{ "schema": "ausmt-station", "version": "0.1", "ausmt_id": "au.tasman-seafloor-1983-84.TP4", "station": "TP4", "survey": "Tasman Project seafloor line 1983-84", "survey_id": "tasman-seafloor-1983-84", "country": "Australia", "organisation": "Australian National University", "location": { "lat": -37.55, "lon": 155.967 }, "data": { "type": "GDS", "n_periods": 14, "period_min_s": 683.994528, "period_max_s": 117028.871022 }, "diagnostics": { "median_relative_error": null, "remote_reference": false, "tipper_available": true, "completeness_smoothness_diagnostic": { "value": null, "basis": "s", "note": "not a quality or geological-value judgement" }, "method": "phase-tensor (Caldwell 2004)", "note": "screening diagnostic, not an interpretation product" }, "processing": { "software": null, "algorithm": null, "remote_reference": false, "remote_site": null, "file_written_by": { "name": null, "version": null }, "note": "Tipper transfer functions minted from Ferguson, I. J. (1988) 'The Tasman\nProject of Seafloor Magnetotelluric Exploration', PhD thesis, The Australian\nNational University, Table A5.1 (Appendix 5). Station positions are Table\n2.1, declinations are Table 6.7, and the calibration correction is the\nthesis's own Addendum of 20 August 1988. Digitisation:\nGDS/inventories/ferguson1988_data.csv (240 rows) and\nGDS/inventories/ferguson1988_stations.csv (20 rows).\n\nWHY THE THESIS AND NOT THE REGISTER: the compilation register's code-2 rows\nare a verbatim copy of this same printed table, so the register inherits the\ntable UNCORRECTED and adds faults of its own. Measured over all six\nstations, the ratio of the register's arrow length to the printed length has\nmedian 1.0005 and no row anywhere near the calibration factor, which is what\nproves the register never applied it. The register also rounds every arrow\nlength to three decimals, losing two significant figures on the small\narrows, and it carries a decimal-place slip at TP5. The thesis is the\nprimary print and is used here.\n\nWHAT THE ARROWS ARE: these are NOT local tippers. Appendix 5 states that\n'the arrows are all calculated using the horizontal magnetic field from CMO\nas the reference horizontal magnetic field', CMO being the Canberra Magnetic\nObservatory near Bungendore, 169 to 640 km from these sites. The relation\nis\nBz(site) = a.Bx(CMO) + b.By(CMO)\nso a and b are INTER-SITE transfer functions. Two consequences a reader\nmust know: magnitudes near or above 1.0 are normal and are not a defect, and\nthe thesis warns that seafloor arrows of this kind 'are difficult to\ninterpret directly, since spatial variations in the arrows are caused by\nspatial variations in both the vertical and the horizontal magnetic fields'.\nThe HMEAS block below declares HX and HY at the site because the EDI format\nhas no way to express a remote horizontal reference for a magnetometer-only\nmeasurement; the horizontal field these transfer functions are referenced to\nis CMO's, not this site's.\n\nCALIBRATION: the Addendum of 20 August 1988 reports an error in the\ncalibration factors for the seafloor (SIO MAG) magnetic field recordings and\ngives the correction factor K = 1.215. Its item 5 reads: 'the length of\nseafloor induction arrows calculated using the magnetic field from CMO as\nthe horizontal reference field should be multiplied by K. Arrows based on\nlocal horizontal magnetic fields are unchanged.' Every row of Table A5.1 is\nCMO-referenced, so every arrow length in this file, real and quadrature\nalike, is the printed length MULTIPLIED BY 1.215. K is a scalar gain on the\nfield, so it scales the length and leaves the azimuth untouched. The\nregister's values, and the published file this supersedes, are the\nuncorrected printed lengths.\n\nFRAME: Table A5.1 prints each arrow twice over, once as a polar pair (length\nand orientation) and once resolved onto a structural frame. The polar pair\nis frame-independent and is what is used here; the resolved columns are not\nwritten. TP4 is printed in both the coastline frame and the Lord Howe Rise\nframe and its polar columns are identical in the two blocks, which is the\nproof.\n\nDECLINATION: the printed orientation is 'the angle clockwise from magnetic\nnorth', while the thesis's own resolution axes are referenced to TRUE north,\nso a rotation is required and the thesis states one was applied: 'in the\ncalculation of the induction arrows a correction for the local declination\n(Table 6.7) was made at each site'. The declination is ADDED,\nazimuth_geographic = azimuth_magnetic + D, with D east positive per the\nthesis's Table 1.2. That direction is not assumed: reconstructing the\nprinted transverse and longitudinal columns from the polar pair over all 240\nrows and both parts, 960 values, agrees to the print precision of 0.001 on\n958 values under +D and on only 41 under -D and 82 under no rotation. The\ntwo failures under +D are defects in the printed source, not in the rule.\n\nCONVENTION: the thesis defines the real arrow at its equation 4.107 as\nC_r = -Re(a).i - Re(b).j\nwith i and j unit vectors to geographic north and east, so a printed length\nR at geographic azimuth A inverts to\nTXR = -R.cos(A) TYR = -R.sin(A)\nwhich is this collection's sign-reversed polar Parkinson convention exactly,\nwith no source-specific flip. The thesis states the physical sense: for a\ngood conductor such as an ocean in a poorly conducting half-space 'the real\ninduction arrow will generally point to the good conductor at land sites, or\naway from the poor conductor at sea-surface sites'. These are deep-water\nsites east of the Australian coast, with resistive continent to the west and\nconductive ocean and oceanic mantle to the east and below, so the real arrow\nmust point OFFSHORE. The thesis gives the coast trend as 25 degrees east of\ntrue north, making the offshore normal 115 degrees true. The best-resolved\nreal arrows point 128, 131, 132 and 134 degrees true at TP8, TP9, TP7 and\nTP6, that is offshore and within 19 degrees of the normal, and never within\n100 degrees of the opposite sense. The lengths also fall off monotonically\nwith distance from the coast. The convention is settled by the thesis's own\ndefinition and confirmed by the physics.\n\nQUADRATURE: the thesis's equation 4.108 prints PLUS signs, C_q = +Im(a).i +\nIm(b).j, and the thesis says why: 'the signs chosen for the quadrature arrow\ndepends on the time-dependence used in the analysis ... for analyses based\non positive time-dependence this result is achieved by choosing the negative\nsigns in 4.108 while for analyses based on a negative time-dependence the\npositive signs should be chosen', and its section 6.5 confirms 'the negative\ntime dependence of spectral terms ... means that the quadrature arrows\n(which are not reversed) should point towards a good electrical conductor'.\nThis file is written under POSITIVE time dependence, the collection's\nconvention, under which the thesis's own rule selects the negative signs.\nSo the quadrature pair takes the same reversal as the real pair,\nTXI = -Q.cos(Aq) TYI = -Q.sin(Aq)\nand the imaginary tipper here is sign-opposite to a literal reading of the\nprinted equation 4.108 while being the identical physical arrow the thesis\nplotted. Reading 4.108 literally, without the time-dependence clause, would\nflip every imaginary tipper value in this file.\n\nVARIANCES: Table A5.1 prints 95 per cent confidence limits on the transfer\nfunctions a and b, in the magnetic north and magnetic east directions; they\nare digitised as conf95_NS and conf95_EW and they carry the same K = 1.215\nscaling by the Addendum's item 7. They are NOT written as TXVAR.EXP and\nTYVAR.EXP. The thesis does not state the relation between its\nF-distribution confidence limit and a standard deviation: its equation 4.161\nstates the bound on the complex error while the text applies it as a\none-dimensional half-width, and the two readings differ by 24 to 39 per cent\nin the variance. The limits are also diagonal in the MAGNETIC frame while\nthe tipper is written in the geographic frame, and the thesis only ASSUMES\nthe real and quadrature errors are equal. A variance built on an\nimplementer's choice of divisor would be a subtler version of the fabricated\nconstant 0.01 that the September 2002 conversion wrote here, so the blocks\nare OMITTED. Reversing this needs one ruling and nothing else: the divisor\n1.96 or sqrt(2.F(4, lambda-4; 0.05)), the degrees of freedom per band being\nprinted in the thesis's Table 6.5.\n\nIMPEDANCE is not written and no electric or remote-reference channel is\ndeclared. The vertical field here is from a seafloor magnetometer; where an\nelectric field instrument was deployed at the same site its data are a\nseparate seafloor magnetotelluric result and are not in this file. Note\nthat the Addendum's item 6 scales those impedances by K to the power -1, not\nby K, so the correction applied here must never be carried across to them.\n\nSUPERSEDES a September 2002 FORTRAN conversion of the register's copy of\nthis table. That conversion truncated coordinates to two decimals, wrote a\nconstant tipper variance of 0.01, wrote hard-coded placeholder impedances\nand Ex/Ey/Rx/Ry channels for a magnetometer-only instrument, copied one\ntemplate header into every file so that all of them claimed the same\nacquirer, date, prospect and location, and declared ORDER=DEC on rows that\nwere not ordered.\n\nCOORDINATES are Table 2.1's, whose note gives the seafloor positions as HMAS\nCook satellite navigation fixes accurate to better than 0.5 km. Kellett\n(1989) prints the same positions independently.\n\nFREQUENCIES are 1/(period in seconds), Table A5.1's period column being in\nhours. Rows are sorted to strictly descending frequency and the ORDER\ndeclaration is verified against the emitted values.\n\nAttribution: Lilley, Filloux, Ferguson, Bindoff and Mulhearn (1989) PEPI 53,\n405-421. The seafloor instruments were developed and built at the Scripps\nInstitution of Oceanography by J. H. Filloux and his team.\n\nFieldwork: the free-fall seafloor magnetometers were deployed and retrieved\nin two Tasman Sea cruises of HMAS COOK over 1983 and 1984. No per-station\nrecording day is recorded in any source on disk, so ACQDATE is absent.\n\nSTATION: TP4, Tasman Sea, seafloor depth 4460 m, instrument SIO seafloor\nmagnetometer + HEF. Table 2.1 position 37.550 S, 155.967 E; Table 6.7\ndeclination 16.2 degrees east, which is the value added to every printed\norientation in this file. The 14 rows are the coastline block of Table A5.1,\n32.508 h down to 0.190 h.\n\nFILENAME: this file is named TP-4660m_14.edi and is published as station\nTP4. The register prints the same FULL_NAME for more than one station in\nthis array, so the filename carries the register STATION_ID as a suffix\nwhile the published identity is the register's SHO code. Take both from the\nidentity map, never one from the other, and never from the depth in the\nname.\n\nIDENTITY: register STATION_ID 14, REFERENCE_CODE 2, thesis site code TP4.\nThis file is published as station au.tasman-seafloor-1983-84.TP4. Dates in\nthis file are ISO 8601.\n\nFRAME: this is the hinge station of the line and Table A5.1 prints it TWICE,\nresolved to the Australian coastline over 14 periods and to the Lord Howe\nRise over 11. The 25 rows are not 25 arrows. The four polar columns are\nidentical between the two blocks at all 11 shared periods, so only the\nresolved components differ. The 14-row coastline block is used, which is\nthe complete period grid and the same grid as the other five stations; the\nLord Howe Rise block would add no arrow and 11 duplicate frequencies.\n\nFILENAME: the register gives this station the same FULL_NAME as TP5,\nTP-4660m, and 4660 m is TP5's depth. Table 2.1 gives this site's depth as\n4460 m. The name is inherited and wrong and is kept exactly as it is,\nbecause the published station id is keyed to it.\n\nDECLINATION: Table 6.7 gives 16.2 degrees for this station and that is the\nvalue used. The register's rows imply 16.3 degrees at every one of the 14\nperiods, so every azimuth in this file is 0.1 degree anticlockwise of the\npublished one, in addition to the calibration factor. The thesis is the\nruled source and its own table is used." }, "distribution": { "edi_available": true, "license": "CC-BY-4.0", "edi_path": "edi/tasman-seafloor-1983-84/TP-4660m_14.edi" }, "provenance": { "pipeline": "ausmt/extract.build_portal", "pipeline_version": "0.2.1", "extractor": "mt_metadata (community canonical)", "software": { "python": "3.12.14", "mt_metadata": "1.0.10", "mth5": "0.6.8" }, "git_commit": "25c90921c42c72bbc5455b4bbdab9137cf8b8e48", "parameters": { "dimensionality": { "beta_per_period_deg": 3.0, "skew_3d_deg": 5.0, "pct_periods_3d_threshold": 40, "ellip_2d_deg": 0.1, "min_rez_row_sine": 0.01, "beta_physical_cap_deg": 15.0, "min_usable_period_frac": 0.5, "skew_aggregation": "median" }, "diagnostic": "completeness/smoothness (median rel error + coverage + smoothness)" }, "generated": "2026-09-09T06:22:47.791693+00:00", "input_file": "TP-4660m_14.edi", "input_sha256": "577f135d747b067684ba57f8c719bcb8331e1468673f8025b9fe0534a43116c6" }, "coordinate_qc": null, "canonical_conditioning": null, "frame": { "evidence": { "branch": "mt", "zrot": null, "trot": null, "rotspec": null, "hmeas_azimuths": { "hx": 0.0, "hy": 90.0 }, "emeas_azimuths": { "ex": null, "ey": null } }, "impedance_rotation_deg_source": null, "tipper_rotation_deg_source": null, "derotated": false, "frame_served": "declared-zero", "declared_azimuth_deg": 0.0, "convention_check": { "verdict": "insufficient", "phs_xy_median_deg": null, "phs_yx_median_deg": null, "n_periods_used": 0, "detail": "only 0 usable period(s) (< 5) — no convention verdict" } }, "resources": [ { "id": "edi", "kind": "transfer_function", "format": "edi", "provenance_role": "source", "representation_role": "original", "path": "edi/tasman-seafloor-1983-84/TP-4660m_14.edi" }, { "id": "mth5", "kind": "transfer_function", "format": "mth5", "provenance_role": "derived", "representation_role": "alternate", "path": "h5/tasman-seafloor-1983-84/TP4.h5" }, { "id": "edi-zip", "kind": "archive", "format": "zip", "path": "bundles/tasman-seafloor-1983-84-edi.zip" }, { "id": "survey-mth5", "kind": "archive", "format": "mth5", "path": "bundles/tasman-seafloor-1983-84-tf.h5" } ] }