elt data processing about noise, calibration capability ... · elt data processing – about noise,...
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ELT Data Processing –
about Noise, Calibration Capability and Synergies
Anja Schlicht, Christoph Bamann, Stefan Marz, Ulrich Schreiber
Technical University Munich
Ivan Prochazka
Technical University Prague
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ELT Data Processing –
about Noise, Calibration Capability and Synergies
1. European Laser Timing: Measurement principle and data analysis
2. Complications I: due to ISS
3. Complications II: Complexity of the measurement on ground
4. Comparison: ELT versus MWL
5. Synergies: ELT and microwave techniques
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Measurement principle
Optical link, pulsed
ACES/ELT
Ground stationtstart1 tstop2
tstop1
calibration
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Measurement principle
Principle of ELT (optical link, pulsed)
- One way:
𝑡𝑜𝑓1W = 𝑅𝐶𝑜𝑀 + τ𝑡𝑟𝑜𝑝𝑜𝑠𝑝ℎ𝑒𝑟𝑒 + τ𝑆𝑎𝑔𝑛𝑎𝑐 + τ𝑆ℎ𝑎𝑝𝑖𝑟𝑜 + τ𝑎𝑡𝑡𝑖𝑡𝑢𝑑𝑒𝐷𝑒𝑡𝑒𝑐𝑡𝑜𝑟- Round trip:
𝑡𝑜𝑓2W = 2 ∗ 𝑅𝐶𝑜𝑀 + τ𝑡𝑟𝑜𝑝𝑜𝑠𝑝ℎ𝑒𝑟𝑒 + τ𝑆ℎ𝑎𝑝𝑖𝑟𝑜 + τ𝑎𝑡𝑡𝑖𝑡𝑢𝑑𝑒𝑅𝑒𝑓𝑙𝑒𝑐𝑡𝑜𝑟 + 𝜏𝑅𝑒𝑓𝑙𝑒𝑐𝑡𝑜𝑟
with 𝑅𝐶𝑜𝑀: Distance between spacecraft CoM and station reference point
- Time transfer:𝜏 =𝑡𝑟𝑒𝑡𝑢𝑟𝑛+𝑡𝑠𝑡𝑎𝑟𝑡
2− 𝑡𝑑𝑒𝑡𝑒𝑐𝑡𝑜𝑟 + 𝜏𝑐𝑜𝑟𝑟 =
𝑡𝑜𝑓2𝑊
2+ 𝑡𝑠𝑡𝑎𝑟𝑡 − 𝑡𝑑𝑒𝑡𝑒𝑐𝑡𝑜𝑟 + 𝜏𝑐𝑜𝑟𝑟
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Round-trip measurements
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One-way measurements
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Time transfer
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Multireflector problem
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Multireflector problem
For reflectors 𝑖 = 0…𝑁 with distances 𝑑𝑖 ≤ 𝑑𝑖+1 with respect to the
observer the probability of detecting a signal is:
𝑝𝑖,𝑒𝑓𝑓 = 𝑝𝑖
𝑗=0
𝑖−1
1 − 𝑝𝑗
The single-reflector probabilities 𝑝𝑖 may account for differences in
the effective cross section among the reflectors.
With a constant background noise rate, the noise statistics follows
an exponential distribution in single photon mode:
𝑝𝑠𝑖𝑔𝑛𝑎𝑙.𝑖 = 𝑝𝑒𝑓𝑓,𝑖𝑒−𝑛𝑛𝑜𝑖𝑠𝑒Δ𝑡𝑖
1 2 3 4 5 6 7 8 9 10
detector sorted by distance
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
pro
ba
bili
ty o
f d
ete
ctin
g a
sig
na
l [-
]
pi = 0.20
pi = 0.15
pi = 0.10
pi = 0.05
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Detector identification
Timebias calculation
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Complexity of ELT for ground stations
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ACES clock prediction
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New noise reduction algorithm
𝑇𝑥
𝑇𝑦13
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New noise reduction algorithm
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Simulation capability
Geometric components
- ISS attitude simulation
(3 axes, constant offsets and oscillations)
- Detector and multi reflector positions
- Intra-reflector delay (function of incidence angle)
- Visibility constraints (minimum elevation, clouds)
- Tidal motion and atmospheric loading
Stochastic components
- Background noise
- Laser Jitter
- Pulse width
- Clock noise and offsets
- (Fluctuations in the troposphere)
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Clock simulation
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Ground segment
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Comparison with MWL
ELT: MWL:
Optical -> calibration -> 50 ps accuracy
no wet tropospheric delay
Time tagging of events -> jitter per detection
pulse length 10 ps / 1 kHz -> 4 ps @ 300s
7ps @ 1 d
Microwave -> no calibration -> 100 ps accuracy
wet tropospheric delay
Phase locked loop -> jitter per contact
100 Mchip/s / 14 GHz -> 230 fs @ 300s
8 ps @ 1 d
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Calibration
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Calibration of MWL
Calibration of MWL for time transfer
and ranging
Troposphere
Short arc orbit adjustment
Systematic effects
Try a common parameter estimation
and compare to time transfer in
Lambda configuration
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Calibration of GNSS links
Calibration of GNSS receiver
T2L2 only in common-view
ELT now also in non-common-view
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ELT Data Center delivers the following products:
Space to ground clock comparison
Ground to ground clock comparison in common-view
Ground to ground clock comparison in non-common-view
MWL calibration
Conclusions
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