1. A streamer for collecting seismic data related to a subsurface of a body of water, the streamer comprising: a body having a predetermined length; plural detectors provided along the body; and plural birds provided along the body, wherein the birds are configured to float, when deployed under water, at predetermined depths from a water surface such that a first portion of the body assumes a non-linear, variable-depth profile while being towed underwater, the non-linear, variable-depth profile being a parameterized curve, and the plural detectors being distributed along the parameterized curve at different depths from the water surface such that recorded seismic data has an increased low-frequency content relative to seismic data recorded with a same-depth streamer, wherein the parameterized curve is described by at least three parameters, a first parameter z 0 is a depth of a first detector along the body relative to the water surface, a second parameter s 0 is a non-zero slope of the body at the first detector of the streamer relative to the water surface, and h c is a predetermined horizontal distance between the first detector and an end of the non-linear, variable-depth profile of the body.