Which detection challenge is characterized by targets that cannot be heard but are not visible?

The detection challenge characterized by targets that cannot be heard but are not visible is attributed to a camouflaged target. Camouflaged targets are designed to blend in with their environment, which can make them difficult to detect both visually and audibly. These targets take advantage of natural or artificial surroundings to conceal their presence, making detection a significant challenge for operators.

Understanding this concept is vital for effective target recognition and engagement strategies. In contrast, the other options present different scenarios that either involve targets that can produce some level of sound, are identifiable under specific conditions, or are not inherently designed to be stealthy in the same manner as camouflaged targets. Recognizing camouflaged targets requires heightened awareness and mastery of observational skills, emphasizing the importance of training in environments where such challenges are present.