UVIS Team Meeting Report
June 2010
Josh Colwell
UVIS Team Meeting June 28-30, 2010, Boulder
1
RWG Solstice Mission Update
• 399.1 of 400 PIE hours allocated.
• UVIS has 17 ring occs as PIEs (2 in
EQ1), plus additional handful of Apo-PIEs.
• Rings Science Traceability Matrix
completed and submitted.
–No open items.
–Some convolution of the language to link
observations to goals.
UVIS Team Meeting June 28-30, 2010, Boulder
2
Solstice Mission Inclination Profile
UVIS Team Meeting June 28-30, 2010, Boulder
3
Ring Science EM and SM
Status Update
• Three more ring stellar occs in 2010: Alp
Vir (next Monday), Beta Ori (Aug. 16 and
Sep. 23).
• Next ring stellar occ after that are two
PIEs in EQ1 (Jan. 2012). Iot Ori.
• IN1 occs begin in June 2012.
• 99 ring occ requests in CIMS from bridge
through EOM. Aiming to capture 40-50 of
4
these.
UVIS Team Meeting June 28-30, 2010, Boulder
Dedicated UV Imaging
Observation
• Took advantage of a 4-hour hole in the
timeline for dedicated UVIS ring imaging
observation.
• July 5 2010 (Monday)
• 9 fixed pointings, 3 each on C, B, and A
rings.
• Offsets between the pointings to allow for
sub-pixel resolution.
UVIS Team Meeting June 28-30, 2010, Boulder
5
Cassini orbit
Projected field of view
SM PIE Occs
• Tracking occs:
–Eps Sgr (1.1 km/s) in 2016
–Kap CMa in 2012
–Zet CMa (0.1 km/s) in 2012
–Zet Pup (1 km/s) in 2012
• Azimuthal structure:
–Bet Cru (496 km from Bleriot) in 2017
–Zet Cen (147 km from Daphnis) in 2016
• Occs with VIMS (Alpha Lyrae)
• Orionis occs (low elevation angle to rings)
• Kap Ori 10 hour occ
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UVIS Team Meeting June 28-30, 2010, Boulder
PDS Deliveries
• Calibration process defined in paper
submitted to Astron. J. (currently out for
review)
• High-level ring occultation files are being
delivered to PDS containing:
–radius, time, longitude, optical depth, binned
counts, number of bins, I0, background, taumax
–1 km and 10 km resolution
UVIS Team Meeting June 28-30, 2010, Boulder
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Sample Product: Cassini Division
UVIS Team Meeting June 28-30, 2010, Boulder
10
Sample Product: B Ring
UVIS Team Meeting June 28-30, 2010, Boulder
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UVIS Team Meeting June 28-30, 2010, Boulder
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Sharp Edge Modeling Update
Josh Colwell and Richard Jerousek
UCF
UVIS Team Meeting June 28-30, 2010, Boulder
Modeling Sharp Edges:
Viewing Geometry
The line-of-sight path from the star to the spacecraft pierces the ring
plane at various angles, , with respect to the ring plane normal and
various angles,  , with respect to the radial direction.
We use these angles to compute  , the projection of in the radial
direction.
UVIS Team Meeting June 28-30, 2010, Boulder
Step-function Model with Constant Optical Depth
Normal Optical Depth
For a step-function edge geometry with constant normal optical
depth, , inside the ring, the vertical thickness, h, of the ring plane
is easily determined from the radial distance, dr, over which the
optical depth transitions from its maximum value to its minimum
value.

dr
Ring Plane Radius (km)
dr
h
tan(  )
UVIS Team Meeting June 28-30, 2010, Boulder
Sigmoid Optical Depth Model
Using the same step-function geometry, we introduce a new
parameter, ∆, representing a radial length scale over which the
transition from ring to gap is softened. The functional form of the
optical depth becomes
 (r) 
1
rred g e
1 e

representing a sigmoid particle density distribution.

z (vertical thickness of ring plane)
Outer edge of ring or ringlet
optical depth =
(r)
UVIS Team Meeting June 28-30, 2010, Boulder
r (radial distance from Saturn)
A More Physical Model
Using the same step-function geometry, we vary the particle number
density (and thus optical depth) vertically as well as radially. We
chose a functional form of
(x h / 2)2
 (r, z) 
1
2
2

e
2
2
r red g e
1 e

representing a gaussian particle density distribution, centered on the
half-width of the ring plane, vertically and a sigmoid density
softened over a transition region, ∆, radially.
distribution,
z (vertical thickness of ring plane)
Outer edge of ring or ringlet
optical depth =
(r,z)
UVIS Team Meeting June 28-30, 2010, Boulder
r (radial distance from Saturn)
A More Physical Model
By integrating the optical depth along the line-of-sight, we produce a
new edge profile depending on the parameters, h, ∆, , and  .
 l (t) 
h cot( )

0
(tan( )rh / 2)2 / 2
1 tan ( ) e

(rr0 redge )/  dr
2
2
1 e
2
2
z (vertical thickness of ring plane)


(r,z)
UVIS Team Meeting June 28-30, 2010, Boulder
line-of-sight path, l
r (radial distance from Saturn)
Knife-edge model fits.
Fixing ∆ = 0, we reproduce the original knife-edge geometry. There is
no vertical or radial variation of particle density near the edge, and the
only unconstrained parameter is h.
Best-fit lightcurve corresponding to the data/lightcurve pair
UVIS
Team Meeting
June 28-30, 2010, Boulder
with
the minimum
 2-value.
Best-fit lightcurve corresponding to the data/lightcurve pair
with the maximum  2-value.
Knife-edge model fits.
UVIS Team Meeting June 28-30, 2010, Boulder
Huygens Ringlet Inner Edge: Complex Edges
UVIS Team Meeting June 28-30, 2010, Boulder
Huygens Ringlet Inner Edge: Simple Edges
UVIS Team Meeting June 28-30, 2010, Boulder
Huygens Ringlet Inner Edge:  =100h vs.  =h/8
UVIS Team Meeting June 28-30, 2010, Boulder
UVIS Team Meeting June 28-30, 2010, Boulder
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Huygens Ringlet Outer Edge: Complex Edges
UVIS Team Meeting June 28-30, 2010, Boulder
Huygens Ringlet Outer Edge: Simple Edges
UVIS Team Meeting June 28-30, 2010, Boulder
Huygens Ringlet Outer Edge:  =100h vs.  =h/8
UVIS Team Meeting June 28-30, 2010, Boulder
Dependence on 
UVIS Team Meeting June 28-30, 2010, Boulder
Dependence on ‘B’
UVIS Team Meeting June 28-30, 2010, Boulder
C Ring Wave Analysis. Kevin Baillié
• Performed WWZ analysis on individual
occultations.
• Co-added power to look for weak periodic
signals.
• Identified 38 total waves or wavelike
features in the C ring, 16 of which
previously unreported.
• Calculated resonance locations for all
known moons to eighth order.
• A handful of waves have promising
associations with resonances. Most do30 not.
UVIS Team Meeting June 28-30, 2010, Boulder
Biggest Wave in the C Ring
UVIS Team Meeting June 28-30, 2010, Boulder
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UVIS Team Meeting June 28-30, 2010, Boulder
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UVIS Team Meeting June 28-30, 2010, Boulder
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UVIS Team Meeting June 28-30, 2010, Boulder
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UVIS Team Meeting June 28-30, 2010, Boulder
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