## 3 Results and Discussion
In 2021 and 2023, the Minister of Education and Science established the Polish Metrology program. The basic principles of the program are as follows:  
* Support for the conduct of scientific research or development work in areas related to metrology by entities of the higher education and science system, in cooperation with the President of the Central Office of Measures, hereinafter referred to as \"GUM\". * Supporting the implementation of projects aimed at increasing the level of research capabilities of metrological institutions, strengthening intellectual capital, increasing the competitiveness of the Polish economy in strategic areas for the country, developing modern technologies, and stimulating the development of metrology, in particular in the areas of health, environment, energy, and advanced measurement techniques, as well as development of digital technologies. The consortium consisting of Maritime University of Gdynia (leader), Gdansk University of Technology, and the University of Gdansk is currently conducting the second project related to the development of the \"concept of building metrological infrastructure in the area of underwater acoustics at GUM\". The development of underwater acoustics is closely related to the intensification of work in the marine areas of the Baltic Sea, correlated with the broadly understood economic development of Poland and marine research. The list of plan infrastructure is presented in Table 3. Figure 6 presents a general view of buildings intended as metrological infrastructure in the area of underwater acoustics. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No** & **Institution/Source of Guideline** & **Calibration Uncertainty [dB]** & \begin{tabular}{c} **Range of** \\ **Frequency [Hz]** \\ \end{tabular} & \
\begin{tabular}{c} **Method of** \\ **Calibration** \\ \end{tabular} & **Project/References** \\ \hline \multirow{7}{*}{
\begin{tabular}{c} 1 \\ 1 \\ \end{tabular} } & & 20–2000 & Pressure chamber & \\  & & B\&K 8104: & & \\  & T\&B\&K 8106: & & \\  & T\&T\&K &B\&K 8106: & \\  & & T\&K & 02–0.5 & & \\  & T\&Kive & Acoustics SM4M recorder & & & [27] \\  & & & 1.0 & & 20–1000 & Pressure chamber \\ \hline \multirow{7}{*}{2} & & & 5–400 & Pressure chamber & \\  & & B\&K 8104: & & \\  & & 0.5 & & 5–400 & Pressure chamber & \\  & & B\&K 8106: & & Free-field & EURAMET 15 RPT02 \\  & NPL & 0.5 & & 250–2000 & & \\  & & & 1.0–0.5 & & & [27] \\  & & Wildlife Acoustics SM4M recorder & & & & \\  & & 0.5 & & & \\  & & & 5–315 & Pressure chamber & \\ \hline \multirow{7}{*}{3} & & DFM & & & \\  & Danish National Metrology & B\&K 8104: & & \\  & Institute & 0.2–0.5 & & & \\  & FOI & B\&K 8106: & & \\  & Swedish Defence Research & 0.3–1.0 & & & \\  & Agency & & & & \\ \hline \multirow{7}{*}{4} & & B\&K 8104: & & \\  & FOI & 0.8 & & & \\  & & B\&K 8106: & & \\  & & Agency & & & \\ \hline \multirow{7}{*}{5} & & CNR/ISPRA & & & \\  & National Research Council of & Wildlife Acoustics SM4M recorder & & & \\  & Italy/Italian National Institute for & & & & \\  & Environmental Protection and & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: A list of calibration facilities for frequencies below 1 kHz. Figure 5: An acoustic coupler for calibrate hydrophones at low frequencies in GUM (Gdynia): a—acoustic coupler for calibrating hydrophones, b—vibration exciter inside the sound-absorbing casing, c—laser mounting point, d—B&K Pulse system for registering and analysis data, e—B&K hydrophones cables, Acc1—vibration exciter shaft displacement meter (B&K), Acc1, Acc2—B&K 3D displacement meters (vertical axis for comparison displacement from laser), f—hydrophone positioning system (allows: rotation about the axis of one or two hydrophones and vertical (independent 2 hydrophones B&K 8106 and 8104) and horizontal (2 hydrophones together) shift), g—operator’s station in an adjacent room, communication with the system via Ethernet.