I have some questions about speckle filtering:
1- I have about 70 images and I want to analyse their change through the time. If this means that I have to use “Multi-temporal speckle filtering”, then seems I just can insert one product per time to speckle filter tool. Is it any possibilities to choose and insert all 70 products at once?
2- What is the best filter type you suggest for very small target featuress? (I am studying medium to small lakes and ponds)
3- What is the difference between window size and target window size And because my study features are small do you recommend the smaller filters?
4- In my pre-processing I forgot to do speckle filtering before “Range Doppler Terrain Correction”. I wanna do it right now on my images (Gamma). Do you thin it may affect my results and I should do all preprocessing from the scratch to include Speckle filtering OR that is ok t do it as the last filter?
I do appreciate any guide
- To use all 70 scenes for the speckle filtering you first have to make a layer stack by coregistration.
- If your targets are small, you should use one of the adaptive filters which try to discriminate real edges from speckle. Refined Lee, Lee Sigma or Gamma Map, but you will have to compare and try different parameters (maybe test on a subset of your stack to reduce computing time)
- You have target window sizes for filters where the image’s character is locally estimated. For example, you use a 9x9 pixel window to detect if an area is speckled or divided by real structures and then apply the filtering for thw window size of 3x3 pixels.
- Filtering before terrain correcting makes sense, because resampling is involved at the step of terrain correction which already changes the pixel’s values (especially for bilinear or cubic resampling). If your targets are really small, you should consider using the nearest neighbor resampling to preserve the values before filtering.
Thank you so much, so based on the last answer about the order of the preprocessing. As you said i have to consider resampling before filter it is like i did it by terrain correction already! does that make sense to do a speckle filtering and again do the terrain correction?
Speckle filtering should be done before terrain correction
Do you know if there is any way to clip data to a smaller study area to reduce the preprocessing time? Seems based on your answers i need to re pre process from the scratch! So i need a way to reduce the time? Or can i make a stack and preprocess that instead of do it one by one? thanks for your help in advance
Hi,sir !tanks in advance .Can you help distinguish the difference between Lee , Lee sigma , and Refined Lee?
The differences are described in these papers: Speckle filtering with Lee filters