## 2 Materials and Methods
### Other Factors Affecting the Total MBES Survey Time  
In addition to the time necessary to perform measurements on the survey lines, the following three parameters should also be included in the time calculations:  
* Time to perform patch test calibration--\(T_{kal}\);
* Total time devoted to cross-check \(T_{cc}\) maneuvers;
* Time to reach the research area and return to the port--\(T_{rej}\).  
Before the start of the survey, the hydrographer should perform the calibration of the multi-beam echosounder called patch test. The test enables the determination of errors in measuring the mounting angles of the MBES sonar head. As a result, corrections are obtained for which the initial angular values of the transducer should be corrected. Calibration should be performed, if possible, in good weather conditions, and in an area with a depth and bottom type similar to the planned survey area [39].  
A cross-check maneuver is performed, especially in the outermost beam sectors, to check the correctness of the sonar operation and measurement accuracy [41]. The multi-beam echosounder performance should be checked each time before and after the hydro graphic works, but also during the survey if the hydrographer deems such action necessary and justified. The cross-check maneuver consists of making two passes on profiles perpendicular to each other and then comparing the readings of outer acoustic beams with the readings of vertical beams. The total time allocated to cross-check \(T_{cc}\) maneuvers is calculated according as follows:  
\[T_{cc}=n_{cc}\cdot T_{cc1}, \tag{16}\]  
where \(n_{cc}\)--number of _cross-check_ maneuvers; \(T_{cc1}\)--time of a single cross-check maneuver [s].  
The time of reaching the survey area and returning to the home port \(T_{rej}\) is calculated according to the following:  
\[T_{rej}=2\cdot\frac{S_{rej}}{V_{rej}}, \tag{17}\]  
where \(S_{rej}\)--distance to the area of hydrographic works [m]; \(V_{rej}\)--vessel's speed at the transition to the survey area and return to the port [m/s].  
The time spent on calibration, control maneuvers, and transition to the survey area are forecast variables given as an approximation. These parameters may change after, e.g., deterioration of weather conditions, resignation, extension of the patch test time, or an increase in the number of cross-check maneuvers.  
It is extremely important that the survey plan is flexible, that is, that it considers possible delays caused by changing weather conditions, survey equipment malfunctions, or failures of main power plant of the vessel, which cannot be predicted or avoided. Hence, the total time required to perform a specific hydrographic survey should also take into account the so-called \(T_{op}\) survey delay time:  
\[T_{op}=T_{wp}+T_{us}, \tag{18}\]  
where \(T_{wp}\)--time of the survey interruption due to weather conditions [s]; \(T_{us}\)--time of the survey interruption due to equipment failure [s].  
In the event of detection of underwater objects (i.e., navigational obstructions) lying in the area of the survey works, additional hydrographic research should be performed to obtain as much information about the target as possible. It often happens that the object is a new object that has not appeared in the available digital databases and has not been plotted on the charts. As part of additional activities at sea, bathymetric and sonar measurements are carried out to assess the type and size of the object and the degree of risk to navigation. Such bathymetric and sonar verification is associated with additional time \(T_{wcr}\) to be predicted in the time calculation. The time is calculated based on the following formula:  
\[T_{wcr}=n_{ob}\cdot(T_{batt}+T_{sss}), \tag{19}\]  
where \(T_{batt}\)--time of bathymetric measurements in the area of the newly detected underwater object [s]; \(T_{sss}\)--time of sonar survey in the area of the newly detected underwater object [s]; and \(n_{ob}\)--number of detected underwater objects.