Geoscience Reference
In-Depth Information
Fig. 3. Eclipse orbit geometry for the NPI observations during 2004 (top) and early
2005 (bottom). The time periods correspond to the dates given in Table 1. From left to
right the
yz
-,
xz
-, and
xy
-planes in the Mars Solar Orbital (MSO) coordinate system,
where the
x
-axis is toward the Sun, the
z
-axis is perpendicular to the planet's velocity,
in the northern ecliptic hemisphere, and the
y
-axis completes the right handed system
(and is approximately opposite to Mars' velocity vector).
Fig. 4. Examples of NPI FOVs for eclipse observations in (a) 2004 and (b) 2005. The
coordinate system is ecliptic with longitudes on
x
-axes, and latitudes on
y
-axes. The
32 NPI sectors' FOVs (look directions) is the continuous band with sectors 0 and 8
indicated. For comparison, the FOVs of the six NPD sectors are also shown. Mars limb
is the closed line with the planet center indicated. The sun direction is shown by a small
disc, and Earth by a square. We can note that MEX is in Earth communication pointing
in (a) and nadir pointing in (b).
estimates were achieved. There is also priority effect due to the electronics,
where some counts are shifted to higher numbered sectors that we have
not attempted to compensate for in the present analysis. This effect can
be viewed as a reduction of the in-plane angular resolution of the sensor,
since we get a smoothing between adjacent sectors. During calibrations, the
effect was responsible for moving approximately 40% of the counts in sector
n
to sector
n
+1.
The position of the spacecraft and the look directions of the NPI sec-
tors as a function of time were computed using the CSPICE
11
subroutine
