Gold presentation lastri

Gold presentation lastri

• 1.
  Data Processing Chainfor the ALISEO Instrument: from Slanted Interferograms to At-Sensor Radiance Spectra C. Lastri , A. Barducci, I. Pippi CNR – IFAC Sesto Fiorentino, ITALY IEEE GOLD REMOTE SENSING CONFERENCE 29-30 april 2010 Italian Naval Academy - Livorno
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  Contents The ALISEOimaging interferometer Theoretical aspects of imaging interferometry Data processing chain Experimental activities
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  The ALISEO instrument ALISEO Aerospace Leap-frog Imaging Stationary interferometer for Earth Observation 0.4-1.0 μm: VIS-NIR spectral range Equipped with 1024x1024 pixel detector ALISEO LABORATORY PROTOTYPE Optical layout of the Sagnac interferometer The two beams travel on opposite paths, and exhibit exactly  phase-delay (for a point source on the optical axis) due to a difference of reflections between the two rays. The Optical Phase Difference (OPD) linearly increases with the slope on the optical axis of the input ray. ALISEO has been selected by ASI as the main payload for the MIOSat mission
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  Imaging interferometer inSagnac triangular path configuration : every frame contains the scene superimposed on the stationary fringe pattern The interferogram of a given pixel is dispersed along a slant direction of the acquired data cube. Sensor OPD y x The “Leap-frog” operating mode OPD Frame sequence
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  Imaging Interferometry Mainadvantages: Absence of the entrance slit, a feature characteristic of the leap-frog technique Absence of any moving mechanism Choice of the spectral range and resolution by acting on the instrument sampling step and field-of-view. Principal critical points: Higher dynamic range of the sampled signal: a large information amount is held in the tiny ripple found in the interferogram wings Possible aliasing effects in both image (spatial domain) and interferogram (optical phase difference domain) Complex processing algorithms to retrieve the at-sensor spectral radiance: interferogram interpolation, vignetting compensation, apodization and Inverse Cosine Transform
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  Re-alignement is neededto obtain the interferogram relative to each pixel in the third axis: - retrieval of pixels trajectory along the frame sequence, - linear interpolation Frame sequence acquisition Dark signal acquisition Instrument spatial response acquisition - / Third axis of data cube re-alignement Vignetting remotion, DC-offset subtraction, apodization Adapted inverse Fourier transform: At-sensor radiance spectra Reflectance spectra Reference reflectance spectrum Parameters for OPD-axis calibration
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  In a Fourierimaging spectrometer, like ALISEO,the acquired physical information is the interferogram I(x). I(x) is the power of the interference pattern generated by the two rays at the position x in the focal plane of the instrument. S(k) is the spectrum of the pixel at location x, k=1/ λ : S(k) =∫ R+ I ( OPD ( x ))cos(2π kOPD ( x )) dOPD But: x=j-j 0 uncertainty in sampling the interferogram centre causes phase effect, OPD(x, λ )=(a+bn( λ )) x Solution: norm of Inverse Fourier Transform, calibration of OPD axis
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  635 nm 543nm OPD(x, λ )=w( λ ) x= (a+bn( λ )) x homogeneous and isotropic radiation distribution inside the instrument FOV. Nf = f(D, ω( λ )) Fitting procedure to obtain the correct value of OPD Five laser diode from 405 nm to 980 nm
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  At-sensor radiance spectra for a white and a blue tile. Retrieved spectrum for 635 nm laser diode
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  Retrieved reflectance spectrausing the described data processing procedure
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  Conclusions The operatingmode of the Aliseo imaging Interferometer has been presented. Advantages and disadvantages of this methodology have been assessed. Data processing chain has been described in detail, with particular emphasis on the modification to be made to Inverse Fourier Transform to obtain correct spectra retrieval. Experimental results shows good accordance with the theory.
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  For further information:http://www.ifac.cnr.it/corsari [email protected]