Abstract
This paper is based on the principles of two-medium photogrammetry, with the purpose to perform a bathymetric survey of a reef in the South China Sea, using aerial imagery acquired by UAV. The first objectives are to introduce the basic principles of two-medium photogrammetry, discuss the technical requirements of this methodology to determine an accurate refractive index of sea water, and propose a new method to calculate seawater refraction and calculate corrected reef elevations. The second objective is to analyse and integrate the elevation and depth datum for both the land mass and the undersea reef. The final objective of this paper is performing stereoscopic mensuration on the UAV photography in order to transform reef elevation and depth datum. Our test shows that aerial two-medium photogrammetry is feasible in practical application, but requires relatively high aerial photography conditions.
Highlights
Bathymetric surveys of the reefs surrounding the offshore islands are primarily performed by sonar surveys, which require considerable manpower and expensive
Aerial two-medium photogrammetry provides high spatial resolution to describe submarine topographical features required for the 3D landscape model, the water depth measurement and detection precision are lower accuracy than terrestrial mapping
2.1 Research situation of two-medium photogrammetric technique Z.Z.Wang (1979) describe the two-medium photogrammetry definition is the technology of using image space and object space of images taken in two different media to determine the geometrical characteristics of the subject target
Summary
Bathymetric surveys of the reefs surrounding the offshore islands are primarily performed by sonar surveys, which require considerable manpower and expensive. Multi-spectral satellite data is used for water depth inversion, a technique which on the control point and retrieval model. This technique is imprecise and difficult for most engineering applications. Another potential method for undersea mapping is two-medium photogrammetry, but to date there has been little practical application. S.L.Liu (2011) studied the direct referenced relative orientation calculation methods of airborne POS systems, based on the two-medium photogrammetry. Aerial two-medium photogrammetry provides high spatial resolution to describe submarine topographical features required for the 3D landscape model, the water depth measurement and detection precision are lower accuracy than terrestrial mapping. The third objective is to summarize the deficiencies in our method and the significance to our test results
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