9ff9f257-cfa0-4f50-a7e0-ec0c279d45a3 urn:uuid eng UTF-8 nonGeographicDataset nonGeographicDataset 2018-05-31T04:35:30 creation ISO 19115 2016 AGL - 2013 Gloucester Airborne Survey 9ff9f257-cfa0-4f50-a7e0-ec0c279d45a3 ## **Abstract** This dataset and its metadata statement were supplied to the Bioregional Assessment Programme by a third party and are presented here as originally supplied. Collect Magnetic and Radiometric data over the Gloucester Basin in PEL285 - AGL ## **Dataset History** Airborne Survey (Heli). _____________________________________________________________________ Thomson Aviation Pty. Ltd. _______________________________________________________________________________ GEOPHYSICAL SURVEY DATA REPORT _______________________________________________________________________________ Date : 28 July 2013 This readme file describes the equipment and specifications of a geophysical airborne survey conducted by Thomson Aviation Pty. Ltd. The readme also summarises the data processing parameters and procedures used. CLIENT DETAILS --------------- Company Flown by : Thomson Aviation Pty. Ltd Company Processed: Thomson Aviation Pty. Ltd Client : AGL Energy Limited Company Job : Thomson 13018 AIRBORNE SURVEY EQUIPMENT: ------------------------- Aircraft : Bell Jet Ranger Magnetometer : Geometrics G822A Magnetometer Resolution : 0.001 nT Magnetometer Compensation : Post Flight Magnetometer Sample Interval : 0.05 seconds Hz Data Acquisition : GeOZ Model 2010 Spectrometer : Radiation Solutions RS 500 Crystal Size : 16.5 lt downward array Spectrometer Sample Interval : 1 seconds GPS Navigation System : Novatel OEMV-1VBS GPS Receiver AIRBORNE SURVEY SPECIFICATIONS ------------------------------ Area: Gloucester, NSW Flight Line Direction : 090 - 270 degrees Flight Line Separation : 50 metres Tie Line Direction : 180 - 000 degrees Tie Line Separation : 500 metres Terrain Clearance : 35 metres (MTC) Survey flown : June 2013 DATUM and PROJECTION -------------------- Datum : GDA94 Projection : MGA56 RADIOMETRIC PROCESSING PARAMETERS: ---------------------------------------- Tot.Count Potassium Uranium Thorium Height Attn 0.007434 0.009432 0.008428 0.007510 CPS to Eq 29.601 111.508 10.833 5.940 RADIOMETRIC STRIPPING RATIOS: ------------------------------ Alpha = 0.276 a = 0.048 Beta = 0.418 b = 0.003 Gamma = 0.759 g = 0.001 _____________________________________________________________________________________________ DATA PROCESSING : MAGNETIC DATA _____________________________________________________________________________________________ ____________________________________ MAGNETIC PROCESSING FLOW ____________________________________ The final magnetic data processing was performed using the following processing flow: - Aircraft magnetic data QC - Diurnal magnetic data QC - System parallax removal - Diurnal variation removal and addition of the mean diurnal base value - IGRF removal and addition of mean IGRF value. - levelling using polynomial Tie line levelling, - Micro levelling if required - Reduction to the pole. - Gridding using Minimum Curvature algorithm MAGNETIC QUALITY CONTROL ------------------------ The processing of the magnetic data firstly involved the routine quality control in the field of both the aeromagnetic and diurnal data during the acquisition phase. Any data found not meeting the required specifications were reflown. MAGNETIC PARALLAX CORRECTION ---------------------------- The total magnetic intensity aircraft data was firstly corrected for the effects of system parallax. The parallax parameters were determined and checked from the results of opposing test line flights. MAGNETIC DIURNAL CORRECTION --------------------------- The base station magnetometer data was edited and merged into the main database. The aeromagnetic data was corrected for diurnal variations by subtracting the observed magnetic base station deviations. There were no magnetic storms recorded by the diurnal monitoring station during the survey. The mean value was then added back to the data. MAGNETIC IGRF CORRECTION ------------------------ The data was corrected for the regional gradient of the International Geomagnetic Reference Field (IGRF). The IGRF was calculated for every point along the lines with respect to GPS height using the IGRF Model for 2005 with secular variation applied. The mean IGRF value was then added back to the data. MAGNETIC PROFILE LEVELLING -------------------------- The magnetic traverse line data was then statistically levelled from the tie line data using Intrepid polynomial levelling. The steps involved in the tie line levelling were as follows: - A primary tie line was chosen as a reference tie. - All other ties were levelled to this tie line using 1st degree polynomial adjustment. - lines were adjusted individually to minimize crossover differences, using 2nd degree polynomial adjustments. Any residual flight line effects were removed using Intrepid micro levelling techniques and the resultant line data saved as a separate field. MAGNETIC GRIDDING ----------------- The data was gridded to a cell size of 20% of line spacing using a Minimum Curvature algorithm. _____________________________________________________________________________________________ DATA PROCESSING : RADIOMETRIC DATA _____________________________________________________________________________________________ ____________________________________ RADIOMETRIC PROCESSING FLOW ____________________________________ Radiometric data processing consists of the following processing flow: Full spectrum 256 channel Overview: - Noise Adjusted Singular Value Deconvolution (NASVD) noise reduction - Dead Time correction - Energy calibration - Cosmic and Aircraft background Removal. - Radon background Removal - Extraction of IAEA Window data Windowed data processing Overview: - Compton Stripping correction. - Height Attenuation correction using IAEA coefficients. - Gridding The specific processing steps are described below: ____________________________________ 256 CHANNEL PROCESSING ____________________________________ NASVD Noise Reduction: --------------------- Noise-Adjusted Singular Value Decomposition (NASVD) Smoothing. Correction of the radiometric data involved the reduction of the 256 channels of raw gamma spectrometer data using Noise-Adjusted Singular Value Decomposition (NASVD) noise reduction method. The signal to noise ratio of the multi channel spectra can be substantially enhanced using Noise-Adjusted Singular Value Decomposition (NASVD) as described by Hovgaard and Grasty (1997), Schneider (1998) and Minty (1998). This method involves a general linear transformation of groups of spectra (a whole line or flight), using NASVD to compute the different spectral shapes that make up the measured multi-channel spectra. New multi-channel spectra are created by recombining the statistically significant spectral components. Each spectral component contributes an unequal amount to the features observed in the measured multi-channel spectrum, until a point is reached where the spectral components represent only noise. The 1st spectral component is the spectral shape that represents most of the features in the measured multi-channel spectra. The 2nd spectral component represents those features not described by the 1st spectral component, etc. By excluding from the recombination those spectral components that do not represent significant features in the measured multi-channel spectra, the resulting reconstructed multi-channel spectra have a much larger signal to noise ratio than the measured multi-channel spectra. Dead Time Corrections: ---------------------- The raw 256 channel spectra were corrected for spectrometer dead time using the recorded live time and the standard formula. N = n / (1 - t) N = corrected counts in each second; n = all counts processed in each second by the ADC; and t = the recorded dead time Where the live time (L) is recorded, the dead time t is replaced by (1 - L). Energy Calibration: ------------------- Energy calibration was undertaken line by line using a maximum of 3 calibration peaks; and a minimum of 2 calibration peaks dependent upon their clear identification in the spectra. The 3 calibration peaks used were Bi 214 at 0.609 Mev, K-40 at 1.46 Mev and Tl-208 at 2.615 Mev Cosmic and Aircraft Background Correction: ------------------------------------------ Cosmic and aircraft background removal utilised the data recorded from a series of calibration flights over water. These flight produce a normalised cosmic spectra for the system installation, together with a 256ch spectra for the aircraft background. The combined correction is calculated using: N = a + bC, where: N = the combined cosmic and aircraft background in each spectral window; a = the aircraft background in the window C = the cosmic channel count; and b = the cosmic stripping factor for the window. The values of a and b for each window are determined from the calibration flights over the sea. Cosmic coefficients and aircraft background coefficients were derived using INTREPID CAL256 program. Atmospheric Radon: ------------------ The influence of atmospheric radon has been minimised using the spectral ratio method described by Minty (1992). However the effect of radon in the Uranium channel can be considerable; and some effects of the radon are visable in the character of the final processed data. Extraction of Four Standard Windows: ------------------------------------ The fully processed 256 channel spectra were reduced to the four IAEA (1991) standard windows or Regions of Interest (ROI): As given by the following Energy windows and channel numbers: Total Count 0.41 to 2.81 Mev (channels 33 to 238) Potassium 1.37 to 1.57 Mev (channels 116 to 133) Uranium 1.66 to 1.86 Mev (channels 140 to 158) Thorium 2.41 to 2.81 Mev (channels 205 to 238) ____________________________________ WINDOW PROCESSING ____________________________________ Spectral Stripping of Standard Window Data: ------------------------------------------- Corrections for Compton stripping and height attenuation were applied to the windowed data using constants supplied by Radiation Solutions Inc. Due to scattering of gamma rays in the air, the three principle stripping ratios ( Alpha, Beta and Gamma) increase with altitude above the ground: Stripping Ratio Increase at STP per metre Alpha 0.00049 Beta 0.00065 Gamma 0.00069 Following adjustment of the stripping ratios for altitude, the technique for producing the corrected (stripped) count rates in the potassium, uranium and thorium channels (NKC, NUC and NThC) are given by Grasty and Minty (1995) The Compton coefficients for the system are given above: Height Corrections ------------------- The stripped count rates vary exponentially with aircraft altitude. Adjustments for variation in altitude were made using the formula: Nc = No e^ -u(H-h) Where No = uncorrected counts, Nc = count rate normalised to height H, h = measured height above the ground, H = nominal flight height, u = attenuation coefficient for the channel being corrected. Calculation of Effective Height ------------------------------- The Effective Height, which is the aircraft terrain clearance corrected to Standard Temperature and Pressure was determined as follows: - Filtering of the temperature field was applied to remove spikes and smooth out the instrument noise. - Filtering of the barometric pressure field was applied to remove spikes and to smooth out the instrument noise. - Filtering of the radar altimeter was applied to remove spikes, spurious reflections from groups of tree and very narrow gullies and to smooth out the instrument noise. - The formula option in the spread sheet editor was used to combine the terrain clearance, pressure and temperature. h x P x 273 E_height = _____________________ 1013 x (T + 273) Where: E_height= the effective height; h = the observed radar altitude in metres; T = the measured air temperature in degrees C; P = the barometric pressure in millibars. Reduction to Ground Concentrations: ----------------------------------- The fully corrected window data is then converted to effective ground concentrations by dividing by the conversion coefficient to produce the following equivalent concentrations for each element. Total Count : Dose Rate Potassium : Percent Uranium : PPM Thorium : PPM Radiometric gridding --------------------- The data was gridded to a cell size of 20% of line spacing using a Minimum Curvature algorithm. ## **Dataset Citation** AGL (2014) AGL - 2013 Gloucester Airborne Survey. Bioregional Assessment Source Dataset. Viewed 31 May 2018, http://data.bioregionalassessments.gov.au/dataset/5cffc19a-0ff4-402c-824a-88935f70931a. Gloucester subregion New South Wales elevation geoscientificInformation imageryBaseMapsEarthCover planningCadastre AGL - 2013 Gloucester Airborne Survey documentDigital Data File ZIP