- Track association: which measurement belongs to which target? Errors lead to ghost targets or, conversely, missed targets.
- Time and position registration: all sensors must run on the same clock and in the same coordinate system, otherwise the fusion does not "add up".
- Conflicting data & false alarms: fusion has to weigh noise and deception, not blindly add them up — otherwise a well-placed decoy actually reinforces the wrong picture.
EW relevance
Sensor fusion cuts both ways. Defensively it makes detection robust against any single countermeasure: a stealth shape that avoids radar can still light up in IR or passive RF. Offensively it means you do not have to defeat one sensor but the whole fusion process — stealth (Electronic Counter Measures) and emission control (Doctrine & EMSO) and counter-detection across several domains at once. It explains why modern survivability has to be multispectral, and why EW rarely succeeds with a single trick.