Iridium uses radio frequencies around 1.6 GHz or 18.75cm wavelength.
Atmospheric absorption at these frequencies is very low:
Clouds contain water droplets, though. So, let's have a look at rain attenuation:
...no problem either at 1.6GHz. So your answer is: overcast weather should be absolutely fine. The designers wouldn't have picked a frequency that ...
There is one thing to bear in mind about making safety equipment mandatory and that is the effect of risk compensation. Basically it means whenever you make something safer, a certain group of people tends to use the perceived gain in safety to take additional risk. Often the additional risk may be bigger than the safety gain introduced by the equipment and ...
There are a few methods possible:
Old school -
Find where you are on the map
Mark this location on the map
Another option - mark to your camera using temporary trail markers (day-glo paint, flagging tape, even bent over ferns etc.) Just make sure you remove these marks once you are done.
Newer school -
GPS tag using dedicated GPS, your GPS watch or ...
You can take a satellite phone if you want. But you can also decide to take the risk to go without one. Satellite phones cannot prevent all kinds of accidents, just like any technical equipment cannot achieve that either. If you want to make sure that nobody gets hurt or even takes the risk of being hurt you would have to prohibit life in general. People ...
Here is what I found for most countries,
If you have an Inmarsat satellite phone:
You will need to obtain the full international access code, country code, and phone number for the local fire, police, or ambulance depending upon the nature of the emergency and store it in your contacts.
How to call emergency numbers from your Sat Phone
Incoming messages count against the limit of text messages.
Yes, any message sent back to your inReach device, including replies to preset messages, count against your monthly message allotment.
But it will not cost the person sending you a message.
I have an inReach and have used it in all sorts of conditions and terrain. Overcast weather is not a problem but a reflective tarp or deep canyons can be.
If a message fails to get through the device will flash red and that means you need a better position.
Normally it’s not a problem.
I looked at some different plans and it looks like you could buy a prepaid plan and not activate it for up to 2 years. See the pricing here.
However that seems like the really expensive option.
Since you only want something for use in emergencys and want to be able to communicate with rescuers which rules out PLBs, I would suggest a inReach instead. That ...
Iridium currently offer a very basic entry-level Emergency Plan for $25 a month, which suggests that you will not get any emergency facilities without an active plan.
You don't say what your usage will be, but before you make your choice you should research the pros and cons of your three main options.
The PLB is, currently, one-way only ...
You are supposed to be able to load custom points of interest onto Garmins from a PC. Here is a full set of instructions, though they may be rather dated.
Rather simpler is loading waypoints. On my old Extrex the name was limited to very few characters, but that was partly because of the very simple screen.
Many applications of GPS technology are now ...
That would be a mandate. We don't like those.
Telling people they must expend resources to exercise a right they do possess is generally not permitted, and certainly not politically acceptable. Saying they must have a smartphone to vote would be a poll tax. The healthcare mandate was tossed out last year.
So telling people they need a sat phone to use public ...
I have a Garmin Oregon, and while it is possible to load gpx files with custom points of interest using the Garmin Basecamp software (https://www.garmin.com/en-US/software/basecamp/), there are a couple of restrictions that make it less than optimal.
the software seems a bit outdated
sometimes it just doesn't work, but you don't get any good error messages
Short answer: yes, and I do this with my Inreach Explorer+. Garmin supports GPX files, among other file types. I have a monthly charge because I wanted the messaging/SOS functionality.
It seems you can do similar with a 65S and Base Camp and no montly charge.
And yes Garmin software is clunky. I have learned to mutter and shake my head.
If I was going to leave an object in the backcountry I would use a GPS to record the location of the object and add a Tile tracker (I haven't checked if there are other similar devices) to what I was leaving. GPS will get me within range of the tracker.
They have a waterproof version of the tracker that you can stick to the outside of your camera. If you ...
OP has qualified his question to be specific for mountaineering, and has clarified to mean 'best practice' instead of 'required by law or guild'
In mountains many mishaps are close to instant, or are weather related. A communication device may just mean that people get the unpleasant news sooner.
If something happens, being able to call for help is not as ...