ENVISAT/ASAR Dual Polarisation Case 6. ENVISAT/ASAR DUAL POLARISATION CASE 6.1 ASAR dual polarization data formats 6.1.1 Supported ASAR data formats 6.1.1.1 Alternating Polarization modes The ASAR instrument may be configured to acquire data according to one of the Alternating Polarization (AP) modes. Classical fully polarimetric SAR devices perform data acquisition with two emission and reception polarization channels. ASAR, instead, emits signals on a single polarization channel (H or V) while reception is performed on one or two orthogonal polarizations (H and/or V). The different possible configurations are summarized in the following figure. PP configuration Received polarizations Emitted polarizationH PP 1 V H H PP2 V V 1 ENVISAT/ASAR Dual Polarisation Case H H PP3 V V where PP stands for Partial Polarization or Partially Polarimetric. 6.1.1.2 Supported AP data formats Partial polarization data sets are delivered under different formats adapted to specific types of application. Among the different AP data formats, three are supported by PolSARpro and can be exploited to provide an interpretation of the polarimetric properties of scattering. Alternating Polarization mode Single-look complex (APS) data format Data type Sets of complex scattering coefficients corresponding to the selected PP configuration Geometry Slant Range Coverage 100 km along-track, 56 - 100 km across-track Pixel spacing Equal to Resolution : e.g 7.8m * 4m Alternating Polarization mode Precision (APP) image format Data type Images of real reflectivity corresponding to the selected PP configuration Geometry Ground Range Coverage 100 km along-track, 56 - 100 km across-track Pixel spacing 12.5 m * 12.5 m 2 ENVISAT/ASAR Dual Polarisation Case ASAR Alternating Polarization mode ellipsoid Geocoded (APG) image Data type Images of real reflectivity corresponding to the selected PP configuration Geometry Geocoded Ground Range Coverage 100 km * 100 km Pixel spacing 12.5 m * 12.5 m 6.1.2 Relation with fully polarimetric representations Fully polarimetric quantities are measured from two acquisitions performed with orthogonal polarization states (generally H and V) in order to form each pixel scattering matrix S The coherent scattering matrix modifies the polarization of an incident wave according to the following expression i s E S E = (1) The scattering matrix is built from two acquisitions as follows sv sh vv vh hv hh E E S S S S S = = with = = vh hh vv vh hv hh sh S S S S S S E 0 1 and = = vv hv vv vh hv hh sv S S S S S S E 1 0(2) where sh E and sv E correspond to the scene response to normalized incident horizontally and vertically polarized waves respectively. 6.1.2.1 APS format APS format images are composed of coherent scattering coefficients and my then be expressed directly from the expression given in (2) according to the selected PP configuration PP1 A pixel is represented by a Jones vectors formed with two of the scattering matrix coefficients = = vh hh vv vh hv hh PP S S S S S S E 0 1 1(3) PP2 A pixel is represented by a Jones vectors formed with two of the scattering matrix coefficients 3 ENVISAT/ASAR Dual Polarisation Case = = vv hv vv vh hv hh PP S S S S S S E 1 0 2(4) PP3 A pixel is represented by a two element complex vector formed with two of the scattering matrix coefficients = = vv hh vv vh hv hh PP S S S S S S E 1 0 0 1 3(5) One may note that, oppositely to the vector s E , the Jones vectors sh E and sv E are received in a polarization basis. It is then possible to represent sh E and sv E into any desired polarization basis using classical Special Unitary transformation matrices E U E ) , , ( = (6) Such a transformation may also be applied to s E in PP3 configuration, but without the physical interpretation associated to the formalism of changes of polarization basis. This might be particularly useful to perform a transformation similar to the one linking C and T matrices + = = hh vv vv hh s s S S S S E E 2 1 1 1 1 1 2 1(7) 6.1.2.2 APP and APG formats APP and APG format images are composed of intensities and my then be expressed from the square moduli of the Sinclair matrix elements, according to the selected PP configuration PP1 = 2 2 1 vh hh PP S S I (8) PP2 = 2 2 2 hv vv PP S S I (9) PP3 4 ENVISAT/ASAR Dual Polarisation Case = 2 2 3 vv hh PP S S I (10) One may note that APP and APG mode data do not exactly correspond to intensities derived from equivalent APS data, due to the slant range to ground range mapping transformation. 6.2 Speckle filtering 6.2.1 APP and APG format data filtering As it was seen in th