Surge Protection Device vs. Grounding in Transmitters

I'm a bit confuse about differences between surge protection device and grounding in electronic transmitters.
As a general rule, housing of all instruments shall be grounded. Also as requested by our Client, all transmitters (and F&G detectors) shall be equipped with SPD (either internal or external).
About internal overvoltage caused by switching, I'm OK about what SPD does but when it comes to lightning, I cannot distinguish between tasks of SPD and grounding of instrument housing itself.
It would be highly appreciated if someone can tell me the difference.
Earthing and surge protection are 2 different areas where you should always go back to basics, then do your research. All instruments shall be grounded - define ground ....

Even a small system uses several earth bars, but how do you use them ?!
In any system you have to make absolutely sure that no earth currents (AC,DC or spikes ) go down your instrument screens / instrument earth bars.

Surge protection is more of a nightmare. Overvoltage surges should be taken care of by power supplies.

Lightning Protection is a subject in itself, but you have to make absolutely sure no lightning currents (mindful of external instrument cabling) reach your intrumention.

You’ve mentioned F&G but I’ll relate to the Rail Industry.
You might assume the steel in the rails are at earth potential - but not so on an electrified line when a train is passing over it at your section of line. The line side boxes carry signal power, where the earth is connected to the DNO supply who may/may not allow earth rods several kilometres down the line from the power house. These boxes are connected to signal gantries which may/may not be ground earthed. In short every new design/design change justifies a design study in earthing, especially where instrumentation is housed.