Add W to ADCP measurements

[ammedd]

W (Upward sea water velocity) is only available in the Global Ocean Physics Analysis and Forecast. Nevertheless, would it be nice to add this variable to the ADCP when possible (2020 onwards)?

[j-atkins]

I agree it would be nice but I do worry slightly for ease of communication of the fact that W is only available sometimes and it's not immediately clear to users/students why.

Do you propose we add it by default to record W when it's available and then state somewhere in the docs that it will only appear in your results if your expedition is > 2020?