leo-rain/gnssr_synth

Obtain and analyse GNSS-R water level observations and create synthetic SNR data

In this repository are functions for obtaining, analyzing and estimating the precision of ground-based GNSS-Reflectometry sea level observations. This includes functions for creating synthetic SNR data and obtaining sea level measurements via spectral analysis or via inverse modelling of SNR data, as per https://doi.org/10.1109/JSTARS.2020.3010413.

The codes can be cited as follows: Purnell, D.J., Gomez, N., Chan, N.H., Strandberg, J., Holland, D.H. and Hobiger, T. (2020). Quantifying the uncertainty in ground-based GNSS-Reflectometry sea level measurements. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing (JSTARS) doi: 10.1109/JSTARS.2020.3010413.

For any questions or suggestions or issues please contact Dave Purnell: [email protected]

See the code 'example_code.m' to see examples on how to use some of the following functions written by David Purnell: analyzesnr_fun makesnr_fun readsp3file noisefun noisefunresid gnss2azelv scalenoisepower trop_delay_tp rinex2snrfile spectralanalysis_kl tidemod_kl tidemod_kl_plot coef2ampphase invsnr invsnr_plot bspline_spectral bspline_js

The directory 'data' contains a short period of data from site 'sc02' that is used to show how to run functions in 'example_code.m'

IMPORTANT: To run these functions, you will need to download some or all of the following codes / models and copy them to the directory:

1. Download the multipath simulator model by Nievisnki & Larson, place directory in 'functions' and rename to 'mpsim' Download link: https://geodesy.noaa.gov/gps-toolbox/MPsimul.htm

2. You also need to download the following 3 codes from the Geodetic toolbox made by Mike Craymer and place them in the 'functions' directory: doy2jd.m jd2gps.m cal2jd.m Download link: https://www.mathworks.com/matlabcentral/fileexchange/15285-geodetic-toolbox?focused=6513448&tab=function&s_tid=mwa_osa_a

3. For tropospheric delay corrections, download the following codes and place in the https://vmf.geo.tuwien.ac.at/codes saasthyd.m asknewet.m vmf1_ht.m gpt2_1w.m gpt2_1w.grd

4. ecef2lla.m by Michael Kleder https://github.com/dhale/idh/blob/master/bench/src/gph/ecef2lla.m

5. 'The Fastest Lomb-Scargle Periodogram estimator in the West' by A Eleuteri: http://www.mit.edu/~gari/CODE/Lomb/fLSPw.m

6. Download the the 't_tide' model by Rich Pawlowicz: http://www.eos.ubc.ca/~rich/t_tide/t_tide_v1.4beta.zip And move the directory inside the 'functions' directory

7. Download b-spline codes for matlab by Levente Hunyadi, place the directory in the 'functions' directory. https://www.mathworks.com/matlabcentral/fileexchange/27374-b-splines

IMPORTANT: The directory 'functions/fresnel' contains outdated codes written by Kristine Larson and others to produce fresnel zones. An updated version of these codes can be found at: https://geodesy.noaa.gov/gps-toolbox/GNSS-IR.htm I am using the old version because I prefer it to the newer version.

ADDING OTHER SITES: The directory 'functions/station_inputs' contains parameters for several different sites. If you want to analyze data at a site that is not there, you will need to create a station_input.m file for the new station. A description of the parameters is given in the 'sc02_input.m' file

OBTAINING GNSS DATA AND ORBIT FILES: The directory 'functions/getsfiles' contains some codes for obtaining GNSS data and sp3 files via ftp

NOTE: apologies for the mess and bad code writing practices