A question about threshod value

I’m studying in change detection, I want to konw how to decide the threshod. Now I can just set threshod by myself, can I decide threshod by Ostu or other method with SNAP? Or can I export data so that I can analyse and get threshod in matlab? thank you.

SNAP only supports global thresholding (one threshold for the entire image) which can be applied in the band maths as described in this video (starting at around 11:00). The histogram and profile tool help you to identifiy suitable thresholds. Filtering is also a good option.

A more powerful method is the combination of masks with the mask manager, as described in this tutorial: SAR Polarimetry and Analyses (starting at page 23), so you can apply thresholds to multiple layers and combine them to a final binary raster.

If you need Otsu’s threshold, you can export your image (or simply use the img of the BEAM DIMAP product inside the data folder) and apply python scripts as described here:

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In order to decide what threshold to use, this depends on the complexity of your AOI.
otsu method assumes that the image consists of two classes, background and foreground. In that case, you will have two distinct histograms, so, its easy to implement an automated thresholding algorithm such as otsu, where it can find the optimum threshold between the two histograms.

If the histogram of your AOI does not have two distinct histograms, then automated thresholding techniques such as otsu will not perform very well. In that case, user should be involved and manually investigate the image to find the optimum threshold