Issue with Double Coastline Detection in CoastSat Due to Nearby Water Body

[JPedro18]

I’m encountering an issue when using CoastSat for coastline detection. There is a water body very close to the shoreline. This results in detecting two separate coastlines.

I tried modifying the parameters min_beach_area and min_length_sl but the main problem is that the max_dist_ref parameter is set to 280 meters because there is a section of the beach that protrudes significantly due to coastal engineering works, and I will have a transect passing through this section, making this adjustment necessary.

I have attached an example image of the output showing the issue.

inputs:

Settings:

Is there any way to filter or exclude water bodies like this from being detected as a coastline?
Are there any specific settings, pre-processing steps, or post-processing techniques I should try to resolve this issue?

[JPedro18]

just noticed this is a problem only for Landsat 7 images.

[kvos]

hi @JPedro18 , I would suggest to leave the double intersections in the shoreline mapping step as they will be treated in the intersection step. There you can specify what to do in case of a double intersection. you can either assign the 'max' (further point seawards) or a 'nan' value to the instances where there are double intersections. The only way you could address it at the shoreline mapping step is with 'max_dist_ref' but it seems like the lagoon is too close to the beach. I recommend you set min_length_sl to something like 500m / 1km, otherwise you will loose too much data.

[kvos]

read this part of the README on computing intersections:

If you set the origin of your transects seawards of the lagoon, you can also discard those double shorelines using the min_chainage parameter (basically it tells you how far landwards from the origin you look for intersections). Let me know if anything is not clear. But don't worry this is a common case and can be resolved.