Welcome!
How can you calculate speed from a single observation?
For speeds that are less than infinite, calculating speed from a single observation by definition its impossible.
Speed is distance/time. You need to observe distance and time to get speed.
In order to observe time you need
two observations: One at the start of the time frame and one at the end.
In order to observe distance you need
two observations: One at the start of the distance and one at the end.
The only way you could observe speed in a single observation is by either:
Observing a cause of speed (i.e. the settings in the ships control room)
or:
Observing a product of speed (i.e. the size of the bow wave)
but I'm not aware of anyway this is possible with any accuracy.
I'm gonna be very impressed if you have found a way! It's got me thinking. :hmm: