1. Mullard Space Science Laboratory CAA Cross-Calibration Meeting ESTEC 16 th May 2006 H. Khan, A. D. Lahiff, A.N. Fazakerley, I. Rozum, R. J Wilson MSSL-UCL PEACE Cross Calibration studies WHI and CIS comparison

2. MSSL Calibration Procedure

3. MSSL Count Rate to Phase Space Density ianode jazimuth angle kenergy step  ijk arriving particle rate P ijk dead time corrected arriving particle rate t acc sensor accumulation time  i electronic dead time f ijk phase space density G i geometric factor v k effective energy for energy step k  0 energy independent efficiency  (v k 2 ) I energy/anode dependent efficiency  gain correction factor  ijk flux dependent gain correction factor

4. MSSL In-flight Calibrations Inter-experiment – CIS Velocities Velocity (or strictly speaking drift velocity V ┴ ) – Reference sources: EDI gives V ExB EFW/FGM give V ExB (if E.B = 0) CIS – Adjustment principle: G  cancels – therefore can test the velocity without the WHI data Assume  ijk = 1 (usually ok except HEEA in magnetosheath) Optimisation technique to adjust energy efficiencies to achieve “correct” v

5. MSSL In-flight Calibrations Inter-experiment – WHI Density Density – Reference source: WHI sounder – Adjustment principle: – Note, does not reveal if the energy efficiencies  (v k 2 ) I are correct or not, but these are determined via velocity cross-calibration – WHI n e range 0.2 – 80 cm -3 (SSR paper) is narrower than PEA (~0.001 to 1000 cm -3 )

6. MSSL In-flight Calibrations Inter-Sensor – HEEA/LEEA Checking for “identical” behaviour in same plasma – Compare sensors on all spacecraft at small separations

7. MSSL Calibration Parameters Energy-Response Surface with anode dependence. Need to determine the correct weighting for each anode within a specific energy range and then apply

8. MSSL The fitting software imposes the following criteria: – Minimise the difference between the density from each PEACE sensor to WHISPER. – Minimise the difference between the z-component of velocity from each PEACE sensor to CIS Vz. – PEACE inter-sensor and inter-spacecraft calibration is good Ensuring the Phase Space Density (PSD) from consecutive anodes pairs (i.e. 0-1, 2-3, 4-5, 6-7, 8-9, 10-11) on all PEACE sensors and spacecraft give the same results for the same plasma - in practise small spacecraft separation. – The correction factors are only appropriate for the specific energy range used in the fitting procedure. Correction Factor determination

9. MSSL The correction factors are determined in a least-squares fit by minimizing – n' PEA and v' z,PEA are the PEACE density & velocity calculated using the correction factors through the iteration process. Initially correction factors of 1 are used by default. – W n, W v, W PSD are density, velocity and PSD weighting factors with default values of 1, however can be varied to give better fits Due to the requirement of inter-sensor and inter-spacecraft calibration, the correction factors must be determined for multiple sensors simultaneously. Correction Factor determination

10. MSSL Applying the Correction Factors To determine moments, the energy-independent correction factor calculated using the above criteria is multiplied by the PSD from each anode. For 3DR/3DXP data we have 6 free parameters per sensor, corresponding to the 6 anode pairs, with a total of up to 48 free parameters for each fit. Note: To improve PEACE calibrations across the full energy range it is imperative to have CIS and WHISPER data from different plasma regions, such as solar wind, magnetosheath, plasmasheet etc, to conduct the cross calibration studies thoroughly. We are still lacking a good set of intervals covering all regions.

11. MSSL Reference Calibration Interval : 28 April 2002 PEA 3DXP LEEA DEFlux CIS HIA Vx Vy Vz WHI pre- Feb06 Data This event shows the C1 travelling through the magnetosheath and into the solar wind with S/C separation at 100 km. A portion of the magnetosheath interval was used for the calibration studies. The WHI Data ‘pre- Feb06’ was provided by the WHI team for the PEA calibration study

12. MSSL C1 C2 C3 C4 Prior to the last meeting WHI Team provided densities for the cross-calibration studies 28 th April 2002: WHI PP (red) WHI data pre- Feb06 (black)

13. MSSL Updated WHISPER data Since the last Cross Calibration meeting, WHISPER have provided us with new data for the original calibration event – Orbit 283 These new files (post-Feb06) are higher time resolution than the ‘pre-Feb06’ densities and are considered to be better quality than before. Only 2 intervals have been provided, and we are in the process of incorporating the new data into the fitting procedure.

14. MSSL C1 WHI densities Solid line – WHI data ‘pre-Feb06’ Green line – New WHI post-Feb06

15. MSSL C1 WHI densities Solid line – WHI pre-Feb06 Green line – New WHI post-Feb06 Blue line – New WHI post-Feb06 Smoothed

16. MSSL C1 WHI densities Solid line – WHI data pre-Feb06 Blue line – New WHI post-Feb06 Smoothed

17. MSSL WHISPER density improvements WHI has given us two sets of improved (post-Feb06) densities for the 28 th Apr 2002 event since the last X-Cal meeting. The first were very high time resolution but still quite noisy. The Quality flag (Q>0.3) was used to filter the data (not shown here) but this did not make a great deal of difference to improving the dataset. WHISPER Team came back with a modified dataset: sup = (freq(i) + uncertainty(i)) ; i=1…N inf = (freq(i) + uncertainty(i)) ; i=1…N – Perform average smoothing on both time series: sup_smth, inf_smth – Retain only those freq in range: freq (i) > inf_smth(i) and freq(i) < sup_smth(i) – Resulting freq: (inf_smth + sup_smth)/2. This is shown as the blue line in the previous plot.

18. MSSL Calibration event – orbit 283: WHI post-Feb06 28/04/2002, 05:50 – 08:50 correction factors time interval : 05:50 – 06:20 boxcar smoothing for the fit : 200 sec boxcar smoothing for the plot : 60 sec HIA data: C1 & C3 NEW WHISPER data post-Feb06: C1, C2, C3 & C4 s/c potential offset 2 = 0 LEEA/HEEA energy range: 9.5 eV < E L,H < 6990 eV WGT_psd = 1 MIGRAD method (codes-v1.2)

19. MSSL Orbit 283 – Before Corrections Density Vz PSD ratios

20. MSSL Orbit 283 – Calib. results WHI post-Feb06, WGT=1 Density Vz PSD ratios

21. MSSL Calibration event – orbit 283 28/04/2002, 05:50 – 08:50 correction factors time interval : 05:50 – 06:20 boxcar smoothing for the fit : 200 sec boxcar smoothing for the plot : 60 sec HIA data: C1 & C3 WHISPER data pre-Feb06: C1, C2, C3 & C4 s/c potential offset 2 = 0 LEEA/HEEA energy range: 9.5 eV < E L,H < 6990 eV WGT_psd = 1, 5, 20 MIGRAD method (codes-v1.2)

22. MSSL Orbit 283 –Calibrated results, WGT=5 Density Vz PSD ratios

23. MSSL Orbit 283 –Calibrated results, WGT=20 Density VzPSD ratios

24. MSSL Vx original Vy original

25. MSSL Vx calibrated Vy calibrated

26. MSSL Orbit 283 – Correction factors:  2 (WGT_psd = 1) = 0.98  2 (WGT_psd = 5) = 0.95  2 (WGT_psd = 20) = 0.94

27. MSSL Orbit:Date DOY Available data interval PEACE and WHI Sensor dataModeMCP GainSC sepRegion 283: 28-29/04/02 118-119 28/04 - 3DX data from 0600-0850UT HEEA/LEEA overlapping energy range: 6.9keV- 9.5eV Peak energy ~100eV WHI data (pre-Feb06) New WHI data (post-Feb06) 0600-0850UT C1234 LEEA C24 HEEA BMGOOD100kmMS 288: 09-10/05/02 129-130 09/05 - 3DX data from 1920-2045UT HEEA/LEEA overlapping energy range: 26.4keV-14.2eV Peak energy ~ 20eV NO NEW WHI data (post-Feb06)- waiting for reprocessed data 10/05 - 3DR data 0000-0850UT WHI data (pre-Feb06) - 0430-0855UT C24 LEEA C1234 HEEA C1234 LEEA C1234 HEEA 0000-0325UT BM NM GOOD 100km PS MS 305: 20-21/06/02 171-172 20/06 - 3DX data from 0600-0830UT HEEA/LEEA overlapping energy range: 6.9keV- 9.5eV Peak energy ~50eV WHI data (pre-Feb06) - NO EFW corr C1234 LEEA C24 HEEA BMGOOD100kmMS 410: 24-25/02/03 55-56 24/02 - 3DX data from 0800-1145UT. Sheath after 1020UT HEEA range: 26.4keV-34eV; LEEA range: 4.5keV-7.1eV Overlap: 4.5keV-34eV Peak energy ~100eV WHI data(pre-Feb06) 1000-1145UT NEW WHI data (post-Feb06) 0700-0930UT BUT C4 0700-0750UT C1234 LEEA C24 HEEA BMGOOD200kmMS Sample of study intervals: WHI input

28. MSSL Summary Main Development: The fitting code has been improved to include inter-sensor and inter-spacecraft constraints that ensures consecutive anode pairs on all sensors give the same results when in the same plasma. – this is the most critical criteria of the fit Weighting factors for density, velocity and inter- sensor/spacecraft constraint having been introduced. – Weighting the inter-sensor/spacecraft condition stabilises the fit and gives the best results

29. MSSL Further Work Event 410 is to be processed, with the aid of WHISPER providing better densities in various plasma region. Supply from WHI is the controlling rate of progress for full calibration, though work on Vz only can be done with CIS comparison only. The fitting software has been optimised to provide the best fits using the data provided, with weighting factors to stabilise the results. More events are required in the tail and plasmasheet to determine correction factor for all energy ranges. Possible collaboration with WBD will also be appreciated

30. MSSL End slide