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testbsc - testing Beam Smearing Correction algorithms


testbsc [parameter=value]


testbsc tests various Beam Smearing Correction schemes to a velocity field. Currently only Begeman’s correction is available, but expect to try out Leung’s (2018) method in an upcoming version.

Begeman’s (1989, Appendix B, eq.(8) ) recipe reads as follows:

     v = V + b^2/n * ( Vx*Nx + Vy*Ny + N * (Vxx + Vyy) / 2)
where the correction terms (beeg=t below) have single and double derivatives. (N,V) are the model density and velocity, (n,v) the observed/smoothed values, in this case with a circular gaussian beam with sigma (not FWHM) of b (see beam= below) points per pixel.


The following parameters are recognized in any order if the keyword is also given:
Input Model Density image file []
Input Model Velocity image file []
Input Observed (smoothed) Density image file []
Input Observed (smoothed) Velocity image file []
Output file, depends on the values of diff= and beeg=.
Override sigma_beam/pixel ratio. Recall FWHM = 2.355 * SIGMA. By default the beam size will be in the header.
Compute a Difference map? (as opposed to Computed Observed). Normally the Observed velocity field is computed from the Model and BSC terms, but turning this option on, the input Observed is subtracted from the computed Observed. [f]
Use the Begeman correction terms. This is of course the default, but by turning this off, a simple different of V-v (Model - Observed) can be computed, as can be seen in the EXAMPLES below. [t]

See Also

ccdmath(1NEMO) , rotcur(1NEMO) , image(5NEMO)


In this example we show off the interplay of the diff= and beeg= keywords:
  testbsc N.ccd V.ccd n.ccd v.ccd map1 diff=f beeg=f
  testbsc N.ccd V.ccd n.ccd v.ccd map2 diff=t beeg=f
  testbsc N.ccd V.ccd n.ccd v.ccd map3 diff=f beeg=t
  testbsc N.ccd V.ccd n.ccd v.ccd map4 diff=t beeg=t
Now the four maps will have the following meaning:
  map1:  V
  map2:  V - v
  map3:  V + bsc       (should be close to ’v’)
  map4:  V + bsc - v   (should be close to 0)




Peter Teuben

Update History

3-jul-2019    V0.4 Created/released    PJT

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