Radar, SAR, FMCW, and WiFi CSI are not four unrelated tricks. For coherent wave instruments, the simplified linear, coherent, single-scattering model below maps an observation to bounded k-space support. General multipath CSI is not automatically a direct scene-k-space sample. Move the carrier and geometry to see the modeled vector change.Other observations join the world model without being mislabeled as k-space.