Description
A spectrogram is the magnitude of an STFT, plotted as a 2D image with time on one axis and frequency on the other. CSI / radar spectrograms are the canonical input representation for CNN-based HAR, gesture, gait, and fall pipelines because human motion produces visually distinctive Doppler patterns at familiar locomotion frequencies.
When it's used
- Input to CNN backbones for HAR / gesture / gait
- Visual analysis of micro-Doppler signatures
- Doppler-bin extraction for crowd flow
Limitations
- Throws away phase information
- Time-frequency resolution trade-off in window choice
- Hardware artefacts (CFO drift) can dominate the low-frequency band