Tutorial HD-2: Calibration of Aperture Synthesis Radiometers: The MIRAS/SMOS Case

Presented by: Francesco Torres
Universitat Politècnica de Catalunya (UPC), Barcelona, Spain

SMOS is the acronym for the Soil Moisture and Ocean Salinity mission by the European Space Agency (ESA). Its single payload, the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS), was launched in November 2009. After a six months Commissioning Phase SMOS entered in operational mode in May 2010. Since then SMOS has been delivering a large amount of data to successfully produce the first relevant scientific results.

MIRAS requires a complex multi-step calibration procedure that was successfully tested both during pre-flight ground tests and Commissioning Phase activities. Additionally, an assessment of SMOS system performance in terms of short and long term stability, radiometric sensitivity and radiometric accuracy was also produced.

In this context, this tutorial is devoted to provide an overview of MIRAS calibration scheme by focusing on the rationale behind it. The course will be illustrated with relevant calibration and system performance plots from SMOS ground, commissioning and operational phase tests.

1.-Basic calibration concepts in aperture synthesis radiometry
2.-SMOS calibration rationale
   2.1.- Error model and error budget
3.- SMOS calibration modes classification
   3.1 Internal, external and ground calibration
4.- SMOS Calibration performance
   4.1 Residual calibration errors
   4.2 Calibration periodicity
5.- Brightness temperature retrievals
   5.1.- The "black box" approach
   5.2.- Radiometric sensitivity (pixel resolution)
   5.3.- Image distortion (pixel bias)

Francesco Torres was born in Ibiza, Spain, in 1962. He received the Ingeniero and Doctor Ingeniero degrees in telecommunication engineering from Universitat Politècnica de Catalunya (UPC), Barcelona, Spain, in 1988 and 1992, respectively. In 1988/89, under the Young Graduate Trainee scheme, he was a Research Assistant in the RF System Division at the European Space Agency (ESA) devoted to microwave device testing and modelling. In 1990 he joined the Antenna- Microwave-Radar group of UPC (now Remote Sensing Lab) where he currently holds a post as Full Professor. In 2005/06 he held a sabbatical year in the Microwave Systems Section of the Jet Propulsion Laboratory, Pasadena (CA), where he was involved in the GeoSTAR pilot project, a passive microwave interferometric geosounder demonstrator. He has been participating in a number of projects related to the SMOS mission by the European Space Agency since 1995. In 2007, he was a founder, as vice-president, of the Barcelona SMOS Expert Centre on Radiometric Calibration and Ocean Salinity and, currently, a member of its steering committee. Prof. Torres has authored or co-authored 52 papers and more than 100 participations in symposia related to the SMOS project.