SalSA Telecon 10/18/06 1 Attenuation Length Measurement at Cote Blanche Amy Connolly and Abby Goodhue

SalSA Telecon 10/18/06 2 Goals of Second Trip to Cote Blanche Transmit over long distances through solid salt Make measurements at many different distances  Many more measurements can be made with antennas against walls than in boreholes  Drill a few boreholes at places where we made wall measurements to compare results

SalSA Telecon 10/18/06 3 New System Diagram Pockel’s Cell Driver: HV pulses at 125 kW Frequency band filtered on receiving end: MHz 300 MHz

SalSA Telecon 10/18/06 4 Antenna Transmission Transmitting Antenna Rated transmission band in air is MHz Frequency band in salt is lowered and overlaps with band we filtered for ( MHz) Antenna Transmission folded in with FFT of PCD pulse

SalSA Telecon 10/18/06 5 Transmission Map -1500’ Level Transmitting station 27 ft. from the corner Observed signals through up to 270 meters of salt!

SalSA Telecon 10/18/06 6 At Work Underground

SalSA Telecon 10/18/06 7 Preliminary Results from Cote Blanche Took the fourier transform of the signal and binned it in three frequency bins Difference between borehole and wall measurements is similar to the variation between measurements made against the wall at similar locations Do not see a strong frequency dependence

SalSA Telecon 10/18/06 8 Comparison with First Trip On first trip, receiving station was 35 ft. from corner & transmitting stations along a wall (similar setup as first two measurements on this trip) Slope of first trip’s data is consistent with the second data set Note: The points are not normalized to the same scale factor. Only the relative slopes should be considered

SalSA Telecon 10/18/06 9 First Fit Fit only the measurements made after we went around the corner

SalSA Telecon 10/18/06 10 New Model- Fractured Salt Along Walls Fracturing along walls would make the bulk of salt appear more lossy than it actually is Explains additional attenuation seen for measurements made along the north wall Consistent with the data from the first trip Maximum path through “fractured salt” would be just before turning the corner

SalSA Telecon 10/18/06 11 Fit for Depth of Fractured Salt – Work in Progress Use systematic errors of 75%: dominated by variation in borehole and against the wall measurements Shape seems consistent with theory, but the errors are large and there are too few points in crucial region along the wall Theta measured from straight across (radians) ln(v*d), Arbitrary Units

SalSA Telecon 10/18/06 12 Fit for Depth of Fractured Salt – Work in Progress Cont’d Fit is consistent with no fractured region We can possibly include points from the previous Cote Blanche trip We are looking at Hockley data to see if it is consistent with this theory Central value of the attenuation length in solid salt only increases by 20% over our exponential fit (from 25.3 m to 30.1 m)

SalSA Telecon 10/18/06 13 Conclusions From This Measurement Fracture zone near the walls could be lossy  Would be bad for the planar array idea  Need to focus on drilling holes in salt Even deep salt measured seems to have an attenuation length that is too short Contradiction with GPR Measurements?  “ [GPR] transmission in Cote Blanche salt has been better than that in any other mine visited” - Stewart & Unterberger (1976)  They measured signals reflected from 3177 ft., giving a total path length of 6354 ft. of salt Miners have told us that they can drill downward deep (over 50’) “easily” if we want