Fig.1

SVPs and their gradient changes (a) shows the classic SVP in water depth. (b)—(e) show the characteristics of SVP gradient variations. (b)—(c) show the SVP gradient transfer from positive to negative, from negative to positive respectively, while (d)—(e) denote the slow positive gradient variation and negative variation respectively. a and e are the starting and end points, b~d are the inflection point of sound velocity variations."

Fig.2

SVP and its equivalent SVP The green and the red denote the origin SVP and its equivalent SVP, while the yellow is a constant gradient SVP. Z1~Z6 represent the sampling points in the original SVP. z0~zB show the starting depth and end depth. The filling areas are on behalf of the area difference between the original SVP and its equivalent SVP. The yellow filling is marked as positive, while blue filling is marked as negative."

Fig.3

Flowchart of SVP simplification by the proposed algorithm Part Ⅰ and Part Ⅱ denote the SVP sequences with depth less than 2000m and more than 2000m respectively."

Fig.4

Original SVPs and its simplification ones (a) shows two original SVPs, (b) is the section of SVP1, (c) and (d) are the part I of SVP1 and SVP2 respectively. in (b), a and h are the starting and end points, while b~g are the inflection points of the SVP. In (c), the circle denotes that the inflection point is reserved by MOV method and discarded by the proposed method, while the rectangular box shows that the inflection point with similar situation as that in the circle is reversed by the MOV method and the proposed method. In (d), the ellipse shows the obvious difference between the two methods in SVP simiplifications."

Tab.1

The parameters of the simplified SVPs"

Fig.5

A section of SVP2 Simplified by the two methods (a) and (b) show the simplifications by the proposed method and MOV method respectively. The green circle denotes the reserved sound velocity."

Fig.6

Relative depth errors of the three simplification methods"

Tab.2

Accuracies obtained by the three simplification methods in the simulation experiment"

Fig.7

Seabed topography obtained by original SVP"

Fig.8

Biases of seabed topographies obtained by the SVPs from the three SVP simplifying methods"

Tab.3

Accuracies obtained by the three simplification methods in the multi-beam bathymetric data processing"