HDAC Instrument – Cassini/Huygens Mission
Data analysis of photometric observations by
HDAC onboard Cassini:
3D mapping and in-flight calibrations
Yuri Skorov, Horst Uwe Keller, Karl-Heinz Glassmeier
IGEP, TU Braunschweig, Germany
UVIS Science Team Meeting
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HDAC Instrument – Cassini/Huygens Mission
The Cassini project is a NASA mission being built at
the Jet Propulsion Laboratory. The Cassini spacecraft
was launched on October 15, 1997. It will reach Saturn
on July 1, 2004.
The Hydrogen Deuterium Absorption Cell (HDAC) is
part of the UltraViolet Imaging Spectrograph (UVIS)
experiment onboard the Cassini spacecraft, a remote
sensing instrument for atomic D/H measurements on
Saturn and Titan, as well as for LISM observations.
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Saturn position from 2001 to 2017
relative to the upwind direction of
interstellar hydrogen (arrow).
30 May 2016
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HDAC Instrument – Cassini/Huygens Mission
Diagram of features of the heliosphere. The shape depicted may be incorrect, based on preliminary
results from the Interstellar Boundary Explorer.
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HDAC Instrument – Cassini/Huygens Mission
The first axisymmetric kinetic-continued model
of the interaction of the solar wind and
supersonic flow of partly ionized interstellar
hydrogen plasma was developed in the
laboratory (Baranov and Malama, 1993). The
figure shows general physical pattern of the
flow obtained in the framework of the model.
The interaction of the local interstellar medium
(LISM) with the solar wind (SW) results in
formation of the interface, including the outer
shock layer (the region between the bow shock
BS and tangential discontinuity HP called
heliopause) and the inner shock layer (the
region between the heliopause and solar wind
termination shock TS).
The model of interaction of the solar wind with the interstellar medium is modifying
continuously by inclusion of new physical effects: heliolatitude dependence of the solar wind
velocity, dynamical influence of galactic and anomalous cosmic rays, influence of the solar and
interstellar magnetic fields, solar activity cycles, multi-component nature of the plasma flow
and so on.
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HDAC Instrument – Cassini/Huygens Mission
The bore sight directions of the FOV of HDAC year by year. The direction from the Sun towards Saturn is
indicated in each plot. The SOV directions are projected onto the ecliptic plane from the north direction.
Directions pointing north are marked with blue and those pointing south are marked with red crosses.
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HDAC Instrument – Cassini/Huygens Mission
HDAC Status 2011:
- 1552 data sets in 2011, 725@2012
- HDAC run in photometer mode
- 8 in mod 2011, 67@2012
- Sensitivity seems constant or…
decreases very slowly
- Today 12 cts/s/R
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HDAC Instrument – Cassini/Huygens Mission
HDAC long-term Evaluation
Sensitivity between 2003 and 2012
HDAC-sensitivity 2010: 12 cts/s/R
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HDAC Instrument – Cassini/Huygens Mission
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HDAC Instrument – Cassini/Huygens Mission
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HDAC Instrument – Cassini/Huygens Mission
Roll over correction
The Channeltron generates pulses when the
incoming photons hit the KBr photocathode.
After amplification inside the HDAC electronics
the Cassini counter adds up the pulses
within a selected integration period.
The counter is only 16bit, hence the maximum
number of recognized counts is 65536.
If an overflow is detected by the counter, then
its value is reseted (roll over), leading to the
spikes which can be seen in the data.
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HDAC Instrument – Cassini/Huygens Mission
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HDAC Instrument – Cassini/Huygens Mission
HDAC long-term Evaluation. SPICA observations
•Off Axis Response
•Spectral sensitivity
•Absolute calibration
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HDAC Instrument – Cassini/Huygens Mission
HDAC long-term Evaluation. SPICA observations
•Off Axis Response 2002
SPICA Raster Scan 2002
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HDAC Instrument – Cassini/Huygens Mission
HDAC long-term Evaluation. SPICA observations
•Off Axis Response 2003
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HDAC Instrument – Cassini/Huygens Mission
HDAC long-term Evaluation. SPICA observations
•Off Axis Response 2003
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HDAC Instrument – Cassini/Huygens Mission
HDAC long-term Evaluation. SPICA observations
•Off Axis Response 2005-2011
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HDAC Instrument – Cassini/Huygens Mission
HDAC long-term Evaluation. SPICA observations
The star spectra was obtained from the INES (IUE Newly Extracted Spectra) database. The data
originates from the International Ultraviolet Explorer.
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HDAC Instrument – Cassini/Huygens Mission
HDAC long-term Evaluation. SPICA observations
Absolute sensitivity: green line – „hot model“, red bullets –SPICA observations.
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HDAC Instrument – Cassini/Huygens Mission
CONCLUSIONS
•Sensitivity decreases very slowly. Today 12 cts/s/R.
•LISM hydrogen and SPICA observations give us very
close values of absolute sensitivity.
•Sensitivity variations across the FOV (off-axis response)
are almost constant.
•Angular distribution of sensitivity is not axisymmetric.
•Central noisy part of FOV plays only minor role for
analysis of LISM hydrogen observations.
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HDAC Instrument – Cassini/Huygens Mission
FUTURE WORK
Comparison of HDAC Lyman α with FUV based on LISM
observations. Cross-calibration.
Modernization of the hot model used for data analysis and
parameter optimization.
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