Range-gated active imaging is a prominent technique for night vision, remote sensing or vision
through obstacles (fog, smoke, camouflage netting…). Furthermore, range-gated imaging not only
informs on the scene reflectance but also on the range for each pixel. In this paper, we discuss 3D
imaging methods for underwater imaging applications. In this situation, it is particularly difficult to
stabilize the imaging platform and these 3D reconstruction algorithms suffer from the motion between
the different images in the recorded sequence. To overcome this drawback, we investigated a new
method based on a combination between image registration by homography and 3D scene
reconstruction through tomography or two-image technique. After stabilisation, the 3D reconstruction
is achieved by using the two upper-mentioned techniques. In the different experimental examples
given in this paper, a centimetric resolution could be achieved.
Underwater laser imaging is a useful tool for high resolution mapping and identification of threats in coastal and
also turbid waters of harbors and ports. In the recent past, the French-German Research Institute of Saint-Louis
(ISL) and the German Naval Research Department (WTD71-FWG) have performed different measurements in
the Baltic Sea in the field of submarine laser imaging with the aim to evaluate the performance of laser gated
viewing (LGV) and underwater laser scanning (ULS). Different scenarios were tested with respect to varying
environmental conditions. Working near a harbor or on the open sea under sunny and calm or windy and
rainy weather conditions, the measured turbidity, i.e. the attenuation coefficient of the water column, ranges
from 0.4 m-1 to 3 m-1. The experiments and imaging results are discussed with respect to 2D and 3D image
processing under the given environmental conditions.
Radar and infrared propagation drastically depend on the meteorological and oceanographic conditions. Concerning a joint sea trial of German research institutes at the Baltic Sea 2001, FWG was responsible for the environmental characterization of the marine boundary layer. In-situ measurements included recordings of atmospheric properties and sea surface parameters. They were studied by two multi-sensor buoys, on board a vessel and with radiosondes. Pressure, air temperature and humidity were measured from the sea surface to 1 km altitude. The free drifting buoys which have been constructed at FWG offer the opportunity to gain unperturbed, time resolved information about environmental parameters up to 5 m above sea level. Based on the in-situ measurements refractivity profiles can be calculated. With the help of the vertical refractivity gradient and the air sea temperature difference, conditions for radar and infrared propagation are determined. Further experimental results include wind speed and direction, wave height, rain rate and other important parameters. Taking advantage of the parabolic equation model radar propagation is calculated numerically. In conclusion, the experimental results and calculations underline the importance of the environmental characterization of the marine boundary layer with high temporal and spatial resolution.
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