The flexible endoscope consists circularly ar-ranged optic fibers

702 32 Analyzing Particle Movements at Soil Interfaces

Figure 32.2: Setup of the endoscope: a vertical cross section through the en-doscope; and b horizontal cross section with the new illumination setup using LED’s.

Section 32.4.5). The other endoscopes are placed directly at the gravel-sand interface. Additionally, a flexible endoscope is used within the gravel layer to study the water flow within the pore volume.

32.3 Experimental setup 703

a length of 80 cm. For illumination, a cold light source is coupled to a ring of fiber conductors. For utilization in the rough environment of the pressure tank, the actual endoscope is surrounded by a protection cover, increasing the diameter to 1.4 mm. The end is covered by a 2-cm long steel tube with a glass window at the end. In order to introduce as little disturbance to the water current as possible, the endoscope is placed in a PVC sphere of similar size as the surrounding gravel stones to form a pore volume. Figure 32.4 shows the described setup.

32.3.3 Flow visualization