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@ -47,6 +47,30 @@ individual site navigation files into one. The archive for the daily file can
be downloaded from: https://cddis.nasa.gov/archive/gnss/data/daily/. Access be downloaded from: https://cddis.nasa.gov/archive/gnss/data/daily/. Access
to this site requires registration, which is free. to this site requires registration, which is free.
After registration, automated downloads can be done in a script by adding
the following entry to one's netrc file (filling in the appropriate values
for username and password):
```bash
echo machine urs.earthdata.nasa.gov login <your username> password <your password> >> ~/.netrc
chmod 600 ~/.netrc
```
and then including the following code (or similar) in a script:
```bash
day=$(date +%j)
year=$(date +%Y)
yr=$(date +%y)
RINEX_NAV_FILE="brdc${day}0.${yr}n"
curl \
--cookie-jar /tmp/cookie \
--netrc \
--location \
--output "${RINEX_NAV_FILE}.gz" "https://cddis.nasa.gov/archive/gnss/data/daily/${year}/brdc/${RINEX_NAV_FILE}.gz" \
uncompress --force --keep "${RINEX_NAV_FILE}.gz"
ls -al "${RINEX_NAV_FILE}"
```
These files are then used to generate the simulated pseudorange and These files are then used to generate the simulated pseudorange and
Doppler for the GPS satellites in view. This simulated range data is Doppler for the GPS satellites in view. This simulated range data is
then used to generate the digitized I/Q samples for the GPS signal. then used to generate the digitized I/Q samples for the GPS signal.