Compensation of sonar image data primarily for seabed classification

A system for enhancing an image of a survey area comprising:

• (a) a transmitter for transmitting sonar pulses from a reference origin repeatedly towards the survey area;
• (b) a detector for measuring the amplitudes of echoes received at the reference origin, said echoes being scattered back from a plurality of survey points in the survey area, each survey point having a known position measured from the reference origin;
• (c) means for calculating the range to each survey point as the distance from the reference origin to each survey point;
• (d) means for calculating the angle of incidence at each survey point as the angle between a line from the reference origin to each said survey point and a vector normal to the survey area at each said survey point;
• (e) means for compensating the amplitude of the echo for each survey point by applying a selected function of the range and angle of incidence to adjust for the attenuation of the echo amplitude due to range and angle of incidence;
• thereby to obtain an enhanced image of the survey area.

A method of classifying a survey area, substantially covered by a plurality of two dimensional patches, according to an attribute determined for each patch, comprising the steps of:

• (a) transmitting sonar pulses from a reference origin repeatedly towards the survey area;
• (b) measuring the amplitudes of echoes received at the reference origin, said echoes being scattered back from a plurality of survey points in the survey area, each survey point being located in a known patch and having a known position measured from the reference origin;
• (c) calculating the range to each survey point as the distance from the reference origin to each survey point;
• (d) calculating the angle of incidence at each survey point as the angle between a line from the reference origin to each said survey point and a vector normal to the survey area at each said survey point;
• (e) compensating the amplitude of the echo for each survey point by applying a selected function of the range and angle of incidence to adjust for the attenuation due to range and angle of incidence;
• (f) calculating, for each patch, a vector of features, each feature being calculated as a selected function of the compensated echo amplitudes of the survey points associated with that patch;
• (g) calculating one or more components, each component being a set of factors defining a linear combination of the features whereby the inner product of any one of the feature vectors of a patch with all the components produces a Q-vector having as many elements as there are components, said Q-vector being representative of the acoustic nature of the patch;
• (h) identifying the centroids of one or more clusters as points in the space of Q-vectors and assigning each patch according to its Q-vector to a cluster;
• and
• (i) associating each cluster with a distinct value of the attribute by empirical examination of said attribute at representative survey points in the survey area;
• thereby to obtain a refined classification of the patches according to the attribute.

A system for classifying a survey area, substantially covered by a plurality of two dimensional patches, according to an attribute determined for each patch, comprising:

• (a) a transmitter for transmitting sonar pulses from a reference origin repeatedly towards the survey area;
• (b) a detector for measuring the amplitudes of echoes received at the reference origin, said echoes being scattered back from a plurality of survey points in the survey area, each survey point being located in a known patch and having a known position measured from the reference origin;
• (c) means for calculating the range to each survey point as the distance from the reference origin to each survey point;
• (d) means for calculating the angle of incidence at each survey point as the angle between a line from the reference origin to each said survey point and a vector normal to the survey area at each said survey point;
• (e) means for compensating the amplitude of the echo for each survey point by applying a selected function of the range and angle of incidence to adjust for the attenuation due to range and angle of incidence;
• (f) means for calculating, for each patch, a vector of features, each feature being calculated as a selected function of the compensated echo amplitudes of the survey points associated with that patch;
• (g) means for calculating one or more components, each component being a set of factors defining a linear combination of the features whereby the inner product of any one of the feature vectors of a patch with all the components produces a Q-vector having as many elements as there are components, said Q-vector being representative of the acoustic nature of the patch;
• (h) means for identifying the centroids of one or more clusters as points in the space of Q-vectors and assigning each patch according to its Q-vector to a cluster;
• and
• (i) means for associating each cluster with a distinct value of the attribute by empirical examination of said attribute at representative survey points in the survey area;
• thereby to obtain a refined classification of the patches according to the attribute.