# H-Alpha Plane Problems

@tim.patelscheck, I’m interested in determining my own boundaries for dualpol H/Alpha Plane. Do you have any suggestions on how to do this practically?

Many thanks

if you want to adress this empirically, you could use an image where you have sound knowledge about (field information would be best) and manually select regions with Double bounce scattering (urban), multiple scattering (e.g. forest canopy), surface scattering, dipole scattering, multiple scattering and bragg scattering and then systematically compare their entropy/alpha values. This could lead to mathematically derived thresholds, which seperate them best.

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Hi, I recommend the paper from Shane Cloude : THE DUAL POLARISATION ENTROPY/ALPHA DECOMPOSITION:A PALSAR CASE STUDY

He is explaining how the surfacew and volume scatttering changes in the DUAL POL Case

Hope it helps

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@lveci
is there any update on the decomposition problem in SNAP?

@tim.patelscheck, did you find out what H/Alpha zone related to which class in the end?

@agw2
No, sorry. As I started this discussion here, I tried to use the zones in SNAP for doing a classification. Then I realized that the result of the classes didnt fit to the zones. I thought that it is a problem of the SNAP program, but it isnt. I figured out that the H/Alpha Classifier in SNAP is not intended for the SENTINEL 1 SLC Data. It is made for Quadpol Data like Radarsat.
So the Problem is, that the H/Alpha Classification in SNAP based on the entropie and alpha (thats fine) but the Classifikation is based on the 9 Zones of the standard H/Alpha Plane. That means, that the Witshart-Algorithem in SNAP trying to find the cluster-center based on the 9 Zones for Quadpol Data, but you are using Dualpol.

You can still use the images of the entropy and alpha from the Decomposition and doing some analyzes with it but dont use the H/Alpha Classifcation for DualPOL! It is wrong!!!

So you have to detremine your own algorithem for the entropie and alpha image to classify data from SENTINEL 1.

Doing CLassifcation based on PolSAR Data and especially with DualPOL Data is a really difficult thing!

I just wrote down my experience of the last few months and I hope, that this confusing stuff helps you.

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I have same problem with H-Alpha plane. I read the discussion in this forum but I couldn’t find the solution for this problem. Any help would be appreciated.

Hi, what kind of data are you using for your classification? I am not up to date if the development team of snap have done something to solve this issue?! @lveci

I am using dual polarization of Sentinel-1.

Hi Yusup,

Did you manange to find any solutions to this problem? I too have been experiencing strange results as highlighted above when using ‘Sentinel-1a SLC’ for an ‘Unsupervised H-Alpha DualPol classification’.
Thanks,
William

Sorry, I don’t have any solution to get a correct H-Alpha plane using SNAP. So I have been trying to do it using PolSARpro, unfortunately I get an error message “NOT ENOUGH MEMORY SPACE” even my laptop with enough RAM (32 Gb). So far, I don’t have any solution for this issue.

Hi sorry for the really slow reply! No i havent been able to find a solution to this problem, however for the purpose of my paper i think its enought that i write that there has been issues with this classifcaiton. Thanks and good luck, let me know if you find a solution

William

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@ABraun

ESA seem to think its doable with duel pol, at least with HH/HV:

On this topic, the “polarimetric parameters” method has these wonderful indices:
[] Pedestal Height
[] Canopy structure index
[] Volume scattering index
[] Biomass Index
[] Co-pol HH/VV Ratio

But they are only available to quad pol, so practically useless to S1.
I would be very interested to know if anyone has found duel pol solutions to creating any of these indices

your experience is very useful for me ,thanks .

if you have got the method ,please share it , thanks

technically, you can derive entropy and alpha, yes. But the results are not very useful, especially for cross polarization. It just doesn’t give all the information needed for polarimetry:

Thus, HH-VV SAR is a suitable alternative to full-polarization SAR in certain cases. Meanwhile, the extraction performance of the other two dual-polarization SARs is badly degraded due to the lack of co-polarization. Therefore, HH-HV and HV-VV SARs cannot effectively extract the scattering mechanisms in the H-α plane.

As you can see, HH-VV works quite fine, but the identification of

• Z3 = low entropy multiple (dark red)
• Z4 = mdium entropy surface (cyan)
• Z5 = medium entropy dipole (blue)
• Z8 = High entropy dipole (green)

just goes miserably wrong in cross-polarized (HV or VH) modes. You just have to consider that polarimetry needs the information of all four polarizations in order to correctly decompose the different scattering mechanisms within the matrix.

All the parameters you name are found on an empirical base. You can search for dual-pol publications specifically which try to find a way around but as for entropy/alpha decomposition on cross-pol data you have to be careful.

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Thanks @ABraun, my original aim for this, if only roughly, was a classifier using radar that makes use of all the information available in the SLC product.

I have come across this paper which seems promising: