Sensor decisions and Kit

Hi all,
I am very new to the Arduino scene and I am looking to build an automated windshield wiper for a controls system class. Am having a tough time deciding appropriate sensor(s) to use for this project. The problem is; this sensor has to be able to detect HOW MUCH moisture or water or vibration is present and not just the presence of water or moisture or vibration. I am also looking to purchase an Arduino kit as I believe I would be able to use one to complete this project. Any form of input or help would be appreciated.
Thank you

Malcolm

This describes how commercial systems work:

There are a number of patents regarding using this infrared/reflection method. You can start with patent 4463294 and also check the other patents it references (bottom of the page).