AGL - 2013 Gloucester Airborne Survey

## **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.

Tags: Gloucester subregion, New South Wales, elevation, geoscientificInformation, imageryBaseMapsEarthCover, planningCadastre
Organization: Bioregional Assessment Program