THE ROLE OF LOZA RADAR IN EXPLORATION

Transcription

1 THE ROLE OF LOZA RADAR IN EXPLORATION 25 MINUTES NOVEMBER 2016

2 Georadar development at IZMIRAN and mathematical aspects of subsurface radio probing Introduction LOZA GPR series Applications Spatio-temporal GPR radiation pattern Tomographic inverse problem Conclusion

3 Introduction IZMIRAN is a research institute of Russian Academy of Sciences specialized on: Magnetism of the Earth and planets Solar physics Space plasma physics Ionosphere Radiowave propagation R&D works on ground penetrating radar (GPR, georadar) at IZMIRAN started in early 90ies in frames of planned Mars 94 space mission (not realized). Our engineers, trying to increase the potential-over-weight ratio, developed a novel GPR construction: high voltage spark transmitter discharged upon a resistively loaded dipole antenna, electrically independent receiver being opened by the first coming air wave, direct registration of the subsurface echo waveform. In this way we have obtained a very efficient device combining deep penetration with high pulse quality and signal-to noise ratio.

4 Introduction This construction concept was implemented in LOZA series of commercial GPR produced by a Russian company VNIISMI and is widely used in industrial geology, archeology and civil engineering. Now IZMIRAN continues georadar research developing new GPR models, efficient survey schemes, mathematical theory of subsurface EM wave propagation, and methods of buried object reconstruction. Antenna offset Ground Bedrock Scan step Buried object New analytical solutions have been recently found to the key model problems of subsurface sounding: spatio-temporal radiation pattern of a wide-band line current source placed on the ground-air interface, determination of the antenna current pulse form, and distributed subsurface emitter reconstruction from measured GPR data.

5 LOZA GPR series: main concepts Produced by JSC VNIISMI, Moscow,

6 LOZA-V GPR: technical characteristics nn

7 LOZA-V GPR: applications Penetration test: Railway tunnel (~15 m) Yingshan park, Beijing, 2007 Through-water operation: Lake bottom sediments Solovki archipelago, 2005 Underwater operation: Black sea, 2007 Archeological research Giza, Egipt, 2008

8 LOZA-V GPR: applications Tunguska meteorite,1908 Explosion epicenter Loza-V survey (V. Kopeikin, 2010) Early Soviet expeditions (Suslov, Kulik, ) found underground lenses of pure ice in the event epicenter, which may indicate its comet origin Our GPR survey confirms this hypothesis Transparent ice blocks (confirmed by drilling)

9 LOZA-V GPR: applications Russian-Italian archeological mission, Meroe Island, Sudan (P. Morozov, 2009) N КОМ1. КОМ2. КОМ1 1 Research sites 3D survey Ancient walls found by excavation

10 LOZA-N GPR: low frequency, deep penetration Transmitter Receiver Console Receiver Receiver antenna Resistively loaded dipole antennae are mounted on elastic nylon bands up to 6 m long. Pulse duration is increased to 25 ns. Discharge voltage increased up to 15 kv. Lower characteristic frequency of GPR pulse ensures deeper penetration: Transmitter Transmitter antenna antenna General view of GPR Loza N Main concepts and electronics are basically the same as in LOZA-V. Broad time window and constructive solution make LOZA-N suitable for field operation in geology and industrial works

11 LOZA-N GPR: applications Typical geological section (LOZA-N, Mikkeli, Finland, 2011) Bedrock. Wet sand Karst inspection, (Moscow, 2011) Sand 4 2 Clay 3 Limestone 4 Karst cave

12 LOZA-N GPR: applications Ecology: mazut leakage (Ryazan, 2010) Geology: copper mine (Manto Verde, Chili, 2010) LOZA-N, 10 m antennae (raw data) Copper ore body, 50 m depth

13 LOZA-N GPR: applications Through-water operation, oblique drilling inspection (Pechora river, 2010) break of drilling equipment - alluvio interface - trias sediments - topsoil layers - bowlders-pebbles Spurious multiple reflections

14 Spatio-temporal GPR radiation pattern For GPR data processing we must know EM wave radiated by GPR antenna into subsurface medium. A good mathematical model of dipole antenna is an infinite current line source stretched along ground air interface Radiation of harmonic waves has been studied in a number of classical works sophisticated asymptotic analysis (Sommerfeld, Weil, Fock, Leontovich, Brekhovskikh, et al., ies) air soil 1 n 2 x Ground wave front z Critical TIR angle 1 arcsin n Far field radiation pattern found by Engheta (1984) Physical picture is predicted by geometrical optics (GO): cylindrical EM waves are emitted into air and ground half spaces with different velocities; lateral Cherenkov plane wave binds their wave fronts;; maximum ground wave amplitude expected at critical TIR angle Here, we obtain an exact analytic solution of the radiation problem

15 Model verification Experimental CMP hodographs Numerical simulation Aerial wave Direct subsurface wave Lateral wave Bottom reflected wave Multiple reflections Siberia Summer 2010 LOZA V Moscow river Winter 2010 LOZA N Edt (, ) Simulation reproduces main signal components

16 Direct surface wave Typical GPR scan (lake bottom) Every subsurface feature recurs due to initial pulse oscillation. This correlates with regular strips in upper part of radar image, corresponding to signal propagating directly from transmitter to receiver along the earth surface. To remove the fringes by deconvolution we have to know the initial pulse form

17 Deconvolution algorithm E ( p, x), E ( p) - Raw data Laplace image G ( p, x) Real data processing 0 G p x G ( p) 0 (, ) E( p, x) E 0( p) - Laplace spectrum of virtual GPR scan (unit current step) G ( p) 0 - Green function spectrum: E 0( p) J ( p) G 0( p) E(, (, tx) ) Gtx (, ) Lake bottom GPR scan Cleaned picture

18 GPR scan interpretation Each localized scatterer produces a hyperbola Raw data To visualize them, GPR data are to be focused ( migrated ) term borrowed from seismic exploration time, ns Simple algorithms (since 1960s): displacement, m depth, m Hyperbola summation Ellipse superposition Aerial power line Migrated data Cable

19 Advanced approaches Wave equation migration wave propagation backwards in time (J. Claerbout, 1976) E E E v t x z 0 Solving methods: Exploding reflector concept Finite differences, Parabolic equation (J. Claerbout, 1976) Fourier transform (R. Stolt, 1978)

20 Numerical example round table source Measured field w( x, z) Direct problem Model source gxt (, ) wxz (, ) hxt (, ) mxr (,) Unit current step induced field Semicircle average Reconstructed source

21 Numerical example layered currents w( x, z) model w( x, z) mxr (, ) semicircle average Perfect reconstruction Similar to real GPR scans! reconstruction

22 Conclusion Nearest plans: Equipment: Holographic radar Airborne GPR Survey schemes: GPR positioning Chaotic path y, m Scan path Mathematics: Finite-length antenna Soil conductivity y, m Real depth x, m 3D problem x, m

23 Loza Moves to Africa..?? Receiver Console Donkey, burro Receiver on the Receiving Antenna Transmitter on the Transmitting Antenna

24 200m!! No way! Tx peak voltage / Rx sensitivity Extract from letter to clients

25 21kV!! Is this safe?! Certification: Loza systems are certified to comply with EU Directives on: Electromagnetic Compatibility (Directive 2004/108/EC) and Voltage Limits (Directive 2006/95/EC) Patent: Patented with Trademark office of the Russian Federation, expires April 15 th 2023

26 CONFIGURATION Transmitters: 5kV, 10kV, 21kV, 48kV Antennas: 1m, 1.5m, 3m, 6m, 10m, 15m 1 Console. 0 12m 0 26m 0 50m 0 100m DEPTH RANGE RESOLUTION 0 200m 0 400m

27 Real Time Display Profile Build Up Last shot waveform

28 Processing Display

29 Compatible with

30 3D Integration

31 Loza Radar in Africa (1) DRY (2) GOOD CONTACT WITH THE GROUND (3) SPEED a. 1KM /HR (Manual) b. 2KM / HR (Towed) Next generation Loza can be deployed on faster moving platforms with WiFi!

32 PRODUCT MINERAL TIME REPORT COAL: 20 minutes to collect Processed in minutes. Depth (m) Distance (Scale compressed = vertical exaggeration) Coal/shale Coal Target Sandstone Bedrock Faults

33 CALIBRATING THE RADAR Measurements are made in time (nanoseconds) Conversion to depth is made using wave velocity (cm/ns) The value of wave velocity (V) is usually not known!! V is a function of: 1 dielectric permittivity (ɛ) 2 magnetic permeability (µ) 3 electrical conductivity (σ) 4 frequency of the signal (f) V = V (f, ɛ, µ, σ) A point of reference is required to fix the true depth of geological contacts typically borehole intersections or local outcrop

34 MAPPING KIMBERLITES (with DH Info) Lots of DH references, Radar completes the picture

35 MAPPING KIMBERLITES (with no DH Info) Australian Intrusive Oct 2016

36 ALLUVIAL EASIER NO URGENT REQUIREMENT FOR DH DATA 2250m River 25m 25m 1. Weathered Surface Alluvial Material 2. Second Level Alluvial Material 3. Third Level Alluvial Material 4. Intrusion 5. Bedrock 6. Faults Diamond Exploration: Alluvial Terraces

37 TRACKING ALLUVIAL GRAVEL CHANNELS IN BEDROCK Above & Right: Grid Profiling in Transition Zone Deliverables - 2D mapping slices at differing depths - Requires disciplined lane profiles

38 TRACKING ALLUVIAL GRAVEL CHANNELS IN BEDROCK 4.5m Depth 5.0m Depth 5.7m Depth 6.0m Depth Plan View - changes in bedrock at varying depths

39 ANALYSIS OF A SAND QUARRY FOR ROAD BUILDING Sand and the sand-gravel resources of the quarry were evaluated. With Borehole No. 2, the lack of commercial sand gravel stocks was confirmed. 1: Waveform Mode 2: Derivative waveform mode May 2016 Borehole. 1. Borehole Borehole No. 1 (150 m) No Soil type depth 1 Soil and clay to 4 m 2 White sand, coarse grained 4-15 m 3 Sand gravel mix (36 59% gravel) m 4 Hard elastic clay, green gray from 32 m

40 Water most valuable of all Chile, May 2016 Agua!!

41 Value Proposition Mobility no generators, cables, electrodes, just 4 suitcases and 2 operators Limited logistical support required one vehicle Speed and non intrusive nature of survey Real time assessment immediate adjustment Speed of data analysis within hours Complements ERT IP and Seismic data at useful depths Targeting Drilling Exploration to Drilling Budget Ratio 30/70 to 40/60? Where NOT to Drill rapid condemnation Presentation Product: Communicate to the Board, to Investors

42 Some Clients to date