overview of efi instruments status and recent events i. coco swarm data quality workshop potsdam...

Overview of EFI instruments status and recent eventsI. CocoSwarm Data Quality Workshop Potsdam02/12/2014

EFI status | I. Coco | Potsdam | 02/12/2014 | Swarm Data Quality Workshop | Pag. 2

SUMMARY

1. Instruments status and general health after one year in operations.

2. TII image anomaly: operations, evolutions and progresses from June up to

November.

3. Langmuir Probe data processing improvements and open points.

4. Swarm plasma measurements validation.

5. Summary of major discussion points for the DQW.

Instruments status (1)


Langmuir Probes (IRFU)

– No life limited items have been identified

– There are no signs of degradation (such as slowly decreasing densities)

Ion Imagers (UofC)

– There has been no degradation in CCD dark current

– Detector lifetime – MCPs still considered young per manufacturer

– Voltage and temperature levels very stable

Instruments status (2): LP


– Langmuir Probes estimate differences on Swarm C S/C potential

- In August 2014 it was identified that in low density regions the estimated spacecraft potential on Swarm C was significantly more positive than on Swarm A.

- The cause was found to be different NCO setting for P1 on Swarm C compared to Swarm A or B (the NCO controls the ripple amplitude of the bias modulation in the retarded electron region)

- Settings corrected on Sept. 11

Instruments status (3): LP


Satellite A B C

High Gain (P1) 8.51% 6.99% 6.44%

Low Gain (P2) 1.12% 1.56% 2.01%

Both P1 and P2 0.07% 0.08% 0.09%

- Langmuir Probes 0-tracking failure statistics from March 19 – Oct 29

0-tracking is performed to find the right bias for measuring retarded and linear electron currents.

- When both probes fail, Te and Vs estimates are low quality or unusable- When only one probe fails, Te and Vs can still be obtained from the other probe, e.g. low gain P2 is used whenever the 0-track of P1 fails- The effect of these (rare) 0-tracking failures reduced by modifying the l1b algorithm

Instruments status (4): TII


- Ion Imagers CCD radiation effects*:

- Large values in the Sw-C H sensor from May onward are believed to be due to anomalous signal appearing at the edge of the detector.

- This does not affect the main signal region nor the data products

Sw

arm

AS

warm

BS

warm

C

*Courtesy of ComDev and Univ. of Calgary

Instruments status (5): TII


– Ion Imagers - High-voltage power supply monitors – Swarm A*

H sensor

V sensor

TII Image anomaly (1)

Document title | Author Name | Place | Data doc | Programme | Pag. 8

• The “TII image anomaly” is a progressive degradation of the TII raw images: instead of measuring the ion distribution peak, the sensors record a broad signal which implies a degradation of the instrument gain throughout sensors active area. Updating of the gain maps has only a limited benefit.

Nominal Image* Poor Quality Image*



• In August the situation became dramatic up to a point when no more usable images were recorded. A decision has been made to power down the sensors for a couple of weeks (example figs for SC B*).

• 2nd y moment is a rough measure of the image “broadening”: after the power on the sensors is ramped up again, images appear rather good (2nd y mom. < 5 pixels).

• After few days for SC A and B, and only few orbits for SC C, degradation starts to show up again.

• Several switch on/off cycles have been tried during Sept./Oct. on all SC, with different durations, but we could not reach a better understanding of the degradation root cause.



• Hypotheses concentrate on possible contaminants (ionospheric neutral particles, water vapor trapped during mounting phase or launch, etc...) in the MCP and/or Phosphor screens. After consultations with manufacturers, a “burn-in” procedure was decided: MCP and Phosphors would have been excited with voltages higher than nominal, sweeping through several Vg values, in order to “scrub” away contaminants.

• Executed in two steps on Swarm C first during late October/November: first MCP scrubbing only (-1800/-1900 V on MCP, 1000 V on Phosphors), then MCP + Phosphors (-1900 MCP, 5000 V Phosphors). MCP scrubbing started on Swarm A and B too. Under discussion: a more “aggressive” procedure, ramping the phosphor voltage up to 6000 V.

Impressive improvements*: good quality for several days in a row. Further work to be done in the Swarm C V sensor.

*Courtesy of Univ. of Calgary

LP data processing (1): the sweep mode


- Vsc before improvements*

- Vsc after improvements: better detection of overflows and clever filtering of disturbances*

*Courtesy of T. Nilsson

• Sweep products are still different than harmonic mode products.

• Differences change in sign and magnitude over time, so that it would be very difficult to model them and/or filter them away.

• How to cope with sweep mode? Could we state sweep results are, in general, “worse” than the harmonic mode results?

LP data processing (2): the harmonic mode


• As “side effect” of the sweep mode activation, the S/C is charged more than expected. This causes small spikes ( tens of mV) in the S/C potential corresponding to sweep intervals and extending 1-2 seconds after the sweep (recovery time). Also the electron temperature is affected (see figure below)

• The effect has been mitigated at instrument level, but it cannot be completely removed.

• It affects the plasma velocity and electric field calculations.

• Is it possible to model it and remove it?



• Ion current is now used to calculate Ne instead of e- current

• Gives same estimates in high density regions,

• Gives higher estimates in low density regions (not necessarily a bad thing),

• Get rid of overflows of the electron current and 0-tracking failures.

Ne from ion current

Ne from electron current



• The positive “side effect” on the calculated S/C potential is impressive.

Before the cure: features hard to explain (too sharp transition at the terminator, too high night side positive values)

After the cure: smoother day/night transitions, values more in line with expectations

Validation of plasma data (1)


• Incoherent scatter radars are considered the only mean to have independent plasma measurements co-located with Swarm EFI measurements.

• Large statistics of EFI-ISR measurements pairs are needed in order to build-up “error matrices” to be looked-up for obtaining reliable estimates of electron density and temperature in the full dynamic range of measurements.

• Ionospheric models (e.g. IRI) can also help for assessing the overall behavior of EFI data.

• Plasma data are not yet validated: only relative variations of the measured parameters can be considered as reliable, rather than their value itself.

• Nevertheless, we have now a 1-year climatology indicating good overall data quality with respect to the main expected features of the ionospheric plasma.

• A preliminary plasma dataset has therefore been made available to a group of expert users.

Validation of plasma data (2)


EISCAT – LP el. density comparison

1. 2014-04-04 (SW C): el. density derived using electron current. Underestimate of a factor 1.3

2. 2014-04-04 (SW C): el. density derived using ion current. Overestimate of a factor about 1.2

Main Plasma data quality group discussion points


•Thermal Ion Imagers related topics:

1.Discussion on the image anomaly: activities done, overall image quality, way forward.2.Processing algorithms improvements and evolutions.

•Langmuir Probes related topics:

1.The sweep mode: status of the improvements, general discussion on the reliability of this method with respect to the harmonic mode.2.The sweep effects on the S/C potential and electron temperature.3.LP data processing major improvement: ion current used for determining density, el. Temp., and S/C potential.4.LP datation: consequences on time-stamping when the ion current is used.

•Data Validation for both TII and LP: ISR-Swarm campaigns status and way forward; comparisons with IRI model; other possible suggestions...

•Preliminary plasma dataset status and evolution:

1.Feedback from expert users on data quality.2.Gathering of comments and suggestions for improvements.3.On the opportunity to open the dataset to the general users: when and how?

•AOB:1.Communication strategy throughout the Plasma quality working group and plasma experts.2.Technical discussion on the way forward for the cross-verification PP-OP. 3.EFI calibration strategy in operation.4.…

overview of efi instruments status and recent events i. coco swarm data quality workshop potsdam...

Documents

swarm b swarm c

tii efi status

lp efi status

coco potsdam

low quality

swarm c sc potential

data products

tii image anomaly