Airborne and marine quantum gravimetry

Workshop on « Quantum gravimetry in space and on ground »May 27, 2021

Yannick Bidel

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Presentation outline

• Introduction

• Marine and airborne atom gravimetry

• Atom accelerometer for space geodesy

• Conclusion

Gravimetry

Navigation

Gravity map, terrain aided navigation

Geodesy

Measuring the Earth's gravity field to improve knowledge of

the geoid, which serves as a reference for altitude

Geophysics / Exploration

Measurement of mass distribution and variations

�Earthquake, volcano, ice melting, hydrology

Fundamental physics/ metrology

Kibble balance, equivalence principal, gravitation theory

test

Applications :

0 2.10-3 m/s²- 2.10-3 m/s²

Measuring the Earth's gravity field and its spatial and temporal variations : g = 9.81… m/s²

Gravity field measurement from space

- Measuring sea heights by space altimetry

Mean sea height ~ gravity equipotentialResolution ~ 20 kmOnly sea area are covered

- Measuring satellite orbital perturbations

- Measuring the gravity gradient in a satellite

Use of electrostatic accelerometers to measure non-gravitational accelerations

Resolution ~ 100 kmThree pairs of electrostatic accelerometers

Resolution ~ 400 km, temporal variations

Better resolution � terrestrial gravimetry

GRACE 2002 - 2017GRACE FO 2018 -

Terrestrial gravimeter

Static0.001 - 0.01 mGal

Dynamic (plane, boat)0.1 - 1 mGal

Relative Superconducting, Spring

Spring, force balanced accelerometer

Absolute Optical, Atomic Atomic

FG5

i Grav

Micro-g Lacoste

(MGS-6)

?

KSS32

iMAR

1 mGal = 10-5 m/s² ~ 1µg

Quantum gravimeter / accelerometer principle

vm

h

⋅=λ

- Measurement of the acceleration of a test mass in free fall

Test mass = gas of cold atoms

- Acceleration measurement technic = atom interferometry

- Matter wave = cold atoms

De Broglie wavelength :

- Matter wave manipulation = atom laser interaction

Light pulse atom interferometry

ab

b

a

a

Lase

r pu

lse

Lase

r pu

lse

Lase

r pu

lse

t

z

b

a

Cloud of cold atoms in free fall submitted to three laser pulses

2

)cos(1 φ−=bP

2Tgk ⋅⋅= rrφ

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0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

α MHZ/s

T T

Atoms detection by fluorescence

Scale factor proportional to T² and thus to the instrument sizeFirst experimental demonstration : 1991

Cold atom accelerometer principle

- Creation of a cloud of cold atoms (106-109 atoms, µK, mm)MOT, Optical molasses, Zeeman selection

- Cloud of cold atoms in free fall

- Acceleration measured by light pulse atom interferometryTwo photon Raman transition

- Detection by fluorescence

Cold atom accelerometer

- Strong points- Absolute measurement, no calibration needed, no drift- Excellent sensitivity- No moveable mechanical parts (low maintenance constraints, high repetition rate)

- Weak points- Experimental complexity: laser, electronics, RF, vacuum chamber- Output signal proportional to the acceleration cosine

� limited acceleration range (50 µg pour T=20ms)- Measurement dead times (cold atoms preparation, detection)- Rotations induces contrast lost

�need a gyro-stabilized platform

Hybridization with a classic accelerometer

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0.9

α MHZ/s

Developments needed on reliability and miniaturization

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Girafe 2 gravimeter

• Sensor head miniaturized (22x32 cm)

• Integration in a gyro-stabilized platform (0,1 mrad)

• Short falling distance (14 mm) T=20ms

• High repetition rate (10 Hz)

• Hybridization with a classical accelerometer (Qflex)

• Static tests (accuracy 0.06 mGal)

• Dynamic tests on motion simulator

motion simulator

Control unit Sensor head

Gyro stabilized platform

Hybridization with classical accelerometer

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Implementation of a robust hybridization algorithm - Continuous estimation of offset and contrast of atom interferometer fringes- Continuous estimation of the bias and the scale factor of the classical accelerometer- Automatic determination of the atom interrogation time

100 ms

40 mst

Deadtimemeas.

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α MHZ/s

Accélération (U.A.)

Sig

nal d

e l'a

cc. a

tom

ique

S. Merlet et al., « Operating an atom interferometer beyond its linear range », Metrologia, vol. 46, p. 87, 2009.J. Lautier et al., « Hybridizing matter-wave and classical accelerometers », Appl. Phys. Lett., vol. 105, p. 144102, 2014

Marine and airborne campaigns

Oct. 2015, Jan. 2016 : First marine campaign (Shom, DGA)First marine absolute gravity measurementPrecision : 0,4 - 0,9 mGalY. Bidel et al., Nat. Com. 9, 627 (2018)

April 2017 : Airborne campaign in Iceland (DTU, ESA)First airborne gravity measurement with a quantum sensorPrecision : 1.7 - 3,9 mGalY. Bidel et al., J. of Geodesy 94:20 (2020)

April - Oct. 2018 : Long term marine campaign (Shom)Precision : 0,2 - 0,5 mGal

April, Mai 2019 : Airborne campaign in France (GET, DTU, SHOM, CNES, ESA)Precision : 0.7 - 1.4 mGal

Jan. - Oct. 2020 : Long term marine campaign (Shom)Precision : 0.3 - 0.5 mGal

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1 mGal = 10-5 m/s²

Integration of the atom gravimeter in a boat and a plane

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Marine gravity surveys

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Airborne gravity surveys

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Coastal areas

Mountain areas

Ice cap and volcanoesVatnajökull

Measurement errors estimation

Repeated line over a profile

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Crossing points differences

mGal

Comparison with classic gravimeters

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Estimated precision during the 2019 airborne campaign in France (mGal)

2015-2016 2018 2020

GIRAFE 0.6 0.3 0.4

KSS32 n°1 1.1 0.5 0.6

KSS32 n°2 / / 0.8

GT2M / 0.5 /

Estimated precision over the different marine gravity campaigns (mGal)

Bay of Biscay

Reference profile

Pyrenees

GIRAFE 1.38 0.91 1.08

iMAR 1.44 1.02 1.24

Lacoste & Romberg

/ 2.45 5.6

Measurement stability over the reference profile

GIRAFE

iMAR

L&R

3 times more stable

Comparison with satellite altimetry (Sandwell v24)

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� Strong interest of marine gravimetry for coastal areas

Comparison with ground measurements

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Ground measurement in Iceland

Hybrid electrostatic-atomic accelerometer for space missions

Study of the hybridization between electrostatic and atom accelerometer

- Gravity field retrieval performance simulation- Experimental study of a atom/electrostatic accelerometer

- long term stability improvement of electrostatic accelerometer- rotation compensation with the electrostatic proof mass

- Preliminary design of space accelerometer

Future space geodesy missions need high performance accelerometers

- Electrostatic accelerometers in CHAMP, GRACE, GOCE, GRACE FO, …+ : Short term sensitivity, cont. meas., maturity- : Long term stability, accuracy

- Atom accelerometer+ : Long term stability, accuracy, sensitivity- : Low measurement rate, dead-times, low measurement range

Complementary technologies

ONERA has expertise on both technologies

Experimental demonstration of atom/electrostatic hybridization

Cellule en quartz

Pompe ionique

tube à queusoter

Passages courants getters

Passages courants dispensers

Hublot bridé

Vers pompe ionique 60 l/s

Improvement of low frequency noise of the electrostatic accelerometer

Long term drift of the electrostatic accelerometer corrected by the atom accelerometer

Rotation compensation

- Satellite rotation � contrast loss

Validation of the impact of contrast toatom accelerometer contrast

- Satellite rotation compensation

Proof mass in rotation during atom interrogation� compensation of satellite rotation

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Preliminary design of the atom/electrostatic space accelerometer

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Estimated volume, masse and power consumption of the overall hybrid instrument~ 58 L~ 90 kg~ 145 W

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Conclusion

- Onboard quantum gravimeter - Absolute airborne and shipborne gravimetry demonstrated (classical sensors perform

only relative measurements)

- Better precision than classical sensors

- Reliability of the technology on long term demonstrated (10 month)

- Toward the industrialization of onboard quantum gravimeter (Muquans)

- Preparation of the second generation of onboard quantum gravimeter- Strap down � decrease mass, volume and cost � new carrier (drone)- Improved precision � access to time variable gravity signal

- Quantum accelerometer for space geodesy- Hybridization between atom and electrostatic seems promising for future space geodesy

mission

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Thanks

ONERA, Cold atom inertial sensor teamY. BidelJ. BernardI. PerrinN. ZahzamA. BonninC. BlanchardM. CadoretS. SchwartzA. Bresson

ONERA, Electrostatic accelerometer teamE. HardyP. A. HuynhV. LebatB. Christophe

ShomFrench hydrographic and oceanographic officeD. RouxelM.F. Lequentrec-LalancetteC. SalaunS. LucasG. Delachienne

GET Geosciences Environment Laboratory ToulouseS. BonvalotL. SeoaneG. Gablada

DTU, Technical University of Denmark T.E. JensenA. V. OlesenR. Forsberg

TUM, Technical University of MunichP. AbrykosovR. PailT. Gruber

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