Icy Satellites Update
UVIS Team Meeting
July 2006
Boulder
topics
• Topics of analyses:
– Distribution along slit (stare observations) (Ly-a, dust, 1304)
– Reflectance - compositional models
– Phase curves: solar + orbital at long s, 1335Å and Ly-
• General analysis methods
• Instrument scattering issue
– Long  into short  (filled slit, bright source)
– On-body pixels into off-body pixels
• Signal at short wavelengths
– we can use reflected signal at solar lines to get albedo there
• Spectral models
• Red patch
11 July 2006
UVIS Team Meeting
General analysis methods
• Multiply by cal (1999), LASP FF, red patch
– Output is kR/Å
• Background subtraction
– Off-body
– Night side
• Overplot scaled solar - look for emission features
– Scale at reflected solar 1335 Å feature
• Divide by solar - to get reflectance
– simulator output (x cal)
– SOLSTICE makes reflectance noisier
• But need accurate Ly- values for day of each obs
– Determine reflectance at Ly-, other solar lines
11 July 2006•
Better SNR than at other mid-FUV s
UVIS Team Meeting
(Increase in bkgd signal
at long  due to red patch)
11 July 2006
UVIS Team Meeting
Enceladus scattering issue (1)
for filled slit, bright source, does signal at bright long  contaminate short ?
**At the end of this observation,
when we are very close and the
slit is ~filled, there is a lot of
scattering of light at the shorter
wavelengths and the reflectance
shape is not accurate. **
11 July 2006
UVIS Team Meeting
Enceladus scattering issue (2)
for unfilled slit, bright source, does signal bleed into off-body pixels?
00CRH_icylon013_cirs
long-
11 July 2006
UVIS Team Meeting
11 July 2006
UVIS Team Meeting
USING SOLAR LINES (NOT CONTINUUM) TO GET ALBEDO
FOR <1600 Å
Red points=Rhea albedo obtained by dividing signal by solar at
solar lines;
black line=Rhea albedo obtained by dividing by solar
continuum
Comparison of icy satellite albedos at similar ;
Note asterisks mark albedo values at short 
11 July 2006
UVIS Team Meeting
Spectral models
Bidi. ref=(w/4)(0/(+0))[(1+B)*p+H()*H(0)-1]
The most important parameter driving the spectral shape is w.
w=Qs=Se+(1-Se)(1-Si)s/4 (for D>>1)
w=Qs=Se+(1-Se)exp(-D)
(for D<<1)
w=Qs=Se+(1-Se)*(1-Si)*/(1-Si)
=exp(-D)
(for D<<1)
=[ri+exp{-((+s))0.5D}]/[1+riexp{-((+s))0.5D}]
ri=[(1-/s)0.5-1]/[(1+/s)0.5+1] (Hapke, 2001)
or:
ri=[1-(/(+s))0.5]/ [1+(/(+s))0.5] (Hapke, 1993)
s= internal scattering coefficient
Si=0 or Si=1-4/[n(n+1)2]
Se=[(n-1)2+k2]/[(n+1)2+k2]
11 July 2006
UVIS Team Meeting
D vs 
11 July 2006
UVIS Team Meeting
H2O imaginary index of refraction, k
11 July 2006
UVIS Team Meeting
11 July 2006
UVIS Team Meeting
11 July 2006
UVIS Team Meeting
=0.91
0=0.4
11 July 2006
UVIS Team Meeting
Spectral model - good fit to Tethys
Bidi. ref=(w/4)(0/(+0))[(1+B)*p+H()*H(0)-1]
w=Qs=Se+(1-Se)*(1-Si)*/(1-Si)
=[ri+exp{-((+s))0.5D}]/[1+riexp{-((+s))0.5D}]
ri=[(1-/s)0.5-1]/[(1+/s)0.5+1]
(D>>1)
ri=[1-(/(+s))0.5]/ [1+(/(+s))0.5] (D<<1)
s=1.5
Si=0
Se=[(n-1)2+k2]/[(n+1)2+k2]
D=0.35 & D=2d/3 where d=grain diameter (equiv to ~0.5 um)
p=H-G phase function, g=0.8
11 July 2006
UVIS Team Meeting
Phoebe models (in progress)
11 July 2006
UVIS Team Meeting
new red patch
• Long wavelength reflectance shape - not
flat
– Could be red due to non-ice materials, but…
11 July 2006
UVIS Team Meeting
February 2005
FUV2005_048_01_34_33_UVIS_003EN_ICYLON005_VIMS
Many rows summed.
Note different shapes at longest wavelengths
Feb 2006: first red patch
11 July 2006
Current: with AS FF + red patch
UVIS Team Meeting