Presentation made by Prof. Adriano Camps (Universitat Politècnica de Catalunya) at ICMARS 2010 (India, 16-December-2010) on the MIRAS instrument aboard ESA's SMOS mission.

1. SMOS: Principles of Operation of the MIRAS instrument Prof. A. Camps Dept. de Teoria del Senyal i Comunicacions Universitat Politècnica de Catalunya and IEEC/CRAE-UPC E-mail: [email_address] … on behalf of many people (many anonymous) that kept this dream alive and make it happen devoted to Prof. Cal Swift… the pioneer

4. 2.1. Synthetic Aperture Radiometers using Fourier Synthesis: VLA, New Mexico, Socorro ESTAR (1 D Aperture Synthesis)  NASA Radioastronomy Earth Observation (concept proposed in 1983 by LeVine & Good) MIRAS (2 D Aperture Synthesis)  ESA 2. Imaging in Synthetic Aperture Radiometers

6. . After the successful results of ESTAR radiometer (1988), the European Space Agency starts in 1993 the first feasibility studies to apply synthetic aperture microwave radiometry in two dimensions: . MIRAS concept is born : Microwave Imaging Radiometer by Aperture Synthesis . First studies ( 1993-95 ): led by Matra Marconi Space as the prime contractor . 1995 Soil Moisture and Ocean Salinity Workshop (ESTEC, the Netherlands) Aperture Synthesis Microwave Radiometry is the only technique capable of measuring soil moisture and ocean salinity with enough accuracy and spatial resolution. SSS image derived from the ’“Electronically Steered Thinned Array Radiometer (ESTAR)”. Error = 0.3 psu (D. M. LeVine et al., NASA Goddard).

7. Antenna Positions Spatial frequencies ( u , v ) u v Periodic extension 21 elements + 2 redundant elements/arm Antenna spacing d = 0.875  Hexagonal grid in ( u , v ) plane Nyquist criterion: d< Overlapping of 1 alias Alias-free Field Of View (AF-FOV) Overlapping of 2 aliases 2.2. Image Reconstruction Algorithms: Ideal Case

12. MIRAS consists of a central structure (hub) with 15 elements, and 3 deployable arms, each one having 3 segments with 6 antennas each. [credits EADS-CASA]

14. LICEF: the LIght and Cost Effective Front-end [credits MIER Comunicaciones]

16. SMOS NIR: T NA   + T A = T U T NA + T A = T REF + T NR  Normal mode of operation: Calibrating internal noise source mode: known (cold sky) ? [Colliander et al., 2005] [credits HUT]

17. 4.4. DIgital COrrelator System (DICOS) Digital signals from each LICEF are transmitted to DICOS to compute the complex cross-correlations of all signal pairs. 1 bit ADC (comparator) in each LICEF Correlator = = NOT-XOR + up-counter

19. CCU: the Correlator and Control Unit [credits EADS-CASA]

22. OVERALL SEGMENT ARCHITECTURE [credits EADS-CASA]

23. [credits EADS-CASA] 6 LICEF / segment

24. [credits EADS-CASA] MOHA

25. [credits EADS-CASA] CAS

26. [credits EADS-CASA] CMN

29. 5.2. Radiometric Performance: definition of terms Radiometric accuracy (pixel bias) Spatial standard deviation Radiometric bias (scene bias) Spatial average Systematic errors (instrumental errors) Radiometric sensitivity Temporal standard deviation 0 Zero Temporal average Random errors (noise due to finite integration time) Error maps:  T B (  ,  ,t)

30. Cut for   =0 Dashed lines. Theoretical formula: Radiometric Sensitivity over ocean [credits I. Corbella]

31. Accuracy < 0.5 K Moon Galaxy (yellowish) Galaxy Alias Galactic radio-source (TBC) Cosmic Background Radiation at 3.3 K Sun Alias [credits DEIMOS]   Scene Bias < 0.1 K

37. MIRAS Internal calibration Calibrated visibility: (*) (*) PMS gain PMS offset Correlation amplitude

38. Formulation of the Problem: Instrument Equation After Internal Calibration [credits I. Corbella] To be corrected using the Flat Target Response

41. 5.4. Imaging Modes: Dual-polarization and full-polarimetric Dual-polarization radiometer: MIRAS has dual-pol antennas, but only one receiver  polarizations have to be measured sequentially, with an integration time of 1.2 s each [credits M. Martin-Neira]

42. Full-polarimetric mode: (selected as operational mode for SMOS) [credits M. Martin-Neira]

47. Thanks for your attention!