RAW TRANSCRIPT -- NOT YET REVIEWED FOR CORRECTIONS BY CASSINI PERSONNEL

**FTS-NASA-VOICE**

**Moderator: Amanda Hendrix**

**September 25, 2007**

**1:00 pm CT**

(Essam Marouf): People are busy with too many other things. Learning to
EM is not simple.

(Amanda Hendrix): No especially while you're doing the regular
(unintelligible).

(Essam Marouf): That's right.

(Amanda Hendrix): Right.

(Essam Marouf): Yes.

(Amanda Hendrix): EM for all you who don't know what that stands for,
it's Extended Mission.

(Essam Marouf): I guess that PSG then is called XXM.

(Amanda Hendrix): Yea.

(Amanda Hendrix): Well before we officially get started here I'll just
make a couple of announcements. Kind of reminders so a lot of people who
call in all the time know a lot of this stuff already.

But as a reminder throughout the presentation if you want to ask
questions you're free to ask questions as we go along, but otherwise
please be sure to mute your line. And you can do that by pushing star 6
and you can unmute again by doing star 6.

We'll be recording the meeting, the presentation, so I'll go off and ask
the operator to record in just a few minutes. But and I will officially
get started when we come back, but any questions or issues before we
actually get started?

And then for (Essam) if you can, as you're going through if you can - as
you progress - go through your sides, if you can try to remember to tell
us which side your on or that you're advancing to the next slide so
everybody can keep up.

(Essam Marouf): Sure.

(Amanda Hendrix): Okay. So I'll go off and start the recording and then
I'll come back and introduce our speaker. I'll be right back.

Coordinator: I'd like to inform everyone the call is now being recorded,
if you do have any objections you may disconnect at this time. You may
begin.

(Amanda Hendrix): Okay thank you. Well welcome everyone to September
2007 CHARM Telecon. And I'm (Amanda Hendrix) and I'll be hosting the
telecom today, the presentation. And I'd like to introduce our speaker
who's (Dr. Essam Marouf). And he is a professor at the San Jose State
University here in California and is a member of the Cassini Radio
Science Subsystem team or the RSS team. And today he's going to be
telling us about Radio Science, the way that they do things and some of
the results that they've been getting.

So with that I will let you take over.

(Essam Marouf): Thank you (Amanda).

(Amanda): Thank you.

(Essam Marouf): Okay first I'd like to encourage you to interrupt and
ask questions whenever you think there is something that - a point you'd
like to make or a issue that's not clear, please interrupt and ask
questions.

I also would like to say that the presentation today is just a small
(facet) of what radio science actually does. It is a selected set of
subjects based on some the experiments we completed the last two years.
But the experiment include many other things, which I'll try to say in
passing, but I have not tried to make a whole complete kind of
presentation. I presume in the future there would be presentations that
would also cover the subject on (devalue).

So the presentation today will cover some of our - some of what we do at
Titan and some of what we do at Saturn. And I've had mention in passing,
as I've said the other things we do both at Titan and Saturn and other
(unintelligible).

So the experiments I'm conducting by a team, so if you go to Slide
number 2, you will see a listing of the team, there are 11 members of
the NASA Selected Team and then the two associate members also. And they
come from a broad range of institutions, three of them are from Italy
and the rest are from the United States. So the work is - the work I'm
presenting is a collective work and I'm just \-- the one that has the
chance to tell you about what we do today.

But it - I would also like to mention that the Cassini Radio Science
team is complemented by Cassini Radio Science Engineering team that
actually implement these experiments. And their contributions are just
as valuable as the contributions that the scientists make. So I'd like
to recognize their efforts today, because they have been instrumental in
making many of these experiments work.

Slide 3 introduces you to the system we use to do the experiments I
discuss today. The radio science experiments are conducting - conducted
in more than one configuration, this is one then called the Down-link
configuration. And that is a configuration which the spacecraft
transmits radio signals to the earth receiving stations. The Deep Space
Network, earth receiving stations.

So the instrument is really two pieces, one is onboard the spacecraft
and one is on the ground. And the spacecraft itself generates a sinusoid
signal, which the basis for all the experiments generated from an ultra
stable oscillator. It's a crystal oscillator that's kept in an oven
onboard the spacecraft so that the frequency (unintelligible) function
of time.

And that's very critical for the kind of experiments we do, because the
experiments, all the experiments whether they are misconfiguration or
other experiments they rely on measurements of the frequency of that
sinusoid. Then therefore the frequency has to be extremely stable on the
spacecraft by using a crystal oscillator. In other experiments then we
use masor on the ground which is an atomic frequency reference with much
better stability.

But for these experiments of discuss today, the spacecraft generates the
three sinusoid actually. We have all drive from that ultra stable
oscillator, which has stability of about 1 part in 10th of the minus, so
(unintelligible) 92 better than any watch or clock that you have here on
the earth for normal purposes.

And it transmits these three sinusoids simultaneously, so we get to
study the effect of the medium probe on the signal at multiple
wavelengths at the same time.

On the ground the three sinusoids are usually received by two separate
stations. One receives the longest wavelength and the shortest one
called X-Band and X-Band and the table shows wavelength to these
(unintelligible) (centimeters) 3.6 centimeters. All these experiments
are microwave range kind of experiments, so the wavelength is in the
centimeters kind of range.

And the X-Band is the prime signal we use, which is the 3.6 centimeters
and the S-Band and the K-Band are supplementary wavelengths that add
information to the one we get from the prime signal, the X-Band signal.

The power transmitter is very small, 9 to 20 - I mean 10 to 20 watts
kind of range. The table actually is messed up a little bit in the PBS
version. I think that just because of the compression of slides. But
there is a 7 under the (SNR) that should have been next - right on top
of 19 and 48, right on top of the 54.

But the power transmitted at these three frequencies are from the 10 - 7
to 20 watts kind of range, so it's very little. But because of the use
of these giant antennas on the ground and because we are all also
(gigantically) cooled we get a very respectable kind of signal-to-noise
ratio, which is critical for the kind of signals you'll see in a second,
some of them are pretty signals.

So the affect then on this down-link signal of the medium we (probe),
provide us with a information about the medium, but it's important to
know what the system looks like so that you understand what kind of
experiments we do after one.

So if I go to the slide, Slide 4, it shows in words the types of all the
alterations lumped in two main types, one conducted in that
configuration I just mentioned called down-link configuration or one-way
configuration, because of the fact that the - just the spacecraft to
earth kind of signal. And that includes the- some of the experiments
I'll talk about today, they be the occultations of the rings, so the
rings will interrupt the down-link.

We study the rings by the sector under-down link and the same with
Saturn atmosphere or Titan atmosphere or Ionosphere. And we do a third
type of experiment called the bistatic experiment, which I'll actually
start with in a short while.

But I'd like to mention also - I'm not going to talk about Saturn
occultations today, except in passing (across) the Titan occultations to
give you the (sliver) of the experiment and what we do with an
occupation of an atmosphere. And Saturn would be just a modification of
the same thing, but for a totally different target.

The summary of experiments also include what's called up-link, down-link
of two-way observation. So the radio signals that are actually
transmitted from the ground to the spacecraft and then \-- that's the
up-link. And then the spacecraft returns the signal back to the ground
at coherency, that's just to say preserving the phase of the sinusoid
with transmit.

And that's because in measuring very small frequencies when a spacecraft
goes by a body like Saturn or a satellite like Titan or like Insubtilis
or like any of the relatively large satellites of Saturn. Then frequency
or the gravitational feed of the satellite preserves the frequency, but
the (preservations) are very, very small, so you need a much more stable
frequency reference.

And therefore a masor on the ground is used, the (unintelligible) on the
ground is used instead of crystal oscillator onboard the spacecraft. And
this way the reference frequency comes from the ground and not from the
spacecraft and the (doctoral) measure is measured to a lot more
accurately.

So these - this summary of experiment gravity feed observations of
Saturn, Titan and the major satellite is a whole measure (in and of
itself) and deserves the whole talk by itself in the future. But it's
not a subject I'll touch upon today, because of the time limitations.

So next slide shows the configuration with the medium being included
also. The medium also here is just chosen to be the Titan atmosphere, so
I'll start by talking about Titan occultations and Titan bistatic
observations. And as you can see here the link - the down-link I just
described a second ago is now being interrupted by the atmosphere of
Titan. And therefore the affect on the radio signal are observed at the
DSN at the Deep Space Network Station and then analyzed for information
about the atmosphere of Titan itself.

All on the right you'll see a cartoon where it says from spacecraft to
DSN. This is the spacecraft pointing to Titan and illuminating the
surface by the radio signals, which are then reflected from the surface
to the Deep Space Network to tell us something about the surface of
Titan.

But the geometry here is such that the normal to Titan, the thin black
line you see emanating from the surface of Titan divides the angle
equally between the direction from the spacecraft and the direction to
the Deep Space Network. So we're really looking for metal-like
reflection or (quad ispecular) kind from the surface. There the radio
signal is used as a probe over the surface while in the first phase it
uses the probe of the atmosphere and ionosphere.

In both these cases we - as a function of time will maneuver the
spacecraft in a very elaborate way so that the signal from the
spacecraft reaches the earth, so in the case of an occultation, because
the radio signal bends in the atmosphere. The picture you see here is
highly simplistic it shows a line just going through the atmosphere,
going to earth.

But in reality the line of refraction, the line is a wave and the wave
goes through an inhomogeneous atmosphere of Titan so it bends. And we
have to maneuver the spacecraft so that when the ray bends the signal
still goes to earth.

So we execute what called the (len tract) maneuver during occultations,
which is a demanding kind of a design because Titan - the fly by of
Titan are usually very fast. So we have to keep the spacecraft pointed
in the right direction as a function of time by using the flusters,
because the - they can move things very quickly, much more quickly than
using the reaction wheel.

And in the case of the bistatic from the surface of Titan we have to
maneuver the spacecraft (unintelligible) simply as a function time to
look at the region of the surface where this metal-like is expected. So
both of these experiments are not static in the sense that the
spacecraft has to be moved as a function of time in very specific
directions.

And therefore when these experiments are conducted we need to know the
trajectory of the spacecraft very accurately. And usually the trajectory
is predicted long time ahead, I mean, long time before the experiment.
But because we're so sensitive to errors in the trajectory at the level
of one second or sub one seconds of time, what happens is that the
navigation team - one week before the experiment gives us their best
estimate of the trajectory.

And then we use that estimate to do what's called the live update, we
update all the pointing on the spacecraft and uplink to the new sequence
of the spacecraft. And then execute it based on the best knowledge we
have at the time. If we don't that we would miss all these occultations,
because they happen so fast. And as you will see in a second we did four
of these and all worked very nicely, so. So without this kind of a
capability we would not be able really to do these occultations.

So the next slide I'll start with the Titan, but the surface part of it,
the bistatic part of it, then I'll discuss the occultations. And then at
the end I'll take the rings of Saturn as a example from Saturn
observations.

So the - we've done so far four experiments that all relate to this
bistatic experiment. They were the flybys, number 12, 14 and then
recently - those were last year March and May of last year. And then on
March and May of this again we did - I'm sorry, on March and July of
this year we did two more, 27 and 34.

And the chart you see here shows the location on the surface of Titan
where this metal reflection happened. The technical term for that is
specular reflection, so these are called the specular tracks or the
ground tracks for the specular point. And what you see here is the
latitude of the point on the surface of Titan where beam penetrated the
surface or illuminated the surface, and the longitude, so this is just
location on the surface.

And you can see the best red line is the equatorial, so this is (zero)
latitude. So you can see most of them where at near equatorial at least
on T12, T14 and T34. Only T27 diverted substantially from the near
equatorial and illuminated on the inbound side or the (egress) side, the
very high south latitude kind of regions on the surface of Titan and on
the outbound or (egress) side near 20 degrees latitude, 20 to 30 degrees
latitude.

So the examples I'll give you today will seem like (static echo) on most
of these, as some are weak, some are strong. And only one of them we
haven't seen anything and that was the 27 outbound one (ingress). And
you - I'll describe for you today why we see echo sometimes and why not,
it all depends on the nature of the surface that we illuminate.

And the next slide will show just the Cassini Web site, a schematic
illustration of the - one of the experiments on T27. And the reason I'm
showing this is just to make the point that if you look at the
spacecraft on the right and earth is on the lower left. The spacecraft
is pointing directly to earth, through the atmosphere of Titan in a
(continuous) kind of way.

And then the spacecraft on the left illuminates the surface and the
reflected signal, which are the blue bubbles you see emanating from the
surface back to earth. You can see that it takes a very large change in
geometry to go from the occultation geometry to the bistatic geometry.
And the spacecraft has to be maneuvered to change that trajectory, that
kind of orientation in a very short time. So there is a very elaborate
maneuver involved that allows doing the occultation and the bistatic on
the same flyby.

Hendrix: And that phase is on T27?

(Essam Marouf): That on T27 and T14, both of them.

Hendrix: And if I just like, (pick) that ones to ask you \-- you said
you didn't get a signal back on the egress - oh no - oh was it the
egress of T34?

(Essam Marouf): No, on the egress of T27. That's the only one we didn't
get a signal.

Hendrix: Because I see blue points up in the northern hemisphere.

(Essam Marouf): Are you talking about Slide 6?

Hendrix: Yes.

(Essam Marouf): Yes the - T27E is the one from 20 to 30 degrees latitude
north, north latitude. And that's the one that did not show any echo at
all.

Hendrix: Oh I see, okay. I thought this was somehow showing your output.
Okay. It's just showing where you...

(Essam Marouf): Yes that's only where we looked at the - where on the
surface we've looked.

Hendrix: Okay.

(Essam Marouf): The spacecraft looked. So Slide 7 was just a schematic
illustration of the fact that you need to change orientation
substantially over a very short period of time.

So here is - Slide 8 shows the actual - just to get a feel for the
complexity of these experiments it shows the timeline that we followed
for executing this T27 experiment. So on the top right you'll see Titan
as viewed from earth. And you'll see that the spacecraft was coming -
towards the south pole of Titan and then hiding behind Titan for awhile
and from one observer on earth and then exiting close to mid northern
latitude on and then continuing again.

You see the tick marks at only 5 minutes apart, so the duration of the
bi-second occultation are short and you'll see the exact time in the
detailed diagram below.

So if you take Titan and just turn it on its side so that you can catch
time running from left to right \-- that's the picture on the bottom. So
you see again Titan and the red line is the trajectory of the spacecraft
as you see it from the earth. And the spacecraft is coming from the left
moving to the right and the tick marks are again, Titan and the red line
is the trajectory of the spacecraft as you would see it from the earth.
And the spacecraft is coming from the left moving to the right and the
tick marks are again 5 minutes.

And centered on Titan itself, if you look at the colored line just below
Titan you'll see a block called occultation, which lasts from 01:10 to
01:46, 36 minutes. During that period with it the occultation is
prevalent. And on the wings outside before that and off of that where it
turns to do the bistatic experiment on the inbound on the outbound side.

And before that the green box show that we have directed the spacecraft
to collect a baseline by pointing the spacecraft to earth and looking at
the signals before we do anything.

And before that the brown boxes show that we've done some calibration so
that we know exactly the performance of the system we're using. And
therefore we actually measure the system noise temperature so that we
can characterize the strength of the echo in an accurate way.

So coming from the left to the right, the sequence of events are as
follows. We calibrate the system for some time before even Cassini turns
to earth. Then when Cassini turns to earth we collect the baseline, then
we turn to Titan and do our bistatic experiment. Then we turn from Titan
to earth an occultation and then do the opposite going out.

And the observations during that period are observed by the DSN of the
stations that indicated with the bottom two lines. Both the Madrid
complex and the Goldstone complex were observing during that day. With
two stations each, as I've said the s and X-Band are received usually by
the large 70 meters station. So this is (BSF63) in Madrid and (BSF14) at
Goldstone here in California.

And then the K-Band and a backup X-Band are observed by the smaller
antennas the 34 meter antenna, which are (BSF55) in Madrid and 25 and 26
in Goldstone.

So there were five stations observing that night, each on of those two
frequencies, so that's 10 channels and then each one recording also two
polarizations at each frequency, 20 receiving channels. I'm not really
aware of any radio science experiment ever conducted that approaches
this kind of complexity where there are 20 receiving channels being
recorded at the same time.

All that's done in real time, the DSN operators are in touch with the
engineering in the operations room. And everything has to be executed to
perfection really to collect the details during the little period of
time. And that's why I say the engineering team did a wonderful job,
because this is not easy to do. Usually occultation's happen at one
frequency with one station, with one polarization or two polarizations
and two frequencies, but never really with this kind of complexity.

Cassini is the most radio science capable kind of spacecraft utilizing
two wavelengths and of course when we do bistatic observations we have
to record two polarizations like I'll describe in a second.

And therefore this is the most complex kind of experiment you can think
of. And the other people, the (unintelligible) of dimension in
thankfulness also are the DSN people because we have - somehow they have
to - since we part of the instrument that night, they just don't do the
usual job of just recording a down-link.

They actually have to participate in the experiment that have the
instrument in a configuration that is proper for the experiment. And
they have come throughout all the experiments we've done so far and do
deserve to be thankful for their effort.

So I will just give you a feel for what kind of geometric conditions
apply from an experiment like that by going to Slide 9. And there are
four kind of that I'll run through very quickly counter clockwise, I'll
start on the top left. And so all these are the horizontal axis at the
time, the time of the experiment relevant to closed approach to the
bistatic for...

This T14, it started at about minus 50 minutes before closed approach -
that's the vertical dash line and ended at about minus 20 minutes where
we have turn start the occultation. And we have actually - yes we have
to turn to start the occultation. So the experiment typically last a 30
minutes. It's usually of that order for all of them; this is just a
typical example.

And the angle on the vertical axis is an angle I yet to define, so let's
leave that for to the next slide. But the things that you'll see here
that has been arranged called the booster angle range and I'll describe
in a second what that means exactly and why that's important. But T14 as
you can see here is well within the booster angle range.

Next one on the right is the distance of the spacecraft from the
specular point on Titan. And as you can see as a function of time the
spacecraft is approaching Titan in this case, it changes quickly from
about 15,000 kilometers, typically 20 to 15,000 kilometers. And when
we're close to Titan typically a few thousand kilometers; 5, 000
kilometers or 6 to 7,000 in this particular case, kilometers from Titan.

So we do experiment relatively close to Titan and that's because we
would like the echoes weak and would like to maximize the signal to
those ratios, so we can not do it while the spacecraft is very far away
from Titan.

And next bottom right is the expected bandwidth of the echo, which is
typically in the range of few kilohertz. And finally the one on the
left - on the left bottom is a very important one. It shows that as a
function of time the expected frequency of the center of the echo
changes very quickly as the function of time starting from about 160
kilohertz and ending at about 120 kilohertz.

That means if we don't do anything, if we just listen to the echo,
waiting for it with a receiver that has a fixed kind of a frequency, it
will drift very quickly out of the band and we wouldn't be able to see
it. So the only way to see the echo is to turn the receiver so that it
follows in Doppler - it follows in frequency, the changes due to the
Doppler shift of the echo \-- expected Doppler shift of echo.

So it's like I try to track a moving train, if you just stand at the
station and watch the train go by it zaps by you and don't see the echo
except for a very short period of time. So the only way to track the
train is you have to ride a train that's moving on a parallel track sort
of speak and therefore you're watching it all the time if you're going
with the same speed.

So what we do is we tune the receiver based on (unintelligible)
estimates of what's expected to happen. So we have to construct a model
for what the experiment looks like so we know the trajectory, we know
what Titan is, we know what the specular point is, we predict the
doppler shift including the effect of the atmosphere on the signal.

And then tune the receiver the night of the experiment based on these
predictions. And if we've done a good job then the echo should be
spatially in the center of the band during the time of the experiment if
it's present.

So the next slide then, Slide 10 just quickly shows the basic principle
behind an bistatic observation and I will take just a minute to explain
what's going on here, because it's critical for understanding the
result.

And - so the top right picture shows the spacecraft looking -
illuminating the surface and the surface has a mean surface, which is
the dash line, the dash horizontal line, that's just the mean surface in
this case. Then axle surface may be rough and will ovulate randomly
around that dash line. So that's the solid line to surface in there, in
the diagram.

If the surface was exactly flat then the signal would bounce from the
surface much like metal reflection happens, where the angle of the
incidence called (Fizeal) in the diagram, which is the angle between the
ray connecting the spacecraft with Titan and the normal to the surface
called (Fizeal).

And would reflect in the circular direction at also (Fizeal) and we
would see only one in that case. We would see a spike in the spectrum of
the signal corresponding to that one single ray coming from the
spacecraft connecting to earth through this mirror reflection.

In reality the surface is not really exactly flat and ovulates like
you're seeing here. So individual facets of the surface that are
slightly different from the mean orientation reflects the echo from a
slightly different angle than (Shezeal). And because the echo is Doppler
shifted it received at the ground at slightly different frequency from
the original ray I jus told you about where the surface is exactly flat.

So in the video randomly oriented facets, reflect the echo or reflect
the signal at slightly different sequences. And what one receives on the
ground then is a spectrum rather than just a single light. And the
cartoon of the so called received power with the frequency that you see
in the diagram is a cartoon of a spectrum, of spreading frequency around
the expected frequence.

And rougher the surface is the more spread that spectrum is. And of
course if it's very smooth then the spectrum becomes a very narrow kind
of a spectrum, which we call quasispectral of spectrum in this case.

And the (unintelligible) of this curve, under this spectrum is the total
power in that reflected signal. And that total power is controlled by
the reflection coefficient of the surface. So this is the reflection
coefficient we all study as an under - as undergraduate. If you have an
interface between media and there is a plane wave incident, the
reflected wave has a reflection, power reflection coefficient that's
controlled by the incidence angle and then directed properties of the
surface.

So on the left then there is the standard plot of this reflection
coefficient as a function of the incidence (Fizeal). So it's called
(unintelligible) because the diagrams are taken from different
references. I should have six steps, but the horizontal axis is the
angle (Fizeal) in the diagram on the right. And if you see blue curve
and the red curve, each one of them is a different reflection
coefficient that depends on the polarization of the incident wave.

So if the electric shield is in the plane or (subtler) to the plane of
the page you have, you'll get different answer from the electric field
being in that plane. So this is what's called the TE for (Transit)
Electric where the electric is normal to the page and (transmits) the
electric wave, the electric field is in the plane of the page.

The spacecraft transmits a circular polarized radio signal, so it has
both TE and (TM) in the incident wave, but they - when it hits the
surface it's affected - these two components are affected by very
different, by electric - by very different reflection coefficients.

So in the - at an angle (Fizeal), which is closer to the angle where one
of them dies, the (TM) component completely goes to zero. The reflected
signal is essentially TE only and TE is a linear polarization which has
equal amounts power in the right circular and left circular. So at this
particular angle that is to say the vertical dash line here where one of
the (unintelligible), one of the reflection coefficients go to zero.

The reflected signal will always have equal power in the right circular
and left circular. Even though the incident signal is only right
circular and in general it angles away from that. It will be both right
circular and left circular, but in (varying) amounts depending on how
far one is from this angle. That angle is the booster angle, the angle
at which the one of the reflection coefficients goes to zero. And it
depends totally on the directive quiescent of the surface.

So by doing experiments in the neighborhood of the booster angle and
measuring the power in the RCP right circularly polarized and LCP the R
and L components, the right and left components of the reflected echo
and ratio in these, you get a very good indication of what the directive
quiescent is. And that's the last curve at the bottom here, which
shows - after given by electric quiescent which, for what these curves
are here at 3 - just a number.

And going again is a function of angle measuring the relative power in
one of the tools here at the opposite circular, so if the incident is
right circular this is the left circular power over the sum of the two
as a function of the incidence angle. You see that the ratio changes
considerably as a function of incidence angle.

At the booster angle exactly is 1, it passed to because with summing of
two \-- was mobilizing by the sum of the two, but half year means that
the two components that would reflect this component have about the same
power. And it favors one or the other if you move away from the booster
angle.

If you change the directive quiescent you change the booster angle. So
one important measurement and that give the - give direct information
about the directive quiescent is measuring the power in both polarized
components and ratioing them and that will be the key for the couple of
results that you'll see in a second.

But it's a little bit of a complicated concept, but it's really nothing
but the fact that the incident wave is RCP and the reflected echo in
general will have both, RCP and LCP in an amount, in a mixture of amount
that depends on the directive quiescent straight forward way. And the
straight forward way is the curve at the bottom left you see there.

So by measuring the power in each component and ratioing that power you
get an indication for what a directive quiescent is. And because it's a
ratio measurement you don't really need to know the absolute value of
each one very accurately. The uncertainties added to each one of them
are removed in that ratio and the ratio itself becomes a very indicator
directive quiescent is.

And the next slide will show that the experiments we've done extend in
incidence angle range that cover the booster range, so the booster range
for the kind of materials that we expected on the surface of Titan are
50 to 70 degrees or so. And T14 the two red arrows point to the T14
change the angles as a function of type for T14 inbound and the T14
outbound. And both of them were smack into the booster angle range.

T27, as I said the data I'm presenting today come from T14 and T27, so
T27 is where the green arrow points and that's outside the booster range
or at least closely to outer boundary and outside that. So you would
expect the echo to phase on one polarization and would be weak at the
other polarization.

And yet we see that we - we also detected polarization for T27 inbound
and that's really very good, because you need to detect both
polarizations to get to the directive quiescent of the surface.

So moving on to Slide 12, this is the T27; this is the experiment we did
on March 25 this year. The T27 inbound, this is where we looked at the
south pole of Titan; south pole region of Titan. And I'm just showing
you what we monitor in the operation room during that experiment; we
look at the spectrum of the signal. So we're trying to see whether there
is an echo or not in the spectrum of the signal by looking at all three
frequencies and looking at two polarizations.

Here I'm showing only one polarization, but all three frequencies. And
if all works well, if the receivers are tuned properly and if there is
an echo it should show in the center of the band. And as you can see
here the X-Band shows a very nice strong echo right in the center of the
band.

And the S-Band shows also a very reasonably strong echo at the center of
the band, but not the key. The one on the right is the key band, doesn't
show any echo at all. And I'll try to explain why is that as we go
along.

But the thing we monitor in real time are spectral (unintelligible) a
function of time with, usually with our heads and hearts looking at the
center of the spectrum trying to see whether there are bumps above noise
baseline or not, but then of course we take the data home and we look
for very weak echoes in a much more careful way.

But it's always nice when you can see the head of time in real time and
these are the detection of the echo from the surface Titan, very clear
echo from the surface of Titan from the south polar region.

The next slide shows the actual spectra that's computed after the fact.
And so the slide (unintelligible) shows the spectra of (tech) in time,
so if you'll - this is a (speedomation) of clock with frequency running
from left to right at the bottom. And then the spectra that are measured
as a function of time stacked one after the other to form what's called
a spectrogram or a plot of (spectorize), a function of time.

And you can see that over most of the time we looked at the south polar
region, which here is about from about 43 to about 65, it's about 22
minutes of observation for T27 inbound. Over 19 of these we see very
strong echo and that was not the case in T14. In T14 as you'll see in a
second, it seemed to echo only to be over a very localized region of the
surface and only for a very short period of time to about 3 or 4 minutes
on one side and about 7, 8 minutes on the other side.

So there are very strong echoes from the polar region of Titan as you
can see here. We usually don't show the spectra in this format, (three
dimensional prompt). We use frequency and time as the (unintelligible)
of an image and then the strength of the echo, which is the third
dimension here where it presents using color.

So the next slide shows such kind of a representation. So the vertical
axis, this frequency, the horizontal is time and the color which is the
color axis you see on the right represents the strength of the echo, so
red will be very strong here and blue would be the noise. And as you can
see the noise (unintelligible) and blue background you see in the image.
And the strong echo that comes all the time for at least the 22 minutes
of the observation is the color line that's in the center of the plot.

You can see that here the bandwidth of that we use to record the data is
16 kilohertz, so we've centered the echo; we tuned the receiver so that
if there is an echo it would show at the center, which is 8 kilohertz.
And indeed you see the bright line in the center here is at about 8
kilohertz and it stays all the time.

The top picture is for the X-Band and RCP, so this is the same
polarization as the incidence signal. And then the left one - the right
one is the LCP component. So here you see even though this experiment is
outside of the booster angle range we still detect the LCP component.
And it's just a lot weaker than the RCP component, but it's there you
can see the line at the center of the (plot).

And this is one of the first experiment where we also detected S-Band
which are the bottom two slots at both polarizations, so as you can see
there is a line in the middle in most cases on both the RCP and the LCP.

So this is a beautiful bistatic data set that will tell us something
about the directive quiescent of the south polar region. It's a problem
we continue to work on, I'm not going to report some results today, but
last year we did a similar experiment on T14 where the echo was much
weaker.

So the next Slide 15 shows the echo from T14 where again the LCP the RCP
sequence of spectra are shown and again at the center of the band, which
we tuned to show the echo as spread and to be at the center of the band.
At 8 - at the number 8, which is 8 kilohertz in frequency, you see that
the signal climbs above the noise and that is a very weak echo from the
surface of Titan.

As you can see the strength here is no more than \-- if the noise is 1
like in all these diagrams, it's no more than 10% of the noise flow, but
like a weak echo, but it's real, it's very clear, that it is very
different from the noise flow around it. And we can use again,
spectrograms to show that echo.

And so the next slide, number 16 shows the spectrogram now in terms of
an image, again frequencies on a vertical axis and time is on the
horizontal axis. And the color is the color of picture at given time and
frequencies, this links to the echo.

You see that - if you look at near the center of the band most of the
time you don't see anything. And then near the very end of experiment,
the last few minutes of the experiment the color changes to red
indicating the weak echo I just showed you. It' shows both in the RCP
component, which is the left top and the LCP component, which is the
right top.

On the in - so this is the inbound side, so this is - these are the last
few minutes of the inbound observation. And then the outbound is at the
bottom, so this is still X-Band, but now coming out from the occultation
and doing the bistatic on the outbound side. And again there is no echo
most of the time and then the echo shows for about 7 or 8 minutes in
both the RCP and the LCP.

And the next slide shows interpretation for this by summing out, summing
up the power in the echo. Both the RCP and the LCP are ratioing the sum
so that you get the measurements of the ratio for the observation angle
for which T14 (unintelligible) with (unintelligible) was conducted.

So again the axis (unintelligible) are the vertical axis, is the ratio
of the power in the two polarizations and the horizontal axis is the
angle (Fezeal) or the called the bistatic angle or the incidence angle.
And the two red squares show the measured value for this incidence angle
corresponding to the observations geometry.

And then we compare that to expected theoretical behavior for different
directive quiescent of assumed surfaces. So for (Epsilon) equals 1 1/2,
we have a curve for a (Epsilon) 2 we have a curve, 3, 4 1/2 and 6. And
again the measurements indicate a (bilective qualiscense) of about 1.6
and very different from the -from the, as you can see it's well
separated from the curve for 2 or 3 and etcetera.

That is the (unintelligible) for 1.6, are usually attributed to liquid
hydro carbons. So we may have seen a liquid hydro carbon on the surface
at these locations. But one has to careful to say also that you can
synthesize that (unintelligible) in many different ways.

So let me show the last slide on the subject, which shows that if you
have a medium of directive quiescent 1.6 that you measure, that could be
liquid hydrocarbons, that brown block that you're seeing, but it can be
also in homogeneous.

This can be due to taking a medium of higher directive quiescent and
then reducing the directive quiescent artificially by either introducing
voids in the volume, so this would be like a (polis) medium. Like the
picture you see at the bottom right or it could be a solid ice surface
that is covered by fluffy material in the form of a snow, snow
particles. Where the wave then where (isn't) on the surface, you're
seeing most of the uncompacted snow particles at the top of the (H2I).

But within the domain of the solution there is also the liquid
hydrocarbons in here. So we still have to look at what we got from the
other experiments and how they compare. The nature of the surface
appears to be very different depending on where the location, where the
place look is. So we need to look at this also collectively as a
complete analysis for the other cases, but definitely the T14 data
suggests that we may have looked at liquid hydrocarbon kind of region.

And I said it's not a definitive kind of an answer, because we only
measure an effective directive quiescent and as I just mentioned you can
synthesize media to have this effective directive quiescent, in
different way. So...

(Trina): A question.

(Essam Marouf): Yes.

(Trina): This is (Trina), hi.

(Essam Marouf): Hi (Trina).

(Trina): Liquid hydrocarbons that's a really exciting result and as you
say you could be fooled. Is there some observation that some other
instrument can varied? Like maybe a radar observation that would really,
you know, in your mind sort of nail it down one way or the other?

(Essam Marouf): I think the opposite may be true, which is where you
think radars see liquid hydrocarbon, that is to say the little
reflection from the surface. Because what they really see is the fact
that the surface is relatively flat. And therefore it does not reflect
much energy to their instrument. So they say that is liquid hydrocarbon,
but not only based on that based on some other influences; that relate
to - show lines and things like that.

But if there was an opportunity for us to do our bistatic over one of
regions to be able to measure the directive quiescent or if we look in
(normal emission) on the (extended mission) and see tracks that we
overlapped over regions where they think they have seen liquid
hydrocarbons then we can check definitely one of the directive
quiescent, the computer agrees with that one though.

(Trina): Okay thanks.

(Essam Marouf): But we unfortunately what we do measure is a directive
quiescent, so if you can synthesize an occultation medium with this
directive quiescent then that's the likelihood also. It's just how - if
you look at flat regions that other's also think that they are liquid
hydrocarbons, then that's more of a supportive kind of an answer.

(Hendrix): And then one more question, I might have missed, so the Slide
17 results are from T14?

(Essam Marouf): Right.

(Hendrix): And what about the T27?

(Essam Marouf): I did not finish the analysis for that yet. So, but...

(Hendrix): Oh got you, okay. That'll be interesting to see
(unintelligible).

(Essam Marouf): It has very promising results too, yes. Yes, there the
echo, I mean, the south pole has a much more flat kind of a nature. The
(unintelligible) regions are much more rough; because as you can see the
spectra we see, the spectra gram I just showed, they ensure echo most of
the time.

(Hendrix): Right.

(Essam Marouf): And that means that the reflected echo is not quasi
specular, so it's spread in frequency over a very broad range and it's
very weak over any part of this range, so it's hidden in the noise. And
in that case we don't see an echo and only when the surface gets to be
more flat that the - all the energy are concentrated in a very narrow
band and we see very clear understanding above the spectrum, above the
noise floor, so we see it in the spectrum.

So T27 shows - if you look carefully at the specter I showed they hardly
show any spread in frequency, so they look very much like they came from
a very, very flat surface. And so the nature of the South Polar Region
is definitely very different from that near the equatorial region.

Although as I said if we have a liquid hydrocarbon - here it's a lot
more confined in the - in T14 case it's a lot more confined in terms of
the (spatial) extent and we only see it over a very short period of the
experiment. In the South Polar Region we're basically looking all the
time at the flat surface region.

But whether that's liquid hydrocarbon or not, that's not really very
obvious at all at this time. But it will be interesting because the data
there is much - the signal to the noise ratio for their measurements are
much better.

Okay so moving on to the Titan occultations. I'm moving very slowly
unfortunately, but I'll try to speed up the rest of it a little bit. So
the Titan occultations much like a bistatic we completed four types of
occultations during the (normal emission), all of them completed, two of
them last year and two of them this year.

So again I'll select just one example of Titan occultation and discuss
it in a little bit more detail, but there is ongoing work on all four of
them to try to characterize the results collectively.

So the first on, Slide 19 here shows the - one of the - this is actually
the last one T31 conducted in May, on May 27 this year, which was a
south coming, the (unintelligible) comes from the south pole to the
north pole sort of speak. The latitudes covered are indicated on the
right; they are 74.6 degrees, so negative 75.4 that's the ingress.
That's the south latitude and 74.6 degrees on the north.

The four of them are collectively shown on the next slide. And so first
two T12 and T14 were east, west kind of occultations, the ingress is on
the east side, the egress is on the west side. And the last two the T27
and T31 are north or south, north occultations.

And the one I'll talk about mostly today is T12, which is the first one.
But as I said there is good progress being made on analyzing all these
four together and there is a paper in preparation on that issue. But
since the results are not completed yet they weren't included here.

The next Slide 21 shows roughly the basic concept involved. I don't want
to spend too much time on it, because it's a little bit of a detailed
kind of a slide.

Well the point it tries to make is that a signal as it goes through a
gases atmosphere, which is represented schematically here by the red
line going through the atmosphere that the radio signal - radio ray from
the earth to the spacecraft, the spacecraft actually transmits the
signal and earth receives the signal. So it's the opposite of what I
showed here, but the concept is the same, there is (unintelligible) here
and the concept is the same.

So the signal goes through the atmosphere and picks up feed using to the
path through the atmosphere, so when it exits from the atmosphere - the
blue line on the right - is the wavefront and on the wavefront there are
phase preservations called (Tesavar). And these phase preservation carry
information about the density of the atmosphere along the path. If the
atmosphere is more dense then the phase is larger, etcetera.

And then the wave front propagates to the spacecraft and suffers from
the fracture as it does that, but if we forget that for a second then
the phase fluctuations on the blue line, on the wave front exiting from
the atmosphere is what the spacecraft thrust (feed) measures, it's
really measured after being diffracted. And one would like to recover
the properties of the atmosphere for the measure phase preservation.

And that's a equation at the bottom where the phase preservations are
related to the so called refractivity of the medium and capital M. And
the refractivity relates to the number of density, so one would like to
recover from the measured of phase, the refractivity as a function of
radius. So one must invert this equation to recover capital M from
measured (phase).

We don't really measure (phase) directly we measure the rate of change
of (feed) any time the phase changes as a function of position or as a
function. Since the spacecraft is flying pattern to this blue line
radius of time or related. So rate of change of phase is Doppler shift.
And therefore what the spacecraft really measures is the Doppler shift
and we invert the Doppler shift directly, we don't invert the (feed).

But if you think conceptually you are recovering from the measurement,
the refractivity as a function of radius. And then assuming
(hydrostatic) equilibrium and knowing the number density you can recover
the pressure. And then assuming the equation of state and knowing the
pressure under number density, you have can recover the temperature
given that you know the composition also.

So occultations don't measure composition very well we have to rely on
other people, measurements of the composition, but for Titan it's a very
simple assumption, we just use nitrogen or nitrogen with a small
percentage of heat or methane.

So the composition on (unintelligible) is not as high as in other cases.
But essentially what spacecraft occultation provides here, it provides
temperature as a function of (height) pressure, as a function of
(height) number density, as a function (height). As well as the
structure of the atmosphere like you will see in a second from other
preservations in the signal.

But to do this properly you have to account for all what I listed on the
lesson here including. The fact that the ray value - I just
schematically showed at the top - are really (bedded) in the atmosphere
so that if changes in the signal properties due to the (spending). The
atmospheres are not finically symmetric; they usually have a symmetry in
them. They blend in the atmosphere; there is absorption along the path
and maybe also scattering along the path.

So you have to account for everything, but the concept is you'll measure
phase preservations or frequency preservations due to the atmosphere.
And then try to recover the properties of the atmosphere from the
measurements.

The next slide shows the case for T12 and the measurement here is the
frequency residual, so the sinusoid that go through the atmosphere has a
frequency and phase and amplitude. All these will be preserved when the
signal goes through the atmosphere. And here I'm showing the measured
preservations in terms of frequency as a function of time.

And again the frequency here is not the full frequency it's just a part
(due) to the atmosphere. So we've taken out part due to propagation in
free-space. And so what's left is what preservations the atmosphere
introduced on the frequency. In free-space of course there are no
preservations and you see the residual starting as the spacecraft
approaches Titan, so this ingress.

And you see that the frequency residual is zero, but once the signal
starts probing the atmosphere the frequency turns and changes very
quickly, because of the refraction in the atmosphere. And one thing
you'll notice right away, which is unfortunately, because the state here
is not very good.

Something that clobbered into conversion to PDF, the vertical axis
numbers are gone, but the two numbers that are important are preserved
still, which is the increased space, the (residual Doppler), by the end
of a experiment the Doppler (is at the order) of 4 kilohertz.

So here also we have to tune the receiver to keep the signal into
bandwidth, much like in the bistatic case. But the important thing is
look over what time seeing that, (mysterious) effects are happening. The
horizontal axis, the tick marks are separated by 50 seconds, so it took
a minute to minute 1/2 to pull the signal to go from the top of the
atmosphere all the way to the surface of Titan when we lost the signal
here.

Experiment Titan occultations are extremely fast, nothing like we ever
done before in any occultations of bodies of the solar system. And
therefore the maneuver that has to be executed, as I said is a very
demanding one. And fortunately that all of them worked, so that's just a
testimony to these kind of complicacy that people that designed
maneuvers, which is the frequency team of the radio science group, it's
a testimony to their competence really.

Because the experiment is extremely fast and very sensitive to pointing
if you have a trajectory error, if you have a pointing error, you would
lose the signal immediately. Yet as you can see here the Doppler is
being tracked all the way to we've reached the surface. I know we
reached the surface because of the other slide, which I'll show you in a
second.

But that's the kind of information one needs then to recover the
temperature profile, which is shown on the right. That's through this
(oval) inversion process, which I described schematically in the
previous slide. So what you see here is the first temperature profile
that was measured after - this was only the second occultation after
Voyager, Voyager did one occultation of Titan, this was the second one.

I'll compare with the Voyager answer in the second, but the real
important number that or the real important part here is that the
measurements are from an altitude of about 200 kilometers where we start
being sensitive to the atmosphere all the way to the surface. And
therefore it's a characterization of the (unintelligible) profile in the
atmosphere with a very high (spatial) resolution, because the
(trajectory) effects - limits our resolutions to (fenounce kil) and the
(fenounce kil) here is the order of a kilometer.

So it's one of the few experiments that capture the (sentiment fracture)
of Titan atmosphere with very high (spatial) resolution. But only over
the bottom to 100 kilometers, we're not to (sensitive) very much about
that.

And clearly the stratosphere and the troposphere here, I mean the
structure is very different over these two main regions of the
atmosphere. The temperature (unintelligible) surface is still very close
to what Voyager measured, which is about 94 degrees (unintelligible).
And the pressure is about 1 1/2 (unintelligible), just like in the
Voyager (key).

The next slide compares the measurements on Voyager with the
measurements from Cassini, so the different colors here, black and red
are the T12 experiment on the inbound and outbound side, ingress and
egress. So you see that in the stratosphere there is - there are
differences. Some of that difference, these differences can be deceptive
sometimes because of errors in the trajectory being affect the earth at
more prominently, at the very highest altitude.

But as you go down in the troposphere of the curve, essentially
identical, so there's four curves on top of one another. And in the
troposphere they're almost identical. The fourth one is the
(unintelligible) probe (unintelligible) measurements of the atmosphere,
which agrees very well with both the (unintelligible) observations as
well as the Cassini observations.

And I'm always struck by the fact that the temperature in the
stratosphere is so stable. The - it indicates that the - I'm sorry in
the troposphere, is so much identical, it indicates a very stable
atmosphere in this near equatorial region.

We continue to see very similar behavior in the other occultations, but
there are small differences, so the occultations show some differences
between these profiles. And of course the differences get to be larger
in the stratosphere and some of them actually show very unusual kind of
behavior. But that all tend to be worked out in the (tail), but I'm not
going to talk about it anymore here.

I just want to show here that the - at least from one observation the
atmosphere of Titan at least in the part it appears to be stable with 25
years between Voyager and Cassini, but yet their temperature structure
appears to be extremely well preserved.

The ionosphere also is another target of the observations and this is -
Slide number 24, shows what we get from the frequency residual in that
case, the residual are caused by phase changes. But the phase changes
are not due to the neutral atmosphere, but they are due to the plasma in
the ionosphere. And therefore the outcome is the number of density, the
electro number of density in the atmosphere.

So what the slide is showing here is the electro number density on the
vertical axis and the horizontal axis and altitude on the vertical axis.
And there are multiple curves showing here, one is the yellow curve as a
theory, but the measurements are the Voyager and the T12 in ingress and
egress.

So the Voyager, which is the blue curve appears to show a higher electro
number density at the latitude probe, Voyager probe near equatorial
latitude, at T12 or slightly south, was about 30 degrees south on the
ingress and about 50 degrees south on the egress.

So the green and red show a peak at about the same location, about 1200
kilometer altitude, but with slightly different values of somewhat
different value. And different values are because one measurement is on
the (dusk) terminator where the plasma has be - where atmosphere has it
in sunlight for a long time. So the electro number density are somewhat
higher.

And the red curve is on the dawn side where the plasma was much, a lot
less in sunlight and therefore the peak number density is smaller. We
have collected 8 of these, because the four occultations ingress and
egress and we variable kind of a picture for Titan atmosphere, things
are not the same at similar latitudes. So there is a year of stories
still to be told about availability in the ionosphere structure as a
function of latitude from the rich set of great observations.

So this is the end of my Titan part - oh no I'm sorry, there is a little
bit of information about \-- Titan also comes from the fact that the
sinusoid changes not only in frequency. But also in (thincs), in
(thincs) changes come from two sources, one is the fact that the rays in
the atmosphere are - bend in the atmosphere. So the energy drops because
of ratio (diversioning).

So this is called a refractive defocusing and that's just a geometric
effect that one can take out from knowledge of the fact of the - how
rays reflect as a function of altitude.

But the other one is a real change in intensity due to absorption of the
signals in the atmosphere. So this is real absorption of signal in
(unintelligible). Again if you look at the top panel, this is the
ingress coming from free-space, you can see the signal is almost
unchanged. But as the ray hits the atmosphere then density starts
dropping down and doing so there is a large scale kind of a drop down,
but also there are small scale fluctuations as (unintelligible).

The small scale fluctuations are signatures of turbulence in the
atmosphere as well as gravity wave. And the large scale structure is a
signature of the two absorptions in the atmosphere.

And then by the time you get to the surface the signal drops all of a
sudden as you can see here and then hits the lowest baseline. The red
curve and the blue curve are two separate stations on the ground
observing at the same time. So you can see here that even though one
station is in California and the other station is in Madrid, they were
observing almost identically the same signal.

So all this structure is real, you know, this is not noise, this is not
an artifact of observations at the station of the artifact observing
system at the station, these are all, real Titan signatures. If you look
at the wiggles in both the red and blue lines they are almost identical
except when you get into the noise and there the noise is totally
independent.

And then on the ingress side again, coming - that's the bottom curve -
that's about 50 degrees south. You'll see again the signal climbing
suddenly from behind the limb of Titan. It's not really sudden, because
of the fraction effect. So there is a finite tapering, but that's just -
limb diffraction.

And then again the climbing instincts and the wiggles, the wiggles are
signature of gravity wave and turbulence. And then going back into
free-space and the signal being (unintelligible) after you get out of
the atmosphere.

The next year graph or Slide 26 shows - the previous one was just
X-Band, shows after you take the trajectory into effect and translate
time to heighten the atmosphere. And after you remove the effect of
refractive defocusing, the fact that they too diverge, what's left is
the real absorption.

First showing the extinction in the signal, the absorbed - the strength
of the signal on the horizontal axis, but on (large) scale in decimals.
And the vertical axis is height, so instead of time now that's height
above the 25, 75 reference radius. And you can see that the three
curves, the two (petals), one for the ingress, one for the egress. And
there are three curves, one for each of their frequencies we use.

And three frequencies are affected very differently as you can see the
red curve is the longest wavelength S-Band and the green is X-Band and
the blue is K-Band. So you can see that the K-Band, the shortest
wavelength is being extinguished much, much more quickly than the other
two. In fact it's completely lost at about 10 kilometers above the
surface. While the other two, again, X-Band is extinguished more than
S-Band, but both of them reach the surface, the surface is a zero, that
kind of a level.

Again the zero means 25, 75, so the less one extinguishes at about this
radius, but the right keeps going for slightly more (unintelligible)
kilometers, so (unintelligible).

Again the fraction here is very important, so we have to take the
fraction out before finding what the radius of the surface really is at
these locations. But the point I'm trying to make here is that the three
frequencies are affected very, very differently.

And that is a new measurement, that Cassini is a new, is a spacecraft -
the first spacecraft to characterize a extinction in the atmosphere of
Titan, the microwave absorption in the atmosphere of Titan in this level
of detail.

The Voyager only had X and S-Band and did not have the stability to find
the extinction to this kind of a level, so there are no extinction
profiles from Voyager, there's only up or down on the extinction. Here
we have a detailed profile, both ingress and egress at 8 different
latitudes, so that's a quantum leap over what's Voyager has already
provided in terms of extinction characterization.

If you are following - if you think in terms of (para lateral) for earth
kind of observations, a key then is being used on lots of satellite
communications. And one enemy of K-Bin for satellite communication on
earth is green in the atmosphere. So we've seen this large extinction in
the atmosphere, the first thought that came in mind is that we may be
seeing rain in Titan's atmosphere, in the troposphere of Titan.

So we done a enormous kind of - hours of work to try to characterize how
much rain and what kind of particle sizes would be responsible. This
is - I'm talking about methane and ethane rain, potential conjectured
methane and ethane the troposphere of Titan.

So we done some marveling of what extinction we would expect to observe
for models in the atmosphere of Titan that include rain. So the next
slide 27 shows at least the - in a causal way, that's not the keen way.
But just a picture to show that if you do assume rain to be responsible
then you have - so what's shown here again on a vertical axis is the
ratio of the K-Band, X-Band extinction you would expect for a particle
for rain that has a droplet size that's shown on the horizontal axis.

And we see a ratio of about 10 - and that's the horizontal that line. So
for particles of different refractive index, so if these were liquid
methane they would be about 1.7 radio directive quiescent. But the
(measuring) part would be uncertain and so the individual color curves
are for different (measuring) parts.

But you can see that there is two ranges of solutions right away. One is
for particle sizes that are less than a millimeter, which are pointed to
by the red arrow to the left. And then there are also droplets of about
a size of 3 to 1 centimeter that are highly insensitive to the
(measuring) part the directive quiescent. So rain composed of particles
of these size ranges could explain what we see.

But when we calculate the number of density so that we get the
extinction we see, we get a large optical (depth) from the small
particles. We get small optical debts from the large particles, but we
don't get the X-Band - we don't get the S-Band absorption we see.

So both of them have contradictions and now we believe that what we are
really seeing is what is in the 28, Slide 28, which is the extinction,
is caused by (unintelligible) of absorption rather than particulate of
absorption. They are due to the nitrogen collision in use of those, you
know, sometimes also nitrogen can explode (unintelligible) absorption.

So the stories evolving, and just like what you do in science all the
time, you try to find a best reason for what can explain what you
observe, but and also the most self consistencies.

And if the, I mean, based on the radio measurements, only you can't
(phase) rain, but you would need so much of it that it could block the
\-- it would essentially - the optical (conductor) would be large enough
for the ORS instruments to see the surface, which we know not to be
true. So the most likely reason really is the (gaches of goshen) and
that is the result shown in 28.

So time is running short and I need to finish the rings quickly, but the
rings are the most interesting kind of data to me, so I'm going to try
to run through it quickly, as quickly as I can and. We do similar kind
of observations of the rings, at least an occultation of the regions
also.

So Slide 29 is one of the last - one of the latest occultations, we did
the year also on (route 44). We did two (route) this year, two ring
occultations this year, (route 44 and 46) and those were in May and in
June of this year.

And the picture you see on 29 on the Slide 29 is the pass of the
spacecraft again as the blue line, as seen from earth. Coming from the
right to the left and passing behind the north - very high northern
latitude of the southern atmosphere on the inside. Coming near
equatorial on the egress side and then passing behind the rings.

So this is an egress - only ring occultation and it was really the first
one-sided occultation we do in the tour. And on most other ring
occultations we see both the inside and the outside; those were the
diametric occultations at the beginning of the tour. But from now on
they are all - almost all one-sided like this here.

And again the rings were only 15 degrees open at this time, so the next
slide shows what I mean by only 15 degrees ring opening. So the - again,
in occultations the spacecraft will pass the down-links taking them
through rings. And for an observer on earth you see the rings are much
likely to hover space that are called PSCs, the rings over time - when
the rings are fully open - the picture on the very top right - and then
the rings close systematically as a function of time.

And this picture happens almost exactly during the 40 years (normal
emission) of the (unintelligible). So as a function the rings are
closing down and the first set of occultations we did were when the
rings were nearly fully opened and then the occultations on route 44 and
46 are happening essentially near the middle of this diagram. And then
near the end of the mission another set of occultations when the rings
are closing.

So the path link of the signal through the ring changes as a function as
a function of time. And that means when the rings - when we look at
(opaque) parts of the rings they become more and more noise limited as
time goes on. On the other hand when we look at tenuous parts of the
rings they become more and more detectable as time goes on.

So these geometries compliment one another, but was it was important to
do the early occultations so that we are not noise limited over ring B,
which is really a major ring that was not probed by Voyager, because the
Voyager occultation happened when the rings were almost closed, 6
degrees open, so it's like the bottom picture you see in this diagram.

So the route 44 and 46 are beginning to add information about how things
change as the rings become more closed. And that will compliment the
information we get from the last set occultations and also the ones in
the extended mission where the rings are almost fully closed. And
therefore were extremely sensitive to tenuous structure that will be
completely locked by dense structure.

So next slide, which again that - unfortunately (lift) up in the PDF
conversion. Shows that ring open angle on the vertical axis as a
function of time and that's for the wiggles here are - the rings that
are closing as a function of time the ring open angle going to 25 down
to 0.

And the wiggles are just because earth moves around the sun and
therefore every year the geometry changes and the (unintelligible) are
roughly a year apart, so this is just a (arch) attack of the earth's
motion. And the circles, red circles represent the (action) occultations
we do, so that's 7 to 13 are the ones that are done when rings were
nearly fully open, not fully exactly, but 20, 26 or so, this is - the
were from 23 1/2 to 20, so it's 19 1/2.

And at the end of the mission from left, 53 to 67 we do the close ring
occultations or nearly close ring occultations. The rest of it - the
extended mission occultations follow 67 and therefore they are at a much
more ring opening angle, at least in (unintelligible) actually, we do
one at 2 degrees.

But basically these two are the set of three occultations I show here on
left 28, 24, and 46. So capturing this range of variation allows us to
study how the signal is extinguished and scattered as a function of ring
opening angle. And therefore tells us about the physical structure of
the rings, in particular vertical structure of the rings.

But what I'll concentrate on here today radio science profiles ring
structure and does that with exceptionally high resolution. And as it
does that with multiple occultations it essentially provides a very
detailed characterization of how ring structure vary from location to
location in a quantitative way. So that would be the emphasis.

And the topic I'll leave out for our future talk not included in the
slides is extending that knowledge to the particle size level and
talking about the physical properties of the particles. There sizes, how
they clump together, how they distributed it vertically in ring plane,
etcetera. That would take another talk by itself and therefore that's
left out. So the talk here is primarily showing you how we map ring
structure, with exceptionally high resolution in the examples of what
we've seen.

So we map ring structure by observing how this technology is
extinguished. So Slide 32 shows again in a cartoonish way the difference
between an imaging observation and a radio occultation or a stellar
occultation for that matter. While an image shows the rings as an whole
in either deflected or transmitted light and therefore what you see
really depends on - not really on the optical depth of rings but also on
what they are made of and their details of the green - the surface - the
details of the particle surface as it reflects light.

In an occultation the radio signal penetrates the ring, so if you look
at the red line at the top with incident intense (I zero), it goes
through the rings and it comes out - the equation at the bottom here, (I
zero) (into) the minus, optical depths over sign the (find) opening
angle. The extension in the radio signal gives you immediate
characterization of the ring structure. But it does that as the
quantitative characterization insensitive to the tails of the particles
themselves.

So it - for example, the albedo of the particle, that's not immediately
coupled in here, except in the optical depths value itself. So by
characterizing optical depths as a function of location you characterize
ring structure in a quantitative way.

And in the case of radio occultation you do that at three frequencies or
three wavelengths. And each one of them sees the rings with a different
eye, that's because the optical depth is a function of particle sign.
And therefore as particle size relative to their wavelengths and
therefore for one wavelength light - in this case the red curve.

So what you see at the bottom is the optical depth side over the range
of the image from the Cassini - inner part of the Cassini division all
the way to the edge of the outer ring E, depicted at the bottom here as
extension of the signal of the function of ring radius. So this is the
curve that you should try to simulate, because it - all the other curves
look like it, so (real) here means the signal is in free-space, it
hasn't been extinguished at all.

And then as you add optical depth (I zero) drops to (I zero) equals a
minus (power) of (sign B). So what we're (plotting) here is the drop in
the signal (extinct). So as we drop more there's more material. And we
characterize the drop in terms of the optical depth where the optical
depth is (plotted) increasing downward versus ring radius.

And any time we go back to zero, we will come back to free-space. And
any time we dip at various far away from zero that means more and more
material in count of the longer ray.

So the Cassini division as you can see, the signal stays very close to
free-space, but in the body of the (E) ring there is a much bigger drop.
Then we come back to free-space near the edge of the ring (inky) gap and
then in the (kelar) gap before we hit the outside of the ring.

And the fact that there are (C) colored curves here are because we're
doing C wavelengths and the fact that the are separated - separating
from one another as you move outward meaning that they are experience
different optical depths along the path.

So because the optical for the red curve is then smaller than for the
other two, that means there is material S-Band that does not see what
the other two frequencies see. And that immediately says there are
particles that are of size less than the wavelengths of the S-Band
wavelengths.

So there are particles less than 10 centimeters in size not seen by the
S-Band, but seen by the other two. And near the very edge of rings,
you'll see the green and the blue curve also separate from one another.
Again the green is the S-Band - is the X-Band at 3.6 centimeters and the
blue is the K-Band at .94 centimeters.

Again the fact that the green is less than the blue says that the green
is not seeing particles that the blue are seeing and those are particles
of size much less than 3.6 centimeters, millimeter size particles. So
the three wavelengths allows you to relate structure also to small sizes
in the - the small particle sizes in the ring.

For example, in the Cassini division you also see the frequencies
separate, especially in the outer part of the Cassini division where
there is structure here where the optical depths (unintelligible), it's
called the ramp. And you can see the (stewave) length separating very
clearly indicating centimeter, millimeter as well as super stunt
disameter.

All three wavelengths see the size particles, but S-Band stopped losing
vision of particles that are less than its wavelength, similarly X-Band.
So the three wavelengths measure three different kind of structures
where the structure in sizes are coupled together.

So the next -all slides then will show optical depth increasing downward
versus radius and there is a line at the top showing free-space level,
usually there would be a line at the bottom also showing the noise
level. But here the structure is Cassini and well above the noise level
so there is no bottom line in here.

So radio science provides - radio science occultations provide a radio
structure - a map of the radio structure, we call it the profile of
radio structure so rings. But has exceptionally high resolution that
approaches few 10 of - few 100s of meters like you'll see in a second.
But unfortunately it doesn't come from free we have to do very elaborate
processing to do that.

But this is just an example taken from region of rings where the signal
level is not very highly extinguished, this is Cassini division. And at
the beginning of the Cassini division there is the (quagins) gap where
the signal level is close to the dash line, the free-space level.

And I'm sorry to show you dirty laundry here, the free-space level is
not stable in this slot, but we compensate for a pointing problem and we
have profiles that are much better than this one. It's just that is the
one I could find at the time, so I used it. But the free-space level is
usually a lot more stable than what you see in here.

And that gap has two ringlets in it - well the gap is a (Huygens) gap so
these are the (Huygens) ringlets. One is the - it's called the main
ringlet and then one near the edge is called the outer ringlet. So I'll
just use these as my examples to show you how we get to profile the
structure with very high resolution.

But gap in themselves are very interesting because gaps in Saturn's
rings are envisioned to be open by bodies embedded in the gap, so one
envisions a satellite in each one of these gaps and the (torp) that the
satellite (exerts) from (enabling) particles would be responsible for
opening a gap. But like I'll describe, we only know of two satellites
embedded in the ring, yet we have so many gaps, here I show you 8 of
them in the Cassini division that are yet to be explained.

This may or may not contain satellites of course everybody's looking
very hard they can see direct or indirect signature of the satellite
including radio signs. But so far the - all the gaps in there are not
clearly associated with satellites except for two the (inky gap) and the
(kelar gap). And both of them are in the E ring, in the outer part of
the E ring.

And so next slide shows the (Huygens gap) main ringlet and it shows it
by blue curves on the left and red curves on the right. The blue curves
show what the spacecraft actually measured when it went behind that
ringlet. And it shows the strength of the signal on the top, it
characterize in terms of optical depths, again, zero mean free-space so
this is a gap.

And the ringlet is the dip in the - that you see in middle. And radio
science measures not only the strength of the sinusoid, but also the
frequency and the phase, so the phase is plotted at the bottom in here.
And you can see that associated - when you're in free-space there is
very small change in the phase, but when we run behind the ringlet there
is a large change in the phase.

And you see wiggle - and you see the regular occultations near the edge
as they go, transition from the edge of the ringlet to free-space
bottom, (unintelligible) on both sides of the ringlet and also in
phasing (solution).

Yet this is what we measure - that we - what we measure is the fraction
limited. So if we remove - if we somehow use - if we somehow find a way
to reverse the fraction instead, then we would see the rings actually
look like. So this is a garbled image and one has to do work to remove
the fraction effect in order to see the exact profile of the ring.

So radio science does not measure the ring structure directly, it
measure a diffracted limit - defracture limited version of it and that's
represented by the blue curve. And what it does is it takes these
measurements and inverts it using techniques I'll discuss very briefly
in a second to get to true profile.

And the true profiles are on the right I'm showing now that the wiggles
are all gone and the edge of the embedded ringlet - this is extremely
sharp like you see in here and most of the phase occultations that were
in the blue curve are gone also. And there are some phase fluctuations
due to the ringlet itself. The red curves are what the rings exactly
look like, the blue curves is what the spacecraft actually measures.

And the process for going from one to one, from one to the other is
exactly like the process that one goes from a recorded hologram to a
played hologram. At a fraction wavefront is a hologram; it preserves
information about the strength and the phase of the signal. And you need
to play the hologram to get to the true image. And we do that on the
computer through very significant (kind of processing) to get to the red
curve you see on the right.

But the red curves are - because we've taken the fraction out the
resolution the (feature) resolution are a few hundred meters, (in all
state) of the fraction typically few kilometers, 5 kilometers. So when
we remove the fracture we get the profile with exceptionally high
resolution at 400 meters (unintelligible) and were pushing toward 200
meters now a day.

So the concept behind that is shown in slide 35 where you can see the
model of the rings just a random resolution of particles where the wave
coming from the left goes through. And the preservations due to the
rings are called (Textrime) on the right of the model (flap). But by the
time the preservations get to the spacecraft the feel on that wavefront
(reaches) the spacecraft (after individual parts of it) interfere with
one another.

So the spacecraft sees the (feno) diffraction pattern, much like the old
studying optics is that the feed behind the (split) is not the feed you
observe from distance of the (split), but one of those is the feno
diffraction pattern or the (frown half) of the diffraction pattern. Here
is (unintelligible) (feno) diffraction pattern.

So what the spacecraft measures and what's desired, which is the profile
of the rings are different. And equations at the bottom show how we go
from one to the other through what's called the inverse (feno)
transform. So there is very elaborate processing to be able to (read
from spectrum) what's measured, the actual ring profile.

Next slide shows the outer ringlets of the (Huygens gap). Again, the
blue is what is measured and the right is what the ring really looks
like. And there is a world of difference between the two, as I said you
can not get high resolution profile of rings on this that is done. And
that's what we have done for all the detail we measured to be able to
get the high resolution profile that is (really) our product from - one
of our main product from this kind of an observation.

The point this slide makes is that it shows you - also if you look at
the red curve at the bottom, the vertical axis is phased and phase is
the tick mark, are .05 degrees apart - .05 (pie) is an 180 degrees, so
.05 out of (pie), the tick marks are 90 degrees apart. So as you can see
here the measurements are - we need to measure a phase which is as small
as 9 degrees. Every time the wave propagates one wavelength and X-Band
at 3.6 a year wavelength it suffers a phase of 360 degrees.

So to measure a phase change of 9 degrees means you measure - you need
to measure changes in the phase path that are a fracture of a
wavelength. So even though the distance to Saturn is 1 1/2 billion
kilometers, when the phase path changes by a millimeter we need to be
able to detect that. And that's why there's ultra stable oscillator in
the spacecraft, is that you can measure such small phase.

So this is one thing that most people don't really recognize about radio
science. It's an exceptionally sensitive kind of an experiment to any
phase changes along the path. This is how we get to do profiles of the
rings at 100 meter resolution; this is how we measure very small effects
in the atmosphere of Titan. It's by the fact that we have a US (owned)
on the spacecraft that allows us to measure very small phase changes.

And now I will just go through examples of profiles of ring structure
that we measured...

Hendrix: Essam.

(Essam Marouf): From some of our occultations we've completed; so in the
next slide 37...

Hendrix: Essam?

(Essam Marouf): So the cuts in the ring I (chose) 10 out of 15 cuts was
completed so far. The first cut cuts most the inside and the outside, so
the inside is on the left the outside is on the right. And the four
colored lines are the (unintelligible) 7, 8, 10 and 12, which were
(excluded) in 2005. And then 46 and 44 are also shown what executed the
(sphere). So these are these 10 cuts as I used as the (unintelligible) I
used results from these cuts as examples in the slide to follow.

And the thing that you have to keep in mind that we really have 15 cuts,
so even though I show you profiles at a time it's just because I can't
show 15 profiles at a time. But essentially the occultations
(dissectoring), the more occultations we have the more dissections you
have. And each dissection will show you the structure of the rings at
very high resolution and the video ability in this structure with
longitude.

So...

Hendrix: Essam?

(Essam Marouf): Yes.

Hendrix: I hate to interrupt you, because this is really great, but I'm
worried that we're going to run out of time because I think we're (ruin)
in about 10 or 12 minutes.

(Essam Marouf): Okay I will just go for five more minutes and then stop.
How's that?

Hendrix: Okay well however you want to do it, because, I mean, it's all
really interesting stuff - there's a lot great stuff here. So however -
if you want to just go ahead or skip into your highlights or however you
want to do it. I just wanted to...

(Essam Marouf): Okay I will - I think I will make the point with the
next slide and then I'll stop and take questions.

Hendrix: Okay.

(Essam Marouf): How is that? Because the rest of the story is a bit
structured in a way that it fits into one another and therefore it's not
easy to jump from one piece to the other.

Hendrix: Okay.

(Essam Marouf): So I will just make the point with the next slide and
then stop and take questions.

Man: And what number slide will that be? Are they correspondent with the
numbers on these things?

(Essam Marouf): Thirty-eight. So I just finished 37.

Man: Okay and you have a total of 59 slides in this.

(Essam Marouf): I have 60.

Man: All right thank you.

(Essam Marouf): You're welcome. So why is it that one does multiple
occultations? So I showed you on Slide 37 that we have 15 cuts so far
and so one will tend to think that as you do an occultation you see the
ring structure so why do multiple occultations? So that was the point
made by my last slide.

Thirty-eight - which shows again the (Huygens gap) were the two, so this
is - these are 6 cuts out of the 15 I just spoke about. On 7 on the
inbound side, on the left hand side, there's 7 on inbound, 8 inbound and
10 inbound. And on the right hand side there's 7 egress; 8 egress and 10
egress.

All of them, here looking at the part of the rings, which I just
described, the (Huygens gap). And including the two ingress, the one in
the middle, the one broader one and the one near the outer edge that
(unintelligible) one. And as you can see here every experiment sees the
(Huygens gap) differently.

The edge of the (Huygens gap) the inner edge, which is the outer edge of
the ring B moved in and out and is from experiment to experiment. You
don't see the edge at the same location. The ringlet itself changes
position and profile as you cut the rings multiple cut and so is the
outer one.

You see different dynamical structure every time you do an occultation.
And it's a collective analysis of these profile that provide one with
complete - with a more complete characterization of a given dynamic of
phenomenon.

So this is not only the case for the (Huygens gap) and this ringlet,
it's for the case of many dynamical structures in the ring. I was going
to show you more examples of this and also show you the example of ring
B, which is a totally new ringlet, total new structure that we haven't
observed before in any of ring of C or ring B \-- ring A.

But because of time limitations I didn't realize it was going to take
that long, I had hope to move a lot more quickly, but I - my problem is
I try to show the concepts also behind these and not only the results,
but...

Hendrix: And I think it's really great and helpful too.

(Essam Marouf): Yes but, I mean there is a price to pay for everything.
So I'll stop here and entertain a question or two if you any before they
take the line away from us.

Man: Hello, hello, hello?

Hendrix: Do people have questions?

Man: Yes please go I'm ready.

Man: Hello?

(Essam Marouf): Hello?

(Matthew): Okay this is (Matthew) I have a question going back to
measurements done at Titan. When you're trying to measure these rain
drops and you came up short with nothing that does not totally discount
the methane rain. I would assume, because this was as short term
measurement and I would imagine that there is actually a lot of active
weather in that atmosphere?

(Essam Marouf): Absolutely, if you go - if you roll back to Slide 28, if
you have the \-- what we tried to do is explain the whole of the -
(unintelligible) and throughout the troposphere. And we tried to account
for the extinction by saying the whole thing is due to rain.

But that's to show that we need too much rain to do it, but it doesn't
disclose the fact that we still have rain. We still can have absorption
due to (unintelligible) so if you are looking at Slide 28 you'll see -
so concentrate on the left slide and the blue line. You'll see a dash
blue line and that the model of the computation if we have (gaches)
absorption only.

But you see the solid line, which is what we measure, shows deviations
from that. And those deviations could still be very well due to rain.
And that also we have not discounted the fact that rain can exist, we
just show - we just - we can not explain what we see fully (as this
rain), we would need too much of it.

So there are two things happening at the same time, there may be rain,
but a large part of what we see is due to gases absorption also. So rain
is still a much a very much likelihood in the prophecy of Titan.

(Matthew): Okay thank you.

(Essam Marouf): You welcome.

Hendrix: Is there another question?

(Essam Marouf): Yes there was, but it disappeared.

Hendrix: Okay well I think this is all really great stuff (Essam) and
thank you so much for taking the time to put it all together. The rest
of the - I mean, everybody has your presentation, so people feel free to
go through on their own with your examples and just the rest of the
material in here.

So...

(Essam Marouf): My apology again, it's the tendency to try to explain
reasons more than get into the results right away.

Hendrix: And I think it's - I think it's really (unintelligible)...

(Essam Marouf): I think you don't want me to just throw the answers at
you.

Hendrix: Thank you so much and thank you for going into so much detail
on the behind the scene stuff and all the ideas behind it, we really
appreciate it. And I'd like to thank everyone for participating. And
remind you that our next CHARM Telecon will be on October 30. And the
topic of that one will be the (Iapetus) flyby that in preliminary
results from a few (unintelligible) from (Iapetus).

(Essam Marouf): Well thank you for inviting me to talk.

Hendrix: Thank you very much for doing it. And thanks everyone for
participating.

Hendrix: Okay thanks.

Woman: Bye.

Hendrix: Bye-bye.

Man: Bye.

Man: Thanks.

END