UVIS calibration update
Greg Holsclaw
Bill McClintock
Jan 8, 2013
1
Outline
• Calibration observations – obtained, planned,
future opportunities
• Calibration status
• EUV wavelength issues
• Data compression
2
Calibration observations
• Recently obtained standard cal
– EUV2012_358_08_02_13_UVIS_177IC_ALPVIR001_PRIME
– FUV2012_358_08_02_13_UVIS_177IC_ALPVIR001_PRIME
• Planned standard and STEFFL
– UVIS_196IC_SPICARAST001_PRIME
– 2013-230T14:00:00 to 231T08:30:00
– Target: Spica
– Data volume: 320 Mbits
3
Comparison of recent stellar
calibrations
EUV
FUV
These plots show the total signal on the detector as a
function of star position along the slit
4
All stellar calibrations
EUV
FUV
These plots show the total signal on the detector as a
function of star position along the slit
5
Decline in FUV in sensitivity over time
Total signal from Spica vs row position
of the image, for all calibration
observations.
Mean value of the signal when the star
was located between rows 18 and 22,
then normalized to the first.
6
Data vs model
Total FUV signal with linear trend divided out.
Also shown is the predicted variation in flux from
the model.
Variation in flux is given by [Shobbrook, 1969; Sterken et al, 1986]:
dE = A M2/M1 (R/D)3 (1+e cos(TA+Φ))3 (1-3cos2(TA+TA0+Φ) sin2i )
Data vs model
r = Linear Pearson correlation
coefficient using IDL’s correlate()
function, value ranges from -1 to 1
7
Future calibration opportunities
• Our desired approach
– Two standard calibrations per year using Spica
– One STEFFL calibration per year using Spica
• Look for opportunities within XD segments
where either:
– Saturn-Spica angle is < 30deg as seen from the s/c
– Earth-Spica angle is ~90deg
8
XD periods where Saturn-Spica angle is
below 30 deg
period_name
XD_183_184
XD_187_188
XD_196_197
XD_200
XD_200_201
XD_201_202
XD_203_204
XD_205_206
XD_206_207
XD_209
XD_209_210
XD_210_211
XD_223_224
XD_231_232
XD_232_233
XD_235
XD_235_236
XD_236_237
XD_237_238
start
2013-069T14:29
2013-113T11:32
2013-226T09:51
2013-362T01:47
2014-003T05:48
2014-037T17:07
2014-101T13:00
2014-170T14:29
2014-212T05:09
2014-279T01:01
2014-299T06:00
2014-351T03:15
2015-289T07:31
2016-038T00:48
2016-050T00:05
2016-109T18:43
2016-129T19:14
2016-161T10:30
2016-183T00:59
end
2013-078T13:45
2013-119T11:02
2013-254T08:03
2013-365T01:48
2014-031T23:51
2014-064T21:56
2014-133T10:46
2014-197T12:41
2014-229T10:37
2014-293T06:30
2014-340T21:30
2015-008T01:47
2015-301T00:30
2016-045T00:34
2016-068T22:52
2016-124T19:29
2016-155T17:15
2016-178T15:44
2016-202T07:28
TWT
XD
XD
XD
XD
XD
XD
XD
XD
XD
XD
XD
XD
XD
XD
XD
XD
XD
XD
XD
2013-070
2013-113
2013-230
2013-364
2014-031
2014-064
2014-131
2014-192
2014-223
2014-291
2014-339
2015-007
2015-300
2016-044
2016-067
2016-119
2016-148
2016-173
2016-197
date_min angle_min
// 12:00
15.6
// 12:00
16.7
// 12:00
13.5
// 12:00
23.4
// 12:00
17.0
// 12:00
10.5
// 12:00
4.7
// 12:00
6.9
// 12:00
7.7
// 12:00
4.0
// 12:00
0.7
// 12:00
19.8
// 12:00
29.4
// 12:00
19.5
// 12:00
3.9
// 12:00
10.5
// 12:00
17.9
// 12:00
24.9
// 12:00
24.9
9
angle (deg)
150
100
50
Saturn to Spica angle
Earth to Spica angle
0
2013
2014
2015
date
2016
2017
10
Solid line is the
angle between
Saturn and Spica
XD
2013
SOST
SATURN
TOST
MAPS
RINGS
angle (deg)
150
100
50
0
Jan
Feb Mar
Apr
May
Jun
Jul Aug
2013
Sep
Oct
Nov
Dec
11
Solid line is the
angle between
Saturn and Spica
XD
2014
SOST
SATURN
TOST
MAPS
RINGS
angle (deg)
150
100
50
0
Jan
Feb Mar
Apr
May
Jun
Jul Aug
2014
Sep
Oct
Nov
Dec
12
Solid line is the
angle between
Saturn and Spica
XD
2015
SOST
SATURN
TOST
MAPS
RINGS
angle (deg)
150
100
50
0
Jan
Feb Mar
Apr
May
Jun
Jul Aug
2015
Sep
Oct
Nov
Dec
13
Solid line is the
angle between
Saturn and Spica
XD
2016
SOST
SATURN
TOST
MAPS
RINGS
angle (deg)
150
100
50
0
Jan
Feb
Mar
Apr
May
Jun
Jul Aug
2016
Sep
Oct
Nov
Dec
14
Notes
• s/c ephemeris kernel used:
110818AP_SCPSE_11175_17265.bsp
• The spacecraft ephemeris is sampled in 24 hour increments
• I obtained the XXM segmentation list (xxm_segments.xls)
from this site:
– https://cassini.jpl.nasa.gov/sp/xxmsp.html
– Labeled as "XXM segments/sequence spreadsheet: [XLS]" under the
title "XXM References" on the right side
– Retrieved on Oct 19, 2012
15
EUV wavelength scale issues
• The group at U of Arizona/LPL (Roger Yelle,
Tommi Koskinen, Fernando Capalbo) have
noted that the nominal EUV wavelength
vector does not adequately fit solar
occultation spectra.
• A linear shift would be expected given that the
solar image is not constrained by the entrance
slit, but there appears to be variation in
dispersion as a function of spatial position.
16
Pointing stability of dataset for analysis
angle in spatial dimension (mrad)
20
10
0
-10
0.25 mrad (1 spectral pixel)
-20
0.40
0.45
0.50
0.55
angle in dispersion plane (mrad)
0.60
• Position of Sun
in EUV solar
occ port frame
from SPICE
• Max drift in
dispersion
plane of
0.056mrad
(20% of a
spectral pixel)
Data file: EUV2007_108_00_47_04_UVIS_043SU_SOL001_PRIME
Objective: solar calibration
Design: Point solar occultation port to sun. Slew 10 mrad in +Z direction to start. Slew 20 mrad in the -Z
direction at 20 micro rd/sec
17
Measure of the spectral position of several solar lines at each detector row
629.732
36
37
38
column center
703.854
949.745
977.020
1025.724
1031.914
1084.582
60
60
50
50
50
50
50
50
50
40
40
40
40
40
40
40
30
30
30
30
30
row
60
row
60
row
60
row
60
row
60
row
row
584.335
30
30
20
20
20
20
20
20
20
10
10
10
10
10
10
10
0
39 111
0
112
113
114
column center
234
235
236
column center
0
237
641
642
643
column center
0
644
686
687
688
column center
0
689
766
767
768
column center
0
769 776
0
777
778
779
column center
864
865
866
column center
Data file:
EUV2007_108_00_47_04_UVIS_043SU_SOL001_PRIME
Emission line reference:
“Predicted XUV Line Intensities CHIANTI database - Version 7.0”
584.3350,
629.7320,
703.8540,
949.7450,
He I
O V
O III
H I
977.0200,
1025.7240,
1031.9138,
1084.5820,
C
H
O
N
III
I
VI
II
18
867
Filled-aperture, filled-slit comparison
58.4 nm
102.6 nm
0.8
sun, rows 0 to 15
sun, rows 48 to 63
Sun
occ-port
0.6
0.4
0.2
0.0
580
normalized counts
normalized counts
1.0
1025.724 angstroms
1.0
0.8
582
584
586
wavelength (nm)
Venus, rows 0 to 15
Venus, rows 48 to 63
588
Venus
telescope
0.6
0.4
0.2
0.0
580
582
584
586
wavelength (nm)
588
1.0
590
sun, rows 0 to 15
sun, rows 48 to 63
0.8
Sun
occ-port
0.6
0.4
0.2
0.0
590
1020
normalized counts
normalized counts
584.335 angstroms
1.0
1022
1024
1026
wavelength (nm)
1028
Venus, rows 0 to 15
Venus, rows 48 to 63
0.8
1030
Venus
telescope
0.6
0.4
0.2
0.0
1020
1022
1024
1026
wavelength (nm)
1028
1030
19
Performance check with raytrace
detector
grating
Aperture
stop
Telescope
mirror
• Only a small
fraction of the
optics are
illuminated by
the solar beam
• Pickoff mirror is
a cylindrical
surface with
R=500mm in the
spatial
dimension, with
an effective
area of ~1x1mm
20
Raytrace results
1025.7240
60
50
50
40
40
row
row
584.3350
60
30
30
20
20
10
10
0
0
44
45
46
column center
47
765
• Slight spatial curvature.
• No evidence for spatially dependent dispersion.
766
767
column center
768
21
One hypothesis for spatially
dependent dispersion
• A spatially dependent
groove spacing could
explain the observed
effect
• Because we do not see
this effect for a filled
aperture, this
abnormality would
need to be localized to
the small part of the
grating illuminated by
the Sun (area of
3x3mm)
Grating grooves
Solar beam on grating
22
Data Compression
• The UA/LPL group have expressed concern
regarding the impact of compression used for
stellar/solar occultations
• This led to a realization that the compression
algorithm is not adequately documented
• I wrote a short description of the algorithm
and its effect on the data, with the intention
to include this in the PDS user’s guide
23
Data Compression algorithm
• The default compression implemented is SQRT-9.
The square root algorithm can be described by
the following pseudocode:
IF VALUE > 128
COMP. VALUE = ROUND( SQRT(VALUE * 2) ) + 128
ELSE
COMP. VALUE = VALUE
END IF
24
reconstructed value
Quantization error
1000
800
600
400
200
0
0
200
600
400
800
1000
800
1000
fractional error
input value
0.15
0.10
random error, sqrt(input)/input
0.05
-0.00
-0.05
-0.10
-0.15
0
200
600
400
input value
• Let Ni be the
input number of
counts
• Uncertainty in
Ni: σ=sqrt(Ni)
• It can be shown
that the
uncertainty
introduced by
the compression
is: σ/sqrt(2)
25
Summary
•
•
•
•
No significant changes in FUV sensitivity
STEFFL observation planned
Many opportunities for future XD calibrations
EUV solar occultation wavelength scale exhibits a
spatially-dependent dispersion (~2 pixels), different
than normal mode
• Compression algorithm is now documented
• To do:
– 2D wavelength scale for EUV and FUV
– Update PDS User’s guide with compression algorithm
– Continue work on revised flat-field approach
26