# Deepwater 3D Measurements with a Novel Sensor System
## 2 Materials and Methods  
### Underwater 3D Sensor System  
#### 2.1.1 Sensor Hardware  
The new sensor system (called UWS) was developed as part of a publicly funded joint project in cooperation with project partners from industry and research. Two demonstrator variants (UWS1 and UWS2) of the same hardware configuration with different geometric designs were set up and used in the measurements. The sensor system consists of the following components:  
* Two monochrome measurement cameras (type Baumer VLTX-28M.I with lenses SCHNEIDER KMP-IR CINEGON 12/1.4);
* A projection unit (in-house manufactured with lens SCHNEIDER STD XENON 17/0.95);
* A color camera (type Baumer VLTX-71M.I with lens SCHNEIDER KMP CINEGON 10/1.9);
* A Fiber Optic Gyro Inertial Measurement Unit (IMU, type KVH 1750 IMU);
* Two flashlights (using Cree CXB3590 LEDs);
* An electronic control box (in-house manufactured);
* Cylindrical underwater housing for individual components;
* Wiring for power supply and data transfer. A schematic view of the sensor system is shown in Figure 1.  
The components of the sensor system are integrated into four underwater housings. Two monochrome measurement cameras are installed as a stereo pair in the outer two housings. These are used in combination with a pattern projector installed in one of the central housings for 3D measurements. The projector generates aperiodic-sinusoidale fringe patterns for the 3D measurement and consists of an LED operating in the blue wavelength range with a high light output, a rotating glass mask, a motor, and a projection lens, which is the so-called GoBo-projection [29]. In addition, electrical drivers and control electronics are integrated into the same housing. Next to the underwater housing for the projector,there is another housing that contains the color camera and an inertial measurement unit (IMU) with a fiber optic gyroscope. The underwater housings are mounted together on a carbon fiber rod, which is decoupled from the support frame. There are also two LED flashlights on the outside of the sensor carrier. These are arranged such that they primarily illuminate the measurement object and do not illuminate particles in the close range of the camera to minimize backscatter. On the sensor carrier, there is a fifth underwater housing with the electronics of the power supply and network technology for data transmission. All sensor data are transmitted via a network. For this purpose, a glass fiber from the tether of the diving robot is used during the measurement. The 3D calculation and evaluation of the data takes place outside the water on a PC workstation on the ship, which is connected directly to the sensor via a ten-gigabit fiber optic link. This means that there is no need to integrate powerful hardware for calculations in the underwater housing, thereby saving cost and weight. The 3D reconstruction and parts of the further processing take place online to enable the direct quality control of the recordings. The difference between the UWS1 and UWS2 versions lies in the more compact arrangement of the components in the UWS2 sensor. This means that the image fields and the standard measuring distance change for identical cameras and lenses. Consequently, the UWS2 system results in a reduction in the standard measuring distance from 2.0 m to 1.3 m, a smaller field of view of 0.7 m \(\times\) 0.6 m, and a brighter illumination of the scene. However, due to the necessary shorter distances to the measurement objects, the UWS2 system must be navigated more precisely by the ROV pilot to avoid collisions with the seabed or the measurement objects. The monochrome measurement cameras are arranged in a typical stereo configuration [29] and are used to record images for the calculation of the detailed 3D data sets. They can be operated with a resolution of 2.8 MPix at a frame rate of 411 Hz. In the typical measurement mode, a 1 MPix resolution is used, with a frame rate of up to 900 Hz.