Gamma DIFF: Reference Manual

quad_fit

ANSI-C program: quad_fit.c

NAME
quad_fit - Estimate 2-D quadratic polynomial model phase function from an unwrapped differential interferogram

SYNOPSIS
quad_fit <unw> <DIFF_par> [dr] [daz] [mask] [plot_data] [model]

<unw>	(input) unwrapped differential interferogram (float)
<DIFF_par>	(input/output) differential interferogram parameters
[dr]	(input) range sampling increment (enter - for default: 4)
[daz]	(input) azimuth sampling increment (enter - for default: 4)
[mask]	raster mask file (Sun raster or BMP), 0 valued pixels are excluded for fit (enter - for none)
[plot_data]	(output) plot data file (enter - for none)
[model]	polynomial phase model: 0: a0 + a2x + a1y + a3xy + a4x^2 + a5y^2 (default) 1: a0 + a4x^2 + a5y^2 2: a0 + a1y + a2x + a3xy 3: a0 + a1y + a2x 4: a0 + a2x + a4x^2 5: a0 + a2*x

EXAMPLE
quad_fit i1.unw i1_i2.diff_par 32 32 i1.unw.ovr.ras i1.quad_fit 0

estimate the phase model coefficients using all 6 terms in the polynomial

DESCRIPTION
quad_fit reads an unwrapped phase image and determines the best 2-D quadratic phase model using the least-squares error criterion. The estimated model parameters are written to the DIFF_par parameter file. The subtraction of the phase mode using the fit parameters is done using quad_sub.

The user can specify a mask file in SUN raster or BMP format to exclude specific regions during the estimation of the fit parameters. A raster image of the scene can be edited using the any standard image manipulation program such as GIMP (www.gimp.org). Select black (value = 0) as the region fill color for regions that should be excluded from contributing to the model fit.
quad_fit is generally used to remove a residual phase ramp from a differential interferogram. If there is a range dependent differential phase ramp, such as occurs in GPRI data, then models 4 and 5 are applicable.

model 0:  a0  +  a1*Y   + a2*x  
  +  a3*x*y  +  a4*x^2  +  a5 *y^2

  model 1:  a0  +  a4*x^2 + a5*y^2    
       a1 = 0.0, a2 = 0.0, a3 = 0.0  

  model 2:  a0  +  a1*y   + a2*x + a3*x*y 
   a4 = 0.0, a5 = 0.0

model 3:  a0  +  a1*y   + a2*x  
           a3 = 0.0, a4 = 0.0, a5 =
  0.0

  model 4:  a0  +  a2*x   +
  a4*x^2          a1 =
  0.0, a3 = 0.0, a5 = 0.0

  model 5:  a0  + 
  a2*x

                    
  a1 = 0.0, a3 = 0.0, a4 = 0.0, a5 = 0.0

The 6 output model parameters are stored in the DIFF_par parameter file.

Data written to an plot data file permits plotting the phase fit results at the points. Plotting the data can be performed using Gnuplot or other plotting program
The plot data file is a text file with 4 columns. The first column has the measured phases from the differential interferogram, the second column has the phase from evaluating the polynomial model, the third column has the range pixel numbers, and the forth column has the azimuth line number:

phase  model_phase  range_pixel
  azimuth_line

SEE ALSO
quad_sub, typedef_ISP.h, typedef_DIFF.h.