We All Live in a Virtual Submarine
Our seas and oceans hide a plethora of archaeological sites such as ancient shipwrecks that, overtime, are being destroyed through activities such as deepwater trawling and treasure hunting. In 2006, a multidisciplinary team of 11 European institutions established the Venus (Virtual Exploration of Underwater Sites) consortium to make underwater sites more accessible by generating thorough, exhaustive 3D records for virtual exploration. Over the past three years, we surveyed several shipwrecks around Europe and investigated advanced techniques for data acquisition using both autonomous and remotely operated vehicles coupled with innovative sonar and photogrammetric equipment. Access to most underwater sites can be difficult and hazardous owing to deep waters. However, this same inhospitable environment offers extraordinary opportunities to archaeologists because darkness, low temperatures, and low oxygen rates are all favorable to preservation. From a visualization pipeline perspective, this project had two main challenges. First, we had to gather large amounts of raw data from various sources. Then, we had to develop techniques to filter, calibrate, and map the data and then bring it all together into a single accurate visual representation.
The Ngongotaha river UDPS experiment: low-cost underwater dynamic stereo photogrammetry
We propose to integrate the newest developments in stereomatching theory, affordable parallel processing capabilities (using GPU e.g. PC gaming/graphic card) and statistical surface analysis to implement and test an in-situ Underwater Dynamic Stereo Photogrammetry (UDSP) system for civil engineering applications. The proposed UDPS system aims to provide underwater Digital Elevation Models (DEM), for applications such as a two-dimensional discrete matrix of data underwater elevations. Experiments on river bed stereophotogrammetry in the Ngongotaha Stream near Rotorua using consumer grade stereo cameras including Go-Pro and Fujifilm W3 are used in through-water and underwater calibration and stereo measurements of 32 pebbles on the river bed. Pebbles are measured and identified. Initial results highlight the need for specialised equipment for through-water and underwater photogrammetry experiments to limit blurring effects caused by the water-plastic-air interfaces. Despite poor optical quality of the images obtained, we were able to correlate pebble sizes from calibrated stereo depth maps and actual measurement.
Effect of stress conditions on collapse deformation behavior of a rockfill material
A set of saturated and dry-saturated large-scale triaxial tests were conducted in order to explore the effects of stress conditions on the saturation-induced collapse deformation behavior of a rockfill material. Specimens were tested in different confining pressures and for dry-saturated tests the specimens were submerged in various shear stress levels. The results indicate that in all of the dry-saturated tests a sudden reduction in the volume of the specimens was observed during the submerging process. The ratio of the minimum axial strength of a submerged specimen (at the end of the saturation process) to the shear strength of the specimen before saturation is defined as the coefficient of stress recovery, Csr. Results of the dry-saturated tests showed that this ratio increases as the confining pressure increases and decreases by increasing the shear stress level. According to the results of dry-saturated tests the values of internal friction angle reduction caused by saturation (Δϕc), the ratio of the elasticity modulus of the material after saturation to its elasticity modulus in dry condition, i.e., Ewet/Edry, and also the saturation induced sudden volumetric strain (εvc) decrease as the confining pressure increases. However the shear stress level does not have any meaningful effect on the variation of Dfc, Ewet/Edry and (εvc).