# A New Online Service for the Validation of Multi-GNSS Orbits Using SLR
## 2 Materials and Methods
### Structure and Functionality  
The main tasks of the developed service are to: (1) store archival and current information about the ILRS laser stations and multi-GNSS satellites; (2) store the multi-GNSS microwave orbit validation results using SLR; (3) allow for fast and advanced online analyses on the stored dataset; (4) provide an autonomous computing center; and (5) generate up-to-date dataset and reports. Therefore, the GOVUS system consists of advanced database system, seven main modules of the web-based application and server-side, and time-scheduled computational scripts. The client-side of the application has been developed using Django Framework. The database system responsible for storing and managing data is the PostgreSQL, which provides a good performance for the query requirements and allows for performing spatial analyses using PostGIS extension. Currently, no spatial analyses are available in GOVUS, but the core database system is prepared for supporting the future extension of the service. Four major tables are publicly available and directly used in data analyses: (1) observations (SLR residuals); (2) laser stations; (3) multi-GNSS satellites; and (4) time-variables for multi-GNSS satellites (see Figure 3):  
* The table called \"observation\" contains one record for each SLR residual row resulted from the validation process. Additionally, local time of observation is calculated, in reference to the related station's longitude. * The table called \"station\" describes the features of each single SLR station including information about: code (4 letter shortcode), id (4-digits number unique for the station), country, tectonic plate, operational sub-network, CDDIS number, coordinates, primary wavelength, detector type, signal processing, mode of operation, timer type, max repetition rate, laser power, laser type, beam diameter, pulse width, max energy and date of update. All information is filled in based on the official ILRS stations site logs. * The table called \"satellite\" describes features of each satellite from all systems, GPS, GLONASS, Galileo, BeiDou and QZSS, and contains information about: Satellite Vehicle Number (SVN) (unique for each satellite but not generally structured), NORAD, COSPAR, slot in orbital plane, \begin{table}
\begin{tabular}{c c} \hline \hline  & **SLR Validation** \\ \hline Software & Remorse GNSS Software 5.2 with modifications [39] \\ GNSS considered & GPS, GLONASS, Galileo, BeiDou-2 MED and XSQ, QZSS \\ Considered orbit providers & CODE \\ Validation routine & daily \\ Time span & since DOY 146/2012 (GPSWEEK 1689) \\ \hline \hline \multicolumn{3}{c}{**Models for Processing**} \\ \hline Reference frame & SLRF2014 with posthesemic deformations from ITRF2014 [13] \\ Solid Earth tides & IERS 2010 Conventions [35] \\ Ocean tide & FE30204 [43] \\ Toposphere & Mendes and Pavlis 2004 [11] \\ Relativity & IERS 2010 Conventions [35] \\ LRA offsets & according to the recommendations of the ILRS [7] \\ \hline \hline \multicolumn{3}{c}{**Orbit Reconstruction**} \\ \hline Satellite positions & CODE MGEX ephemerides \\ Earth Rotation Parameters & CODE MGEX ERP files \\ Albedo model & GPS, GLONASS, Galileo, QZSS applied since 08/2017; BeiDou not applied \\ Antenna thrust & GPS, GLONASS, Galileo, QZSS applied since 08/2017; BeiDou not applied \\ Attitude model & yaw steering assumed for all satellites \\ SRP model & ECOM2 \\ Stochastic pulses & every 12 hours in along-track, cross-track, and radial \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of observation modeling and parameter estimation strategy.