Which method best detects surface deformation over large areas using radar signals?

• A. GPS alone without any remote sensing.
• B. Seismic refraction.
• C. InSAR detects surface deformation using radar phase changes; GPS measures point displacement.
• D. Magnetotellurics.

Answer: (C)

InSAR is designed to map surface movement over broad areas by using radar signals. It works by comparing the phase of radar waves from repeated satellite or airborne passes. If the ground shifts between acquisitions, the path length changes slightly, causing a phase difference that encodes how much the surface has moved along the radar’s line of sight. This technique can produce deformation maps over thousands of square kilometers in a single dataset, making it ideal for large-area monitoring.

GPS, while highly accurate, provides displacement data at specific points, so you’d need many stations to cover the same area. Seismic refraction and magnetotellurics are about subsurface properties, not surface deformation detected with radar signals. Keep in mind InSAR measures motion along the radar line of sight, so combining with different look angles or GPS can help recover full 2D movement.