How to achieve sub-meter accuracy in remote locations?

[Stalemate]

Activity: Create 3D reconstructions of geological outcrops. Using imagery from a DJI Phantom 4, and SfM-MVS algorithms. To orientate the SfM-MVS reconstruction I will use ground control points (GCPs). I require sub-meter accuracy to measure these GCPs.

Areas: Remote, places with no mobile or RTK networks. First project will be in southwest Tibet.

Question 1: Is a SBAS solution the best way to go (I do not need cm accuracy)?

Question 2: How can I find out the coverage of SBAS, India has GAGAN, does that cover Tibet? China also has SNAS, but is that functional? Where can I confirm the coverage before I find out in the field that I am not within range? Are there commercial SBAS that I can pay for that cover Tibet?

Question 3: What receiver do I look for? I believe that the Arrow 200 GNSS and the SXblue II+ GNSS receivers will do what I want? The Bad Elf GNSS Surveyor and Juniper Systems Geode are much cheaper, can they also work in Tibet?

Question 4: Is there a better (cheaper) solution that I am unaware of?

Question 5: How can I check if there is a RTK network available before I arrive to the field?

I appreciate any help.

 

[Nuvi-Nebie]

I would say that a dual/multi band receiver like the Arrow 200 (L1+L2) or Arrow Gold (L1+L2+L5) will contribute to sub-metre accuracy much more than the ability to receive an SBAS signal on a single band (L1 only) receiver like the SXblue II+

Dual band (L1+L5) receivers are also built into some smartphones, see link (Click HERE)

 

[Stalemate]

Thanks for the info, the GPSTest is great, amazing to get dual band in phones. Will have to upgrade my s7.