Detect 2-dimension-like deformation on a 2-dimensional surface
We measure the change in distance between a SAR antenna and a target on the ground to detect surface deformation using InSAR. There are many targets on the ground surface but a SAR satellite has just one antenna at this time. So, the change in distance between a SAR antenna and a target on the ground is only measured along a line of sight.
InSAR using a satellite can observe the same target on the ground in almost the opposite directions, one from ascending orbit (northward), the other from descending one (southward).
By combining these two kinds of observation,
we can detect deformation in any direction lying in the surface containing LOS directions as shown in right figure.
Targets on the ground are distributed over a 2-dimensional surface and their deformations are detected on a 2-dimensional surface containing LOS directions. Therefore, this is called a 2.5-dimensional observation.
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