Attenuation Commands

ATTENUATION

    Runs the Attenuation algorithm in OMA on the image in the buffer. Attenuation parameters are specified using ATTVALUES. The OMA buffer contains the corrected intensity image. Other intermediate images are in the temporary buffers:

    Temp[0]: The original image

    Temp[1]: The K_div image (laser fluence correction for divergence)

    Temp[2]: The local transmission fraction in a pixel due to extinction by particles, K_trans

    Temp[3]: The Ck image   

    Temp[4]: The mean Particle cross-section distribution

    Temp[5]: The number of standard particles in each pixel (N_p)

    Temp[6]: The extinction history at each point.


ATTPRINT

    Prints the Attenuation parameters to the OMA Command Window. Attenuation parameters are set with ATTVALUES.


ATTLSTHICKNESS <microns>

    If <microns> is specified on the command line then the Attenuation parameter for Laser Sheet Thickness is set to that value. If this command is called without arguments then the Attenuation dialog box is opened.


ATTDIAMETER <microns>   

    If <microns> is specified on the command line then the Attenuation parameter for Mean Particle Diameter is set to that value. If this command is called without arguments then the Attenuation dialog box is opened.


ATTIPRESOLUTION <microns>

    If <microns> is specified on the command line then the Attenuation parameter for In-Plane (CCD) Resolution is set to that value. If this command is called without arguments then the Attenuation dialog box is opened.


ATTSCALE <arg1>

    If <arg1> is specified on the command line then the Attenuation parameter for Ck scaling parameter is set to that value. If this command is called without arguments then the Attenuation dialog box is opened.


ATTVALUES <xloc> <yloc>

    Called with two arguments, this command sets the location of the  Virtual Origin for the Attenuation algorithm. The V.O must be off the  LHS of the image. If this is not the case, use FLIPH or ROTATE to make it so. The location of the V.O. is with respect the OMA origin, which is top-left corner of the image. If this command is called without arguments then the Attenuation dialog box is opened.


Attenuation Algorithm for Correcting the Mie-Scattering Signal in Collimated and Diverging Laser Sheets


Peter A. M . Kalt,    University of Adelaide, Australia.



An algorithm has been developed based on a simple ray-tracing model of light scatter that is able to adjust the local incident energy in any given pixel to account for laser sheet extinction by the presence of a dense second phase. The corrections work for cases where the seeding/2nd phase is so dense that the attenuation of the laser sheet is up to 40%. Furthermore, the corrections may be implemented for both collimated laser sheets and diverging laser sheets where additional corrections due to divergence need to be incorporated.


The corrections are implemented from the following published papers.


[1] Kalt, PAM, CH Birzer, & GJ Nathan, 'Corrections to facilitate planar imaging of particle concentration in particle-laden flows using Mie-scattering, Part 1: Collimated Laser Sheets', Applied Optics vol. 46, no. 23 (2007) pp. 5823-5834.

 

[2] Kalt, PAM, & GJ Nathan, 'Corrections to facilitate planar-imaging of particle concentration in particle-laden flow using Mie-scattering Part 2: Diverging Laser Sheets', Applied Optics vol. 46, no. 30, (2007) pp.7227-7236.

 


Keywords: Attenuation, Mie-scattering, Image Processing, Signal Trapping