Sub: add support for `WATER_DEPTH` MAVLink reporting

[ES-Alexander]

Feature request

Is your feature request related to a problem? Please describe. Many underwater vehicles have downward facing sonar sensors that are capable of measuring the distance to the water floor. Currently those are reported via DISTANCE_SENSOR and RANGEFINDER MAVLink messages, but both of those have limited export utility without contextual information that then needs to be cross-referenced with other messages (at risk of being incorrect from timing deltas).

Water temperature is also ambiguously reported in ArduSub via SCALED_PRESSURE* messages, which requires a receiver to know which and how many temperature sensors are connected to determine which one(s) refer to the water (e.g. outside the enclosure).

Describe the solution you'd like Rover has support for a WATER_DEPTH message for boats, which seems to include most of the relevant information to be directly usable in map creation / bathymetry situations, and for high level autopilot state reporting. It seems reasonable to expand that support to ArduSub firmware.

Describe alternatives you've considered Do nothing, which keeps things difficult for control station software, and keeps them reliant on cycling/filtering through DISTANCE_SENSOR and SCALED_PRESSURE messages for water depth and temperature estimates.

Platform [ ] All [ ] AntennaTracker [ ] Copter [ ] Plane [ ] Rover [X] Submarine

Additional context Add any other context or screenshots about the feature request here.

[RakshithaMH24]

Hi everyone 👋, I’m new to the ArduPilot community and interested in contributing to the Sub firmware in particular. I’ve gone through the developer wiki and GitHub guidelines, and I’m currently setting up the development environment. If there are beginner-friendly areas in ArduSub or MAVLink messaging that need help, I’d be happy to assist. Looking forward to learning from all of you!

[ES-Alexander]

Hi @RakshithaMH24, welcome to the community! :-)

I'm unsure on what's most beginner friendly at the moment, but to get a sense of things that have been requested you can try looking for open Issues, with the Sub label (or the MAVLink label), or by me or by Willian, since we mostly work with ArduSub contexts.

You could also try looking through / searching on the blue robotics forum, and/or asking in the ArduSub category there if there are any features people want developed or want help with development of.