The Coolpix S31 has a CCD sensor type which is better than most cameras that have been available for around the same time as it. Most similar spec cameras that were released more than two years ago have a MOS sensor type. CCD sensors produce high quality, low-noise images but consume a lot more power than CMOS sensors. CCD is the most common image sensor type used in digital cameras.
A CCD sensor type is actually the best sensor type amongst all waterproof cameras that came out more than two years ago.
A MOS sensor type is the worst sensor type across similar types of camera.