MIRAS: The SMOS Instrument

SMOS: Principles of Operation & First Results Prof. A. Camps Dept. de Teoria del Senyal i Comunicacions Universitat Politècnica de Catalunya and IEEC/CRAE-UPC E-mail: [email_address]

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Channel 2 Channel 1 = antenna spacing normalized to the wavelength Baseline ,[object Object],[object Object],Ideal case : - Identical antenna patterns - Negligible spatial decorrelation - No antenna positioning errors 2D Fourier Transform 1. Basic Principles H 1 ( f ) H 2 ( f ) b 1 ( t ) b 2 ( t ) Complex Correlator

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

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. 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).

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

In SMOS the “ alias-free FOV ” can be enlarged since part of the alias images are the “ cold ” sky (including the galaxy!)  T B image limited by Earth replicas Extension of Alias-Free FOV ,[object Object],[object Object],Iso-incidence angle contours

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],3. The SMOS Mission

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],SMOS Mission: SMOS Proba-2 Transformed SS-19 missile

4.1. Array topology ,[object Object],[object Object],[object Object],4. MIRAS instrument description

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]

4.2. Receivers’ architecture: ,[object Object],[object Object],H V C U SWITCH ISOL LNA BPF RFAMP MIXER IF FILTER ATTEN SLOPE CORR. IF AMPs 1BIT ADC IF FILTER ATTEN SLOPE CORR. IF AMPs 1BIT ADC SYNTH 1396 MHz PMS 1404-1423 MHz 8-27 MHz DI TI TQ DQ REF 55.84 MHz VCO MAIN PATH GAIN = 100 dB PMS PATH GAIN = 65 dB TRF ANTENNA I Q DICOS DICOS

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

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],1 st LICEF unit (V-pol) 2 nd LICEF unit (H-pol) Controller unit (switches, noise injection...) Correlated noise inputs (from Noise Distribution Network) allow phase/amplitude calibration of receivers as LICEFs & for 3 rd and 4 th Stokes parameters measurements [credits HUT]

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]

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

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

[object Object],[object Object],HUB ARMS

[object Object],[object Object],Centralized and distributed calibration These receivers belong to the NIR (□: H-channel) and do not form additional baselines Overlapping between elements (phase & amplitude tracking along the arms) Overlapping between elements (phase & amplitude tracking among arms) Centralized Calibration (separable & non-separable errors can be corrected) Distributed Calibration (only separable errors can be corrected)

OVERALL SEGMENT ARCHITECTURE [credits EADS-CASA]

[credits EADS-CASA] 6 LICEF / segment

[object Object],[object Object],5.1. Angular Resolution ,[object Object],[object Object],Equivalent Array Factor : same response as for an array of elements at ( u,v ) positions ( except for the |(.)| 2 ) 5. Instrument Performance

Response with rectangular window Response with Blackmann window (rotational symmetry) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

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)

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

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

[object Object],[object Object],Fresnel Incidence angle dependence Singularity in the transformation antenna to Earth reference frame (dual-pol mode) [credits I. Corbella]

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[object Object],[object Object],[object Object],T B imaging in a single snap-shot (1 integration time = 1.2 s / polarization in dual-pol) : Aperture Synthesis Radiometer: 2 step calibration T B imaging pixel by pixel through antenna scan: Real Aperture Radiometer: 1 step calibration ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],*** Image Reconstruction Algorithm *** *** Imaging by (e.g.) conical scan ***

Calibration Concept: Brief sketch ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

a. MIRAS internal calibration Instrumental errors correction: set of measurements and mathematical relations to remove instrumental errors INTERNAL INSTRUMENT CALIBRATION ,[object Object],[object Object],Error model

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

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

The Flat Target Response: ,[object Object],defining: Then the differential visibilities to be processed are:

[object Object],[object Object],[object Object],HERE IT GOES THE ANIMATION. T_X_skylook2.gif HERE IT GOES THE ANIMATION. T_Y_skylook2.gif External calibration [credits I. Corbella]

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]

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

6. Geolocalization: from director cosines grid to Earth reference frame grid ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],6. Geolocalization and Retrieval of Geophysical Parameters

L1 processor L2 processor L3 processor ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Auxiliary data Multi-angular emission models OS map (1 overpass) SM map (1 overpass) Spatio-temporal averaging Snap-shot 1 Snap-shot 2 Snap-shot 3 Snap-shot 4

[object Object],[object Object],(pin 5) (pin 3)

Sample results of the application of the downscaling algorithm to a SMOS image covering the Murrumbidgee catchment, South-Eastern Australia, on January 19, 2010 (6 am). First row: 40 km SMOS soil moisture [m 3 /m 3 ] over Murrumbidgee (left), and zoom into Yanco site (right). Second row: 1 km downscaled soil moisture [m 3 /m 3 ] over Murrumbidgee (left), and zoom into Yanco site (right ). Dots indicate the location of the soil moisture permanent stations within the Murrumbidgee catchment used for validation purposes with colors representing their measurement at the exact SMOS acquisition time (only within Yanco site). Empty areas in the images correspond to non-retrieved soil moisture or clouds masking MODIS Ts measurements. (a) 60 x 60 km Yanco site in the Murrumbidgee catchment, South-Eastern Australia, (b) 1 km MODIS NDVI, and (c) and LST [K] on January 19, 2010. ,[object Object],60 km (b) MODIS NDVI [m 3 /m 3 ] (c) MODIS LST [m 3 /m 3 ] (a) Murrumbidgee catchment 1 km downscaled SMOS soil moisture [m 3 /m 3 ] using MODIS VIS/IR data 40 km SMOS soil moisture [m 3 /m 3 ]

MIRAS: The SMOS Instrument

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