What is the difference between coherent and non-coherent integration in radar signal processing?

Coherent integration sums the complex (I+jQ) returns from N pulses, preserving phase information. SNR improvement: N (linear), or 10·log10(N) dB. Requires: phase-coherent radar (stable LO, known Doppler compensation), and target must remain in the same range-Doppler cell during integration. Non-coherent integration sums the magnitudes (or squares of magnitudes) of N pulse returns, discarding phase. SNR improvement: approximately √N (half the dB improvement of coherent). Requires: N independent samples (can span different dwell periods). No phase coherence needed. For N = 100 pulses: coherent integration provides 20 dB improvement; non-coherent provides approximately 10 dB. Coherent integration is preferred when achievable; non-coherent is used when phase coherence cannot be maintained (long integration times, fluctuating targets, or when Doppler is unknown).