Underground Cavity Detection and Visualization

I'm in need of a professional who can help me verify if there's a man-made cavity in a specified location. The ideal candidate should be able to use Ground-penetrating radar (GPR) effectively. The project requires:

- Comprehensive measurements of any detected cavity/void, including height, width, length, and depth from the earth's surface.
- Optional identification of the material content inside the cavity.
- Visualization of the findings.

The ideal freelancer for this project should have extensive experience in using GPR, with a track record of detecting and visualizing underground cavities. Proficiency in creating detailed and accurate visualizations is essential. Experience with identifying material content within cavities is preferred but not mandatory.