----- Original Message -----
Sent: Sunday, February 13, 2011 4:54 PM
Subject: Re: [PSUBS-MAILIST] Navigation
Yes - as long as you know the system state when the IMU is activated, then you can use the IMU output to determine the current state. The IMU only measures acceleration directly, but if your ship is floating with the current, you can get both the initial position and the initial velocity from the GPS. Using both of those values as the startup state, the IMU can provide corrections from then on. Whenever you have a valid GPS fix, you would re-initialize the internal velocity and position to that reported by the GPS in order to eliminate the accumulated errors, "resetting the clock", so to speak. (Incidentally, GPS is actually more accurate in velocity than it is in position. This makes sense if you think about how a GPS receiver actually works.) Similarly, using a Doppler sonar when near the bottom will solve half the problem - you can't get absolute position information, but you can zero the velocity error.
-Sean
On 12/02/2011 5:50 PM, Alan James wrote:
So if the mother ship isn't anchored & is flowing in a current the unit won't pick this up, as the submarine upon
launching won't be accelerating.
If the mother ship was anchored in a current the unit would need turning on prior to the sub being
released into the current to pick up that movement.
There was an additional unit with gyro for $100- US