So I'm performing an experiment at my university in which we've got to construct a sounding balloon payload to measure the relative changes in gravity for up to 100,000 feet. I'm having a bit of trouble, however, sorting out the math and such. So the payload is rising, and its position will be tracked by GPS. We've also got a gyroscope, magnetometer, and single-axis accelerometer that we're planning on using to calculate the payload's accelerations. My dilemma is this: I believe the payload's accelerations would be the "proper acceleration," and the acceleration calculated from the GPS data would be the "coordinate acceleration." So then I could get my change in gravitational acceleration by getting the downward component of my payload's proper acceleration and subtracting the coordinate acceleration from that, right? But the coordinate acceleration would be upward, opposite the gravitational acceleration I'm trying to measure. Advice would be much obliged.