1. Essam Marouf & Richard French Cassini CHARM Presentation
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

2. 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)

3. Radio Science Subsystem (RSS): Downlink Configuration
From Cassini
To the Deep Space Network (DSN)
- Atomic Frequency Standard
- X, S: 70 m
- Ka, X: 34 m BWG
Downlink 
Three Sinusoids Coherent in Phase (Crystal Oscillator-- USO)
l (cm) Pt (W) SNR (dB-Hz)
Ka X
S 
Goldstone, CA: 70 m
Cassini RSS

4. Downlink Configuration is Used to Conduct:
1-Atmospheric / Ionospheric Occultations of Saturn and Titan
DSN
S/C
Saturn
2- Ring Occultations q0
From S/C
To DSN
Titan
3- Bistatic-Scattering From Titan’s Surface
Cassini RSS

5. Hubble Space Telescope
French et al., 2003

6. Cassini Orbital Tour of the Saturn System
75 Saturn Orbits; 45 Titan Encounters
(July 1, 2004 to June 30, 2008)
D. Seal, 2004

7. Typical Ring Occultation Track Geometry (15 m tick-marks)
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

8. Catching the Open RingsB t
Cassini Tour
Year
|Ring-Opening-Angle| (|B°|)
Catching the Open Rings 14 I0 I
Rev 7 Occultation Track
Cassini RSS

9. Rev 7 Radio Occultation Track: May 2-3, 2005
View From the Earth
Live Moveable Block (LMB)
ERT UTC PT
10 m
Cassini
ingress BL
egress BL
10:36 03:36
10:06 03:06
08:32 01:32
08:00 01:00
06:40 23:40
06:00 23:00
04:23 21:23
03:53 ERT 20:53 PDT
Cassini RSS
06: G: DSS 14, 25, 26
11: C: DSS 43, :45

10. * Water-Ice Ring Particles
*Millimeters to Several Meters Main Size Population
* Tens of meters thick
Artist Conception!

11. Observables Cassini RSS Scattered Signal B Direct, or Coherent, Signal
Direct Signal
Scattered Signal
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

12. Radio Occultation: Profiling of Radial Ring Structure
Cassini ISS
Saturn’s Rings
I0 esin(B)
Voyager RSS

13. Planet Saturn and its Remarkable Ring System
(~300,000 km across; ~distance from the Earth to the Moon )
Hubble Space Telescope

14. Rings Structure Ring C Ring B Cassini Division RingA Ring F
Ringscape In Color July 22, Full-Res: PIA Nine days before it entered orbit, Cassini spacecraft captured this exquisite natural color view of Saturn's rings. The images that make up this composition were obtained from Cassini's vantage point beneath the ring plane with the narrow angle camera on June 21, 2004, at a distance of 6.4 million kilometers (4 million miles) from Saturn. The image scale is 38 kilometers (23 miles) per pixel. The brightest part of the rings, curving from the upper right to the lower left in the image, is the B ring. Many bands throughout the B ring have a pronounced sandy color. Other color variations across the rings can be seen. Color variations in Saturn's rings have previously been seen in Voyager and Hubble Space Telescope images. Cassini's images show that color variations in the rings are more pronounced in this viewing geometry than they are when seen from Earth. Saturn's rings are made primarily of water ice. Since pure water ice is white, it is believed that different colors in the rings reflect different amounts of contamination by other materials such as rock or carbon compounds. In conjunction with information from other Cassini instruments, Cassini images will help scientists determine the composition of different parts of Saturn's ring system.
Cassini Division
RingA
Ring F
Cassini ISS

15. Saturn’s Inner and Outer Ring C
Intricate C Ring Details December 7, Full-Res: PIA Saturn's inner C ring spreads across the field of view, showing the characteristic plateau and wave-like structure for which it is famed. The center of this image shows an area approximately 75,000 kilometers (46,600 miles) from Saturn. The dark gap through the middle of the frame is the Colombo gap which houses the bright, narrow, eccentric Colombo ringlet, in resonance with the moon Titan. The image was taken with the Cassini spacecraft narrow angle camera on Oct. 29, 2004, at a distance of about 842,000 (523,000 miles) from Saturn. The image scale is 4.7 kilometers (2.9 miles) per pixel.
Plateaus and Gaps December 13, Full-Res: PIA This fantastic close-up of Saturn's outer C ring shows large and sharp changes in brightness across the rings, owing to the extreme variations in ring particle concentrations at different distances from the planet. The dark gap running through the center contains the Maxwell ringlet, as well as a faint, narrow ringlet discovered in Cassini images. Another very dark region to the right of the Maxwell gap is also a narrow gap. The image was taken in visible light with the Cassini spacecraft narrow angle camera on Oct. 29, 2004, at a distance of about 836,000 kilometers (519,000 miles) from Saturn. The image scale is 4.6 kilometers (2.9 miles) per pixel.
Cassini ISS

16. Interesting Ring Structure Exists at Every Spatial Scale
Inner Ring C
Cassini ISS
1500 km
OPACITY,[3.6]
SIGNAL LOSS (dB)
125 km
4 km res
- Colombo Gap
- Titan Ringlet
- W-Features
Voyager RSS
200 m res
Titan -1:0 Bending Wave
100 m resolution is not luxury !

17. Observations are Diffraction-Limited
Voyager RSS
Fresnel Diffraction by the Inner Edge of the Encke Gap
Voyager ISS

18. Holographic Reconstruction
Finite Observation Interval W (km); T (sec)
Holographic Reconstruction
-W /2 O
W /2
Ring F Example
F = 15 km
DR = 200 m
Signal phase must remain stable over T
Voyager RSS
Radius (km)

19. Cassini RSS: Achievable Radial Resolution
DR = 100 m B
Threshold Optical Depth tTH (SNR=1)
Resolution DR (m)
Cassini RSS

20. Occultations at Multiple Longitudes: Dynamical Ring Structure
Narrow Eccentric Ringlets
Bending Waves
Density Waves
Uranus’ Ring 
Mimas 5:3
Optical Depth,  [3.6]
Signal Loss (dB)
Voyager RSS

21. Occultations at Multiple Longitudes: Detection of Embedded Satellites
Encke Gap
Pan’s Wake
Cassini ISS
Voyager RSS

22. Cassini Rev 7: Optical Depth Profiles of Ring C (X, 10 km Res)
Cassini RSS

23. Cassini Rev 7: Optical Depth Profiles of Ring C, S/X/Ka (R/G/B)
Cassini RSS

24. Cassini Rev 7: Optical Depth Profiles of Ring B (X, 10 km Res)
Cassini RSS

25. Cassini Rev 7: Optical Depth Profiles of Ring B, S/X/Ka (R/G/B)
Cassini RSS

26. Cassini Rev 7: Optical Depth Profile of Ring A (X, 10 km Res)
Cassini RSS

27. Cassini Rev 7: Density Waves in Outer Ring A (Ka, 1.4 km Res)
Cassini RSS

28. Cassini Rev 7: Optical Depth Profiles of Ring A, S/X/Ka (R/G/B)
Cassini RSS

29. Small Particles in Ring A (PIA07875)
Cassini RSS

30. Radio Occultation: Unraveling Saturn’s Rings (PIA07873)
Cassini RSS

31. Multiple Eyes of Cassini (PIA07874)

32. Observables Cassini RSS Scattered Signal B Direct, or Coherent, Signal
Direct Signal
Scattered Signal
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

33. Scattered Signal:
Doppler Contours
Cassini RSS

34. Meter-Size “Particles”
Scattered Signal:
Meter-Size “Particles”
amax = 3, 5, 10 m
F (kHz)
Cassini RSS

35. Cassini Rev 7: Outer Ring B Direct & Scattered Signals
Cassini RSS

36. Rev 7 Radio Occultation Track: May 2-3, 2005
View From the Earth
Live Moveable Block (LMB)
ERT UTC PT
10 m
Cassini
ingress BL
egress BL
10:36 03:36
10:06 03:06
08:32 01:32
08:00 01:00
06:40 23:40
06:00 23:00
04:23 21:23
03:53 ERT 20:53 PDT
Cassini RSS
06: G: DSS 14, 25, 26
11: C: DSS 43, :45

37. TITAN EXTENDED ATMOSPHERE
High Haze in Color October 26, Full-Res: PIA A global detached haze layer and discrete cloud-like features high above Titan's northern terminator (day-night transition) are visible in this image acquired on October 24, 2004, as the Cassini spacecraft neared its first close encounter with Titan. This full disk view of Titan is a colorized version of the ultraviolet image released on October 25, 2004 (PIA 06120). The globe of Titan and the haze have been given colors that are close to what the natural colors are believed to be. The image was acquired at a distance of about 1 million kilometers (621,371 miles) in a near ultraviolet filter that is sensitive to scattering by small particles. The Sun preferentially illuminates the southern hemisphere at this time; the north polar region is in darkness. The well-known global detached haze layer, hundreds of kilometers above Titan's surface, is produced by photochemical reactions and visible as a thin ring of bright material around the entire planet. At the northern high-latitude edge of the image, additional striations are visible, caused by particulates that are high enough to be illuminated by the Sun even though the surface directly below is in darkness. These striations may simply be caused by a wave propagating through the detached haze, or they may be evidence of additional regional haze or cloud layers not present at other latitudes.
Purple Haze July 29, Full-Res: PIA Encircled in purple stratospheric haze, Titan appears as a softly glowing sphere in this colorized image taken one day after Cassini's first flyby of that moon. This image shows two thin haze layers. The outer haze layer is detached and appears to float high in the atmosphere. Because of its thinness, the high haze layer is best seen at the moon's limb. The image was taken using a spectral filter sensitive to wavelengths of ultraviolet light centered at 338 nanometers. The image has been falsely colored: The globe of Titan retains the pale orange hue our eyes usually see, and both the main atmospheric haze and the thin detached layer have been brightened and given a purple color to enhance their visibility. The best possible observations of the detached layer are made in ultraviolet light because the small haze particles which populate this part of Titan's upper atmosphere scatter short wavelengths more efficiently than longer visible or infrared wavelengths. Images like this one reveal some of the key steps in the formation and evolution of Titan's haze. The process is thought to begin in the high atmosphere, at altitudes above 400 kilometers (250 miles), where ultraviolet light breaks down methane and nitrogen molecules. The products are believed to react to form more complex organic molecules containing carbon, hydrogen and nitrogen that can combine to form the very small particles seen as haze. The bottom of the detached haze layer is a few hundred kilometers above the surface and is about 120 kilometers (75 miles) thick. The image was taken with the narrow angle camera on July 3, 2004, from a distance of about 789,000 kilometers (491,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 114 degrees. The image scale is 4.7 kilometers (2.9 miles) per pixel.
Titan's Many Layers December 16, Full-Res: PIA Cassini has found Titan's upper atmosphere to consist of a surprising number of layers of haze, as shown in this ultraviolet image of Titan's night side limb, colorized to look like true color. The many fine haze layers extend several hundred kilometers above the surface. Although this is a night side view, with only a thin crescent receiving direct sunlight, the haze layers are bright from light scattered through the atmosphere. The image was taken with the Cassini spacecraft narrow angle camera. About 12 distinct haze layers can be seen in this image, with a scale of 0.7 kilometers (.43 miles) per pixel. The limb shown here is at about 10 degrees south latitude, in the equatorial region.
Image Credit: NASA/JPL/Space Science Institute
Cassini ISS

38. Atmospheric Limb-Track Maneuver
“Virtual” Earth
“Apparent” Line of Sight
Refracted Ray Path
“Actual” Earth
Geometric Line of Sight
Actual
Virtual
Saturn or Titan
Adapted from D. Wait 05/07/04

39. RSS Saturn Atmosphere
Signal Level (dB)
Cassini RSS

40. RSS Saturn Atmosphere
Signal Level (dB)
Cassini RSS

41. RSS Saturn Atmosphere
Signal Level (dB)
Cassini RSS

42. RSS Saturn Atmosphere
Signal Level (dB)
Cassini RSS

43. RSS Saturn Atmosphere
Signal Level (dB)
Cassini RSS

44. RSS Saturn Atmosphere
Signal Level (dB)
Cassini RSS

45. Are Saturn’s Winds Changing?
Latitude –
250 km
Zonal winds: u (m/s)
Winds derived from the thermal wind equation show strong vertical decay at low latitudes, but the clouds observed by HST & Cassini/ISS would have to be >130 km above those seen by Voyager if changing cloud heights explain the changes in observed wind speeds.
Cassini/CIRS: Flasar et al. (2005)
Cloud tracking by HST and Cassini ISS suggests that Saturn’s equatorial winds have changed or the cloud tops have changed.

46. RSS Saturn Ionosphere
Frequency Residual Hz
Cassini RSS

47. RSS Saturn Ionosphere
Altitude (1bar) km
Cassini RSS

48. RSS Saturn Ionosphere
Frequency Residual Hz
Cassini RSS

49. RSS Saturn Ionosphere
Altitude (1bar) km
Cassini RSS

50. 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

51. Scientific Objectives: Atmospheric/Ionospheric Occultations:
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
Cassini RSS

52. 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