1. 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

2. The Cassini project is a NASA mission being built at the Jet Propulsion Laboratory. The Cassini spacecraft was launched on October 15, 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.
Saturn position from 2001 to 2017 relative to the upwind direction of interstellar hydrogen (arrow).

3. Diagram of features of the heliosphere
Diagram of features of the heliosphere. The shape depicted may be incorrect, based on preliminary results from the Interstellar Boundary Explorer.

4. 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.

5. The bore sight directions of the FOV of HDAC year by year
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.

6. HDAC Status 2011: 1552 data sets in 2011, 725@2012
HDAC run in photometer mode
8 in mod 2011,
Sensitivity seems constant or…
decreases very slowly
Today 12 cts/s/R

7. HDAC long-term Evaluation Sensitivity between 2003 and 2012
HDAC-sensitivity 2010: 12 cts/s/R

10. 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
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.

12. HDAC long-term Evaluation. SPICA observations
Off Axis Response
Spectral sensitivity
Absolute calibration

13. HDAC long-term Evaluation. SPICA observations
Off Axis Response 2002
SPICA Raster Scan 2002

14. HDAC long-term Evaluation. SPICA observations
Off Axis Response 2003

15. HDAC long-term Evaluation. SPICA observations
Off Axis Response 2003

16. HDAC long-term Evaluation. SPICA observations
Off Axis Response

17. 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.

18. HDAC long-term Evaluation. SPICA observations
Absolute sensitivity: green line – „hot model“, red bullets –SPICA observations.

19. 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.

20. 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.