Here's a picture my friends. It sounds a bit more complicated..About 50 kilometers separate the dam from where my lab is. Also, there are a lot of hills/small mountains. However, the phone signal is on at maybe half the distance. My idea with what you guys said so far would be to use 2-3 devices passing through the info with long range, then hit an other device with a sim card using cell phone signal. might not be so efficient, and hills seem to be a problem with long range.
You can get a topographical map of your area and then plot out line of sight for your links,as for LoRa distance, Andreas Spiess (the guy with the Swiss Accent) set a world record at 212 Km by using a balloon.
Does anybody in your team have a ham radio (amateur radio) license? If yes, then that's the way to go.
You need to check the legality of that carefully. Amateur radio licences are normally issued for amateur radio purposes, broadcasting 'messages' that are not intended for another radio amateur might not be legal.
Ok sorry for not answering sooner! So, as you guys have seen, La Romaine is a big project. I am not on the dam building team however. we are scientists sampling and monitoring water quality as dams are being built. The team requires to sample at the target location you saw on the map, for a few days, and the wind is ofter too strong for boat navigation. The point of the windsensor project is to tell us before we get there if we wont be able to use the boat. We then need the device to run for 12 days on the battery. Its not actually made for sampling, really for efficiency. The dam company doesnt have precise windspeed at the location we are interested in, and if it does, it is unable to send the information every morning before we leave! For the 12 days, if the device can tell us the windspeed next to the entrance we use for the boat 2 or 3 times every morning, it is perfect for its purpose