Anyone can use a theodolite to measure the earth’s radius. These can be rented on a daily basis. The procedures are not very difficult and the calculations require high school level math.
- Measure the earth’s radius using reciprocal zenith angles.
- Measure the earth’s radius measuring the drop of the horizon.
that discuss measuring the radius of the earth:
- The Earth’s Equatorial Radius and the Distance of the Moon
- On Detecting Changes in the Earth’s Radius