Hi. I am desperately striving to reproduce a CoVAmCoh processing on my SAR images. It works with interferometry pairs and consists of a combination of 3 bands ==> Coefficient of Variation, a Mean amplitude and a Coherence image. The issue lies in the making of the CoV image. I use the “coef_var” function with the two intensity images from a coregistered interferometry stack. I get a result but doesn’t seem to be quite consistent with the thing I can get from the same function in ERDAS. Too much noise as it is computed on 1 pixel and not a definable window (3x3, 5x5, 7x7 …). Is there any specific parameter to give or something to add to make it run properly ? Any suggestion ? Thanks.

Does the documentation in ERDAS describe exactly what the corresponding function is doing?

Not exactly. It says some basic thing like “*The Coefficient of Variation is the ratio of the Standard Deviation and the Mean, in a local neighbourhood, of the amplitude or intensity of a SAR image.*”

The notion of local neighbouring is probably missing in the **coef_var** function. Based on this, I broke down the CoV function in two successive filtered band functions (Stddev and Mean) within a 5x5 window, applied to each of my amplitude images. I have then Averaged the results and visually got something consistent with what i was initially expecting from the **Coef_var** function. Maybe that’s a workaround.

A next step would be to “Graph” this with the Builder but it seems like I cannot apply from the “Image-Filter” block the same Non-Linear Filters from the “Filtered Band” tool such as a Standard Deviation 5x5 or a Mean 5x5.

So basically that is a textural measure it seems. BTW you might want to try including Intensity-Change between the two images as a feature in addition to the Coefficient of Variation, Mean amplitude and Coherence images you are already using.

@lveci should be able to help with the issue of calling Filtered Band - functionality from a Graph.

Yes, that would be worth trying.

And yes, having the Filtered Band function from the Graph would allow automation of a quite cumbersome process. Thank you.