Underwater mapping apparatus and method

In an apparatus for producing a plan view display of a seabed from a side scan sonar signal system in which the sonar generating and receiving means move with respect to the seabed, said apparatus comprising

• at least one transmitting transducer assembly for repeatedly generating side scan sonar signals in response to a trigger signal, said trigger signals each defining the beginning of a measurement cycle,
• at least one receiving transducer assembly for providing a received electrical signal output, said output having an amplitude corresponding to the intensity of received returning sonar signals,
• means responsive to the receiving transducer assembly output for providing a compressed electrical signal output having a dynamic range less than the dynamic range of said received sonar signals, and
• a display device,
• the improvement wherein said display in linear at least along an axis corresponding to a direction normal to the direction of movement of said generating and receiving means, and comprising
• sampling means for periodically sampling said compressed electrical signal within each measurement cycle to generate a sequence of sampled signal values,
• height determining means for repeatedly determining the height of said sonar generating and receiving means above the seabed,
• and further wherein said sampled signals within each measurement cycle are denoted by S(n), n=0, 1, 2, . . . , N;
• said determined height is h;
• and the range from the generating and receiving means to a position in the seabed corresponding to the sampled signal S(n) is R.sub.n ;
• and further comprising
• means for forming an error function e', substantially of the form ##EQU9## where n=1, 2, . . . , N, ##EQU10## and x=0, 1, 2, . . . , and for generating a sequence of linear data S.sub.1 (x), x=0, 1, 2, . . . , according to the rule
• S.sub.1 (x)=S(n) where
• e'.sub.n,x <0.ltoreq.e'.sub.n-1,x,
• said sequence of linear data values corresponding to a mapping of said sampled signals onto a sequence of equidistant locations along a horizontal seabed-representing axis,
• said display device having means for receiving and displaying said linear data, and
• a display control means for actuating said display device to produce said plan view map of said seabed.

In an apparatus for producing a plan view display of a seabed from a side scan sonar signal system in which the sonar generating and receiving means move with respect to the seabed, said apparatus comprising

• at least one transmitting transducer assembly for repeatedly generating side scan sonar signals in response to a trigger signal, said trigger signals each defining the beginning of a measurement cycle,
• at least one receiving transducer assembly for providing a received electrical signal output, said output having an amplitude corresponding to the intensity of received returning sonar signals,
• means responsive to the receiving transducer assembly output for providing a compressed electrical signal output having a dynamic range less than the dynamic range of said received sonar signals, and
• a display device,
• the improvement wherein said display is linear at least along an axis corresponding to a direction normal to the direction of movement of said generating and receiving means, and comprising
• sampling means for periodically sampling said compressed electrical signal within each measurement cycle to generate a sequence of sampled signal values,
• height determining means for repeatedly determining the height of said sonar generating and receiving means above the seabed,
• and further wherein said sampled signals within each measurement cycle are denoted by S(n), n=0, 1, 2, . . . , N;
• said determined height is h;
• and the range from the generating and receiving means to a position in the seabed corresponding to the sampled signal S(n) is R.sub.n ;
• and further comprising
• means for forming an error function e, substantially of the form ##EQU11## and n=1, 2, . . . , N, ##EQU12## and x=0, 1, 2, . . . , and for generating a sequence of linear data S.sub.1 (x), x=0, 1, 2, . . . , according to the rule
• S.sub.1 (x)=S(n) where
• e.sub.n,x <0.ltoreq.e.sub.n-1,x,
• said sequence of linear data values corresponding to a mapping of said sampled signals onto a sequence of equidistant locations along a horizontal seabed-representing axis,
• said display device having means for receiving and displaying said linear data, and
• a display control means for actuating said display device to produce said plan view map of said seabed.

In an apparatus for producing a plan view display of a seabed from a side scan sonar signal system in which the sonar generating and receiving means move with respect to the seabed, said apparatus comprising

• at least one transmitting transducer assembly for repeatedly generating side scan sonar signals in response to a trigger signal, said trigger signals each defining the beginning of a measurement cycle,
• at least one receiving transducer assembly for providing a received electrical signal output, said output having an amplitude corresponding to the intensity of received returning sonar signals,
• means responsive to the receiving transducer assembly output for providing a compressed electrical signal output having a dynamic range less than the dynamic range of said received sonar signals, and
• a display device,
• the improvement wherein said display is a linear plan view display, and comprising
• a time varying gain amplifier responsive to a sonar triggering signal for multiplying said received electrical signal by a time varying gain dependent upon an elapsed time measured from the time of occurrence of said last triggering signal,
• a logarithmic amplifier, responsive to said time varying gain amplifier, for providing a compressed output signal corresponding to the logarithm of the time varying gain amplifier output signal,
• sampling means for periodically sampling said compressed electrical signal within each measurement cycle to generate a sequence of sampled signal values,
• height determining means for repeatedly determining from said sampled signals, the height of said sonar generating and receiving means above the seabed,
• an angle correction means responsive to said height determination for repeatedly generating a time varying angle correction factor for said sampled signal for compensating said sonar return signal for the grazing angle of said signal relative to the seabed and for the transmitting transducer nonuniformities in the vertical plane,
• means for modifying said sampled data according to said angle correction factor,
• and further wherein said sampled signals within each measurement cycle are denoted by S(n), n=0, 1, 2, . . . , N;
• said determined height is h;
• and the range from the generating and receiving means to a position in the seabed corresponding to the sampled signal S(n) is R.sub.n ;
• and further comprising
• means for forming an error function e', substantially of the form ##EQU13## where n=1, 2, . . . , N, ##EQU14## and x=0, 1, 2, . . . , and and for generating a sequence of linear data S.sub.1 (x), x=0, 1, 2, . . . , according to the rule
• S.sub.1 (x)=S(n) where
• e'.sub.n,x <0.ltoreq.e'.sub.n-1,x,
• said sequence of linear data values corresponding to a mapping of said sampled signals onto a sequence of equidistant locations along a horizontal seabed-represented axis,
• a velocity sensing means for generating a velocity determining output signal representing the velocity of the generating and receiving means relative to the seabed,
• said forming and sequence generating means being responsive to the velocity output signal for generating a line count for each line of linear data values,
• a display control means responsive to each said line count, for printing said associated sequence of linear data a number of times corresponding to said line count, and
• said display device having means for receiving and displaying said linear data.

In a method for producing from a moving said scan sonar signal system a plan view display of the seabed topography, the method having the steps of

• repeatedly generating at least one side scan sonar pulse signal from at least one transmitting transducer, each pulse signal marking the beginning of a new measurement cycle,
• receiving returning sonar signals with at least one receiving transducer and converting said received sonar signal to a received electrical signal output having an amplitude corresponding to the intensity of the received returning sonar signals, and
• reducing the dynamic range of the received electrical signal thereby providing a compressed electrical signal output of reduced dynamic range,
• the improvement wherein said display is linear at least along an axis corresponding to a direction normal to the direction of movement of a sonar transmitting and receiving apparatus, and comprising the further steps of
• periodically sampling said compressed electrical signal within each measurement cycle for generating a sequence of sample signal values,
• determining the height of the transmitting and receiving means above the seabed,
• generating from said sampled signals a sequence of linear data values which correspond to a mapping of the sampled signals onto a sequence of equi-distant locations along a horizontal, seabed-representing axis, said generating step being responsive to the height of the transmitting and receiving means above the seabed, and
• displaying said linear data on a display apparatus for producing said plan view display of the seabed topography.