# Pre-course Activities

*October 9, 2024: Please keep in mind that our code has been updated since this class was given.
We currently require python version >= 3.9 (Feb 2026: Python 3.10 is now the minimum version)*

While it is possible to simply listen to the lecturers in the short 
course, we think that this is a far better learning experience if 
you are able to follow along with the examples. And for this we recommend the following:

## Getting Started 

- [Sign up for an Earthscope account](https://data-idm.unavco.org/user/profile/login)

- Install the software. We have 
[installation instructions](https://gnssrefl.readthedocs.io/en/latest/pages/README_install.html) 
for three different ways to access our code. 

  - The github or pypi install requires you are running linux and 
have python version between >= 3.9 on your system and feel comfortable
installing python packages.  

  - Dockers. Windows users should use this path, but it is also a good way 
for mac and linux users that don't want to install python and/or 
manage dependencies or environment variables.

 - Notebooks for GNSS-IR were created by Earthscope; their maintenance is not supported.
 If you feel comfortable fixing bugs in these older notebooks created by Earthscope, please submit a pull request.

- Check your environment variables (disregard this step if using dockers or notebooks)

Direct installers (github/pypi) need to set environment variables. In a terminal window, you should
check that they are active by typing these commands:

<pre>
    printenv REFL_CODE

    printenv EXE

    printenv ORBITS
</PRE>

If nothing comes back, you haven't set them. **They have to be set every time you run the code.**
That is why we recommend you put them in your .bashrc file. [More on environment variables and file formats](https://gnssrefl.readthedocs.io/en/latest/pages/README_install.html#environment-variables)

## Run the Code 

**Translate a Single GNSS File**

For github, pypi, and docker users, type in a terminal window:

<code>rinex2snr p038 2022 90 </code>

On my machine this returns:

<pre>
SUCCESS: SNR file was created 
/Users/kristine/Documents/Research/2023/snr/p038/p0380900.23.snr66
</pre>

This file was created using:

- a rapid GNSS orbit at GFZ
- GNSS data from EarthScope

If we knew we only wanted to look at GPS signals, we could have typed:

<code>rinex2snr p038 2022 90</code>

If you have any trouble with this command or do not have an Earthscope account, please try:

<code>rinex2snr p038 2022 90 -archive sopac</code>

**Next Step: Look at the reflection data for a single GNSS station**

<code>quickLook</code> is a module for assesing the reflections data from GNSS-IR site. We 
will start by using the simplest request, which evaluates L1 GPS data 
using a standard azimuth/elevation angle mask (i.e. all azimuths and elevation angles from 
5-25 degrees:

<code>quickLook p038 2022 90</code>

This creates two png files. If you are using a direct github/pypi install, they will come to the screen.

<img src="../_static/p038-2.png">
<img src="../_static/p038-1.png">

If you are using a docker, the png files will **not** come to the screen but 
will be stored. 

For example, on my machine the docker said the file was saved here:

<pre>
/etc/gnssrefl/refl_code/Files/p038/quickLook_lsp.png
</pre>

But as I was running the docker from /Users/kristine/docker_friday, I should view 
it from 

<pre>
/Users/kristine/docker_friday/refl_code/Files/p038/quickLook_lsp.png
</pre>

If you are able to download and translate a GNSS file and 
run <code>quickLook</code>, you are doing great.
While we mostly used the defaults, we want to emphasize that there are options 
to both of these codes.

- [rinex2snr](https://gnssrefl.readthedocs.io/en/latest/api/gnssrefl.rinex2snr_cl.html)

- [quickLook](https://gnssrefl.readthedocs.io/en/latest/api/gnssrefl.quickLook_cl.html)


You should read [the overview documentation](https://gnssrefl.readthedocs.io/en/latest/pages/understand.html)

## What is a Reflection Zone 

[Watch this video](https://www.youtube.com/watch?v=sygZMeCHHDg&t=23s)

**First example: ross**

Use the [refl_zones web site](https://gnss-reflections.org/rzones) to try and pick 
reflection zones for station [ross](https://gnss-reflections.org/geoid?station=ross) 
that was used in the introduction section. The web 
app tells you the mean sea level for this site. But 
that is not the reflector height you want to use for the reflection zone.  What value should
you use?  Try a few different values.

Now translate a GNSS file to see if you made a good choice.

<code>rinex2snr ross 2020 211 -archive sopac </code>

Then run quickLook:

<code>quickLook ross 2020 211</code>

What is the RH associated with the lake? Do the good azimuths in the periodogram summary
agree with the google map image? (note: google earth is now using an image from winter, so it 
is quite challenging to see what is going on - so you might look 
back at the [earlier discussion](https://gnssrefl.readthedocs.io/en/latest/pages/understand.html)).

Change the frequency on the command line to L2 (-fr 2). Note how the periodogram plots 
have two peaks instead of one. This is a problem!

Now try to look at the Glonass data. You need multi-GNSS orbits. For data in 2020, you must
specify multi-gnss orbits.

<code>rinex2snr ross 2020 211 -archive sopac -overwrite T -orb gnss</code>


Rerun quickLook:

<code>quickLook ross 2020 211 -fr 101</code>

What comes back?