Methods and apparatuses for obtaining and/or processing slip sweep seismic survey data. The methods compute harmonic weight ratios using two types of data: 1) direct survey data where a harmonic sweep does not overlap with the fundamental component of responses of Earth interior and 2) another set of data representative of fundamental component of responses of Earth interior where the harmonic sweep does overlap with the fundamental component of responses of Earth interior. The set of data representative fundamental component of responses of Earth interior can be extracted from ground force measurements or a different sweep. The harmonic weight ratios using ground force measurements at overlapped frequencies may be calibrated with one or more harmonic weight ratios at non-overlapped frequencies.