So, Tammo Jan is also here in the audience.
And of course, the people from Stockert.
Before I start the presentation, I have something else to point out.
This was yesterday.
Okay, now we can get to business.
Thank you for your patience.
So, luckily, yesterday evening, the last presentation was about Dwingeloo.
And now the first one is.
So I can skip a few things and spend more time on the content.
So this is the telescope in Dwingeloo.
Tammo Jan already talked a bit yesterday about the history.
So here you see actually somebody in the early days watching from the telescope
and we can use it these days for all kinds of fun projects.
So we do pulsars.
You've seen that yesterday. We do hydrogen.
We have done recombination lines.
We have received Voyager and we received all kinds of other satellites.
And that's all received interesting stuff, either satellite
or radio astronomy.
But and again, as Tammo Jan already mentioned yesterday,
we also have a group of radio amateurs using the dish.
Over here you see one of the volunteers, Jan van Muijlwijk, who was doing, moon bouncing, EME.
So they send signals to the moon, and then it bounces back
and they can communicate with people all over the world via the Moon.
And the 25 meter dish is so strong
that if you send the signal to the moon and you switch,
to receive in two seconds, you actually hear your own voice coming back.
That's actually what he's doing here.
Together with a sound artist called Hainbach, they're making recordings
of the echoes, from the moon, for artistic purposes.
The interesting thing is when
you send your voice to the moon and it comes back, it sounds distorted.
So it's not very clear audio anymore.
But you have something which is called fading. Frequency selective fading.
So some of the frequencies are suppressed and some of them are amplified,
and you get a really funny voice back.
For them, that's a distortion because they want to communicate.
So anything that degrades the signal is bad.
For us, it's an opportunity because something happens on the moon
that actually transforms that signal into this distorted signal.
So that is information about the moon.
And that is what this presentation is about.
We have been doing this in many steps, and we've made a lot of mistakes around,
in the path
and I wanted to share a little bit of what we have done and what we
have discovered.
So we're not the first ones to do this.
And there was also a bit in the history talk already, yesterday.
This is the Arecibo dish, that's unfortunately broken now and not active anymore.
But this has been used for radar, to planets.
So they send the signal to Venus, the signal comes back, and from that signal,
they could actually determine the rotation of Venus.
Which is strange, because it's the only planet
which is rotating in the other direction than the rest of the planets.
But due to the atmosphere, you could not see that.
So they actually had to determine it with radar.
This is an article from the 60s.
So a lot of this radar research has been done,
in the 60s, and there are very interesting papers about this.
And we can see maybe, maybe we can do this, maybe we can.
But that was this challenge.
More recent, until Arecibo was broken, it was used to make pictures of Venus.
That's actually a radar map of Venus you see there.
And they do it together with the Greenbank telescope.
So Arecibo sends, Greenbank receives, and they get a picture of Venus like that.
Or they can even see an asteroid.
Now we are going to do the same thing.
So we are Arecibo in Dwingeloo and Wolfgang is Greenbank.
Not exactly the same.
We don't have the amount of power they have.
I mean, Arecibo had something like 1.5MW to transmit.
We have something like 80W,
so it's not the same league, but let's see how far we can get.
Now, there are two interesting books on this topic.
The left book is from the 60s, and it shows
you exactly all these experiments that that have been done.
And the results and, and how they were done.
So you can actually learn on how this is done.
The right book is one of the more recent ones.
And that shows the state of the art of planetary radar.
Now, they’re both second hand books.
And I just want to point out a few interesting things.
The left book actually comes from the Royal Radar establishment here in the UK.
Which in itself is already interesting, but this is also the site
where they had two copies of the Dwingeloo telescope.
So the people who used this book were actually using copies of our
Dwingeloo telescope.
One of them is still there.
The other book, is even stranger.
It comes from the from the Rutherford Appleton Laboratory over here.
So I don't know why they threw this book away.
This is the most recent book on radar astronomy.
Why is it not in the library here with me?
That's strange Anyhow, back to the topic.
So for radar, we transmit something and we receive something back.
So it's important to look at what is involved there.
On the left we have the received power.
This is the power we get back.
It's proportial obviously to the power we transmit.
The more power going out, the more power you get.
But it's also dependent on the gain of the dish.
So the bigger the dish, the bigger the signal you get back.
And it’s also squared.
So the gain really has a big influence on what you get back.
It's dependent on the wavelength squared.
And that looks a bit strange because it would suggests
that with a larger wavelength you would get more signal back.
It's the other way around.
And that is because the gain of the dish is also dependent on the wavelength.
The other one, sigma, is the size of the object.
So the bigger it is,
I mean an asteroid gives you much less reflection than the moon, for example.
But the most important one is this one here. It's R to the fourth,
which is the distance to the object to the fourth power.
And this is our big enemy
because there's nothing
you can do to compensate for something that grows with the fourth power.
So if things are further away, it gets extremely difficult to get an echo back.
So the moon is easy.
I mean, we know we can do it because our amateur radio amateurs are doing this.
But getting further, this is really, really the limiting factor in all of this.
There's no way you can get more power
linearly to compensate for something that grows to the fourth.
Okay, so this is how we do this in Dwingeloo.
On the left, we have our SDR that we actually use to receive signals.
So all these other projects
are done with the SDR, but we also use it to transmit.
Now we have a small amplifier that brings the level up to about one watt,
and then we send it to the power amplifier
the 120 watt power amplifier used by the radio amateurs.
Then there's a cable going all the way back to the dish,
up to the dish, to the feed.
We lose a lot of signal in that cable, so we have an amplifier of 120W,
but I think we get something like 80 out of the dish, which is not not that much.
The other path is the receiver.
And you see there's a relay there.
And that's actually the downside of having both transmit
and receive in the same dish.
The relay has to be there to protect the receiver, otherwise you kill it.
But it also affects your noise figure.
So we are a little bit less sensitive, for example, than the Stockert telescope.
Also because of this relay.
So for radio astronomy this is bad. For this project,
it's nice because now we can switch.
So we do this with two telescopes.
And the key here is that we have exactly the same SDR on both sides.
Because now we need to look at the timing and the frequency
and everything that that we get back.
We need to make sure that the two sides are completely in sync.
Now, these SDR have all kind of delays and offsets and whatnot as well,
but they are exactly the same on the both sides.
And that's really important.
So we have a set of tools that also Tammo Jan mentioned yesterday
that we can use to record and to send data.
So we have a file with some kind of signal in it that we transmit.
And then we get the echoes back into SigMF files,
that's the format to save IQ.
And on that format, on those files, we do our analysis.
In Stockert, we have exactly the same set up.
Only there we receive.
And interestingly we get two files in Stockert because Stockert has
a horizontal and a vertical antenna in the feed.
So later on we can also look at polarization.
Now we can point at anything.
But we start with the moon.
But we can also point at Venus and do exactly the same thing.
Let's see what happens.
So this is how it works.
This is a six second recording.
This is actually Dwingeloo to Dwingeloo.
So this is just our own telescope.
We start the signal with the transmission at one second.
And you see here this is a CW.
So it's just a carrier, just a single tone that we're sending.
Not any modulation. Because the signal is so strong,
you see it completely overloading and you see a lot of images, etc.
Ignore this.
Anything that happens here is just pure overload of the system.
But over here we calculate when we will receive the signal back.
And you see that there's a nice, echo coming back from the moon.
So the signal you see here in this part is actually returned from the moon.
What you also see, it's a bit difficult, maybe, but there's a little offset.
So the signal is not exactly at the same frequency as that we transmitted.
And you also see there's a bit of fading.
You see a few spots where the signal completely disappears.
Well this is this fading that I talked about.
The other interesting thing is that you see these green bands here.
This is basically when the relay switches.
So just before we transmit we protect the receiver.
And because the receiver is protected with a 50 ohm resistor,
the noise is actually higher than the noise of the sky.
So your noise goes up when you switch the antenna off.
So this is what we can transmit and receive.
And now we can start analyzing it.
So this is the the moon.
So this is the the the movement of the moon.
So from our perspective the moon has a certain speed towards us.
And there are three components that are participating or contributing to that.
First of all the orbit of the moon is not completely circular.
So at some point it's moving a little bit more away or towards us.
The axis of the rotation of the moon is not completely aligned with the,
plane of the orbit.
Those are really small effects. So we're going to ignore those.
The big effect is simply our own rotation.
And when the moon is rising, we are moving towards it.
When it's descending, we are moving away.
And that gives a Doppler. Also, because the moon is not a point,
but it has a size, there are differences.
So the left side of the moon has a slightly different speed to us
than the right side of the moon, and that's a difference we can measure.
So we have a big Doppler offset.
But also the Doppler is not the same for all the points on the moon.
So if we look at the same data as the other graph.
But now we plotted in the spectrum.
So this was the frequency we expected our signal back at.
And you see it's widened.
So we started it as a pure tone which basically has
no width, so let's say one hertz.
And we get it back.
And now it's something like nine hertz.
So different parts of the moon
have reflected the signal at a different frequency back to us.
And that's information
because we can make a calculation of the moon on how it will reflect.
And you see that we can predict it reflects at nine hertz.
Eight Hertz actually on the edge at this moment.
Now, this is exactly how they discovered the rotation of Venus.
We do it the other way around
so we know how the rotation works, and then we predict how it will look like
they did it the other way they received this graph.
And then they would know what the rotation of Venus is.
So we can already, replicate that for the moon.
But there's no time information yet.
When we send a tone, every cycle of the tone is exactly the same.
So I have no idea about distance.
And that's interesting because we have already seen
that the left side of the moon
and the right side of the moon send back a different frequency.
So they have a different Doppler.
So we have lines over the moon that have the same Doppler, coming back to us.
And those lines are in this picture vertical.
But also the front of the moon reflects the signal first.
So the first reflection you get is from the front of the moon.
The deeper parts of the moon will reflect later.
So we also have time information.
Now the time information is in a circle.
So on this circle all the information
will get back to us exactly at the same time.
And then you see there’s an intersect.
So every point on the moon has a certain delay and it has a certain Doppler.
And that is what we're going to use to actually make a map of the planet.
There's one unfortunate thing you see, point A
and B, they have exactly the same Doppler and the same delay.
So you will see later two parts of the moon will be folded over each other.
This is called Doppler delay mapping.
And this is the the principle behind it.
Again we're not the first ones to do this.
This is all done in the 60s.
Which is nice to repeat, of course, with a telescope from, from the 50s.
This is the first time they did it.
And what they used here is a very short pulse.
So the moon has a depth in light-time of around 11 milliseconds.
So they make a pulse of something like 50 microseconds.
And then you first see the reflection from the front,
and then you see the deeper parts of the moon reflecting back.
It works really well if you have a two megawatt transmitter,
it does not work so well if you have an 80 Watt transmitter.
So we can not do this, we will simply see nothing.
But, time has progressed and we have computers,
so we can do a lot of stuff that could not do in the 60s.
They wish they would have been able to, but they couldn't.
So here what we do is pulse compression.
So instead of sending a very short pulse, I put all our power in that one pulse.
We spread the pulse over time, and later on you will see that together with Stockert
we could spread it even over 60 seconds.
We send a sequence.
So here you see a few pluses and minuses. This is what they call a Barker code.
And the property of the Barker code is that if you align it with itself
it will add up to seven in this case.
So all the bits will perfectly align.
And you get all the power of these seven bits in one point.
And it doesn't align at all, it gives you zero or almost zero if there’s a difference between them.
So we can use this to actually measure the the distance,
because we can align these things and see exactly when they match.
Then we get all the power back at that point,
and we know the distance and we have much more power
because now we can spread the power over time.
So our 80 Watts we can do times 60 if we do it over 60 seconds.
So this trick we're going to use, we have something
much more advanced than this.
I'll show you later on.
And now it looks like this picture.
So it's the same, six seconds. We transmit from Dwingeloo.
Again, pure overload on this side. We're completely saturating everything.
But here you see a signal coming back, and you see there’s structure now in this signal..
And this is what we're going to use.
So now we compare that signal coming back with the original signal.
And we're going to shift it.
And we're going to find where we get a peak.
And you see very nicely over here that now we get a huge peak
exactly at the moment that the front of the moon starts echoing our signal.
You also see that we get signals echoed from later points.
Because of this code that we use,
we can actually distinguish the first echo from the echo that comes a millisecond later
or two milliseconds later.
So now we can measure where on the moon a certain reflection is coming from.
Now this is key to what we're going to do.
And I don't have enough time to fully explain how this works.
What we use is a Zadoff-Chu sequence, and I'm pretty sure we are the first ones
ever to use a Zadff-Chu sequence for making pictures of the moon.
This is quite modern.
This is used in 5G, for example, for synchronization between your phone
and your base station and we use it for the moon echo.
It works the same way as this Barker codes.
The code only aligns if you align it with itself.
You get all the power back.
If you shift it, you get zero.
So it's really useful.
But it's much more efficient because the binary code
only uses one axis of freedom.
And in the transmission we have with the I and the Q signal,
we have actually two axes. So we can use both.
The signal looks like this. You might think it looks like a chirp,
which is almost correct because it's related to the chirp,
but you see that they actually overlap.
And again, I don't have the time to dive into this, in more detail.
It almost sounds too good to be true.
And that's indeed the case because there's one problem and that's called ambiguity.
Because if you have a frequency translation.
So basically a Doppler, at some point, your frequency
translation and your time translation for sequence become the same thing.
So you get points that you cannot distinguish anymore.
And if you see how that maps, this is what we transmit.
We would expect a single point there at zero, zero,
but we actually get multiple points.
The only trick we now need to do is to make sure that our return, our moon,
will not overlap with one of the fake points, but we have that under control.
We've made a few mistakes on the early echoes, but now we can do this
and then we get to the result.
So this is what we can do between our sites.
This is only a single echo between Dwingeloo and Stockport
that was transmitted for 60s.
And in this picture we can see a lot.
First of all we see again the Doppler.
So we see the width of the moon in Doppler.
We also see the depth of the moon now in time.
So these lines I have plotted where exactly I expect to be the zero point.
So this is why we Doppler compensate for everything
and where I expect the moon, to end.
So you can see that we can actually see all the way to the edge of the moon.
You already start seeing a few of the craters,
which have a different echo,
so they have a stronger echo than some of the other parts.
But most of the energy that comes back to us sits here.
Almost all of it sits in this really small part.
This takes very accurate equipment and also accurate clocks.
The points you see here are something like 50 millihertz in accuracy.
So it takes really accurate clocks to make this work.
And also accurate calculations to find these lines.
So now we have this working.
Oh yeah.
First of all we were doing this and then somebody pointed out to me
oh you're not the first doing this with the telescope.
So Pieter-Tjerk de Boer in 2011 already did the same thing.
This was even more of a challenge because he used the radio amateur equipment.
So he has to do this via
the audio channel of the radio amateurs, which was really challenging.
But he had a very similar picture.
But you also see how far we have progressed since 2011,
which is really the equipment, because Pieter-Tjerk did really smart things,
but he was just limited by the equipment.
We can do this at multiple frequencies.
These example were all done at 23cm because that's where we have the most power.
We also can do this at seventy centimeters with UHF.
But then you have much less resolution in the Doppler because of the longer wavelengths.
Or we can do it at S-band, but it in S-band we don't have enough power.
So that's very limited.
I already mentioned you could see those craters,
and there's something really interesting here, which is,
a benefit of using the Stocker telescope is that they have two polarizations.
So the received signal, if you send a right hand polarized
signal to the moon and it reflects back, you get a left hand polarized signal back.
That's what the radio amateurs do.
But you also get what they call the diffuse reflection.
You also get a bit of RHCP back.
It's not as strong, but it's especially the features.
So basically, the moon is not a perfect sphere, but all the things that stick out
and small hills, etc., they reflect in a certain different way.
So the left picture is the one with the most power,
but the right picture has less power and it.
But you actually start much better seeing the features.
If we look at the power, we
see that the blue one, which is basically the normal reflection, is very strong.
The orange one is weaker.
But it has more information in it.
If we look at the polarization on the difference basically between the two,
and we compare that with the book from the 1960s, you can actually see
that we can perfectly replicate what they have measured back then.
Now basically this is where we stand today.
This is the, let's say the state of the art as we are today.
We need to do need to do more measurements.
But this looks quite impressive, especially on this screen, I must admit.
And also here I can switch
between the left and the right hand polarization.
So the RHCP has more detail and the LHSP has more power.
The combination, of course, is the most interesting.
And now this is, by the way, a combination of a lot of bounces.
So this is 11 times 30 seconds between Dwingeloo and Stockert.
Now it almost looks like this is a photo of the Moon.
And that's very misleading. And we did this on purpose.
We gave it a little bit of a round form so you would get the idea it’s a photo
but it really isn't.
The thing is, as I said in the beginning about this delay Doppler, there’s ambiguity.
You have two points on the moon
that map to a single point in this picture that you are seeing.
So over here you see again the same measurement we have done.
Over here you see how we think it should look based on a known map of the moon.
And you see two colors here blue and green.
And the blue is the northern hemisphere and the green is the southern
or the other way around.
You see very nicely, for example, this crater here, you see, that's showing up over here.
What we have not done yet, and that's the next step
is to map from left to right so we can actually unwrap this.
But we need multiple measurements.
We need this to change.
How that works: This is a nice animation that Tammo Jan made
So this is how we view the moon
compared to the the axis of the of the telescope.
And on the left, you see how the two halves map.
So you see that actually the bottom one is rotating to the left.
The top one is rotating to the right.
So if we do another measurement where these craters are in a different position,
then we can start trying to make a map. So that is work to do.
This is basically where we currently stand.
One more interesting thing is this one.
This is what the radio amateurs experience, which is the fading.
So here we have a movie of the short term.
So this is basically real time
where on the moon your reflection is coming from.
And you see some really interesting points that move around.
And this is the thing that distorts your your audio.
But it's really funny to see it as a movie.
It takes a bit longer.
This is like, like a minute, but I think you get the idea.
If you do this for a minute and you integrate,
then actually this all disappears
and it looks a little bit like the picture that Jocelyn was showing yesterday
of the pool with the the waves in it and the light.
This is a very similar.
I need to move on looking at time.
Now, the moon was easy.
We can do nice things, but this was very close,
so the question is, how far can we get now?
This is Venus.
Venus is the next easiest target.
And this is the orbit from Venus as seen from the Earth.
So the Earth is in the middle here. This is how they in the Middle Ages
thought that the universe was looking like,
and you see that every one year and seven months it's very close to us.
And remember the R to the fourth.
So we can only do this when Venus is very close to us.
And, what was it, last year, it was very close to the.
So we had an opportunity to try this out.
You also see from our point of view, it's very close to the sun.
It's in the line with the sun, which makes sense
because it's actually moving in between us and the sun.
So if you look from the Dwingeloo telescope, which is pointed at Venus,
you see how awfully close it is to the sun.
Luckily, our, beam is quite small, so it is an issue, but we can do it.
Same setup as last time.
The only difference is now we put the amplifier in the front end
so up in the dish, and it's a one kilowatt amplifier,
because this was the only way to make it work.
That's very tricky to do.
Here, you see us going up with the elevator.
That's the picture Tammo Jan didn't show yesterday.
So here you see the elevator being used.
And here you see us up, at the front end.
And here you see the one kilowatt
amplifier, which we're going to move all the way into the back there.
You might wonder where all the heat is going from the one kilowatt.
We didn't think about that.
So we'll get back to that point.
I'm going to speed up a little bit.
With Venus, accurate calculations become really important.
I mean, the signal is away for five minutes.
You're transmitting for five minutes, and then you're listening for five minutes.
So in the meantime, Venus has moved.
So you really need to take all the geometry into account.
The Doppler going out and the Doppler going back is not the same thing.
So you need very accurate calculations.
Luckily, there's a very nice toolkit from, JPL called SPICE
that does all of that for you.
All these pictures from the moon you saw before were all made with which SPICE.
So it's complicated, but actually there's a toolkit that can do all of that.
So we calculate exactly the Doppler but also the Doppler rate.
So how fast is the Doppler changing over the five minutes.
And we correct for all of that.
That's the only way to detect our signal.
This is a simulation made by here by Cees.
On the left you see again the Doppler we expect
this is the power where we expect it to be reflected from Venus.
And on the right you see the Doppler delay map that we expect.
This was the goal. Like how far can we get.
Luckily, because Venus’ rotation is slow and it's also retrograde,
so it's moving against its own moving around the sun, which means
that the Doppler from Venus coming towards us is partly canceled by the fact
that Venus rotates the other way around, so the Doppler is really low.
We had like eight hertz on the moon,
but we have within one hertz most of the signal,
half of the signal is within one hertz, which is really useful
because that gives us a lot more sensitivity.
Now we had two hours to do this experiment, and we had fully automated it.
And we started with four times in CW.
So that's a tone, just a carrier.
And then we had all these interesting signals with radar wave forms in them.
But as you can see, after the first four: failed.
We completely melted the amplifier in the front-end.
So unfortunately, we never got to these other ones.
You can see it's busy.
We're very happy here because the first time
you see the one kilowatt going out of the transmitter.
Here we were still laughing.
And, these are the results.
So we managed to do this four times.
If I split all the measurements out you have Dwingeloo and Stockert,
and Dwingeloo to Dwingeloo
And you see that, actually, in the individual five minutes reflections,
We can see Venus, even in a single measurement.
You also see that on Dwingeloo,
the performance is lower and it's completely disappearing.
Maybe this had to do with the heating up of the whole front-end, we don't really know.
If we combine these things, we see that we have an overall detection of more than ten sigma,
which is a really, really strong, detection of the Venus signal.
So we succeeded in getting something back from Venus.
You can also see there's no information in here.
So we just see it's there.
We don't have enough signal to make a delay-Doppler map of Venus.
So there's no way we can actually make this nice map
that we have of the moon of Venus.
Here's another one to prove that it's a real signal from Venus.
This looks like a plot made for the pulsars.
If we shift in frequency, we lose it.
And if we have the frequency rate, we lose it.
Just to prove that we're really seeing the signal as we expected, there.
Okay, this is the melted amplifier.
So we destroyed that one kilowatt.
It was repaired later on, so no issues there.
The question is, is this the best we can do?
So can we go further?
Quick answer: no.
If you look at next one from Venus.
So Venus is at zero dBm.
Mars is already 20 dB lower.
Well, there was clearly not a 20 dB margin.
So with the current set setup, Venus we can do
and there's another one, later next year,
Which we will try again, but things like Mars etc., are out of our reach.
The other one was I started with the pictures of the asteroid.
We really want to make a moving, picture of an asteroid
with our two telescopes, but, no, that's not going to happen either.
We simply don't have the power and the dishes to to make it work.
So, as I said, this was work by a lot of people.
Of course, the full teams at Dwingeloo and Stockert, because,
you need a lot of people to keep the telescope running
and to make everything work,
Jan van Muijlwijk, who knows a lot about the amplifiers and the whole setup for EME.
Daniel Estévez did an independent analysis of our Venus data, which was really nice.
And we learned a few new things from that.
Pete Syckoff came up with the idea for the the picture of the fading, the movie.
And we also cooperated with Nathaniel Fairfield on Venus.
So there is input from a lot of people in it.
But I think we have nice results and of more to come.
Next time, I really hope we can show you a map of the moon,
where we have unfolded those two halves.
And that’s it.