Classifying small structure in water using IR band

near infrared band in satellites built for cartography have a meaninfull result bewteen water and other structures. My guess is results based on the size of object would be less than meaningfull, lots of false positives, think flocks of white birds or any other surface or near subsurface objects as well as differences in water temprature, shallow water pans, great deal of variability, say mangroves, swamps, wetlands, oceans, ponds, lakes, waves, debris, waterplants, animals, subsurface structures, micro islets, subsurface clutter, Would be hard to pick a true signal from blitter unless tuned say for still deep water. Linear feature are easier to extract or general features such as vegetation, points not so much. depends on how accurate your the result you want needs to be.

IR is usually most useful for mapping vegetation and water, in as much as water does not reflect ir. My guess is that both your water and beacon will not reflect ir. If you have a relatively homogenous background of water you might try a segmentation approach. You will need a few pixels per feature, so if they are 20-30m structures than 5-m pixels will be pushing the upper limit of useable resolution. Do your structures have specific spectral characterisitcs or are they variable?

Can you assemble a vector layer from known beacons and try to do a learning process with the raster?
If you verify the signature of the raster and ir bands your looking for your classification would be very clean.
Not knowing your location. Unless your interest area is open ocean I have had success finding navigation aids gis data.
For Florida
For Hawaii and other data