The data used for the experiments were sonar returns collected from a metal cylinder and a cylindrical shaped rock positioned on a sandy ocean floor. Both targets were approximately 5 ft in length and the impinging pulse was a wide-band linear FM chirp (ka = 55.6). Returns were collected at a range of 10 meters and obtained from the cylinder at aspect angles spanning 90 ° and from the rock at aspect angles spanning 180 °. A set of 208 returns (111 cylinder returns and 97 rock returns) were selected from a total set of 1200 returns on the basis of the strength of the secular return (4.0 to 15.0 dB signal-to-noise ratio)
The preprocessing used to obtain the spectral envelope is indicated schematically where a set of sampling apertures are superimposed over the 2D display of a short-term Fourier Transform spectrogram of the sonar return. The spectral envelope  was obtained by integrating over each aperture. The spectral envelope was composed of 60 spectral samples, normalised to take on values between 0.0 and 1.0.

Dataset Description

The 60 samples of reflected frequencies are given in the data.In each frequency band the strength of the reflected frequency is very low.That indicate, the obstacle through which the reflected frequency received is not a mine.In the same way the strength of the reflected frequency is high when bumped on the some obstacle that can be predicted as a mine.All the frequency band collectively forming a pattern which is similar to a bell shape curve