A laser scanning method for obtaining a geometric characterization of the shape of a surface in an underwater environment, based on the principle of triangulation comprising the steps of: [a] emitting a laser light beam through a laser light emitter, [b] transforming said laser light beam into a planar fan configuration through first diffraction means arranged downstream of said laser light emitter, [c] receiving said laser light beam transformed into said planar fan and redirecting it to project it onto said surface that must be characterized through first light redirecting means arranged downstream of said laser light emitter, [d] capturing a scanning area of said surface that must be characterized through a light receiver arranged with respect to said light emitter, such that said scanning area contains said fan projected onto said surface, and [e] synchronizing the emission of said fan by said light emitter and the capture by said light receiver through control means functionally associated with said light emitter and said light receiver (2, 10), [f] said first redirecting means and said light receiver being separated by a known predetermined distance defining a baseline between both, and said fan forming, [i] once it is redirected, a first angle (α) with respect to said baseline, and [ii] once it is reflected by said surface, a second angle (β) with respect to said baseline, and [g] obtaining, through the first processing means of said light receiver, a plurality of points illuminated in the scanning area by the reflection of the fan, characterized in that it comprises the additional steps of [h] characterizing said plurality of points illuminated in the scanning area by an elliptical cone, such that triangulation is performed by calculating the intersection of the light beam that has illuminated said light receiver with the elliptical cone characterizing said plurality of points illuminated in the scanning area, and [i] rotating said first redirecting means about at least one fixed shaft with respect to said light emitter and said light receiver (2, 10), the rotation of said first redirecting means being controlled by said control means, for displacing said fan within said scanning area along a plurality of different instantaneous positions (P1, P2) in a manner that is synchronized with the operation of said light emitter and said light receiver, and [j] repeating said steps [a] to [i] for a plurality of angular positions of said redirecting means for obtaining a three-dimensional point cloud that geometrically characterizes said surface. [a] emitting a laser light beam through a laser light emitter, [b] transforming said laser light beam into a planar fan configuration through first diffraction means arranged downstream of said laser light emitter, [c] receiving said laser light beam transformed into said planar fan and redirecting it to project it onto said surface that must be characterized through first light redirecting means arranged downstream of said laser light emitter, [d] capturing a scanning area of said surface that must be characterized through a light receiver arranged with respect to said light emitter, such that said scanning area contains said fan projected onto said surface, and [e] synchronizing the emission of said fan by said light emitter and the capture by said light receiver through control means functionally associated with said light emitter and said light receiver (2, 10), [f] said first redirecting means and said light receiver being separated by a known predetermined distance defining a baseline between both, and said fan forming, [i] once it is redirected, a first angle (α) with respect to said baseline, and [ii] once it is reflected by said surface, a second angle (β) with respect to said baseline, and [i] once it is redirected, a first angle (α) with respect to said baseline, and [ii] once it is reflected by said surface, a second angle (β) with respect to said baseline, and [g] obtaining, through the first processing means of said light receiver, a plurality of points illuminated in the scanning area by the reflection of the fan, characterized in that it comprises the additional steps of [h] characterizing said plurality of points illuminated in the scanning area by an elliptical cone, such that triangulation is performed by calculating the intersection of the light beam that has illuminated said light receiver with the elliptical cone characterizing said plurality of points illuminated in the scanning area, and [i] rotating said first redirecting means about at least one fixed shaft with respect to said light emitter and said light receiver (2, 10), the rotation of said first redirecting means being controlled by said control means, for displacing said fan within said scanning area along a plurality of different instantaneous positions (P1, P2) in a manner that is synchronized with the operation of said light emitter and said light receiver, and [j] repeating said steps [a] to [i] for a plurality of angular positions of said redirecting means for obtaining a three-dimensional point cloud that geometrically characterizes said surface.