1. Acoustic Detection Activities in the UK Status and Future Plans Lee F. Thompson University of Sheffield, UK Acoustic Detection Workshop, Stanford, CA 14th September 2003

2. Contents UK groups involved Facilities available Research interests  Rona  Calibration  Future detectors Recent studies  Acoustic pulse shape simulation and flux predictions (see talk by David Waters, UCL)  Signal processing - the matched filter Future Plans

3. UK groups involved Acoustic detection Use of hydrophones Signal processing Noise reduction Calibration techniques Monte Carlo methods Assessment of potential fluxes First contact (Chris-Lee) January 2003 First meeting of all parties June 2003 Since then - education and proposal writing Particle Physicists Particle Astrophysicists John McMillan, Terry Sloan, Lee Thompson, David Waters Lancaster, Sheffield, UCL Electronic Engineers Acoustic Detection Specialists Joe Allen, Richard Binns, Sean Danaher, Chris Rhodes DSTL (MoD), Northumbria

4. Priorities and proposed work Develop a system to simulate and calibrate the acoustic pulse produced by the interaction of the UHE nuetrinos in water which will be detected by the hydrophones Develop a digital data acquisition system (DAQ) to read out the bipolar pulses from a hydrophone produced by the interactions of UHE neutrinos in water Develop the signal processing techniques to extract these bipolar pulses from the noise to as low an energy as possible Prove the techniques by field studies of the noise from the existing MoD hydrophone array at Rona Study the feasibility for UHE neutrino detection of either a standalone acoustic array or an array in conjunction with existing equipment such as an optical array

5. Rona array DAQ upgrade Rona MoD facility discussed in Chris Rhodes’ talk Does not currently run continuously acquiring data Need to upgrade Rona to facilitate acquisition of ~ 1 month’s worth of data Our current rationale is to write all data to shore for noise studies, etc. Potential system has been identified and costed ADC:  4 (or 16) channels  16 bit  Encoding @ 220kHz Storage:  PC with 4Tb of IDE RAID

6. Calibrator ideas (I) Pulsed light sources  Assume dominant mechanism for energy dissipation is thermal deposition  Assuming in the absence of significant quantities of matter in suspension attenuation is dominated by absorption ==> energy loss appears predominantly as heat  Use wavelength range 550-600nm to give an attenuation coefficient ~0.1m -1  May be possible using a collimated pulsed light beam shining through a 10m column of water and reflected back to the source  Significant fraction of light energy will be absorbed in the water

7. Calibrator Ideas (I) Not perfect in the longitudinal profile of the energy deposition (exponentially decaying) However, the angular spread of the light should be very similar to that expected from the shower (especially in the far field) Suitable light sources include  Pulsed laser  Collimated flash lamp (fast enough???)

8. Calibrator Ideas (II) Acoustic (parametric) system via acoustic transmitter  Drive a suitable hydrophone (e.g. B&K 8105) with a pulse generator system  Choice of either standard omni-directional source or driving 1 or more hydrophones at slightly differing frequencies to simulate the “pancake”  Advantages: standard “off the shelf” technology, well understood  Issues: only reproduces an acoustic pulse, not the entire thermal-acoustic process, how accurate will this calibration method reproduce a real neutrino- induced signal? Does this method work with a broadband pulse?

9. Event simulation, rates, etc. An attempt to understand and reproduce the curves and numbers presented in Lehtinen et. al, Also to place this acoustic detection in context of other HE neutrino detection techniques, e.g. Cerenkov, radio, etc. More information in talk by David Waters

10. Ideas on signal extraction A matched filter for the Rona array Important to understand the spectral form of the noise at the array in order to optimise the performance of the filter Knudsen curves represent different “typical” sea states, Rona is between SS1 and SS3 with additional noise in the < 100Hz frequency range

11. Ideas on signal extraction Next fit the Rona noise data spectrum (see figure), optimised such that the transfer function and its inverse are both stable

12. Ideas on signal extraction Basic method:  Use Gaussian pseudo-random number generator to simulate white noise  Use a digital filter to filter the white noise so that it matches the Rona spectrum  Add the signal  Inverse filter the signal+noise  Pass the result through a matched filter (actually a time reversed copy of the inversely filtered pulse)

13. Ideas on signal extraction Original and Inverse filtered pulse (side) Signal plus noise (above) Matched filter output (side)

14. Conclusions We are new to acoustic detection and still learning! Group of 8 academics and researchers from 4 UK Universities plus the MoD Broad range of skills and interests covering some of the key areas relevant to acoustic detection Immediate plans involve starting some calibrator studies Near future plans (assuming successful funding) will involve  upgrading Rona array  acquiring ~1 month’s worth of data  developing and testing calibrators in quiet lakes and Rona  developing signal processing techniques (e.g. matched filtering)  studies of future array topologies In all these efforts international two-way collaboration would be welcome