[Ground-station] Upgrade to the EVE link analysis document - call for help

[Michelle Thompson]

Greetings all!

We have a pretty good earth-venus-earth link analysis here:

https://github.com/OpenResearchInstitute/documents/blob/master/Engineering/Link_Budget/Link_Budget_Modeling.ipynb

With a pdf here:

https://github.com/OpenResearchInstitute/documents/blob/master/Engineering/Link_Budget/Link_Budget_Modeling.pdf

Our next opportunity for inferior conjunction (when Earth and Venus are
closest together) is October 2026.

You can model the conjunction in the Notebook above and see all sorts of
things, but you don't have to open it at all to help make it better. I'll
explain.

There are many things that can be improved in this notebook. One of them is
the reflectivity of Venus. In other words, what percent of a signal, at a
particular frequency, will be reflected back to us? This is radar albedo.
Kind of important.

We generally have one number for this in most link budgets. But, that is
not the whole story for Venus. If a surface is relatively consistent over
time, then we can use one number in the link budget and everything works
out ok. But if there are variations? If we are considering an entire planet
as our reflective surface? If some geographies are way better than others?
Then it stands to reason that we need to know what geographies are going to
be facing Earth during the inferior conjunction. Why does this matter?

Because, the albedo variation on Venus is pretty large. Less than 0.1 to
0.5. More albedo is better for us. So, we want to find this number out, in
order to help sites like Dwingeloo and Stockert and ATA and DSES know what
they are up against.

If the albedo for October 2026 is high, then good. If it's low, then how
low is it? We can put this into the analysis and we are the better for it.

John K5JBT explains:

"Radar reflectivity maps of Venus certainly exist, but it's worth noting
that the main (useful) high reflectivity area is Aphrodite Terra, as
Maxwell Montes is relatively polar (~65N), while Aphrodite Terra is both
bigger in area and equatorial.

Maxwell Montes is in Ishtar Terra, the bright spot on this radar
reflectivity map from Magellan that's right at the top, left of center,
while Aphrodite Terra is the double blob of bright area just east of the
center around the equator.

This is the Global Reflectivity Data Record (GREDR) from the Magellan data
directory, loaded into QGIS.
https://pds-geosciences.wustl.edu/missions/magellan/gxdr/index.htm
Specifically the 'browse.img' data here:
https://pds-geosciences.wustl.edu/mgn/mgn-v-gxdr-v1/mg_3002/gredr/merc/"

If you go to this site, and read the README, and look at the maps, you can
clearly see the reflectivity in the variation, just as John describes.

The challenge before us is to connect these maps to a particular time and
date. This way, we can calculate the radar albedo in the Jupyter Notebook
for that particular date or range of dates. This improves our budget
numbers by a lot! This is well worth doing and we can do it now.

If you have some time and the inclination, please try and find a solid
source of data about "what side of Venus is facing the Earth at any
particular time". Preferably a public source that can go into the Jupyter
notebook as an input, every time it's run. Or, even better, as a class that
produces the result when it's called.

I'm hoping there's an existing database or some sort of observatory that is
tracking this, and we can duplicate the calculation inside the Notebook. If
we know this information, then we can figure out a way to connect that
information (what side of Venus is facing us) to the images that John
found, and then use those images to calculate the "real" radar albedo for
Venus. This would be a big step forward.

For a communications attempt, every dB matters, so this is directly helpful
to the EVE effort.

Reply here or on Slack or send a direct message - whatever works for you.

And, thank you to all for making really nice opportunities for amateur
radio and amateur astronomy happen with EVE messages. This is work that
makes a difference and it has not been done before. We've been able to
bounce carriers off Venus and detect them (2008 AMSAT-DL and 2025 Dwingeloo
and Stockert). Sending a message means that we need more SNR to tell the
difference between "on" and "off" or "0" and "1". Getting the actual albedo
number goes directly to "the bottom line" improvement in SNR.

Yours,
-Michelle
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