# Deepwater 3D Measurements with a Novel Sensor System
## 3 Results  
The underwater 3D sensor system was designed to be mounted on a work-class ROV due to its dimensions and weight (see Figure 6a). For practical use when surveying underwater structures, pipeline systems, or other underwater measurement objects, the control of the UWS is coupled with the ROV control. This means that either the ROV pilot takes control of the UWS or an operator works directly with the ROV pilot. This takes place in a special room aboard the ship, which is equipped with the necessary control technology (see Figure 6b).  
The necessary underwater calibration of the sensor system usually takes place immediately before the measurement. During the measurement operation itself, 2D data are recorded continuously with the two stereo cameras and the color camera until the desired 3D measurement data are completely recorded. The collection of measurement data can take up to several hours.  
During 2D data acquisition, paired image sequences, one from each camera, each consisting of ten subsequent images, are converted into 3D data sets. The reduced 3D models of the current scans are displayed on the monitor. This display provides the operator with the quality control of the current measurement. Since the ROV light must be turned off during the measurement process due to the structured lighting with the projector, the video stream from the color camera is used as an orientation aid for the ROV pilot.  
To prepare the experimental studies and identify typical use cases, the sensor system is configured in three different modes corresponding to three potential application scenarios. These modes differ in the number and frequency of image data recorded and are designed for different speeds during data acquisition.  
The modes differ in detail and are assigned to the following three use cases:  
* Use case 1: The complete measurement of a \"large\" structure (approx. 5-10 m in diameter) on the ground with a mean scanner speed of approx. 0.5 m/s;
* Use case 2: A pipeline is traveled at a high scanner speed of approx. 1 m/s (constant) with minimal changes in direction and an average measuring distance of 2 m;  
Figure 6: UWS mounted on ROV immediately before measurement application (**a**) and control room for UWS and ROV on the ship (**b**).  
* Use case 3: The inspection of an anchor chain or similar object is carried out at a low scanner speed of approx. 0.2 m/s (constant) with minimal changes in direction.  
In addition to the experimental measurements assigned to the three use cases (see Section 3.2), tests were carried out to determine the potentially achievable 3D measurement accuracy. A special experimental schedule was drawn up here. Both static measurements and those with a moving sensor system were carried out.  
The further test sequences were each assigned to one of the three use cases (modes). The result of the data recording is always a 3D model of the sensor system's surroundings scanned during the recording period. This 3D model contains both globally connected 3D data generated using visual odometry and color data with low absolute accuracy, as well as 3D data sets in high detail. A low-resolution model is generated in real-time and can be displayed by the operator or ROV pilot via a monitor with a low latency of less than 200 ms to assess the completeness of the measurement results.  
Figure 7 shows the sensor system before the application and the transport of the ArUco markerboards into the water by a crane.