## 4 Other Oceanographic Measurements  
Numerous long-term studies have shown that hydrophysical processes in the aquatic environment exhibit spatial and temporal fluctuations on a global scale. Therefore, both before and after each series of hydrographic measurements, one must determine precisely the inter-relationships between the phenomena and processes in the aquatic environment in their interaction with the atmosphere, land and seafloor. This issue is dealt with by an interdisciplinary science on the border between biology, geophysics, meteorology, physics, called oceanography [25]. This paper will discuss selected oceanographic parameters, without which it would be impossible to conduct hydrographic measurements. Apart from the water level, as discussed above, these parameters include the temperature of the surface and deep-water layer, salinity, hydrostatic pressure, wind wave and ocean currents. It is not always possible to perform hydrographic measurements with an USV as scheduled. Based on previous experience, a hydrographic survey in the coastal zone using a vessel weighing about 12 kg can be performed in small waves (sea state 0-1 in the Douglas scale) and low wind (wind strength 0-1 in the Beaufort scale). Wind blowing at 10 km/h (2 on the Beaufort scale) forms small wind waves of 10-20 cm on the water surface, which can have an adverse effect on the vessel stability and on the sounding profile (with no significant heel). A short-term weather forecast shared on the Internet, e.g., [[http://www.pogodynka.pl/](http://www.pogodynka.pl/)]([http://www.pogodynka.pl/](http://www.pogodynka.pl/)), can be used to determine the forecast weather conditions. The oceanographic parameters described above (wind wave and wind) play a key role in performing hydrographic measurements with an USV. Adverse hydrometeorological conditions make it impossible to perform such work. Therefore, short-term weather forecasts should be monitored in summer and in winter, and bathymetric measurements should be started on a waterbody when an \"advantageous\" weather window opens. After an advantageous weather window is established, more oceanographic parameters must be assessed, such as temperature, pressure and salinity, which directly affect the speed of sound in water (it is the main factor affecting the accuracy of the depth measurements by a hydroacoustic device). This can be determined with an accuracy of \(\Delta c=\pm 0.03\) m/s, by direct methods, such as a sound velocity profiler (SVP), which measures the actual speed of sound in water as a function of depth. There are also indirect methods, such as CTD (conductivity, temperature, depth) oceanographic sounds, which are used in measurements of ocean temperature and salinity and other physical properties of the ocean depth and surface, such as conductivity and oxygen content [26]. Subsequently, these physical parameters are used to calculate the speed of sound in water with empirical formulas developed by [PERSON], [PERSON], [PERSON], [PERSON], or [PERSON]. The most common is [PERSON]'s formula, which establishes the relationship between speed of sound in water c (m/s), temperature T (\({}^{\circ}\)C), salinity S (\(\%\)\(\%\)) and pressure P (kG/cm\({}^{2}\)). The formula has the form of a polynomial [27]:  
\[c(S,T,P)=1449.14+\Delta c_{S}+\Delta c_{T}+\Delta c_{P}+\Delta c_{STP}. \tag{3}\]  
The other elements of the formula represent adjustments for other non-standard conditions:  
\[\Delta c_{S}=1.39799\cdot(S-35)+1.6920\cdot 10^{-3}\cdot(S-35)^{2}, \tag{4}\]  
\[\Delta c_{T}=4.5721\cdot T-4.4531\cdot 10^{-2}\cdot T^{2}-2.6045\cdot 10^{-4} \cdot T^{3}+7.9851\cdot 10^{-6}\cdot T^{4}, \tag{5}\]  
\[\Delta c_{P}=1.60272\cdot 10^{-1}\cdot P+1.0268\cdot 10^{-5}\cdot P^{2}+3.5216 \cdot 10^{-9}\cdot P^{3}-3.3606\cdot 10^{-12}\cdot P^{4}, \tag{6}\]\[