Fig. 4. Cross-correlation of the artificial sweep with the echoes (the right-hand column shows the time window of expected correspondence on an enlarged scale). (A) The echo of the nylon threads in air yielded no conspicuous correspondence with the sweep. (B) The echo of a mealworm suspended in air had a distinct correspondence peak with the sweep at the expected time. (C) The echo of the empty linoleum screen yielded a conspicuous correspondence with the sweep only from immediately below the ‘artificial bat’. No distinct peak was present in the time window where the mealworm echo would be expected. (D) The echo of the mealworm on the linoleum screen had a distinct correspondence peak with the sweep at the expected time. (E) The cross-correlation of the artificial sweep with the echo of the empty clutter screen was rippled because of the many overlapping echoes. (F) The cross-correlation with the echo of the mealworm on the clutter screen showed no obvious match.