# Laser Observations of GALILEO Satellites at the CBK PAN Astroegodynamic Observatory in Borowiec
## 2 Laser Sensor at CBK PAN Borowiec (BORL)  
The CBK PAN Borowiec laser station (BORL) is located at the Astrogeodynamic Observatory in Borowiec near Poznan, which is owned by CBK PAN, Warsaw, Poland. A satellite laser sensor is a complex device that includes several components such as a transmitting and receiving telescope, laser modules (picosecond and nanosecond), a time scale, and measurement equipment that consists of two important components: the returning photon detection system and the counter for measuring time intervals. The BORL laser station is the only sensor of its kind in Poland. It was integrated into the ILRS on 13 May 1988 and is now part of the EUROpean LASer network (EUROLAS) consortium, which brings together European stations. The station's identification details are as follows:  
* Station code: BORL;
* Station number: 7811;
* Country: Poland;
* CDDIS SOD database number: 78113802;
* IERS DOMES database number: 122055001. The complete setup of the laser station can be found on the ILRS website [15]. The primary telescope is installed in a 65 cm Cassegrain transmitting and receiving system, functioning in the azimuth-elevation system. The current laser light source consists of two independent pulsed Nd:YAG laser modules as depicted in Figure 1.  
The larger laser is the EKSPLA PL-2250 picosecond pulsed laser manufactured by EKSPLA, Vilnius, Lithuania, which is used to observe active satellites equipped with retroreflectors that reflect the laser beam. The smaller laser is the high-power CONTINUUM SURELITE III nanosecond pulsed laser manufactured by Continuum (today Amplitude), San Jose, CA, USA, which is used to observe space debris objects in the LEO region, such as inactive satellites and launch vehicle units (rocket bodies). The basic parameters of the lasers are presented in Table 1.  
One operator controls the entire laser sensor. The sensor control software includes the following functions: preparing an observation plan by taking the ephemeris of objects and converting them to the telescope position, sensor calibration, performing laser distance measurements to observed objects (satellites/space debris), processing measurement data, saving observation results in specific formats, and sending them to databases. The BORL sensor's laser observations cover distances ranging from 400 km to approximately 24,500 km. The tracking list comprises over 100 objects, which includes the entire GALILEO satellite constellation consisting of 28 satellites. More detailed information about the construction of the BORL sensor can be found in [16]. The main tasks of the CBK PAN laser sensor in Borowiec are as follows:  
* Performing continuous observations of laser satellites covered by the ILRS. * Supporting missions such as LAGEOS-1, LAGEOS-2, LARES, LARES-2, GRACE, and others for the needs of modern geodesy and geodynamics. * Providing support for altimetry missions with laser measurements, including missions such as CRYOSAT-2 or JASON-3. \begin{table}
\begin{tabular}{c c c} \hline
**PARAMETER** & **EKSPLA PL-2250** & **CONTINUUM SURELITE III** \\ \hline Frequency & 10 Hz & 10 Hz \\ \hline Pulse energy & 0.05 J & 0.45 J \\ \hline Pulse length & 60 ps & 4 ns \\ \hline Peak power & 833 MW & 112.5 MW \\ \hline Average power & 0.5 W & 4.5 W \\ \hline \end{tabular}
\end{table} 
Table 1: The basic parameters of the laser used by the BORL station. Figure 1: The CBK PAN laser sensor in Borowiec consists of two independent laser modules: a smaller, nanosecond one in the foreground and a larger, picosecond one in the background. * Calibrating GNSS satellite orbits. * Providing support with laser measurements for Special Mission Support (SMS) for remote sensing missions such as SENTINEL-3A, SENTINEL-3B, and SENTINEL-6A/JASON-CS-A, and contributing to the European COPERNICUS program. * Performing continuous observations of space debris under the Space Safety program of the ESA and the Space Surveillance and Tracking program of the European Commission.