Speckle filtering with Lee filters

Hello everyone,

I am a bit confused about the naming of the speckle filters by Lee implemented in the toolboxes.

For filtering intensity data, the “Lee sigma filter” can be selected from the menu. Is this the “Lee sigma filter” from Lee (1983) or is it the “improved Lee sigma filter” from Lee et al. (2009)?

For filtering polarimetric data, now the “improved Lee sigma filter” can be selected from the menu. To my knowledge the “extended Lee sigma filter” from Lee et al. (2015) is the polarimetric extension of the “improved Lee sigma filter”.

Is this just a mixup of the exact naming of the filters? Would be also great to have the exact references for the filters given in the documentation (help files).

Working with SNAP 6.0.3.

Thanks for clarification!

Really? Nobody is using these filters and need correct citations?

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I know almost nothing about these filters. But maybe the implementation helps you to distinguish between the different kinds.

The RefinedLee is referenced in the GUI as “Refined Lee Filter”.
LeeSigma is referenced as “Improved Lee Sigma Filter”.

Exactly. For scientific usage, I would greatly appreciate citations of articles that refer to the methods (in the bottom of the help for example). It would avoid me to dig into the source code for hours just for one small clarification. Is it planned in near or far future @marpet ? Thanks

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I don’t know. Currently, S1TBX is in between two contracts and it is not yet clear when the next contract will start.

thanks for the clarification

A number of help pages do have the citation to the reference papers. We’ll add them for the speckle filters.

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Sometimes, there is a kind of reference in the text but no info to have the title, authors, and so on

For example, in Integer Interferogram Combination :
It is possible to stack several interferograms of the same site to increase their clarity or reduce the number of fringes, thus creating an integer interferogram combination (IIC) [R13]. The combined interferogram can have a better altitude of ambiguity ha than any of the source interferograms.

How do I access to R13 ? I tried the search field but the only result is the Integer Interferogram Combination its self

Thanks in advance

The “Lee Sigma” filter for filtering intensity data implements the “improved Lee sigma filter” algorithm given by [1].

The “improved Lee Sigma” filter for filtering polarimetric data implements the “extended Lee sigma filter” given by [2].

[1] Lee J S, Wen J H, Ainsworth T L, et al. Improved Sigma filter for speckle filtering of SAR imagery. IEEE Transactions on Geoscience Remote Sensing 2009; 47(1): 202-213.

[2] Lee, J. S., Ainsworth , T. L., Wang, Y. & Chen, K. S. 2015. Polarimetric SAR Speckle Filtering and the Extended Sigma Filter. IEEE Transactions on Geoscience and Remote Sensing, 53, 1150-1160.


Which are some non-linear filters which can be used for speckle filtering of S1 GRD data?

according to this source the median filter is non-linear.

Would it be possible to add the Enhanced Lee (https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=62623) and Enhanced Frost on future releases or updates? It would be very useful for ocean applications and so far, no toolbox has it. There was a distribution of pyradar (https://pyradar-tools.readthedocs.io/en/latest/tutorial.html) but got lost in time. Thanks :smiley:

One more question regarding references…

I would like to learn more what’s behind Speckle Filtering -> Single Product Speckle Filtering -> Refined Lee
As there are more than one “Lee” filters (btw Refined Lee is also in Polarimetric Filtering - is it the same algorithm? Looking at github not necessary) and in various articles “Refined Lee” is referenced to different publications, I’m quite lost.
SNAP Help in “Speckle Filter” chapter gives information on four sources of information. I assume information regarding Refined Lee speckle is in J. S. Lee, E. Pottier (2009) “Polarimetric Radar Imaging from basics to applications” to which I do not have access. But according to the book contents which I’ve found it’s 150-152 page. Maybe someone of you has it and could check the references there?..

Also, while looking at github I’ve noticed that the size of the window in this Single Product Refine Lee Filter is blocked to 7x7. Could you please explain me why?
The link to the github.
(I am not good at reading scripts so I simply cannot find the link between the script and any scientific publication, that’s why the question above…)

The algorithm for Speckle Filtering -> Single Product Speckle Filtering -> Refined Lee is the one given in Lee’s book (J. S. Lee, E. Pottier (2009) “Polarimetric Radar Imaging from basics to applications”). The 7x7 window is used for edge detection. Details can be found on page 150-152 in Chapter 5 in Lee’s book.


@jun_lu thanks a lot for the clarification!


An update in the Filters description in SNAP would be very useful. It is not very clear still after which reference the filters are implemented. For example, I am finding that a direct python implementation of the Lee filter is giving significantly different results compared to the same image processed in SNAP using the Lee filter. I am using the original Lee.J.S, 1980, Digital Image Enhancement and Noise Filtering by Use of Local Statistics, IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. PAMI-2, No.2 implementation. However, looking at the code in github, it seems the rationale doesn’t follow the same line there. Could you provide a good reference for all the filters implemented in SNAP? Is important for people that are doing speckle filtering to know exactly what they are using.

Thank you!

Thank you for the reference to Speckle Filtering -> Single Product Speckle Filtering -> Refined Lee. Can you tell me if this is the same reference to Polarimetric–> Speckle Filter–> Refined Lee (SNAP v7)? Or is the reference later in Lee & Pottier’s book, “5.4.2 Refined Lee PolSAR Speckle Filter” pp 161-165?

For single product Refined Lee and polarimetric Refined Lee, the references should be respectively “5.2 Filtering of Single Polarization SAR Data” and “5.4 Polarimetric SAR Speckle Filtering” in Lee & Pottier’s book

I understand that the speckle effect appears in SAR images, but I wanted to know whether is it exclusive to SAR images only, or does occur in images created by passive sensors or by RAR satellites ? If only SAR images show speckles, why?

It is exclusive to coherent sources, so for example lasers produce speckle too. It is signal, not noise.