PHASE_SCREEN
Keywords: mis

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PHASE_SCREEN

            PHASE_SCREEN

        Warning:  This  tasks  is encapsulated into the "phaseeen.map" procedure
        which enables an easy viewing of the result.

        To compute the atmospheric phase errors, this tasks generate a 2-D phase
        screen on a grid with sufficient spatial resolution to sample the anten-
        na diameter (typically 4-m pixels for ALMA, and 4-m  pixels  for  Bure).
        The  phase  screen is generated in the Fourier plane with the constraint
        that its 2nd order structure function is a combination of 3  power  laws
        in  3  different  spatial ranges. The resulting phase screen is averaged
        over the effective dish diameter. Because of the size limitation imposed
        by  the FFT, very long phase screen are built as a linear combination of
        independently generated screens. This is correct since atmospheric path-
        length variations are completely uncorrelated at large distances.

        Dynamic  (anomalous)  refraction  is  directly proportional to the phase
        gradient. This tasks thus computes the phase gradient associated to  the
        phase  screen,  in  order to obtain a coherent derivation of the dynamic
        refraction term. As the phase screen, the  phase  gradient  is  averaged
        over the effective dish diameter.