I am trying to measure vertical and horizontal speed of an object attached to a parachute. It will be launched from a low altitude and in an open area, allowing satellite GPS lock.
Data treatment will be post flight, so no real-time or processing power requirements.
Up to now, I have identified two solutions:
- 9-DOF IMU, sensor fusion to get absolute orientation, accelerometer integration to get the velocity vector.
- GPS, ground speed for horizontal speed and elevation for vertical speed. I would probably fuse GPS elevation with a barometer relative altitude to maximize precision.
I have explored the IMU solution up to now, but I have encountered some problems:
- accelerometer integration is very prone to error, since it depends on the absolute orientation, gravity offset removal, numerical integration methods, noise attenuation, drift correction, etc.
- sensor fusion SDKs are pessimistic about inertial navigation performance, which leads me to think that getting velocities from it is easier said than done.
After reading some GPS datasheets, and I have also identified some problems:
- Weather may block GPS satellite signals and accuracy depends highly on the locked number of satellites.
- Update rates are pretty slow, I should not rely on something faster than 2 Hz.
I have the following questions:
- Am I missing another type of sensor that would be easier to implement and get accurate velocity vectors?
- Would the GPS be a more reliable solution than the IMU?
- Am I correct on the assumption the ground speed I get from the GPS is the horizontal speed of the object?