The Scenario: A sharp, local target (Orange, depth=30m) is superimposed on a deep, broad regional basement trend (Purple, depth=300m).
Ground Level (h=0): You see a small "bump" or spike riding on top of a broad hill.
Upward Continuation (h > 0): As you move the sensor up (drag right), the local spike vanishes rapidly. The curve becomes smooth, representing only the Regional Trend. This is how geophysicists separate deep basement structures from surface noise.
Downward Continuation (h < 0): As you move closer to the source (drag left), the local spike grows taller and sharper, separating from the background. This enhances resolution but is mathematically unstable (see what happens with noise!).