It occurred to me that with comms down, you ought to be able to just fire your phaser up in the air to signal your position, or even fire short bursts to send a morse code message. Why wouldn't that work? It's only like 20,000 miles to orbital range. Ships fire phasers down all the time and modern tech lets you hit the moon with a laser.
But with modern tech, by the time the laser reaches the moon, alot of laser's beam has scattered due to distance. The Inverse Square Law gives you an idea how intense your beam would be by the time it reaches it's target. Remember, the closer you are to the target, the more intense your energy beam would be. Until you have some method of Collimating your Beam into a ElectroMagnetic Pipe to concentrate the energy, your beam would be scattering over distance and losing energy. That's the biggest issue with energy over distance. Light & EM radiation suffer from this Inverse Square Law affect and so would other Beam Types that use some form of EM energy.
Phasers do utilize some form of collimation. Anyway, you're not trying to vaporize anything, you just need a beam strong enough for your ship's powerful sensors to pick up. Memory Alpha: Worf also ordered Nog to do a collimation sequence on the nadion emitters prior to fully charging the phaser array of the Defiant in DS9: "The Changing Face of Evil".
If the goal is simply to send up a 'flare', so to speak, then I think overloading a phaser might be more effective.
I think using the power cell from your Phaser to boost the signal from your Combadge might be more important.
I am envisioning instances of an enemy jamming comms. An overload leaves you without the phaser to keep using, plus it can be very dangerous if you are too close when it goes boom. But otherwise, yeah, it would probably be picked up on sensors.
Honestly, I never understood why a ship couldn't (sometimes) use visual sensors to simply *look* down at crew they couldn't contact (assuming they had line of sight, clear conditions, etc). Archer's Enterprise could freeze-frame an alien's face from orbit. I think writers just forget that is possible.
I concur, with 24th century tech, they should be able to read text off a newspaper laid down on the ground from orbit using only Optical Sensors.
I think I recall a TOS episode where they claimed to not only be able to detect heartbeats on a planet, while in orbit, but they could differentiate different species' heartbeats. In the 24th century their sensor package should be able to determine if you washed your hands before you left the bathroom, and how long ago was the last time you got laid.
The issue with this is that, sure, you can see things with your sensors if you are looking at them. But the ability to see a single face doesn't mean squat in terms of finding that face from the surface of the planet. Might be a search for the face would take fifteen thousand years on the average. Using phaser beams as emergency flares is attractive because they are very visible and visual things. They glow to the sides a lot, and immediately indicate the point of origin as well. You don't need fancy sensors for that: plain or moderately augmented eyes will suffice. We have little idea what a hand phaser beam would look like at the apparent orbital height of a thousand kilometers or so (ships seldom are seen higher up, because it's important to have a good look at the cool planetary VFX, too). We know that beams from starships suffer no visible spreading out or degradation across such distances, though. Except when they are weak beams, as in "Return to Grace"... So perhaps a weak hand phaser would be prone to dispersing where a starship phaser bank is not. Timo Saloniemi