Onboard Science Data Products
TIMAS on board science data products:
(for more detailed information see the on-line Instrument operations and data acquistion discussion.)
The TIMAS instrument samples ion count rates 16 times per 6 second spin period at:
- 64 mass steps
- 28 angular sectors
- 14 energy steps (from a total of 28) plus a background measurement
These (over 10^5) measurements are averaged into a series of on board science data products summarized below. Because of the limited telemetery available not all data products can be transmitted to the ground. The instrument has the capability to vary the parameters of and the order in which these on board science data products are processed. This capability uses Instrument Control Parameter (ICP) tables. Each ICP table describes a TIMAS mode.
Note about coordinate system
The view_edp code gives the particle travel direction in the standard despun Polar coordinate system. Z aligned with the positive spin axis, X in the spin plane in the direction closest to the sun direction, and Y completing a right hand system.
On the view_edp output the look directions are given as azimuth and elevation (both in degrees). 0 degrees elevation corresponds to ions traveling in the + Z direction. 0 degrees azimuth corresponds to ions traveling toward the sun.
| NAME | Mass Resolution | Energy Resolution | Angle Resolution | Time Resolution | Uncompressed size (bytes) |
|---|---|---|---|---|---|
| Spin Header |
Every Spin ( 6 seconds) |
27 | |||
| MS (mass spectra) |
64 mass steps | Each MS data product has data from 1 of 8 energy bands selected from a list of 29 possible combinations | 6 solid angles covering ~98% of the 4 pi solid angle | on board averaging for 2,4,8,16, or 32 spins (12 to 192 seconds) | 229 bytes per energy band |
| MRDF (medium resolution distribution function) |
1 of 4 ranges of mass steps corresponding to one of the major magnetospheric species (H+, O+, He+ and He++) | The 14 of 28 interleaved energy steps sampled during the spin period. OR optionally, the 14 energy steps summed into 7 energy steps. | 104 solid angle segments covering ~98% of the full 4 pi solid angle (See note below) | 1 spin (6 seconds). Note because the two detector Heads sample ~ 180 degrees out of phase, it is possible to obtain 3 second resolution when MRDF’s from HEAD A and B are combined. | 14 E-> 1461 bytes
7 E-> 733 bytes per species per head |
| LRDF (low resoultion distribution function) |
1 of 4 ranges of mass steps corresponding to one of the major magnetospheric species (H+, O+, He+ and He++) | 7 energy steps. | 32 solid angle segments covering ~98% of the full 4 pi solid angle | on board accumulation for 1, 2, 4, 8, 16, or 32 spin periods (6 to 192 second resolution) | 229 bytes per species per head |
| PAD (pitch angle distribution) |
1 of 4 ranges of mass steps corresponding to one of the major magnetospheric species (H+, O+, He+ and He++) | The 14 of 28 interleaved energy steps sampled during the spin period. OR optionally, the 14 energy steps summed into 7 energy steps. | 18 (or optionally 9) angle bins covering a very small fraction of the angle space, but selected to give maxiumum pitch angle coverage one (9 angles) or twice (18 angles) per spin per head. | 1 spin (6 seconds). Note because the two detector Heads sample ~ 180 degrees out of phase, it is possible to obtain 3 second resolution when MRDF’s from HEAD A and B are combined. | 14 E/18 A -> 259 bytes 14 E/ 9A -> 143 bytes 7 E/ 18A -> 133 bytes 7 E/9A -> 70 bytes per species per head |
Note on MRDF data product sampling along the spin axis direction:
The two-dimensional MRDF data structure has 7 rows and 16 columns. Each row (~elevation angle) has counds from two paired annode sectors. Each of the 16 columns has counds from a single spin angle sector, corresponding to a single energy sweep….with one exception. The first row on the A side and the last row on the B side has counts from two spin sectors subdivided equally between those two spin sectors. This was done to avoid oversampling of look directons. The two exceptional rows have look directirons along the s/c spin axis where the changing spin angle does not alter the FOV very rapidly.
The effect of this is that, on rare occations, short duration ion beams that appear along the spacecraft spin axis will be be “spread” into two spin sectors, corresponding to different times (energy sweeps) during the spin and possibly confusing the temporal location and duration of the ion beam.
Last updated 06/26/2007 by Bill Peterson