UVIS Calibration Update
Greg Holsclaw
June 4, 2013
1
Outline
• EUV solar occultation anomalies?
• Comparison of LASP and Shemansky
calibration approach
• Potential calibration update
2
EUV solar occultations
normalized total signal
EUV2013_004_20_59_33_UVIS_178SU_USUNOCC001_PRIME
1.04
1.02
1.00
0.98
0.96
0
1000
2000
3000
time (seconds)
4000
5000
normalized total signal
EUV2013_111_15_58_23_UVIS_187SU_USUNOCC001_PIE
1.04
1.02
1.00
0.98
0.96
0
1000
2000
3000
time (seconds)
4000
5000
normalized total signal
EUV2013_121_06_24_12_UVIS_188SU_USUNOCC001_PIE
1.04
1.02
1.00
0.98
0.96
0
1000
2000
3000
time (seconds)
4000
• Plots of the total
normalized EUV
signal as a
function of time
for three solar
occultations of
Saturn
• Alain noticed
unusual structure
in the lower two
curves
• An instrumental
origin?
5000
3
2013 JAN 04 20:59:35.537
Sun position in EUV OCC frame
0.10
-0.005
ANG_Y (mrad)
ANG_X (mrad)
-0.010
-0.015
-0.020
-0.025
Pointing errors?
0.05
0.00
Plot of the position of the sun in the
EUV occultation port frame.
-0.05
-0.030
-0.035
-0.10
-0.10
21:00 21:10 21:20 21:30 21:40 21:50 22:00 22:10
time
-0.05
0.00
0.05
ANG_X (mrad)
0.10
Some odd high-frequency structure in
the pointing data, but the angular
excursion is very small (<0.1mrad).
-0.03
ANG_Y (mrad)
-0.04
-0.05
-0.06
Conclusion: pointing is stable.
-0.07
21:00 21:10 21:20 21:30 21:40 21:50 22:00 22:10
time
2013 APR 21 15:58:25.947
Sun position in EUV OCC frame
2013 MAY 01 06:24:14.960
Sun position in EUV OCC frame
0.10
0.10
-0.005
0.00
-0.05
-0.010
ANG_Y (mrad)
-0.05
0.05
ANG_X (mrad)
-0.04
ANG_Y (mrad)
ANG_X (mrad)
-0.03
-0.015
-0.020
-0.025
0.05
0.00
-0.05
-0.06
-0.030
16:0016:1016:2016:3016:4016:5017:0017:1017:2017:30
time
-0.10
-0.10
-0.05
0.00
0.05
ANG_X (mrad)
0.10
06:30
06:40
06:50
time
07:00
07:10
06:30
06:40
06:50
time
07:00
07:10
-0.10
-0.10
-0.05
0.00
0.05
ANG_X (mrad)
0.10
0.08
0.04
ANG_Y (mrad)
ANG_Y (mrad)
-0.06
0.06
-0.07
-0.08
0.02
4
-0.09
16:0016:1016:2016:3016:4016:5017:0017:1017:2017:30
time
Total signal
normalized to
mean of first
100 scans.
Red: average
of first 100
spectra
White: current
spectrum
Current –
beginning
spectrum
5
6
Solar irradiance variation not limited
to one wavelength region
58.0282 nm
61.9014 nm
65.7771 nm
69.6551 nm
1.04
1.04
1.04
1.04
1.02
1.02
1.02
1.02
1.00
1.00
1.00
1.00
0.98
0.98
0.98
0.98
0.96
0.94
0
0.96
0.94
0
0.96
0.94
0
0.96
0.94
0
500 10001500200025003000
73.5349 nm
500 10001500200025003000
77.4164 nm
500 10001500200025003000
81.2991 nm
85.1827 nm
1.04
1.04
1.04
1.04
1.02
1.02
1.02
1.02
1.00
1.00
1.00
1.00
0.98
0.98
0.98
0.98
0.96
0.94
0
0.96
0.94
0
0.96
0.94
0
0.96
0.94
0
500 10001500200025003000
89.0669 nm
500 10001500200025003000
92.9514 nm
500 10001500200025003000
96.8358 nm
1.04
1.04
1.04
1.02
1.02
1.02
1.02
1.00
1.00
1.00
1.00
0.98
0.98
0.98
0.98
0.96
0.94
0
0.96
0.94
0
0.96
0.94
0
0.96
0.94
0
104.603 nm
500 10001500200025003000
108.485 nm
500 10001500200025003000
112.366 nm
1.04
1.04
1.04
1.02
1.02
1.02
1.02
1.00
1.00
1.00
1.00
0.98
0.98
0.98
0.98
0.96
0.94
0
0.96
0.94
0
0.96
0.94
0
0.96
0.94
0
500 10001500200025003000
500 10001500200025003000
500 10001500200025003000
116.245 nm
1.04
500 10001500200025003000
500 10001500200025003000
100.720 nm
1.04
500 10001500200025003000
500 10001500200025003000
500 10001500200025003000
7
Position of the Earth and Sun for each
observation
2013 JAN 04
2013 APR 21
10
angle = 109.9 deg
10
angle = 6.7 deg
angle = 3.6 deg
5
Y_EC (AU)
Earth
0
-5
5
Y_EC (AU)
5
Y_EC (AU)
2013 MAY 01
10
0
-5
0
-5
Saturn
-10
-10
-5
0
X_EC (AU)
5
10
-10
-10
-5
0
X_EC (AU)
5
10
-10
-10
-5
0
X_EC (AU)
5
10
Earth-positioned spacecraft observing the
Sun see the same hemisphere as Cassini
for these dates.
8
Comparison with SDO-EVE
1.00
0.98
0.96
1.04
1.02
1.00
0.98
0.96
21:00 21:10 21:20 21:30 21:40 21:50 22:00 22:10 22:20
time
21:00 21:10 21:20 21:30 21:40 21:50 22:00 22:10 22:20
time
1.02
1.00
0.98
0.96
06:20
06:30
06:40
SDO-EVE
normalized signal
normalized signal
SDO-EVE
1.3
1.2
1.1
1.0
0.9
0.8
0.7
1.04
16:00 16:10 16:20 16:30 16:40 16:50 17:00 17:10 17:20 17:30 17:40
time
1.3
1.2
1.1
1.0
0.9
0.8
0.7
16:00 16:10 16:20 16:30 16:40 16:50 17:00 17:10 17:20 17:30 17:40
time
06:50
time
07:00
07:10
07:20
07:00
07:10
07:20
SDO-EVE
normalized signal
1.02
2013 MAY 01
normalized signal
2013 APR 21
normalized signal
normalized signal
2013 JAN 04
1.04
1.3
1.2
1.1
1.0
0.9
0.8
0.7
06:20
06:30
06:40
06:50
time
QD is the quadrant diode (sum) portion of the ESP channel, with a wavelength range
0.1-7nm. The ESP has a sample rate of 4Hz, while spectra are sampled 0.1Hz. The ESP
channels with bandpass centers at 18, 26, 30, and 37nm seem to have pretty low SNR,
that is why I used QD. I don't believe MEGS-B data (35-105nm) is yet available.
I advanced the EVE time vector by the light time difference between the Earth and
Saturn (4400 sec for second and third).
9
Two calibration approaches
• LASP
– Evil pixels are “removed”
– Calibration based on lab measurements
– Fit of exponential vs time for each pixel, based on the
relative change in response to Spica
• Shemansky
– Data smoothed with 14641 spectral filter
– Reference: stellar model atmosphere fit to observed
Copernicus + IUE spectra
– “The UVIS fuv sensitivity curves are determined by dividing
the data by the model of the fuv spectrograph signal for
αVir.”
10
Processing steps
• Select one observation of the Saturn aurora to
compare the two approaches:
– FUV2008_109_08_30_22_UVIS_065SA_NAURMOV001_PRIME
• Calculate average of all readouts
• Offset subtraction of signal 175-185nm for each
detector row
• Multiply by LASP calibration matrix (get_fuv…)
• Interpolate across evil (NaN) pixels
• Convolve with Shemansky 14641 filter (~Gaussian
FWHM=2.5) to match resolution
• Compare one row of the calibrated data with a
hydrogen model fit to the Shemansky data
11
counts
counts
1000
Total counts, row 45 (first
row 0)
100
10
1
120
140
160
180
wavelength (nm)
radiance
radiance (kR/angstrom)
100
LASP
Shemansky
80
60
40
20
0
120
140
160
180
160
180
wavelength (nm)
ratio (LASP/Shemansky)
4
ratio
3
2
1
0
120
140
wavelength (nm)
12
ratio 2010
2.0
ratio
1.5
1.0
0.5
ratio
random
systematic
0.0
120
160
140
wavelength (nm)
180
wavelength range: 116-165nm
mean
sdv
current
1.06
0.31
13
A slightly revised calibration approach
• Currently:
– Fractional change in each pixel is calculated from
Spica scans, then an exponential fit determined to
provide interpolation over time
– Disadvantages:
• introduced high-frequency artifacts
• difficult to adjust for slow decline in sensitivity
• Proposed:
– The ratio of each Spica spectrum to the first is
calculated and smoothed spectrally, then linearly
interpolated in time
14
Ratio to first Spica observation
count rate
year
150
c/s
2012
100
50
2010
0
120
140
160
wavelength (nm)
180
ratio
2008
1.4
1.2
1.0
2006
0.8
0.6
120
140
160
180
2003
ratio smooth
1.4
2001
ratio
1.2
1.0
0.8
0.6
120
140
160
180
15
Ratio to first Spica observation
count rate
year
150
100
50
2010
0
120
140
160
wavelength (nm)
180
ratio
2008
8
6
4
2006
2
120
140
160
180
2003
ratio smooth
8
6
ratio
c/s
2012
2001
4
2
120
140
160
180
16
Change in sensitivity-1 over time
135 nm
ratio
1.00
0.95
0.90
0.85
0.80
2000
2002
2004
2006
year
2008
2010
2012
2008
2010
2012
185 nm
3.5
ratio
3.0
2.5
2.0
1.5
1.0
2000
2002
2004
2006
year
17
Details
• Assumes lab calibration valid for initial (1999)
flight observation of Spica
• First Spica observations used the occultation lens.
Currently using lab measurement of transmission.
• Smooth ratio derived using LOWESS (LOcally
WEighted Scatterplot Smoother), IDL
implementation by Marc Buie.
• Single readouts used for spectra, rather than
summing all readouts in a scan along the slit
– No flat-field correction used
18
Total Spica signal vs time
5•104
signal (c/s)
4•104
3•104
2•104
1•104
occultation lens
low-resolution slit
Starburn
0
Launch
1998
2000
SOI
2002
2004
2006
year
2008
2010
2012
2014
19
Sensitivity-1 comparison at 2012-358
3.0
current
new
(ph/s/cm^2/angstrom) / (c/s)
2.5
2.0
1.5
1.0
0.5
0.0
120
140
160
wavelength (nm)
180
20
Comparison of most recent standard
Spica scan with IUE and SOLSTICE
8•104
ph/s/cm^2/nm
ph/s/cm^2/nm
8•104
IUE
current cal
new cal
6•104
4•104
2•104
4•104
2•104
0
140
160
wavelength (nm)
0
100
180
1.4
1.4
1.2
1.2
ratio
ratio
120
1.0
0.8
SOLSTICE
current cal
new cal
6•104
120
140
160
wavelength (nm)
180
200
120
140
180
200
1.0
0.8
0.6
120
140
160
180
wavelength range: 116-187nm
mean
sdv
current
0.93
0.12
new
1.05
0.12
0.6
100
160
wavelength range: 130-187nm
mean
sdv
current
0.85
0.06
new
0.95
0.04
21
Current and new calibration vs
Shemansky
ratio 2013
2.0
1.5
1.5
ratio
ratio
ratio 2010
2.0
1.0
0.5
1.0
0.5
ratio
random
systematic
ratio
random
systematic
0.0
0.0
120
140
160
wavelength (nm)
180
120
140
160
wavelength (nm)
180
wavelength range: 116-165nm
mean
sdv
current
1.06
0.31
new
1.11
0.33
22
To do
• Derive lens transmission empirically
• Compare calibration using summed scan
approach and flatfield (i.e. Spica spends equal
time per row)
• Compare Shemansky stellar model to SOLSTICE
• Compare SOLSTICE short-wavelength (~120nm)
measurements
• How to release a 2-dimensional wavelength
scale?
23
Action items
• Review EUV variability with Tom Woods
• Isolate the observed EUV solar occ variation to the CIII line DONE
• Distribute new calibration routine to Amanda for evaluation
- DONE
• Consult with Bill, Alain, Larry, Dave Judd regarding
implementation of the new calibration routine for PDS
reprocessing
• Develop a sensitivity corrector for use with small source
observations where the flat-field adjustment is not advised
• Send Uwe the UVIS FUV data from the s/c roll on Jan 2,
2011 - DONE
24