MIRAS end-to-end calibration: application to SMOS L1 processor

Abstract

Abstract-End-to-end calibration of the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS) radiometer refers to processing the measured raw data up to dual-polarization brightness temperature maps over the earth's surface, which is the level 1 product of the Soil Moisture and Ocean Salinity (SMOS) mission. The process starts with a self-correction of comparators offset and quadrature error and is followed by the calibration procedure itself. This one is based on periodically injecting correlated and uncorrelated noise to all receivers in order to measure their relevant parameters, which are then used to correct the raw data. This can deal with most of the errors associated with the receivers but does not correct for antenna errors, which must be included in the image reconstruction algorithm. Relative S-parameters of the noise injection network and of the input switch are needed as additional data, whereas the whole process is independent of the exact value of the noise source power and of the distribution network physical temperature. On the other hand, the approach relies on having at least one very well-calibrated reference receiver, which is implemented as a noise injection radiometer. The result is the calibrated visibility function, which is inverted by the image reconstruction algorithm to get the brightness temperature as a function of the director cosines at the antenna reference plane. The final step is a coordinate rotation to obtain the horizontal and vertical brightness temperature maps over the earth. The procedures presented are validated using a complete SMOS simulator previously developed by the authors.

Denormalization of visibilities for in-orbit calibration of interferometric radiometers

“…Finally, the PMS gain is translated to the antenna plane as where S LAk , S LCk are the switch S-parameters and η Ak are the antenna losses. PMS k offset, which exclusively depends on PMS k linearity, is retrieved by the four-point method [4] …”

“…The computation of normalized correlations M kj and the fringe wash term G kj is thoroughly detailed in [4]. Extensive experimental results to validate the calibration approach can be found in [5].…”

2000 days of SMOS at the Barcelona Expert Centre: a tribute to the work of Jordi Font

“…However, the receivers of the instrument show some orbital and seasonal drifts, as revealed by the analysis of brightness temperature stability over a full year cycle . The consistency of the amplitude calibration is a crucial issue in an interferometric radiometer such as MIRAS, since it has a major impact on the sensor stability (Torres et al 1996, Corbella et al 2005. Therefore, these drifts need to be compensated.…”

Review of the CALIMAS Team Contributions to European Space Agency’s Soil Moisture and Ocean Salinity Mission Calibration and Validation

“…The MIRAS Testing Software (MTS) was developed by the UPC to process SMOS raw data from level 0 to level 1c and obtain geo-located brightness temperatures [15], applying the calibration procedures detailed in [16], and a number of image reconstruction algorithms. MTS has been extensively used during the on-ground characterization of the instrument to assess the MIRAS instrument performance.…”