I'm trying to measure/estimate the position of a balloon, for that I need the two angles shown in the picture below. enter image description here
The idea is to place a helium filled balloon on a quadcopter to provide lift. As a first step, I imagined a fixed platform with the balloon attached. Next, I would like to estimate the value of the angles α and φ, since the length of the strap is fixed, getting the position of the globe is simply trigonometry.
The problem is that I am not sure how to measure such angles, what would be better and what type of sensor to use. I was thinking of some kind of optical sensor, but I'm not sure.
Can anyone suggest me some ideas?