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Cassini Radio Occultation of Saturn's Rings and Atmosphere: Preliminary Results. Essam Marouf & Richard French. for the Cassini Radio Science Team. Cassini CHARM Presentation. May 31, 2005. Twelve Main Cassini Science Instruments. Microwave Remote Sensing Radio Science Subsystem (RSS) - PowerPoint PPT Presentation
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Cassini Radio Occultation of Saturn's Rings and Atmosphere: Preliminary Results
for the Cassini Radio Science Team
Cassini CHARM PresentationMay 31, 2005
Essam Marouf & Richard French
Twelve Main Cassini Science Instruments
• Microwave Remote Sensing– Radio Science Subsystem (RSS)
– Cassini Radar (RADAR)
• Optical Remote Sensing (ORS)
– Composite Infrared Spectrometer (CIRS)
– Imaging Science Subsystems (ISS)
– Ultraviolet Imaging Spectrograph (UVIS)
– Visual and Infrared Mapping Spectrometer (VIMS)
• Fields, Particles, and Waves– Cassini Plasma Spectrometer (CAPS)
– Cosmic Dust Analyzer (CDA)
– Dual Technique Magnetometer (MAG)
– Ion and Neutral Mass Spectrometer (INMS)
– Magnetospheric Imaging Instrument (MIMI)
– Radio & Plasma Wave Science (RPWS)
To the Deep Space Network (DSN) - Atomic Frequency Standard - X, S: 70 m - Ka, X: 34 m BWGThree Sinusoids Coherent in Phase
(Crystal Oscillator-- USO)
(cm) Pt (W) SNR (dB-Hz)KaX 3.6 19 51S10
€
Δff
~ 10−13
€
Δff
~ 10−14
From Cassini
Goldstone, CA: 70 m
Radio Science Subsystem (RSS): Downlink Configuration
Downlink
Cassini RSS
DSN
S/CSaturn
Downlink Configuration is Used to Conduct:
2- Ring Occultations
3- Bistatic-Scattering From Titan’s Surface
1-Atmospheric / Ionospheric Occultations of Saturn and Titan
From S/C
To DSN
TitanCassini RSS
Hubble Space Telescope
French et al., 2003
Cassini Orbital Tour of the Saturn System
75 Saturn Orbits; 45 Titan Encounters(July 1, 2004 to June 30, 2008)
D. Seal, 2004
Typical Ring Occultation Track Geometry (15 m tick-marks)
(rev 7) 2005 MAY 3,
-23.6, 21.9, 5
(rev 44) 2007 MAY 10,
-15.2, 39.1, 8.3
(rev 46) 2007 JUN 11,
-14.4, 18.4, 5.3(rev 63) 2008 APR 1,
-9.6, 63.8, 6.5
(rev 7) 2005 MAY 3,
-23.6, 21.9, 5
(rev 44) 2007 MAY 10,
-15.2, 39.1, 8.3
(rev 46) 2007 JUN 11,
-14.4, 18.4, 5.3(rev 63) 2008 APR 1,
-9.6, 63.8, 6.5
Occultation Sequence: revs 7 to 14 180° Transfer Sequence: revs 44, 46
High Inc Sequence Orbits 56 to 67
20° ≤ B ≤ 24° B ~ 15°
6 ≤ B ≤ 10°
Rev 7 Rev 44
Rev 46 Rev 63
Cassini RSS
2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5 20090
5
10
15
20
25
30
7
13
28
44
46
53
67
B
I / I0 =exp[− / (sin B)]
/ (sin B) =2.6, ., .6
Cassini Tour
Year
|Rin
g-O
peni
ng-A
ngle
| (|B
°|)
Catching the Open Rings
14
I0
I
Rev 7 Occultation Track
Cassini RSS
04:23 21:23
BL
03:53 ERT 20:53 PDT
06:00 23:00
06:40 23:40
08:00 01:00
08:32 01:32
10:06 03:06
10:36 03:36
10 m
Rev 7 Radio Occultation Track: May 2-3, 2005
View From the Earth
BL
06:50 G: DSS 14, 25, 26
Live Moveable Block (LMB)
11:10 C: DSS 43, 34 02:45
ERT UTC PT
ingress
egress
Cassini
Cassini RSS
* Water-Ice Ring Particles
*Millimeters to Several Meters Main Size Population
Artist Conception!
* Tens of meters thick
B
Direct, or Coherent, Signal
Scattered SignalObservables
• Direct Signal – radial ring structure
– Particle sorting by size
– Thickness of ring edges
• Scattered Signal– Particle size distribution
– Vertical ring profile
– Particle packing and clustering
– Physical ring thickness
Cassini RSS
Direct Signal
Scattered Signal
Cassini ISS
Voyager RSS
I0
I0 esin(B)
Saturn’s Rings
Radio Occultation: Profiling of Radial Ring Structure
Planet Saturn and its Remarkable Ring System(~300,000 km across; ~distance from the Earth to the Moon )
Hubble Space Telescope
Ring C
Ring B
RingA
Cassini Division
Cassini ISS
Rings Structure
Ring F
Saturn’s Inner and Outer Ring C
Cassini ISS
Cassini ISS
Interesting Ring Structure Exists at Every Spatial Scale
Inner Ring C
4 km res
- Colombo Gap
- Titan Ringlet
- W-Features
200 m res
Titan -1:0 Bending Wave
1500 km
OP
AC
ITY
,
[3
.6]
SIG
NA
L L
OS
S (
dB
)
125 km
100 m resolution is not luxury !
Voyager RSS
Fresnel Diffraction by the Inner Edge of the Encke Gap
Voyager RSS
Voyager ISS
Observations are Diffraction-Limited
-W /2 W /2
F = 15 kmΔR = 200 m
OHolographic ReconstructionFinite Observation Interval W (km); T (sec)
Signal phase must remain stable over T
ΔR =2F2
W
FresnelScale:
F ~ DObservationInteval:
T =W /VSC
Radius (km)Voyager RSS
Ring F Example
101 102 1030
0.5
1
1.5
2
2.5
3
3.5
4
Radial Resolution Δ ( )R m
-X Band
SNR=5dB
- : =2Cassini I B deg
- : =5Cassini II B deg
- : =6Cassini III B deg
Voyager
Resolution ΔR (m)
ΔR = 100 m
Thr
esho
ld O
ptic
al D
epth
TH
(SN
R=
1)
B
Cassini RSS: Achievable Radial Resolution
Cassini RSS
Density Waves Bending Waves
Narrow Eccentric Ringlets
Mimas 5:3
Voyager RSS
Opt
ical
Dep
th,
[3
.6]
Sig
na
l Lo
ss (
dB
)
Uranus’ Ring
Occultations at Multiple Longitudes: Dynamical Ring Structure
Encke Gap
Pan’s Wake
Cassini ISS
Voyager RSS
Occultations at Multiple Longitudes: Detection of Embedded Satellites
Cassini Rev 7: Optical Depth Profiles of Ring C (X, 10 km Res)
Cassini RSS
Cassini Rev 7: Optical Depth Profiles of Ring C, S/X/Ka (R/G/B)
Cassini RSS
Cassini Rev 7: Optical Depth Profiles of Ring B (X, 10 km Res)
Cassini RSS
Cassini Rev 7: Optical Depth Profiles of Ring B, S/X/Ka (R/G/B)
Cassini RSS
Cassini Rev 7: Optical Depth Profile of Ring A (X, 10 km Res)
Cassini RSS
Cassini Rev 7: Density Waves in Outer Ring A (Ka, 1.4 km Res)
Cassini RSS
Cassini Rev 7: Optical Depth Profiles of Ring A, S/X/Ka (R/G/B)
Cassini RSS
Small Particles in Ring A (PIA07875)
Cassini RSS
Radio Occultation: Unraveling Saturn’s Rings (PIA07873)
Cassini RSS
Multiple Eyes of Cassini (PIA07874)
http://photojournal.jpl.nasa.gov/catalog/PIA07873•http://photojournal.jpl.nasa.gov/catalog/PIA07872•http://photojournal.jpl.nasa.gov/catalog/PIA07875•http://photojournal.jpl.nasa.gov/catalog/PIA07960•http://photojournal.jpl.nasa.gov/catalog/PIA07874
B
Direct, or Coherent, Signal
Scattered SignalObservables
• Direct Signal – radial ring structure
– Particle sorting by size
– Thickness of ring edges
• Scattered Signal– Particle size distribution
– Vertical ring profile
– Particle packing and clustering
– Physical ring thickness
Direct Signal
Scattered Signal
Cassini RSS
Scattered Signal:
Doppler Contours
Cassini RSS
Scattered Signal:
Meter-Size “Particles”
amax = 3, 5, 10 m
F (kHz)
Cassini RSS
Cassini Rev 7: Outer Ring B Direct & Scattered Signals
Cassini RSS
04:23 21:23
BL
03:53 ERT 20:53 PDT
06:00 23:00
06:40 23:40
08:00 01:00
08:32 01:32
10:06 03:06
10:36 03:36
10 m
Rev 7 Radio Occultation Track: May 2-3, 2005
View From the Earth
BL
06:50 G: DSS 14, 25, 26
Live Moveable Block (LMB)
11:10 C: DSS 43, 34 02:45
ERT UTC PT
ingress
egress
Cassini
Cassini RSS
TITAN EXTENDED ATMOSPHERE
Cassini ISS
Atmospheric Limb-Track Maneuver
“Actual” Earth
“Virtual” Earth “Apparent” Line of Sight
Geometric Line of Sight
Refracted Ray Path
Saturn or TitanVirtual
Actual
Adapted from D. Wait 05/07/04
RSS Saturn Atmosphere
Ka-band Power AttenuationS07 Entry
Time SPM UTC-ERT May 3 2005
21300 21400 21500 21600 21700 21800 21900
Pwer Loss dB
-50
-40
-30
-20
-10
0
10
Ka-band DSS26
Sig
nal L
evel
(dB
)
Cassini RSS
Ka-band Power AttenuationS07 Entry
Time SPM UTC-ERT May 3 2005
21300 21400 21500 21600 21700 21800 21900
Pwer Loss dB
-50
-40
-30
-20
-10
0
10
Ka-band DSS26Ka-band DSS25Ka-band DSS34
Sig
nal L
evel
(dB
)
RSS Saturn Atmosphere
Cassini RSS
X-band Power AttenuationS07 Entry
Time SPM UTC-ERT May 3 2005
21200 21400 21600 21800
Pwer Loss dB
-50
-40
-30
-20
-10
0
10
X-band DSS14
AJK 05/06/2005
Sig
nal L
evel
(dB
)
RSS Saturn Atmosphere
Cassini RSS
X-band Power AttenuationS07 Entry
Time SPM UTC-ERT May 3 2005
21200 21400 21600 21800
Pwer Loss dB
-50
-40
-30
-20
-10
0
10
X-band DSS14X-band DSS25X-band DSS26X-band DSS34X-band DSS43
AJK 05/06/2005
Sig
nal L
evel
(dB
)
RSS Saturn Atmosphere
Cassini RSS
Tri-band Power AttenuationS07 Entry
Time SPM UTC-ERT May 3 2005
21200 21400 21600 21800 22000
Pwer Loss dB
-50
-40
-30
-20
-10
0
10
S-band DSS14
AJK 05/06/2005
Sig
nal L
evel
(dB
)
RSS Saturn Atmosphere
Cassini RSS
Tri-band Power AttenuationS07 Entry
Time SPM UTC-ERT May 3 2005
21200 21400 21600 21800 22000
Pwer Loss dB
-50
-40
-30
-20
-10
0
10
S-band DSS14X-band DSS14Ka-band DSS26
AJK 05/06/2005
Sig
nal L
evel
(dB
)
RSS Saturn Atmosphere
Cassini RSS
Are Saturn’s Winds Changing?
0- 15 -30
100
10
1
Laitude
100125150175200
225
250
275
275
300
325
350
0- 30 -60
100
10
1
Latitude
90
90
95
95
100
100
105
105
110
110
115120 125
130135
140
140
145
145
150155
Latitude–
250 km
Zonal winds: u (m/s)
Winds derived from the thermal wind equation showstrong vertical decay at low latitudes, but the cloudsobserved by HST & Cassini/ISS would have to be >130 km above those seen by Voyager if changing cloudheights explain the changes in observed wind speeds.
Cassini/CIRS: Flasar et al. (2005)
Cloud tracking by HST and Cassini ISSsuggests that Saturn’s equatorial windshave changed or the cloud tops have changed.
Vgr(1980-81)
HST(1996-2002)
CH4 cont.Cassini ISS (2004)
Porcoet al. (2005)
RSS Saturn Ionosphere
Entry Ionosphere Data
Time SPM May 3 2005
20600 20800 21000 21200 21400
Frequency Residual Hz
-0.10
-0.05
0.00
0.05
0.10
DSS 14 S/X
Fre
quen
cy R
esid
ual H
z
Cassini RSS
S07 Ionosphere
Electron Density cm-3
10 100 1000 10000
Altitude (1 bar) km
0
1000
2000
3000
4000
5000
6000
S/X DSS14-entryX/K DSS25-entry
SZA 84o 94o
Lat 7.2 S 9.2 S
AJK 05/20/2005
entry exit
dawn dusk
PIO 11 entryLat=10
o S
SZA= ~ 90o
(exit similar)
Model(Waite and Cravens, 1987)
VGR2 NLat=35
o NVGR2 X
Lat=31o S
Alt
itud
e (1
bar)
km
RSS Saturn Ionosphere
Cassini RSS
Exit Ionosphere Data
Time SPM May 3 2005
30200 30400 30600 30800
Frequency Residual Hz
-0.10
-0.05
0.00
0.05
0.10
DSS 43 S/X
Fre
quen
cy R
esid
ual H
z
RSS Saturn Ionosphere
Cassini RSS
S07 Ionosphere
Electron Density cm-3
10 100 1000 10000
Altitude (1 bar) km
0
1000
2000
3000
4000
5000
6000
S/X DSS14-entryX/K DSS25-entryX/K DSS34-exitS/X DSS43 -exit
SZA 84o 94o
Lat 7.2 S 9.2 S
AJK 05/20/2005
entry exit
dawn dusk
PIO 11 entryLat=10
o S
SZA= ~ 90o
(exit similar)
Model(Waite and Cravens, 1987)
VGR2 NLat=35
o NVGR2 X
Lat=31o S
Alt
itud
e (1
bar)
km
RSS Saturn Ionosphere
Cassini RSS
Scientific Objectives: Ring Occultations
• To profile radial ring structure with resolution ≤ 100 m; characterize structure variability with azimuth, wavelength, ring-opening-angle, and time
• To determine physical particle properties (size distribution, bulk density, surface density, thickness, viscosity)
• To study ring kinematics and dynamics (morphology, interaction with embedded and exterior satellites), and to investigate ring origin and evolution
Cassini RSS
- Determine the global fields of temperature, pressure, and winds in the stratosphere and troposphere of Titan and Saturn
- Determine the small scale structure due to eddies and waves
- Constrain the distribution of methane in Titan’s atmosphere
- Improve the H2/He ratio in Saturn's troposphere- Determine the variations in NH3 abundance in Saturn’s
atmosphere- Search for Titan’s ionosphere; interaction with
Saturn’s magnetosphere- Study the behavior of Saturn’s ionosphere with latitude
and solar zenith angle; investigate its interaction with rings and magnetosphere
Scientific Objectives: Atmospheric/Ionospheric Occultations:
Cassini RSS
Cassini Radio Science Team• NASA/JPL
– Arvydas Kliore (TL)
– Nicole Rappaport (DTL)
– John Anderson
– John Armstrong
• NASA/Goddard– Mike Flasar
• US Universities– Richard French (Wellesely College)
– Essam Marouf (San Jose State University)
– Andrew Nagy (University of Michigan)
• Italy– Roberto Ambrosini (Istituto di Radioastronomia, Bologna)
– Luciano Iess (Universita’ di Roma, Roma )
– Paolo Tortora