looks god but do you know if you can use the canon hack (CHDK) with this camera ,
just to take pics at certain points , to create grid of pics for mapping
With specular reflection the NDVI values will not be accurate. If your camera is at nadir specular reflection will almost always be recognized as sun glint when the sun's rays are being specularly reflected from the water surface and saturating the sensor. The specular reflection in that photo is from the light that was reflected off of the trees, and what ever else you see in the water's reflection, bouncing off the water and going into the camera. The quality of light that is spectrally reflected off of water is relatively unchanged which is why you see NDVI values you'd expect from vegetation on the water. If the camera was at nadir and the sun was overhead you would likely see specular reflection in the form of sun glint.
Sorry if I'm not explaining this very well.