ACC/GPSR Splinter Summary
Christian Siemes
28/09/2016
ESA UNCLASSIFIED - Releasable to the Public
Summary
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SLR tracking priority
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GPS instrument data from Sentinel missions
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GPS instrument
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Setting optimization for phase and code loops
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Antenna phase centre offset
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GPS antenna FoV
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Data release: POD-only and ACC products
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ACC instrument
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New type of scale factor calibration manoeuvre
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Monitoring of spikes
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Christian Siemes | 28/09/2016 | Slide 2
SLR tracking priority
Priority list today
Recommendation
Suggest priorities to ILRS after analysis of GPSR setting optimization completed
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Sentinel 3 (highest)
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Swarm A/C
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Swarm B (lowest)
 Sentinel 3 being an altimetry critically depends
on position accuracy in radial direction
Priorities only become of relevance when multiple (LEO) satellites have a common
visibility over a tracking station. This is naturally the case for the SWARM-A/C pair
and TerraSAR-X/TanDEM-X.
General request to ILRS to critically review the LEO priority based on mission
needs for SLR tracking and related scientific return
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Christian Siemes | 28/09/2016 | Slide 3
Data availability from Sentinel missions
L1b data from Sentinel missions not publically available, which includes GPS
instrument data. However, GPS instrument data, supplemented with satellite
attitude data, is of scientific interest for
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POD and gravity field research
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Analysis of TEC  “TEC tomography”
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Geodetic reference frame research
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Etc.
Recommendation
Swarm and Sentinel DQWs community request public release of POD related L1b
data (RINEX observation files, satellite attitude, etc.) from Sentinel missions
Note
Swarm mission manager agreed to forward this request to Sentinel mission
management
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Christian Siemes | 28/09/2016 | Slide 4
GPS receiver setting optimization
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RMS of carrier phase residuals in polar areas has decreased due to wider L2
bandwidth
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Carrier phase residuals increases slightly at low elevation angles
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Less carrier phase observations are affected by high STEC gradients
No final conclusions can be drawn at this point. More data and analysis is needed.
Recommendation:
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Keep the current settings for now, i.e. L2 PLL bandwidth
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Swarm A 0.75 Hz
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Swarm B 0.5 Hz
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Swarm C 1.0 Hz
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Collect more data, in particular during northern hemisphere winter when carrier
phase observation residuals show a larger RMS, and perform further analysis.
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Then decide how to proceed, considering also potential altitude lowering
manoeuvres
ESA UNCLASSIFIED - Releasable to the Public
Christian Siemes | 28/09/2016 | Slide 5
GPS code loop bandwidth
Code loop bandwidth was reset to original value on 3–4 May 2016. After the reset,
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Code range observations show decreased noise level: RMS 100 cm  80 cm
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Tracking of L2 carrier phase starts about 12 seconds later compare to before
Preliminary assessment suggests that impact on POD is minor.
No final conclusion can be drawn now.
Recommendation:
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Keep current settings for now.
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Further review in view of POD and TEC determination.
ESA UNCLASSIFIED - Releasable to the Public
Christian Siemes | 28/09/2016 | Slide 6
GPS antenna field of view
GPS satellites are tracked in aft direction down to zenith angles of 90o, whereas
the antenna field of view is set to 88o.
Now understood: The GPSR assumes that the antenna boresight is pointing into
radial direction, i.e. along the vector from Earth’s centre to the satellite position
Recommendation:
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No changes needed currently.
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If need arises in the future,
the antenna field of view
setting could be changed.
ESA UNCLASSIFIED - Releasable to the Public
Christian Siemes | 28/09/2016 | Slide 7
New POD-derived acceleration and
thermosphere neutral density products
Two new products are available for Swarm A/B/C for July 2014 – August 2016 :
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ACCxPOD_2_ (non-gravitational acceleration derived in POD) - improved product
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DNSxPOD_2_ (thermosphere neutral density derived in POD) - new product
Recommendation:
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Release the products for Swarm A/C as soon as possible
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Swarm B products should not be release in present form
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Signal level too low compared to accuracy  negative densities
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Revisit processing scheme for Swarm B
ESA UNCLASSIFIED - Releasable to the Public
Christian Siemes | 28/09/2016 | Slide 8
New acceleration and thermosphere neutral
density data sets
ACCxCAL_2_, ACCx_AE_2_, DNSxWND_2_
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Swarm C time series extended: 30 May - to 23 September 2015
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First Swarm B data set for 11-14 December 2015
Recommendations
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Do not release Swarm B products  show no resemblance to force models
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Do not release Swarm C products from 16 July to 7 August 2015  unrealistic
signals at eclipse transitions
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Release Swarm C products: 30 May – 15 July and 7 August – 3 September 2015
 supplement ACCxCAL_2 products with spike index
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Replace “old” ACCxPOD products with “new” ones in the calibration of
accelerometer data and reassess ACCxCAL products
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Christian Siemes | 28/09/2016 | Slide 9
ACC scale factor calibration manoeuvres
Recommendation
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Investigate new type of calibration manoeuvre where a small change in velocity
is created for a limited time  observe in POD and deduce real thrust force
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Repeat the above manoeuvre at different ACC temperatures  variations of
estimated scale factors due to temperature dependency on or varying thrust
force?
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Design the manoeuvre such that hysteresis of ACC data has minimal impact on
the calibration results
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Christian Siemes | 28/09/2016 | Slide 10
ACC monitoring
Spikes stopped occurring after ACC reboot that was triggered by ACC EDAC failure.
ACC reboot due
to EDAC event
Recommendation
Implement the spike index for operational monitoring and trigger ACC reboot upon
degradation of data quality.
ESA UNCLASSIFIED - Releasable to the Public
Christian Siemes | 28/09/2016 | Slide 11