1. PAD SELECTION QUALITY FLAG STATUS

2. PAD Is collected twice every spin on-board and comes from both HEEA and LEEA sensor
PAD data
HEEA
LEEA
2nd half spin
1st half spin
Figure 1
Figure 2
Data from only the azimuthal sectors which contain the onboard estimated field direction will form the PAD distribution (figure 1)‏
For the first half of the spin, polar bins [n to 11] will be telemetered for LEEA and polar bins [(11-n) to n] for HEEA, where n is the polar zone of LEEA in the first half spin containing the magnetic field direction.
In the second half of the spin polar bins [(11-n) to n] will be telemetered for LEEA and [n to 11] for HEEA (figure 2)‏

3. - At the end of each spin 0 PEACE receives a single magnetic field vector from FGM via the Inter Experimental Link (blue arrow)‏
- At the start of spin 1 PEACE uses the magnetic field components from FGM to calculate the azimuthal angle of the field in the PEACE frame. This angle is used to determine which azimuthal sectors to store data from. These are the sector containing the field and the adjoining ones (blue dashed lines)
- At the end of spin 1 PEACE receives another vector from FGM (red arrow). The nearest sector to this vector from the sectors stored is selected as the PAD distribution for spin 1 (red dashed)‏
The polar angle is also determined from the FGM field vector

4. - This works well if the field is not rapidly changing.
- However this is not always the case. If the magnetic field changes significantly during the spin then the PAD data collected during the spin may not represent the true distribution.
- Note that the PAD data is rebinned using the ground calibrated magnetic field data (CFUNIT) which has high resolution and and are measured around 200 times per second.
- The PAD selection quality flag gives an indication of how good the PAD data is by seeing how close the azimuthal sector for which we have PAD data is to the true CFUNIT vector at the time of PAD collection.

5. GOOD – STEADY MAGNETIC FIELD
BAD – UNSTEADY MAGNETIC FIELD c c

6. TYPE 2
Centre of bin taken as midpoints of the lines connecting the midpoints of opposite edges
To determine the flag we calculate the pitch angle between the CFUNIT vector and each corner of the bin and the pitch angle between the CFUNIT vector and the midpoint of the bin

7. PITCH FULL
FLAG EXPLANATION
0 All 4 corners of bin are within 0-15 (or ) degree pitch angle of the CFUNIT vector
Following flags are for when not all 4 corners are within 0-15 or degrees from the CFUNIT vector
1 Mid point of bin is within 0-15 (or ) degree pitch angle of CFUNIT vector
2 Mid point of bin is within (or ) degree pitch angle of CFUNIT vector
3 Mid point of bin is within (or ) degree pitch angle of CFUNIT vector
4 Mid point of bin is within (or ) degree pitch angle of CFUNIT vector
5 Mid point of bin is within (or ) degree pitch angle of CFUNIT vector
6 Mid point of bin is within (or ) degree pitch angle of CFUNIT vector

8. PITCH_FULL
There will be a flag for each sensor for each half spin
PITCH_SPIN
Determined from the PITCH_FULL flags. The flags for each half spin are combined as are the flags for each sensor. So there is only one flag per spin

9. SENSOR MODE
Three sweep modes:
LAR – Low angular resolution
- One spin has 16 azimuths (22.5 degrees)‏
- 60 energy bins sampled per sweep
MAR – Medium angular resolution
- One spin has 32 azimuths (11.25 degrees)‏
- 30 energy bins sampled per sweep
HAR – High angular resolution
- One spin has 64 azimuths (5.625 degrees)‏
- 15 energy bins sampled per sweep
For PAD:
In MAR mode all 30 energy bins associated with the sweep are collected from one azimuthal sector
In LAR mode every second bin is collected from one azimuthal sector
IN HAR mode all 15 energy bins are collected from the magnetic field sector and an adjacent one
LAR: 30 energy bins X 13 polar bins X 1 azimuth bin x 2 sensors = 780
MAR: 30 energy bins X 13 polar bins X 1 azimuth bin x 2 sensors = 780
HAR: 15 energy bins X 13 polar bins X 2 azimuth bin x 2 sensors = 780

10. When we expect bad PAD selection
(i) We had applied corrections to FGM raw data, onboard, incorrectly from launch until a correction was made on June Corrections were added instead of subtracted or vice versa. We would expect the PAD selection flags to be bad at these times on all spacecraft.
(ii) FGM anomalies: FGM on C2 sent strange values between April 2002 and May We would expect our pad selection flags to be bad at these times on C2 only.
(iii) FGM does very occasional calibration runs in the solar wind during which time the FGM data we get onboard is messed up too, but only for ~ 5-15 minutes, shorter earlier on.
(iv) PEACE-FGM IEL link is closed. We do not receive magnetic field data from FGM.
(v) Cases where the field is weak. In these cases we see that the the position of the FGM IEL field received every spin and the azimuth in the LEEA frame determined onboard do not agree. This could be due to the addition of offsets to very small numbers (as the field is weak)‏
(vi) Where the FGM IEL vector crosses over the half spin (180/360) degree boundary from one spin to the next.
All of these will be explained in the user guide.

11. Example of good pitch angle selection
HAR-MAR C :15-10: h m08

12. Bad pitch angle selection due to incorrect treatment of correction to FGM at start of mission
C :02-23: C :27-09:28

13. Improvement of pitch angle selection due to incorrect treatment of correction at start of mission after June when new FGM calibration values uplinked on all SC

14. Q: But the flags do not change ???
Here we have an example of when the IEL azimuth crosses over the 180/360 degree boundary resulting in the chosen PAD azimuth bin being completely wrong.
The IEL azimuth is initially at 176 degrees (blue arrow). PAD is stored for the blue shaded sectors. At the end of the spin the IEL azimuth then changes to 182 degrees (red arrow). Of the three stored sectors only one is returned. The one chosen is the one closest to the new IEL for each half circle (red shaded). As can be seen from the diagram, crossing the 180/360 boundary results in incorrect sectors being chosen for PAD.
LEEA
180 deg
Q: But the flags do not change ???
A: x-component of field in nearly 1 so the field is pointing out of the page.
WEAK FIELD