Whilst underwater, the glider cannot rely on GPS infor
mation for its geographical location. Instead, the glider dead
reckons its position. In the so-called local mission coordinate
is
Earth's sphere, the East and North components of the horizon
tal glider velocity (through water) are integrated by the glider
software
in real-time. The horizontal velocity components are
calculated from the measured heading and the horizontal glider
speed. The latter in turn is calculated from the measured pitch
and the depth rate as measured by the pressure
sensor.Implicitly it has been assumed that the difference in dead
rcoean ( eed Gs loation isferely deat-
reckoned and (corrected) GPS location iS entirely due to a
horizontal current. This assumption ignores errors made in the
dead-reckoning. Errors are introduced by the simplification of
glider dynamics, errors in the measured depth rate, and errors
in measured heading and pitch.
The glider's algorithm relates the horizontal speed Ug to the
depth rate wg according to