Transcript UVIS Team Meeting

UVIS Calibration Update
Greg Holsclaw
Bill McClintock
June 28, 2010
Outline
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Performance update
Flat-Field modifiers
Recent calibration observations
An alternative approach to sensitivity
updates
• Cassini SPICE kernel finder
• PDS updates
• Calibration paper topics
Performance update
• Total signal vs spatial position for the last three
Spica calibration scans
Flat-field Modifiers
• At the last team meeting…
– It was shown that there are significant declines in sensitivity at
localized regions across the detector (the starburn, long-wave
end of the clear aperture occ-slit in the FUV)
– It was decided that a corrector be created based on each UVIS
stellar observation and made available to the team in a timely
fashion
• Laura has made these flat-field modifiers available on
the team website at:
– http://lasp.colorado.edu/cassini/teamsite/tools_software/GregsFlatfieldModifiers.htm
• The use of the correctors in the cube generator
calibration pipeline has been implemented
Flat-field Modifiers
• These correctors provide adjustments for
changes in the relative sensitivity in each column
with respect to the average of several
“reference” rows which are located in the region
obscured by the occultation slit lens holder
• Corrector values are linearly interpolated for
observations which occur between two
calibrations. If an observation occurs after the
last calibration, the last corrector is used
Spatial average
Date: 2009-315
Loss-of sensitivity around Lymanalpha looks like the FUV
occultation slit.
Reference
rows
Spectral average
starburn
undercorrected
Lyman-alpha
Recent Observations
• There have been three calibrations since the last
meeting:
– FUV2010_037_08_01_45_UVIS_126IC_ALPVIR001_PRIME
– FUV2010_088_18_22_56_UVIS_129IC_ALPVIR001_PRIME
– FUV2010_131_01_36_16_UVIS_131IC_ALPVIR001_PRIME
• The first two scans were complete. For the second
observation, a flat-field modifier (for both EUV and FUV
channels) was produced and placed on the website in a
short time.
• The third observation exhibits some missing data in the
middle of the slew. This complicates the automated
processing, and I have not yet found a good solution to
deal with this.
An alternative approach to
sensitivity updates
• The FUV detector experienced a significant increase in
sensitivity (>3x at 185 nm) at long wavelengths early in
the mission
• This change in sensitivity as a function of wavelength
and time was addressed by fitting an exponential
function to the fractional change over time at each
wavelength (in 21 pixel bins)
• Perhaps a better approach:
– Establish a reference spectrum of Spica based on SOLSTICE
measurements (>130 nm) and early spectra of Spica from UVIS
(<130nm)
– Similar to the approach used for the flat-field modifiers, linearly
interpolate the change in sensitivity between calibrations
– Facilitates quick updates to the absolute response of the
instrument
Absolute spectra of Spica over time
Absolute spectra
Ratio of UVIS to SOLSTICE
SOLSTICE
• Overall sensitivity decline
• The time-varying sensitivity is overestimating the
adjustment for the most recent observations
SPICE Kernel Finder - Intro
• Kris Larsen had provided a convenient online tool to
identify SPICE kernels for a given date
• This web-based tool allowed a single date to be input,
and a list of kernel files were provided as links to their
location at the NAIF site
• A more versatile tool would allow the required and most
current kernels not just to be identified, but also
downloaded automatically, organized, and a text file
listing created to facilitate their use with cube generator
• This approach abstracts the user from the details of
SPICE kernel naming conventions and time-consuming
organization
SPICE Kernel Finder - Overview
• Objective: Using IDL, identify and download
SPICE kernels relevant for a specific date
• Input: Year, day-of-year
• Action: identify and download required kernels
• Output: A text file listing the downloaded kernels
which can then be used by cube generator with
the “Load kernel batch” option
SPICE Kernel Finder - Function
• Cassini SPICE kernel repository:
– ftp://naif.jpl.nasa.gov/pub/naif/CASSINI/kernels/
• A list of all files is obtained for each kernel type (ck, fk, ik,
lsk, pck, sclk, spk)
• For kernels which are updated incrementally (fk, ik, lsk,
pck, sclk) the latest version is selected
• For kernels which are relevant to a specific date range
(ck, spk) the filenames are parsed and the appropriate
file is selected based on the date
• Multiple c-kernels can satisfy a specific date. Therefore,
the latest version is selected in this order of preference:
c-smithed, reconstructed, predict
SPICE Kernel Finder - Example
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cassini_spice_kernel_list, 2005, 331, fkernel, local_kernel_path =
'C:\Greg_Holsclaw\Cassini\UVIS\SPICE\'
Local_kernel_path specifies where kernels will be downloaded and stored
locally (contains subdirectories lsk, sclk, pck, spk, ck, ik, fk)
fkernel is an output string specifying the ASCII file containing the metakernel
list for use with CG:
– ‘C:\Greg_Holsclaw\Cassini\UVIS\SPICE\2005_331.mk’
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Contents of fkernel:
lsk\naif0009.tls
sclk\cas00144.tsc
spk\de403s.bsp
spk\060111R_SCPSE_05320_05348.bsp
fk\cas_rocks_v18.tf
fk\cas_status_v04.tf
fk\cas_v40.tf
ck\05305_05334ca_ISS.bc
pck\cpck20May2010.tpc
ik\cas_uvis_v06.ti
SPICE Kernel Finder - Features
• year and doy can be vectors
• Any Cassini instrument (or multiple instruments)
can be specified using a keyword
(instrument=‘uvis’)
• If all identified kernels exist locally, no internet
connection is required (the default)
• A refresh of the NAIF kernel lists can be forced
using a keyword (newlist=1)
• All ftp functions are accomplished using native
IDL routines (version 6.3 and above), no
external code or libraries are required
PDS updates
• The team-endorsed approach to calibrating the
data forces evil pixels to be effectively deleted
from consideration (replaced with NaNs)
• For some heavily binned UVIS observations, the
entire calibration matrix has a value of NaN
• To address this issue, the unbinned calibration
matrix is now included with the PDS data
• Potential inclusion of the flat-field modifiers with
the PDS calibration matrix
Too many calibration topics for one
paper?
• Radiometric calibration
– At a minimum, the lab measurements of H2 emission
• Instrument characterization and time dependent
sensitivity
– flat field, PSF, scattered light, backgrounds, polarization, linearity,
etc
• Spica absolute flux 91.2 – 190 nm (extension of
SOLSTICE to EUV using H2 emissions)
– Comparison with other investigators
• Spica light curve in the UV
• Data analysis approach
– forward model versus inverse approach, I/F derivation,
deconvolution, etc
• Atlas of all stellar spectral irradiance measurements