KPL/IK
MAVEN SWEA Instrument Kernel
===============================================================================
This Instrument Kernel (IK) file contains parameters for MAVEN
SWEA instrument.
Version and Date
-------------------------------------------------------------------------------
Version 1.0 -- February 14, 2014 -- David L. Mitchell, SWEA Lead
References
-------------------------------------------------------------------------------
1. Kernel Pool Required Reading
2. GETFOV, getfoc_c, cspice_getfov headers
3. MAVEN FK file, latest version
4. <additional references, if any>
Contact Information
-------------------------------------------------------------------------------
David L. Mitchell, SWEA Lead, 510-643-1561, mitchell@ssl.berkeley.edu
Implementation Notes
-------------------------------------------------------------------------------
This file is used by the SPICE system as follows: programs that make
use of this kernel must ``load'' the kernel, normally during program
initialization. The SPICE routine FURNSH loads a kernel file into
the pool as shown below.
CALL FURNSH ( 'frame_kernel_name; ) -- FORTRAN
furnsh_c ( "frame_kernel_name" ); -- C
cspice_furnsh, frame_kernel_name -- IDL
cspice_furnsh( 'frame_kernel_name' ) -- MATLAB
Once the file has been loaded, the SPICE routine GETFOV (getfov_c in
C, cspice_getfov in IDL and MATLAB) can be used to retrieve FOV
parameters for a given instrument or structure.
This file was created and may be updated with a text editor or word
processor.
Naming Conventions
----------------------------------------------------------
All names referencing values in this IK file start with the
characters `INS' followed by the NAIF MAVEN ID number (-202)
followed by a NAIF three digit ID code for SWEA or one of
its detectors or components. This is the full list of names
and IDs described by this IK file:
MAVEN_SWEA -202130
MAVEN_SWEA_FRONT -202131
MAVEN_SWEA_BACK -202132
The remainder of the keyword name is an underscore character
followed by the unique name of the data item. For example, the
-202131 boresight direction provided as a part of its FOV
definition is specified by:
INS-202131_BORESIGHT
The upper bound on the length of the name of any data item is 32
characters.
If the same item is included in more than one file, or if the same
item appears more than once within a single file, the latest value
supersedes any earlier values.
Mounting Alignment
--------------------------------------------------------
The SWEA science frame -- MAVEN_SWEA, ID -202130 -- is defined as a
fixed offset frame with respect to the s/c frame (see Ref. [3]).
Nominally, it is rotated from the s/c frame by +50 degrees about Z as
shown on this diagram:
+Z s/c side:
------------ ._____. APP
\_____|
|
|
| +Xsc
| ^
._________._________..-----|-----.._________._________.
| | || .--|--. || | |>
MAG .-| | +Ysc / | \ || | |-. MAG
< | | <-------o ||| | | >
`-| | \ / || | |-'
<|_________|_________|HGA'-----' ||_________|_________|
-----------'
+Xswea <. | `-.
`-. | `-.
.-' `-o `-.
.-' / SWEA `-.
LPW .-' / `-. LPW
/
v +Yswea
+Zsc and +Zswea are out of the page.
The MAVEN_SWEA frame is defined with respect to the instrument's
anode layout. SWEA has 16 anodes (numbered 0 to 15) each spanning
22.5 degrees in the X-Y plane. In flight software and in ground data
analysis software, the +X axis of the frame is at the boundary
between anodes 0 and 15. To put +X in that direction, the MAVEN_SWEA
frame is rotated from the spacecraft frame by +50 degrees about the
Z axis. It is convenient to define two polar coordinates in the
MAVEN_SWEA frame. Phi is the azimuth angle in the X-Y plane.
Phi = 0 corresponds to +Xswea, and Phi = 90 degrees corresponds to
+Yswea. Theta is the elevation angle out of the X-Y plane.
Theta = 0 corresponds to the X-Y plane; Theta = +90 degrees
corresponds to +Zswea (and +Zsc).
Instrument Description and Data Products
---------------------------------------------------------
The Solar Wind Electron Analyzer (SWEA) is a symmetric hemispherical
electrostatic analyzer with deflectors. When the deflector potentials
are both at zero, the instrument has a 360 x 7 degree disk-shaped field
of view (FOV) that is orthogonal to the instrument's symmetry axis
(Zswea). This disk-shaped FOV is swept out of the SWEA X-Y plane by
alternately varying the potentials on the upper and lower deflectors.
The deflection angle depends on the ratio of the deflector potential to
the analyzer potential. These potentials are controlled by a programmable
sweep table.
The sweep table is programmed to cover an energy range of 3-4600 eV with
64 logarithmically spaced energy bins. At each energy bin, the deflectors
sweep the FOV out of the X-Y plane to an extent that is limited by either
the instrument geometry or the maximum deflector potential. Up to energies
of 2 keV, the FOV is limited by instrument geometry, and the deflectors
sweep the FOV from -60 to +60 degrees in theta. At higher energies, the
elevation extent of the field of view is inversely proportional to energy.
At 4600 eV, the FOV is swept from -25 to +25 degrees in theta.
Details of the FOV depend on the instrument's sweep table, which in
principle can be changed during the mission. The values given above are
for the nominal sweep table.
During each 2-second measurement cycle, SWEA generates a 64-energy x
16-azimuth x 6-elevation distribution. In order to make best use
of SWEA's total telemetry allocation, the PFDPU calculates three data
products from this distribution: 3D spectra, pitch angle distributions
(PADs), and energy spectra.
At the highest resolution, a 3D spectrum consists of 64 energies for each
of 80 solid angle bins (phi-theta pairs). Adjacent azimuth sectors are
averaged at the highest positive and negative elevations to provide a
more uniform solid angle resolution. (This decreases the number of solid
angle bins from 96 to 80.) This distribution can be further averaged in
groups of 2 or 4 adjacent energy steps to produce 32x80 and 16x80
distributions, respectively. Finally, the distribution can be sampled
every 2^N two-second measurement cycles, where N is an integer. The
mapping of the 3D distributions into the instrument's FOV is shown in the
following diagram:
^ +Zswea
Full deflected | +Zsc
360 x 120 deg FOV |
(-Xswea) (-Yswea) (+Xswea) (+Yswea) (-Xswea)
Phi = -180 -90 0 +90 +180
| | | | | Theta =
.--.--.--.--.--.--.--.-----.--.--.--.--.--.--.--. --- +60
| | | | | | | | |
| | | | | | | | |
'--'--'--'--'--'--'--'--'--'--'--'--'--'--'--'--' --- +40
| | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | |
'--'--'--'--'--'--'--'--'--'--'--'--'--'--'--'--' --- +20
| | | | | | | | | | | | | | | | | 6
| | | | | | | | | | | | | | | | | 20 deg
'--'--'--'--'--'--'--'--o--'--'--'--'--'--'--'--' --- 0 summed-up
| | | | | | | | | | | | | | | | | deflection
| | | | | | | | | | | | | | | | | steps
'--'--'--'--'--'--'--'--'--'--'--'--'--'--'--'--' --- -20
| | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | |
'--'--'--'--'--'--'--'--'--'--'--'--'--'--'--'--' --- -40
| | | | | | | | |
| | | | | | | | |
'--'--'--'--'--'--'--'--'--'--'--'--'--'--'--'--' --- -60
16 22.5-deg azimuth bins
(summed into 8 bins at the highest deflections)
The most scientifically relevant way to organize the electron angular
distribution is with respect to the magnetic field. The angle between
an electron's velocity vector and the magnetic field vector is defined
as the "pitch angle", which ranges from 0 degrees (parallel) to 180
degrees (anti-parallel). These pitch angle distributions (PADs) are
generated onboard by flight software in the PFDPU. The first step is
to perform a basic calibration of the magnetic field vector and then
rotate the vector into MAVEN_SWEA coordinates, so that the 96 phi-theta
pairs can be mapped into pitch angle. The pitch angle distribution
that is placed in telemetry is composed of 16 values: one for each of
the 16 azimuth sectors. Flight software determines the optimal
deflection bin for each azimuth sector that maximizes the total pitch
angle coverage. The solution is a great circle entirely within the FOV
that contains the magnetic field vector, or comes as close a possible
to doing so. This guarantees that a complete pitch angle distribution
is obtained whenever the magnetic field vector is within SWEA's FOV,
and that any gaps are not larger that the instrument's intrinsic blind
spots (|theta| > 60 degrees).
Since the 16 PAD bins span 360 degrees in azimuth, there is two-fold
redundancy. That is, the pitch angle distribution is measured twice,
once for each half of the detector. No information is lost in
producing a PAD onboard, since it is obtained without averaging in
angle. The pitch angle mapping can later be refined on the ground by
using fully calibrated Magnetometer data. The basic MAG calibration
performed onboard is sufficient to optimize the pitch angle coverage
provided by this data product. PADs can be averaged in groups of 2 or
4 energy steps to produce 32x16 and 16x16 distributions, respectively.
The distribution can also be sampled every 2^N two-second measurement
cycles.
Energy spectra are obtained by taking a weighted average of all 96
azimuth-elevation pairs. The weighting takes into account the solid
angle spanned by each pair and the relative instrument sensitivity
over the FOV. Energy spectra always contain all 64 energy steps to
provide the best possible energy resolution, and they can be either
sampled or summed over every 2^N two-second measurement cycles.
Instrument Detector/Sensor Layout
----------------------------------------------------------
The frame used above to describe the SWEA FOV is the "SWEA science frame",
which is defined in the MAVEN Frames kernel [3]. When the SWEA boom is
deployed, the +Z axis of this frame is aligned with the spacecraft +Z axis.
The orientation (clocking) of the X-Y plane is defined with respect to the
anode layout. SWEA has 16 anodes (numbered 0 to 15), each spanning 22.5
degrees in the X-Y plane. The +X axis of this frame is at the boundary
between anodes 0 and 15, and the anode numbers increase in a right-handed
sense.
This diagram illustrates SWEA sector layout:
Phi=+90
^ +Yswea
| S# indicate the sector "#"
V12 | V11 position in the sensor
V13 ....|.... V10 +Ysc assembly.
.' S4 | S3 `. .->
V14.' S5 | S2 `. V9 V# indicate the sector "#"
. S6 | S1 . view direction.
V15. | . V8
.S7 | S0. For example, for
Phi=180 . o--------------> +Xswea Sector "2" the view
.S8 / +Z S15. Phi=0 direction is the vector
V0 . / . V7 emanating from the
.S9 / S14. aperture center through
V1 . / S13. V6 the point designated
`. / S11 S12 .' by "V2".
V2/ ......... ' V5
/ V3 V4
V \
View direction V +Xsc
of sector "2" Phi=-90
With full deflection (from 3-2000 eV), each sector has a FOV of +/- 60
degrees out of the X-Y plane. At higher energies (2000-4600 eV), the
elevation extent of the FOV is inversely proportional to energy. This
kernel describes the full FOV, which applies to energies below 2 keV.
These keywords contains SWEA sector parameters:
\begindata
INS-202130_NUMBER_OF_SECTORS = ( 16, 1 )
INS-202130_SECTOR_SIZE = ( 22.5, 120.0 )
INS-202130_FRAME = 'MAVEN_SWEA'
INS-202130_SECTOR_DIRECTIONS = (
-0.98078531 -0.19509032 0.00000000
-0.83146960 -0.55557024 0.00000000
-0.55557024 -0.83146960 0.00000000
-0.19509035 -0.98078531 0.00000000
0.19509032 -0.98078531 0.00000000
0.55557019 -0.83146966 0.00000000
0.83146966 -0.55557019 0.00000000
0.98078531 -0.19509031 0.00000000
0.98078531 0.19509025 0.00000000
0.83146954 0.55557030 0.00000000
0.55557042 0.83146948 0.00000000
0.19509038 0.98078531 0.00000000
-0.19509041 0.98078525 0.00000000
-0.55557007 0.83146971 0.00000000
-0.83146954 0.55557030 0.00000000
-0.98078531 0.19509023 0.00000000
)
\begintext
Instrument Pixel-to-3D Coordinate Mapping (if applicable)
----------------------------------------------------------
The pixel to 3D-coordinate mapping is defined in the level 2 metadata
files, since it is energy-dependent, and thus depends on the sweep table
loaded in the instrument. The phi angle mapping of the anodes (in
MAVEN_SWEA coordinates) is independent of the sweep, but the deflection
(theta) angles depend on energy.
This energy dependence implies that the look directions depend on sweep
table, so we do not define individual look angles in this kernel, but
instead define them in the level 2 metadata files. These look angles
will be defined in terms of instrument phi and theta, in the MAVEN_SWEA
coordinate frame.
Instrument Detector/Sensor Parameters (if applicable)
----------------------------------------------------------
All relative sensitivities are defined in the relevant level 2 metadata
files. Also, level 2 data files contain both raw counts and calibrated
differential energy fluxes, providing a consistency check on the data and
geometric factors.
Instrument FOV Definition(s)
----------------------------------------------------------
This section defines the following FOVs:
ID SHAPE FRAME SIZE1 SIZE2 BSIGHT
------- -------- --------------------- ----- ----- ------
-202131 POLYGON MAVEN_SWEA 179.9 120. +X
-202132 POLYGON MAVEN_SWEA 179.9 120. -X
The FOVs are defined in this data block. The "FRONT" and "BACK" FOVs
each cover half of the nominal maximum field of view envelope, valid for
energies up to ~2 keV (reduced theta coverage for higher energies), with
"FRONT" covering the +Xswea hemisphere, and "BACK" covering the -Xswea
hemisphere.
This diagram illustrates these two FOVs in the MAVEN_SWEA frame:
Front FOV:
----------
Front FOV Front FOV
boresight boresight
+Xswea +Xswea
^ ^
| Theta= |
|0 -60 |0 +60
_..--+--.._ .-------------------.
.' V8 | V7 '. |, | .|
.' V9 | V6 '. | `. | .' |
/ V10 | V5 \ | `. | .' |
Phi= . | . | `. | .' |
+90| V11 | V4 |-90 | `.|.' |
<----+-----------o-----------+- ---+---------o---------+--->
+Yswea | +Zswea +Yswea | +Zswea
| |
Back FOV:
---------
+Xswea +Xswea
^ ^
| |
Phi= . .
+90 | -90 |
<----+-----------o-----------+- ---+---------o---------+--->
+Yswea | V12 | +Zswea V3 | | +Yswea.'|`. | +Zswea
' | ' | .' | `. |
\ V13 | V2 / | .' | `. |
'. V14 | V1 .' | .' | `. |
'. _V15 | V0 _ .' |' | `|
''--+--'' `-------------------'
180 | -60 |0 +60
V Theta= V
Back FOV Back FOV
boresight boresight
There is a small phi portion (0.2 deg) centered on the -Y axis not
contained in either of these FOVs. This is necessary for
compatibility with the SPICE toolkit, and does not indicate any
intrinsic gap in the SWEA FOV.
\begindata
INS-202131_FOV_SHAPE = 'POLYGON'
INS-202131_FOV_FRAME = 'MAVEN_SWEA'
INS-202131_BORESIGHT = ( 1.0, 0.0, 0.0 )
INS-202131_FOV_BOUNDARY = (
0.000000 0.500000 0.866026
0.103899 0.489086 0.866026
0.203262 0.456820 0.866026
0.293751 0.404611 0.866025
0.371417 0.334738 0.866025
0.432867 0.250252 0.866026
0.475420 0.154840 0.866026
0.497218 0.052669 0.866026
0.497310 -0.051801 0.866026
0.475690 -0.154011 0.866026
0.433303 -0.249496 0.866025
0.372000 -0.334090 0.866026
0.294457 -0.404098 0.866026
0.204059 -0.456464 0.866025
0.104752 -0.488904 0.866025
0.000873 -0.499999 0.866026
0.000873 -0.499999 -0.866026
0.104752 -0.488904 -0.866025
0.204059 -0.456464 -0.866025
0.294457 -0.404098 -0.866026
0.372000 -0.334090 -0.866026
0.433303 -0.249496 -0.866025
0.475690 -0.154011 -0.866026
0.497310 -0.051801 -0.866026
0.497218 0.052669 -0.866026
0.475420 0.154840 -0.866026
0.432867 0.250252 -0.866026
0.371417 0.334738 -0.866025
0.293751 0.404611 -0.866025
0.203262 0.456820 -0.866026
0.103899 0.489086 -0.866026
0.000000 0.500000 -0.866026
)
INS-202132_FOV_SHAPE = 'POLYGON'
INS-202132_FOV_FRAME = 'MAVEN_SWEA'
INS-202132_BORESIGHT = ( -1.0, 0.0, 0.0 )
INS-202132_FOV_BOUNDARY = (
-0.000873 -0.499999 0.866026
-0.104752 -0.488904 0.866025
-0.204059 -0.456464 0.866025
-0.294457 -0.404098 0.866026
-0.372000 -0.334090 0.866026
-0.433303 -0.249496 0.866025
-0.475690 -0.154011 0.866026
-0.497310 -0.051801 0.866026
-0.497218 0.052669 0.866026
-0.475420 0.154840 0.866026
-0.432867 0.250252 0.866026
-0.371417 0.334738 0.866026
-0.293751 0.404611 0.866025
-0.203262 0.456820 0.866026
-0.103899 0.489086 0.866026
0.000000 0.500000 0.866026
0.000000 0.500000 -0.866026
-0.103899 0.489086 -0.866026
-0.203262 0.456820 -0.866026
-0.293751 0.404611 -0.866025
-0.371417 0.334738 -0.866026
-0.432867 0.250252 -0.866026
-0.475420 0.154840 -0.866026
-0.497218 0.052669 -0.866026
-0.497310 -0.051801 -0.866026
-0.475690 -0.154011 -0.866026
-0.433303 -0.249496 -0.866025
-0.372000 -0.334090 -0.866026
-0.294457 -0.404098 -0.866026
-0.204059 -0.456464 -0.866025
-0.104752 -0.488904 -0.866025
-0.000873 -0.499999 -0.866026
)
\begintext
End of the IK file.