GAMMA Questions

I was trying to find out how to get sigma nought backscatter from TSX intensity image. It implies radiometric calibration and local incidence angle accounting. I found a document Radiometric Calibration of TerraSAR-X Data (attached), there we find the formula for sigma nought calculation on the page 4. In GAMMA manual it states that TSX data are already relatively calibrated , and the absolute calibration is done while producing .slc.par file. However, I'm not sure if it takes the varying incidence angle (from near to far range) into account. Assuming that my intensity values are already sigma nought , I apply 10*log10 and get values in range from 15.8 to 78.5 dB what does not look like true.
There is a GAMMA command radcal_MLI for manual calibration of intensity image.
radcal_MLI <MLI> <MLI_PAR> <OFF_PAR> <CMLI> [antenna] [rloss_flag] [ant_flag] [refarea_flag] [sc_dB] [K_dB] [pix_area]

<MLI> (input) MLI (float)
<MLI_PAR> (input) SLC parameter file of input MLI image
<OFF_PAR> (input) ISP offset/interferogram processing parameter file (or - for image in SLC/MLI geometry)
<CMLI> (output) radiometrically calibrated output MLI (float format)
[antenna] 1-way antenna gain pattern file or - (if not provided)
[rloss_flag] range spreading loss correction (default=0: no correction, 1: r^3 correction, -1: undo r^3 correction, 2: r^4 correction, -2: undo r^4 correction)
(r^3 correction is used except for ASAR APS mode data where r^4 correction is used)
[ant_flag] antenna pattern flag correction (default=0: no correction, 1: correction, -1: undo correction)
[refarea_flag] normalization reference area correction (default=0: no correction, 1: correction to sigma0, 2: correction to gamma0, -1: undo 1, -2: undo 2)
[sc_dB] scale factor in dB (default=0.0, ESA published ERS1 K_dB update=-0.39, recommended for the upscaling scomplex output format: 60.0 dB)
[K_dB] Calibration factor in dB (default: -(value from SLC_PAR) )
[pix_area] ellipsoid-based ground range sigma/gamma nought pixel reference area depending on refarea_flag. (1 or -1: sigma nought ref. area, 2 or -2: gamma nought ref. area; float format)

I use the following parameters:
radcal_MLI $1.mli $1.mli.par - $1.cmli_sigma - - - 1 - - $1.pix_area_sigma

this is my output:

• Radiometric calibration for multi-look intensity (MLI) data ***
• Copyright 2013, Gamma Remote Sensing, v1.9 2-May-2013 uw/clw/of ***
  WARNING: Sensor is not ERS1, ERS2, JERS, ASAR: TSX-1
  SAR sensor (from ISP SLC parameter file): TSX-1
  Sine of reference incidence angle: 1.0000
  reference boresight look angle (deg): 0.0000
  reference slant range (m): 519608.9373
  Antenna diagram correction not applied
  Range spreading loss correction not applied
  Normalization reference area correction applied
  Normalization type: sigma0
  samples per input image line: 2580
  number of input image lines: 7839
  azimuth angle: 90.0000 (right looking)
  deskewed (zero-Doppler) geometry
  reference look_angle : 0.0000 degrees
  reference slant range: 519608.9373 m
  reference range pixel number: -21331

calibration constant [dB]: -49.1879
indicated scale factor [dB]: 0.0000

pixel     range  look_ang   inc_ang     rloss   antgain   refarea  pow_fact
    number       [m]     [deg]     [deg]      [dB]      [dB]      [dB]      [dB]
         0  597203.1    28.283    30.833     0.000     0.000    -2.903   -52.091
       100  597566.9    28.341    30.898     0.000     0.000    -2.894   -52.082
       200  597930.6    28.400    30.963     0.000     0.000    -2.886   -52.074
       300  598294.4    28.458    31.027     0.000     0.000    -2.878   -52.066
       400  598658.2    28.515    31.091     0.000     0.000    -2.870   -52.058
       500  599021.9    28.573    31.155     0.000     0.000    -2.862   -52.050
       600  599385.7    28.630    31.219     0.000     0.000    -2.854   -52.042
       700  599749.5    28.688    31.283     0.000     0.000    -2.846   -52.034
       800  600113.2    28.745    31.346     0.000     0.000    -2.838   -52.026
       900  600477.0    28.802    31.409     0.000     0.000    -2.830   -52.018
      1000  600840.7    28.859    31.472     0.000     0.000    -2.823   -52.010
      1100  601204.5    28.915    31.535     0.000     0.000    -2.815   -52.003
      1200  601568.3    28.971    31.598     0.000     0.000    -2.807   -51.995
      1300  601932.0    29.028    31.660     0.000     0.000    -2.799   -51.987
      1400  602295.8    29.084    31.723     0.000     0.000    -2.792   -51.980
      1500  602659.5    29.140    31.785     0.000     0.000    -2.784   -51.972
      1600  603023.3    29.195    31.847     0.000     0.000    -2.777   -51.964
      1700  603387.1    29.251    31.908     0.000     0.000    -2.769   -51.957
      1800  603750.8    29.306    31.970     0.000     0.000    -2.762   -51.949
      1900  604114.6    29.362    32.031     0.000     0.000    -2.754   -51.942
      2000  604478.3    29.417    32.093     0.000     0.000    -2.747   -51.935
      2100  604842.1    29.472    32.154     0.000     0.000    -2.739   -51.927
      2200  605205.9    29.526    32.215     0.000     0.000    -2.732   -51.920
      2300  605569.6    29.581    32.275     0.000     0.000    -2.725   -51.913
      2400  605933.4    29.635    32.336     0.000     0.000    -2.717   -51.905
      2500  606297.2    29.690    32.396     0.000     0.000    -2.710   -51.898

line 0
line 1000
line 2000
line 3000
line 4000
line 5000
line 6000
line 7000

lines processed: 7839
output file: 20120803.cmli_sigma

user time (s): 0.240
system time (s): 0.370
elapsed time (s): 3.780

We see that incidence angle values are changing from column to column.

Now if I apply 10*log10, I get the values in range from -36.1 dB to 26.5 dB with median -13.9 dB. Look more reasonable.

I wonder how right are my speculations.

Thanks a lot for any input!