Effect of polarization on interferometric products


#1

This is no study to be presented, but rather a test because this topic came up several times in this forum.
It shows how the polarization of a wave effects coherence and interferograms of an image. I found only few studies which directly compare this, so I gave it a try.

I used two ALOS PALSAR images (L1.1) with quad-polarization, freely available from ASF Vertex over a partially vegetated area in North America.

  • 24.11.2007 master
    ALPSRP097610830-L1.1
  • 29.11.2009 slave
    ALPSRP204970830-L1.1

grafik

This is the the T-matrix of the master date:

. grafik

I coregistered both images and created interferograms and coherences for each polarization. I included topographic phase removal using SRTM 1ArcSec and applied MultiLooking on the result for the visualization:

Coherence [scaled between 0 and 0.4 in all images] HH-HV-VH-VV

Interferograms HH-HV-VH-VV

As shown, coherence is clearly higher in HH and VV polarizations. Accordingly, fringes are much clearer in these interferograms.

The difference between HH/VV and HV/VH interferograms might be another with sensors of shorter wavelength (C or X band) and also the degree of vegetation plays a role here.
But speaking of bare and unvegetated areas, better results can be expected with the co-polarization channels.


Using VV and VH to make DEM
Difference between radar channels
#2

Dear Andreas, could you please say how do you form this T-matrix?
Is it just RGB from different polarizations?


#3

Radar > Polarimetric > Polarimetric Matrix generation > T3

Then create an RGB with

  • red T11
  • green T22
  • blue T33

#4

Dear Andeas, thank you for the reply. Obviously I have read about this operator in SNAP :smile: