AUV surveys from a planned track to a usable seabed map

Sentry provides a concrete navigation example

WHOI describes Sentry as capable of operating to 6,000 m and collecting bathymetric, sidescan, subbottom and magnetic maps, as well as bottom photographs. The particular science payload remains part of the mission configuration. [1]

Its navigation combines a Doppler velocity log and inertial navigation with acoustic assistance from USBL or LBL systems. WHOI also describes acoustic status communication and the ability to retask the vehicle while it is on the bottom. Autonomy therefore does not mean that every mission must be isolated from all operator updates. [1]

The useful lesson is to identify which measurements support navigation and which communication functions are available. Do not replace that description with an assumption that an underwater vehicle continuously uses the same positioning and data link as an outdoor ground robot.

Line spacing is part of the required data product

Consider an illustrative rectangular survey area measuring 1,000 m by 400 m. Assume a sensor provides an 80 m usable strip and the plan calls for 20 m of overlap. The line spacing is then 60 m. A simple arrangement uses seven 1,000 m lines to cover the width, with edge coverage checked in the plan.

At an assumed ground-relative speed of 1 m/s, those straight lines take 7,000 seconds, about 1.94 hours. Turning, descent, ascent, transit and any repeated lines add time. The strip width and speed are teaching assumptions rather than Sentry specifications.

This calculation also assumes the strip is usable across its full width. A sensor's maximum advertised reach is not automatically the width accepted by a survey's quality rules.

Keep the estimated position with its uncertainty

A clean-looking map can still contain uncertain positions. Retain the navigation solution, timing, sensor calibration and the information used to assess position quality. The map's visual appearance is not a substitute for that record.

In a trial, separate a route-following error from a sensor-data gap. The vehicle can follow the intended line while the payload fails to record, or collect data while drifting outside the permitted survey geometry. These two cases need different corrections.

Scroll sideways for all columns.

Retain missing regions in the denominator

Suppose a hypothetical survey requests 10 km². The vehicle passes over 9 km², but only 8 km² meets the agreed data-quality requirements. Report 80% accepted coverage of the requested area. The 90% travel-coverage figure answers another question.

Explain why the remaining area failed acceptance and whether another mission is required. Include the time and resources needed to fill those gaps in the operational estimate. Do not describe the entire requested region as mapped solely because the vehicle completed a dive.

A mission includes deployment and retrieval

The operations plan must account for available energy, the permitted working area, updates, termination conditions and recovery. Use the vehicle operator's approved procedures rather than deriving safe limits from a generic runtime figure.

A useful handover package contains the mission definition, configuration, original data, navigation record and coverage assessment. Together, these allow the survey team to decide which questions the mission answered and which require another observation.