Summary on EFI splinter
Igino Coco(1), on behalf of the Swarm EFI quality working group
(1) ESA – Esrin, Frascati, Italy
6th Swarm Data Quality Workshop, Edinburgh, 29/09/2016
Issue/Revision: 0.0
Reference:
Status:
ESA UNCLASSIFIED - For Official Use
Summary
 Very fruitful and stimulating discussion (as usual)!
 A large part of the discussion has been dedicated to data validation
(Ne, Te, Electric field above all): techniques are mature, lot of work
done, need to increase statistics and harmonize different approaches.
 Progresses in the investigations of anomalies in Te: attempt to model
and remove sweep hick-ups; spike trains vs Sun zenith angle still
puzzling.
 Impressive amount of work on-going on TII data:
 Attempt to automate flagging of good/bad intervals basing on raw images
properties;
 Simplifying the processing concentrating on cross-track flow.
Igino Coco | 29/09/2016 | Slide 2
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Data validation: comparison with
other datasets approach; Swarm-ISR
initial
Igino Coco | 29/09/2016 | Slide 3
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adjusted
By L. Lomidze
Data validation: comparison with
other datasets approach; Swarm-ISR
initial
Igino Coco | 29/09/2016 | Slide 4
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adjusted
Data validation: comparison with
other datasets approach; Swarm-ISR
•
Measurements from LP, both high and low gain, seem to overestimate the
electron temperature. “Quasi-linear” adjustments are proposed.
•
The electron density seems to be underestimated, in all S/C as well.
Comparisons with radio-occultation measurements also confirm this picture.
Igino Coco | 29/09/2016 | Slide 5
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•
Other previous results from
Palin & Opgenoorth (IRF)
roughly agree, but clearly
high-latitude features are
better evidenced.
•
Method by IRF is very
robust
in
selecting
conjunctions: only the very
stable radar measurements
in both space and time are
used for comparison
Data validation: comparison with
models (IRI)
•
•
Advantage: climatology of data calibration is given;
Drawback: a model is a model (good statistical information, but would it make sense to fit
it with real data point by point?)
Proposed correction (for Te, same for Ne):
Pdiff = [(TeSW – TeIRI)/ TeIRI]% (known function of local time and latitude)
Tecorr = TeSW *100/(Pdiff+100)
Some evidence of agreement with C-NOFS measurements (Tion) when applying such correction
Igino Coco | 29/09/2016 | Slide 6
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By V. Truhlik
Data validation: Electric Field and
ionospheric conductances
•
Using two different methods for calculating the Pedersen currents (Spherical
Elements Current System, Amm 1997; and empirical theory by Robinson et al.,
1987), one can minimize a “Merit” function and obtain the “best” electric field
values starting from initial values.
Event case, E from prel. dataset
Event case, E from oper. dataset
Initial
Corrected
Igino Coco | 29/09/2016 | Slide 7
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By O. Marghitu
•
We already know OP
dataset is not reliable
for TII.
•
Nevertheless,
the
technique is able to
“compensate” the initial
values in the same way.
Summary and perspectives on validation
•
Proposed corrections to Ne basing on radio-occultation comparisons by two different authors:
S/C
N. Pedatella (2015)
L. Lomidze (2016)
Alpha
1.12 x + 1.95*104
1.14 x + 1.73*104
Bravo
1.31 x – 2.03*104
1.16 x + 1.77*103
Charlie
1.08 x + 1.03*104
1.13 x + 2.26*104
•
Still too early for a definitive proposal of data correction.
•
Need to combine/increase statistics, and harmonize methodologies! Moreover corrections should be possibly
applied as a function of latitude, local time, geomag. activity.
•
Other promising techniques have been proposed and deserve further exploitation: Ionosondes conjunctions
with Swarm at particular conditions (or more systematic use of the ISR plasma line); density gradients from
Swarm GPS (e.g. W. Miloch).
•
Comparisons with models (IRI, convection models…) are valuable, if complementary to other techniques, and
could help to fill the measurements gaps.
•
Electric field validation by means of ionospheric conductance determination is very promising and deserves to
be tested on more cases.
•
Extended dataset from IRF proved very useful: in general, the high gain probe seems to give more reliable Te
measurements.
Igino Coco | 29/09/2016 | Slide 8
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Electron temperature undesired features
ΔTe = A exp( (t-t0) / τ ) + C (t-t0)
•
•
•
Most of the hick-ups can be fitted by exponential functions, filtered and interpolated, but not
all of them.
The decay time is inverse proportional to ambient Ne, the amplitudes of the “hick-ups” are
inversely proportional to the decay times; the dependences change abruptly at terminator.
Amplitudes and decay times of the “hick-ups” seem to be smaller for the high-gain probe
compared with the low gain probe, and the relationships are less distinct.
Igino Coco | 29/09/2016 | Slide 9
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By M. Förster
Electron temperature undesired features
•
Most of the large amplitude hick-ups that cannot be
simply modelled occur in the same conditions
Igino Coco | 29/09/2016 | Slide 10
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•
Recurrent “spike trains” (5000 K
and above) are observed in the
electron
temperature
as
measured
by
the
Swarm
Langmuir probes. The distribution
of such spikes shows a strong
variability around the orbit and
seems to be clearly correlated
with the solar illumination.
•
The overplotted lines show the
angle between the solar panel's
normals and the sun direction
(notified as "COS"-values in the
upper left corner). The "Te spike
trains" follow mostly quite
closely these lines of ~81-83
deg and ~88 deg angles.
Electron temperature undesired features
Igino Coco | 29/09/2016 | Slide 11
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•
spike trains are often
associated
with
sharp
transitions of the solar
panel currents (red circled
areas.
•
Not all the spike trains are
associated
to
such
transitions: some of them
can well be “geophysical”
rather than “instrumental”
(blue circled area).
•
Analysis to be continued.
Where
does
this
illumination effect come
from? Photoelectrons from
the panels? Why LP should
be so much affected?
Towards an automated flagging of TII data
Single Image Criteria:
•
Consider subset of pixels with relatively
large (> 75%) intensities;
•
Distance between the center of the image
and MCP Origin does not exceed 4 pixels;
•
Image effective radius does not exceed 4
pixels;
•
Total number of intense pixels > 5;
Images Sequence Criterion:
Consider sequence of consecutive (>=2) valid
Images only
Igino Coco | 29/09/2016 | Slide 12
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By A. Kouznetsov
New concept of TII production and
distribution
1. L1b Prototype is complex to calibrate – simplify at expense of loss of some
accuracy
2. Derive cross-track flows from flow angles, assuming 7.6 km/s ram speeds (Use
reference frame co-rotating with Earth, remove flows arising from yaw and
pitch motion; Calibrate cross-track horizontal flow against (co-rotation + yaw)
signal; Exclude noisy data)
3. Send latest measurements to ESA regularly
4. Expert judgment needed: data will be first made available to expert users, with
some basic documentation on how to use them, and how to orient the
measurements given in instrument frame.
5. Eventually, good data will be automatically selected.
Igino Coco | 29/09/2016 | Slide 13
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