How to obtain the differential spectrum of each floating target (algal pattern here), that is, the band value of each algal pattern subtract the band value of the adjacent water around it (such as the median water spectrum)
I first extract floating algae from the sea. I can use NDVI, NDWI, etc. to extract the algae and its edges first (See the Fig.1, algae is in viridis palette). My goal is to get the difference between the spectra of the algae and the surrounding water. Therefore, I carried out buffer operation on the edge of algae patterns (See the Fig.2, yellow buffer). The buffer represents the water around algae. My goal was to calculate the difference between algae pattern and the surrounding background water body. I have considered the object-based approach, but this is very memory intensive and has limitations on spot size. Now I want to do it based on pixels and morphology. How to achieve this?
An alternative idea maybe:Fill nodata values (masked algae) using neighborhood water in an image, then using subtraction between the original image and the new one to obtain the difference between the spectra of the algae and the surrounding water.
