1. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Positioning system of the ANTARES Neutrino Telescope Miguel Ardid (IGIC –UPV) on behalf of the ANTARES Collaboration VLVNT’08 – Toulon - April 2008

2. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Contents ANTARES Detector Motivation and Basics for the Positioning system Line Shape Model: –Mechanics –Input and Output Instrumentation: –Compass-Tilmeter System –Acoustic Sytem –Complementary Oceanography Results: –Setting the Local Frame –Acoustic Examples –Comparison Line Model – Acoustics –Comparison Line Model – ADCP Conclusions

3. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Contents ANTARES Detector Motivation and Basics for the Positioning system Line Shape Model: –Mechanics –Input and Output Instrumentation: –Compass-Tilmeter System –Acoustic Sytem –Complementary Oceanography Results: –Acoustic Examples –Comparison Line Model – Acoustics –Comparison Line Model – ADCP Conclusions

4. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope 10 lines + IL deployed, connected and taking data M. Circella’s talk Status of the ANTARES underwater neutrino telescope ~70 m 450 m JunctionBox Interlink cables 40 km to shore 2500m 900 PMTs 12 lines 25 storeys / line 3 PMTs / storey ANTARES Detector (reminder)

5. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Motivation and Basics for the Positioning System A positioning system for the optical modules (OMs) is needed: –Sea currents result on drifts of the top of the strings (and OMs) by several meters –However, muon track reconstruction is based on: precise arrival time of Cherenkov photons to the optical modules (~1 ns) knowledge of the OM position with the corresponding resolution (~20 cm) ANTARES has a positioning system to monitor the position of the OMs continuously. It is based in the reconstruction of the shape of the line from the information of: – High frequency long baseline (LBL) acoustic system: Gives the positions of few hydrophones in the line – Tiltmeters and Compasses: giving the local tilt and heading angles of each storey with optical modules – plus oceanography instrumentation: to determine the sound velocity in sea water and the sea current

6. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Line Shape Model. Mechanics of element j of the line the only unknown is sea current velocity V (Vx, Vy) Inclination of line results from buoyancy P and horizontal force F due to sea current: P = buoyancy – weight F = 1/2  c w A v  j 2 jjj tan  dr/dz Line shape: integration tan    F /   P j=i NN i jj i r(z) = a v z - b v ln[1-cz] 2 2 a, b, c known mechanical constants zenith angle  F P sea current v i i i z r displacement in m height in m Cw j : drag coef. determined by hydrodyn. study of the storey in Ifremer pool

7. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Input: –Positions from hydrophones (5 points along the line) –Tilts and Heading from Compass/Tiltmeter (in each storey, 25 gradients) –Geometrical Constants (cable length, storey parameters etc.) Line Shape Model. Inputs and Outputs Output: –Positions of all Storeys –Storey orientation –Sea current velocity (from the fit)

8. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Instrumentation. Compass-Tilmeter System Integration of Tiltmeter-Compass sensor board in ANTARES electronic containers: –Local measurement of tilts (roll, pitch) and heading of storeys Selected sensor TCM2 by NPI.: –Integrated on a more general instrumental board –RS232 serial link interface, low power consumption (20 mA) –Measurement range : ±20° on 2 tilt axes, 360º on heading –Accuracy : 0.2° in tilt, 1.0° in heading –Compensation of parasitic magnetic fields –Performance, linearity checked at CPPM (good agreement with spec. )

9. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Instrumentation. Acoustic System Positioning is determined using acoustic triangulation between fixed emitters on the sea floor and hydrophones on the lines Distances are obtained from the travel time measurement of the acoustic wave. HF-LBL system characteristics: –Frequency range (40 – 60 kHz) –5 hydrophones per line, (S1, S8, S14, S20, S25) –A transmitter/receiver per line at the BSS (line bottom) + autonomous transponders –Electronic boards for settings, emission, detection, filtering and recording –Full detector positioning obtained every 1-2minutes

10. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Instrumentation. Complementary Oceanography Pressure sensor: –Gives the depth of each line bottom Precision: ±0.01 bar (~ 0.1 m) CTD probe : –Conductivity, temperature, depth used to compute sound velocity Precisions : (±0.01mS/cm, ±0.01 °C, ±0.01 bar) Sound Velocimeter: –direct measurement of sound velocity on a 20 cm basis Precision: ±0.05 m/s Acoustic Doppler Current Profilers (ADCP): –measurement of the sea current velocity Precision: ± 1 cm/s Sound velocity (m/s)

11. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Results. Setting the Local Frame Influence of sea current on fix distances L2→L3 L3→L2average Setting the local frame with fix distances. Distance (m)

12. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Examples of fix distances raw meas. (66 distances, 109 measures) Results. Setting the Local Frame L10 → L5 Pyr4 → L5 L5 → L10 L2 → L10 RMS = 0.4 cm RMS = 0.2 cm All opposite travel measurements agree within 1cm Distance (m)

13. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Results. Setting the Local Frame. 80cm 10cm 100m 400m Setting the local frame: Triangulation ok, but almost in 2D due to planarity of the sea floor –Very sensitive to relative depth of the emitters Accurate relative depth measurement: –Measured with the same sensor pressure with a ROV, and corrections for changes in atmospheric pressure and tides during the operation Checked verticality of the lines at very low sea current Local frame set accurately

14. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Results. Acoustic examples Examples of variation of the vertical distance between the emitter and top receiver on Line 5 compared to sea current:

15. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Results. Acoustic examples Examples of altitude variation on bottom & top Storeys of Line 4 As expected, altitudes show good correlation with higher amplitude variation on top storeys

16. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Results. Acoustic examples Examples of radial displacement on 5 Line 4 hydrophones given by triangulation Origin of the reference frame is the line axis Typically displacement of the line top storeys is of few metres New acoustic data are obtained every minute

17. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Results. Acoustic examples Examples of radial displacement on Line 4 hydrophones given by triangulation Hydrophone displacements followed with few cm accuracy Larger displacements are observed for the top storeys Line movement dominated by East-West heading of the Ligurian current.

18. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Measurements and Results. Examples showing the similar behaviour in the different lines

19. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Results. Comparison Line Model - Acoustics Comparison between hydrophone positions given by Line model and by acoustic triangulation (Feb – June 2007) RMS = 3 cm RMS = 7cm  Y (m) Line 1 Top floor Line 1 Bottom floor 14 m 18 m 14 m 15 days Blue: alignment (no acoustic input) Green: alignment (with acoustic input) Red: acoustic triangulation Y (m) X (m) Hydrophone position Line Model vs. Acoustic directly Hydrophone position Line Model vs. Acoustic directly

20. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Results. Comparison Line Model - ADCP Red: from ADCP Green: from Model (Line 1 fit)) Sea Current Velocity (m/s)

21. VLVNT’08 - ToulonM. Ardid – Positioning System of the ANTARES Neutrino Telescope Conclusions The positioning system (acoustics + tiltmeters) for the 10 lines in operation is functional and within specifications The required spatial reconstruction of 20 cm per OM is achieved The use of independent systems allows cross-checks and to detect and solve possible systematic uncertainties Due to the good performance and flexibility of the positioning system, it provides a good starting point for the design of the positioning calibration system of a cubic kilometre neutrino telescope. Thank you for the attention