Acoustic Detection Activities in the UK

Status and Future Plans

Lee F. ThompsonUniversity of Sheffield, UK

Acoustic Detection Workshop, Stanford, CA

14th September 2003

ContentsContents• 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

UK groups involvedUK 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 PhysicistsParticle AstrophysicistsJohn McMillan, Terry Sloan,

Lee Thompson, David WatersLancaster, Sheffield, UCL

Electronic EngineersAcoustic Detection

SpecialistsJoe Allen, Richard Binns,

Sean Danaher, Chris RhodesDSTL (MoD), Northumbria

Priorities and proposed Priorities and proposed workwork

• 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

Rona array DAQ upgradeRona 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

Calibrator ideas (I)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

Calibrator Ideas (I)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???)

Calibrator Ideas (II)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?

Event simulation, rates, etc.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

Ideas on signal extractionIdeas 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 andSS3 with additional noise in the < 100Hz frequency

range

Ideas on signal extractionIdeas on signal extraction

• Next fit the Rona noise data spectrum (see figure), optimised such that the transfer function and its inverse are both stable

Ideas on signal extractionIdeas 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)

Ideas on signal extractionIdeas on signal extraction

• Original and Inverse filtered pulse (side)

• Signal plus noise (above)• Matched filter output (side)

ConclusionConclusion ss

• 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