Inertial navigation is inherently self-contained, robust with very good short term accuracy but can drift over time. Therefore the INS is aided with complementary acoustic positioning to provide long term accuracy and robustness. The additional integrity offered by inertial integration significantly reduces operational delays during periods of challenging subsea acoustic conditions such as aeration and noise. The precision and update rate of the output allows greater subsea vehicle control and is suitable for ROV station keeping.
USBL aiding is vendor independent using a standard, absolute USBL position message. It can be further optimised with integration to a Sonardyne Marksman LUSBL or Ranger 2 USBL system. Alternatively, tightly coupled LBL aiding from Fusion 6G can be used with either full or sparse (2 to 3 beacon) arrays. LBL observations are optimally time stamped and the rich quality statistics provided with Wideband 2 are used to provide optimal aiding.
SPRINT does not need to be physically co-located with the Doppler Velocity Log. Misalignments are calculated in the field using a freely available calibration utility. This approach allows for more flexible mounting configurations to be considered. A ZUPT (zero velocity) aiding feature is available to provide exceptionally precise positioning during static fixes even if external aiding such as DVL has been lost (e.g. loss of bottom lock).
FLEXIBLE AND EASY TO USE
The SPRINT installed on the subsea vehicle is interfaced using a single serial or Ethernet connection through the vehicle’s umbilical. The SPRINT acts as a subsea multiplexer for it’s own data and all subsea aiding data. Each SPRINT unit is supplied with software to allow easy configuration, monitoring, communications routing and logging. SPRINT can also be provided with a communications hub providing multiple serial/Ethernet ports for input and output.
Futures and benefits
High output rate (100Hz+)
Precise, low noise for smooth navigation
Resilience to outliers keeping the system on track
All computations made inside Lodestar reducing reliance on tethered communications
Topside connection via a single RS232 or Ethernet connection
AHRS and INS
– Continuous AHRS always available (regardless of aiding)
Battery backup to ride through brown outs
Onboard data storage provides redundant storage of log files
Vendor independent USBL aiding
Tightly coupled Fusion 6G LBL aiding option
DVL aiding (user auto configuration)
Subsea multiplexer (raw sensor feeds available topside)
Course or fine time synch (ZDA or ZDA+1PPS) options