GIRAS-GPS-Solutions

GIRAS (GNSS-IR Analysis Software) is an open-source MATLAB-based software for GNSS-IR analysis.

• Version: 1.0.0 (Published in GPS Solutions: Altuntas, C., & Tunalioglu, N. (2022). GIRAS: an open-source MATLAB-based software for GNSS-IR analysis. GPS Solutions, 26(1), 16.)

Overview

GIRAS is an open-source software for GNSS-IR (Global Navigation Satellite System - Interferometric Reflectometry) analysis. It provides tools for file reading, data analysis, and data visualization, developed in MATLAB R2018b.

Features

• Support for multi-GNSS data (GPS, GLONASS, Galileo, Beidou)
• Compatible with RINEX 2 and RINEX 3 observation files
• Support for both broadcast ephemeris (navigation file) and precise ephemeris (sp3) files
• Comprehensive data visualization and analysis capabilities
• First Fresnel Zone (FFZ) calculation and visualization
• SNR-based reflector height estimation

Main Modules

GIRAS consists of three main modules and five sub-modules:

1. Read & Convert Files

This module reads and processes raw GNSS data:

• Supports RINEX 2 and RINEX 3 observation files
• Reads broadcast or precise ephemeris files
• Saves processed files in MAT format
• Creates SNRMAT files for further analysis

2. Pre-analysis

This module provides tools to review the SNRMAT files:

2.1 SNR & dSNR Data

• Visualizes and pre-analyzes SNR data from each satellite
• Customizable options for satellite selection, SNR observation type, units, and angle limits
• Polynomial detrending of SNR data

2.2 Sky View

• Creates sky plots for satellites in the SNRMAT file
• Support for filtering by satellite system
• Highlights selected satellite paths

2.3 FFZ (First Fresnel Zone)

• Generates FFZ graphics and quantities for observed satellites
• Customizable reflector height and satellite elevation angles
• Export as MATLAB plots or Google Earth KML files

3. Analysis

This module analyzes SNRMAT files and estimates SNR metrics:

3.1 Make Estimations

• Processes selected SNRMAT files
• Configurable satellite systems, SNR data type, and detrending polynomial degree
• Customizable elevation and azimuth angle ranges
• Adjustable reflector height and precision settings

3.2 Improve Estimations

• Refines analysis results using filtering techniques
• Options for frequency range, elevation angle, background noise conditions
• Median Absolute Deviation (MAD) filtering
• Interactive plotting and data visualization
• Export of refined results

File Structure

• /data/ - Contains mandatory files, input and output data
  • /constants/ - Pre-defined information files
  • /inp_files/ - Input files (observation, ephemeris)
  • /mat_files/ - Processed MAT files
• /FFZ/ - Contains Google Earth FFZ files
• /functions/ - Contains data reading, analysis, and utility functions
• /results/ - Contains analysis results
• /settings/ - Contains settings files

Mandatory Files

• satellite_list.mat - Contains the satellite PRN list
• wavelengths.mat - Contains frequency and wavelength information
• Settings files:
  • ana.mat - Analysis-1 (make estimations) settings
  • ana2.mat - Analysis-2 (improve estimations) settings
  • pra.mat - Pre-analysis settings
  • rcf.mat - Read & convert files settings

Quick Start

1. Read & Convert Files:

   • Select observation files and ephemeris files
   • Choose between just reading/converting or also creating SNRMAT files
   • Set station position (from RINEX or manually)
   • Click READ & CONVERT

2. Analysis - Make Estimations:

   • Select SNRMAT files created in step 1
   • Configure satellite systems, SNR data type, and polynomial degree
   • Set angle limitations and estimation parameters
   • Enter filename and click RUN

3. Analysis - Improve Estimations:

   • Select results file from step 2
   • Apply quality filters (elevation angle range, background noise condition)
   • View filtered results and examine plots
   • Save refined results

Authors

• Cemali ALTUNTAS (cemalialtuntas@gmail.com, cemali@yildiz.edu.tr)
• Nursu TUNALIOGLU (ntunali@yildiz.edu.tr)

Yildiz Technical University, Istanbul, Turkey

Citation

If you use GIRAS in your research, please cite the following paper:

Altuntas, C., & Tunalioglu, N. (2022). GIRAS: an open-source MATLAB-based software for GNSS-IR analysis. GPS Solutions, 26(1), 16.