding antenna temperatures. The main advantage of this option with respect to using the NIR measurements is that amplitude calibration is more consistent between zero-spacing visibility and the rest. On the other hand, total power radiometers are not usually as stable as noise injection radiometers, so a small loose of stability could be expected. Preliminary results show, however, similar performance.Peer ReviewedPostprint (author's final draft

Optimum Redundant Array Configurations for Earth Observation Aperture Synthesis Microwave Radiometers

Two-dimensional aperture synthesis radiometry is the technology selected for ESA's SMOS mission to provide high resolution L-band radiometric imagery. The array topology is a Y-shaped structure. The position and number of redundant elements to minimise instrument degradation in case of element failure(s) are studied

Considerations about antenna pattern measurements of 2-D aperture synthesis radiometers

Accurate measurement of the antenna voltage patterns of large-aperture synthesis radiometers is critical in order to achieve good radiometric accuracy, and a very time consuming and expensive task. Measurement requirements and a tradeoff study relating radiometric accuracy degradation and number of elements to be measured are presented.Peer Reviewe

Treball: filtres analògics

2019/20202n quadrimestr

Polarimetric formulation of the visibility function equation including cross-polar antenna patterns

The European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) mission will be the first one using two-dimensional aperture synthesis radiometry for earth observation. This study presents the formulation that relates instrument observables and brightness temperature maps including cross-polar antenna voltage patterns, which may be also different from element to element. Finally, the radiometric accuracy degradation if cross-polar patterns are neglected in the image reconstruction is studied.Postprint (published version

The visibility function in interferometric aperture synthesis radiometry

The fundamental equation of interferometric aperture synthesis radiometry is revised to include full antenna pattern characterization and receivers' interaction. It is shown that the cross correlation between the output signals of a pair of receivers is a Fourier-like integral of the difference between the scene brightness temperature and the physical temperature of the receivers. The derivation is performed using a thermodynamic approach to account for the effects of mutual coupling between antenna elements. The analysis assumes that the receivers include ferrite isolators so that the noise wave passing from the receiver toward the antenna can be modeled as uncorrelated ambient noise. The effect of wide beamwidth antennas on the polarization basis of the retrieved brightness temperature is also discussed.Peer ReviewedPostprint (published version

The visibility function in interferometric aperture synthesis radiometry

The fundamental equation of interferometric aperture synthesis radiometry is revised to include full antenna pattern characterization and receivers' interaction. It is shown that the cross correlation between the output signals of a pair of receivers is a Fourier-like integral of the difference between the scene brightness temperature and the physical temperature of the receivers. The derivation is performed using a thermodynamic approach to account for the effects of mutual coupling between antenna elements. The analysis assumes that the receivers include ferrite isolators so that the noise wave passing from the receiver toward the antenna can be modeled as uncorrelated ambient noise. The effect of wide beamwidth antennas on the polarization basis of the retrieved brightness temperature is also discussed.Peer ReviewedPostprint (published version

Polarimetric Formulation Of The Visibility Function Equation Including Cross-Polar Antenna Patterns

The European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission will be the first one using two-dimensional aperture synthesis radiometry for Earth observation. This study presents the formulation that relates instrument observables and brightness temperature maps including cross-polar antenna voltage patterns, which may be also different from element to element. Finally, the radiometric accuracy degradation if cross-polar patterns are neglected in the image reconstruction is studied.Peer Reviewe

Sea state effect on the sea surface emissivity at L-band

In May 1999, the European Space Agency (ESA) selected the Earth Explorer Opportunity Soil Moisture and Ocean Salinity (SMOS) mission to obtain global and frequent soil moisture and ocean salinity maps. SMOS' single payload is the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L-band two-dimensional aperture synthesis radiometer with multiangular observation capabilities. At L-band, the brightness temperature sensitivity to the sea surface salinity (SSS) is low, approximately 0.5 K/psu at 20/spl deg/C, decreasing to 0.25 K/psu at 0/spl deg/C, comparable to that to the wind speed /spl sim/0.2 K/(m/s) at nadir. However, at a given time, the sea state does not depend only on local winds, but on the local wind history and the presence of waves traveling from far distances. The Wind and Salinity Experiment (WISE) 2000 and 2001 campaigns were sponsored by ESA to determine the impact of oceanographic and atmospheric variables on the L-band brightness temperature at vertical and horizontal polarizations. This paper presents the results of the analysis of three nonstationary sea state conditions: growing and decreasing sea, and the presence of swell. Measured sea surface spectra are compared with the theoretical ones, computed using the instantaneous wind speed. Differences can be minimized using an "effective wind speed" that makes the theoretical spectrum best match the measured one. The impact on the predicted brightness temperatures is then assessed using the small slope approximation/small perturbation method (SSA/SPM).Peer Reviewe

Correcting the FRA systematic error in VTEC maps from SMOS radiometric data

The Faraday rotation (FR) is a nonnegligible effect at the L-band, which is the operation frequency of the Soil Moisture and Ocean Salinity (SMOS) mission. This effect introduces a rotation in the electromagnetic field polarization when propagating through the ionosphere that must be compensated. Recently, a methodology was developed in order to retrieve the vertical total electron content (VTEC) from SMOS radiometric data with the aim to better correct the FR effect [1] . In that work, systematic patterns in the retrieved FR angle (FRA) were detected. In this article, these systematic patterns are characterized and corrected to improve the quality of the retrieved VTEC maps. These maps can be then reused in the SMOS level 2 processor for the correction of the FRA in the mission. The impact of using the SMOS-derived VTEC maps instead of the VTEC data from global positioning system (GPS) measurements on the ocean brightness temperatures (TB) measurement has also been analyzed. Results of this analysis show that the usage of those maps allows a significant enhancement in the quality of the TB, which will lead to an improvement on salinity retrievals.This work was supported in part by the European Space Agency, Soil Moisture and Ocean Salinity (SMOS) Expert Support Laboratories (ESL) for SMOS Level 1 and Level 2 over Land, Ocean and Ice Project under Grant RFQ/3-16138/19/I-BG; in part by the SMOS P7 under Contract DME CP12 no. 2015-005 (in joint with Deimos Engenharia, Portugal); in part by the Spanish Public Funds under Project TEC2017-88850-R and Project ESP2015-67549-C3-1-R through the Award “Unidad de Excelencia María de Maeztu” MDM-2016-0600, financed by the “Agencia Estatal de Investigación” (Spain); in part by the European Regional Development (ERDF); in part by the SMOS ESL for SMOS Level 1 and Level 2 over Land, Ocean and Ice Project under Grant ARG/003-032/0315/ICMCSIC; in part by the Spanish Research and Development Project INTERACT under Grant PID2020-114623RB-C31; and in part by the Spanish Government through the “Severo Ochoa Centre of Excellence” accreditation under Grant CEX2019-000928-S.Peer ReviewedPostprint (author's final draft