2.1 
  
  
B 
RECONSTRUCTION OF SEAFLOOR SURFACE MODELS Zo 
BY SHAPE FROM SHADING I(x 
the 
by 
Rongxing Li, Assistant Researcher (Ke 
Pacific Mapping Center, Department of Civil Engineering 
University of Hawaii, U.S.A. 
ISPRS Commission ITI 
whe 
ABSTRACT 
The technique of stereo measurement is applied to extract geometric information from stereo 
images in photogrammetry and remote sensing. In cases where only monocular images are 
available, reconstruction of object locations becomes more difficult. Shape from shading is one Th 
of the methods which derive the geometric information of objects from the analysis of s 
monocular images. Application of this technique with underwater sonar images enables the "Md 
conversion of imposed reflectance characteristics in sonar images to shape information, namely > a 
slopes, about the seafloor surface. Depth information of the surface boundary is needed to build Sot 
up a seafloor surface model by combining the obtained surface shape and boundary depths. rept 
The reconstruction of a seafloor surface model from sonar images is treated as an inverse my 
problem and solved by the regularization theory. Sparse gridded points acquired by multibeam int 
systems are used for boundary constraints. The regularization is implemented as a relaxation f 
procedure with hierarchical structure of multi-resolution grids. IS 
A seafloor surface model thus reconstructed has about the same resolution of sonar images add 
employed, and describes the seafloor surface more exactly than a surface model generated by a 
gridding and interpolation methods. An example using GLORIA side-scan sonar images and ec 
SeaBeam bathymetric data is provided. T 
aw 
KEY WORDS: Image processing, Shape from shading, Seafloor models, Inverse problem. fece 
regu 
and. 
1. INTRODUCTION detailed seafloor topography, interpolation of depths between Tie 
grid points may be used to generate denser depth points. But 
The technique of stereo measurement is applied to extract this does not add new depth information. In fact, distortion of 
geometric information from stereo images in photogrammetry depth information often occurs depending on the interpolation e 
and remote sensing. Information from double or multiple model used. 
images in overlap areas ensures reliable and stable models for 
geometric and radiometric processing. Besides bathymetric data, side-scan sonar images are often h 
available for mapping in ocean related sciences. The wne 
In cases where only single images are available, reconstruction resolution of side-scan sonar images is usually higher than that Ken 
of object locations becomes more difficult. Shape from of gridded bathymetric data. The application of the shape from ( 2 
shading is one of the methods which derive the geometric shading technique makes it possible to derive the shape of the AK 
information of objects from the analysis of single images. sea floor surface from sonar images. By combining the an f 
Application of this technique to underwater sonar images obtained shape information with the original bathymetric data, Suri: 
enables the conversion of recorded strengths of reflected sonar a more detailed description of the seafloor surface can be Is a 
signal from the seafloor surface to depth information. achieved. Thus, the resolution of the bathymetry can be unre 
enhanced close to that of side-scan sonar images. selec 
Bathymetric(depth) data are one of the most important data of of 
categories for ocean mapping. They are usually acquired by The reconstruction of a sea floor surface model from side-scan 
Muiti-Beam systems and available in gridded form for EEZ sonar images is treated as an inverse problem and solved by The 
(Exclusive Economic Zone) mapping. In some cases where the regularization theory, with the gridded bathymetric data Teco 
bathymetric data are not gridded fine enough to describe supplying boundary constraints. to th 
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