The end of a low-velocity lens diffracts energy emerging after reflection at a lower level. Conventional interpretive treatment of such energy as an undiffracted reflection could lead to serious inferences of non-existent structure. Constant moveout down the record is the main criterion for the diffracted reflection situation. The diffractive source, assuming the velocity in the surrounding material to be known, is found as the envelope of emergent travel paths. Reflected energy from the top of the feature, if recognized, can be solved for delineating the upper limit of the body. The thickness can be estimated from observed delay times. For discovering and delineating low-velocity lenses, long reflection spreads should be used.

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