In radar processing, longer integration time can improve detection by increasing processing gain but is limited by target motion and coherence time. Which statement is true?

• A. Longer integration time reduces detection probability.
• B. Longer integration time has no effect on detection.
• C. Longer integration time can improve detection by increasing processing gain but is limited by target motion and coherence time.
• D. Longer integration time only affects non-coherent processing.

Answer: (C)

Longer integration time increases processing gain by coherently accumulating the received signal, which raises the signal-to-noise ratio and improves detection probability when the phase relationship is preserved. This works because adding more coherent samples sums the signal constructively while noise remains random, so the overall SNR improves with the number of integrated samples.

But that gain depends on stability. If the target is moving or the environment changes, the signal’s phase and Doppler shift evolve during the integration interval, causing the phase to decorrelate. Once you exceed the coherence time, coherent summation no longer aligns the signal phases, so the processing gain gains off the longer integration cannot be realized and detection benefits stall or reverse.

So longer integration can boost detection by increasing processing gain, but the improvement is limited by target motion and coherence time. It’s not about a universal reduction in detection, it’s not without effect, and it’s not limited to non-coherent processing—the coherent path is where the processing gain comes from, and it is precisely constrained by coherence.