CYGNSS GNSS-R Raw Intermediate Frequency Data Processing

Reflectometry with Galileo signals

Set of Matlab scripts to process the Galileo E1B reflected signals present in CYGNSS Level 1 Raw Intermediate Frequency Data Records.

Description

Processing of the binary data in the registers to obatin a time series of delay Doppler maps (DDMs) for Galileo E1B signals. Also, it plots the ground tracks of the reflections and their estimated SNR. The input files are the CYGNSS Level 1 Raw Intermediate Frequency Data Record, that contains the samples of the signal to process, the CYGNSS Level 1 Science Data Record netCDF file from the same date and CYGNSS satellite as the Raw IF record file. Both type of registers are available to the public: https://podaac.jpl.nasa.gov/CYGNSS?tab=mission-objectives&sections=about%2Bdata. The netCDF file contains the DDMs processed on board during that day, as well as relevant information for processing and geolocation of the reflections. The important variables values during the time of the Raw IF record (reported in its metadata) is read from the netCDF file and used during the calculation of the DDMs. Also, it requires a rinex Galileo navigation file to get the satellite orbits and estimate specular reflection points position, delay and Doppler shift.

The processing parameters are completely configurable, such as coherent and non-coherent integration time, delay and Doppler resolution, etc.

Executing program

If processing a new register (or using the script for the first time) follow these steps to prepare the data files:

• First, store the Raw If binary file, the Level 1 Science Data Record netCDF file and the rinex Galileo navigation file in the same directory.
• Edit config.m with the appropiate files directory in the variable folder_path.
• Edit case_selector.m to add a new case with the corresponding file names, preferred channel to process and Galileo satellite identification number. Read case_selector.m comments for more details in the case definition.

DDM Processing

• Edit config.m to set the desired processing parameters. The configurable parameters are the total processing time, coherent and non-coherent integration time, decimation ratio which determines the delay resolution, and the resolution, maximum value and optional central offset for the Doppler bins. These are defined in the "Input parameters" section of the script.
• Set plot_tracks flag to 1 to plot the ground tracks of the 4 GPS DDMs processed on board while reading the netCDF file before processing the binary data and the ground track of the selected Galileo reflection.
• After configuration, run the script main.m. It will calculate the Galileo DDMs during the processing time and plot the results.