A projectile detection technique is disclosed. The technique helps improve the self-defense capabilities of strategic platforms such as naval ships against asymmetric threats such as anti-ship missiles (ASMs). These threats can be particularly challenging in a highly cluttered maritime environment, where the threats can be too close for radar to accurately detect. In one example, the projectile detection technique automatically detects ASMs flying above the horizon by using mid-wavelength infrared (MWIR) and visible/near-infrared (VNIR) camera systems, and locating the horizon line and segmenting the imagery into different regions. Projectiles are detected in the near-horizon segment using a Fourier phase-only transform and convolution matched filters to enhance exceedances, then applying multi-frame processing to measure persistence and scintillation (e.g., flicker from missile exhaust) to help filter out background clutter objects. The use of the phase-only transform, matched filters, and multi-frame processing helps detect single-point anomalies and distinguish ASMs from background clutter.