I am working on an experiment with the HC-SR04 sound sensor, and i am using it to record the speed of sound. I successfully measured the speed of sound in air, but when measuring it in water, I encountered a small problem. The sound waves emitted by the sensor are both absorbed and reflected off the water. Obviously, the reflected sound waves are the first ones to reach the sensor, and therefore are the ones used for calculating the speed of sound. Is there a way to code the Arduino program in order to ignore the first set of waves and only record the set of waves that were absorbed by the water? I was thinking of increasing the delay time for the pulse, but I'm not sure that would work.