NPI Sensor Response

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NPI Sensor Response
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Neutral Particle Imager
3
NPI Sector Orientation
31
0
24
7
23
8
16
15
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NPI Data Available

• Cruise Phase data (10 sessions)
• Orbits 44, 47 and 49 (nadir pointing)
• Orbits 97, 100 and 103 (nadir pointing, Sun in
  -Z)

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Cruise data
45
42
July 9
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July 9 1830
5.543e5
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UV-Calibration of VEX NPIat University of
Arizona with Charles Curtis and Bill Sandel

• Hydrogen Lyman a (?121.6 nm)
• During measurements 7 106 s-1 into NPI
  aperture (gross estimation)

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Wavelength nm

• (VEX) NPI has a UV rejection factor of 10-5.
• (MEX) NPI sees 310-5 counts from Sun.

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Simulations
Dusk
SZA
Dawn
SZA 120

• NPI simulation at Mars (based on hybrid model.
  Kallio et al., Geophysical Research, 2001).
• Determine/approximate extent of Sun
  contamination.

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Best Case
11
Worst Case
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NPI Mars Orbit Data
Particle FOV 3
Draw Mars 20
NPI
Draw the Sun 30
S/C
Particle FOV 3
Draw Mars 20/-5
Draw the Sun 30/-5
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Orbit 44
14
Orbit 47
15
Orbit 49
16
Orbit 97
17
Orbit 100
18
Orbit 103
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Orbit 103 With Simulation Contour
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Summary

• NPI is sensitive to Sun (UV rejection 10-5).
• Ghost reflections appear 180 from primary at
  high count rates.
• We only see half of Mars (is the MOCAD for
  sectors 24-31 misbehaving?).
• Simulated ENAs in the Sun-direction for orbit 103
  consistent with data (backscattered ENA from Mars
  not included in model).

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A QUICK LOOK AT NPI
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WHAT IS FALSE?
SHARP CUT-OFF HERE
15-19 AND 0-3 FOLLOW EACHOTHER NICELY!
SECTORS 24-31 TOO LOW!?
NO SHARP CUT-OFF HERE
?
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WHAT IS FALSE?
Autocorrelation over sectors as a function of
time. Y-axis does NOT show actual sector number,
but separation (lag) between sectors for which
the correlation is calculated. NOTE how the
autocorrelation drops significantly below 1 at
1712. This about the time for ecliptic
crossing,and when the sun goes from the
instrumental hemisphere containing the negative
S/C y-axis, to the positive side.
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Orbit 44
GHOST REFLECTIONS
DIRECT SUN
25
Orbit 103
ALBEDO (ENA SUN?)
SHARP BOUNDARY
GHOST REFLECTION OF 0-3?
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0
31
15
16
to here
SUN moves from here.
Sun at 1712 UT
Strong emissions in sectors 11-19 (see previous
slide) goes away abruptly as soon as the Sun
switches sides and is blocked by the S/C. This is
an indication that these sectors see photons
before 1712 UT. One could argue that these
affect sectors 0-3 as well (ghost reflections?).
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WHAT IS REAL?
Ghost reflections
GROUP 2
GROUP 1
ENA albedo (50 of incoming ENA flux) Sun albedo
(30 of sunlight)?
GROUP 1
GROUP 2
Solar wind ENAs and/or sunlight

• Klas and Herbert is comparing to simulations.
  Pontus is just handwaving at this point.
• GROUP 1 Weaker emissions appears to come
  closer to the limb after 1702 UT. This is
  consistent with emissions close to the limb when
  the spacecraft distance is increasing.
• GROUP 2 Sun should be within FOV at 1712 UT,
  but NO sun pulse!? Theres a tiny streak of weak
  emissions running through the sectors. Sunpulse
  or solar wind ENAs?

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SUMMARY

• Sectors 0-8 and 16-23 are susceptive to ghost
  reflections.
• Sectors 24-31 are too low.
• This explains sharp sector boundary 19-20.
• Use cruise data to correct for ghost reflections?
• Other curious sector behaviors exist.
• HOW ARE PRE-AMPS AND SECTORS RELATED?

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SKYMAP DISPLAY

• When NPI scans, it paints the sky just like
  being inside a sphere.
• The scan axis (S/C z-axis) is the north pole of
  this sphere.
• The latitudes of the sphere are the sectors of
  NPI.
• The longitude is the scan angle.
• Close to what a human eye would see.
• NPI is not yet scanning. Only a slit is shown
  (its enlarged to 15 deg. Should only be 5 deg.)
• SPF x,y,z axes are drawn, with annotation on the
  positive end.
• Equatorial rings of planetary radii 2,4,6 are
  drawn.

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