Airborne gamma survey of the Sleisbeck mine area internal report 400 supervising scientist K Pfitzner, B Ryan & P Martin January 2003
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internal
report ���
Aerborne gamma survey
of the S eesbeck mene
area
supervising scientist
Ky Pfrtanery By Ryay&y yMyerfa
yanyeRy 2003
Contents
Plain English summary ii
1 Introduction 1
2 Airborne gamma survey – overview 1
3 Site description 2
4 Image display procedures 4
5 Results 4
6 Discussion 12
7 Conclusions 13
8 Disclaimer requirements 13
9 Appendix – Airborne system including details of the survey parameters, the data preprocessing performed by UTS Geophysics and the received survey data formats 16
References 22
i
Plain English summary A number of small uranium mining and milling operations took place in the 1950s and 1960s in the upper South Alligator River valley area. The sites were abandoned in 1964 with no effort to rehabilitate the effects that mining and milling may have resulted in. A hazard reduction program has since been undertaken. Staff from OSS regularly monitor the abandoned mine sites for erosion and revegetation, which is supplemented with periodic radiological investigations. In May 1997 eriss staff conducted a limited ground-based gamma survey of the Sleisbeck abandoned mine site (the Sleisbeck mine was in the Katherine River catchment – see figure 1). The results and recommendations were subsequently reported in eriss Internal Report 284.
In October 2000, a high resolution (50 m line spacing) airborne gamma survey was flown over the Upper South Alligator River area, funded equally by eriss and Parks Australia North (PAN). This work showed that the airborne gamma survey was particularly useful in providing an overview of radiological issues and highlighting any new radiologically contaminated sites within the area that may not have been identified. The survey also emphasised regions of greater count rates for determining ground-based studies and supported the recommendations of Internal Report 284.
As a result of the upper South Alligator River valley project, eriss and PAN funded another airborne gamma survey, this time over the abandoned Sleisbeck mine. This report describes the initial findings of this Sleisbeck survey.
Because of the small size of the area of interest, a flight line spacing of 25 m and aircraft height of 40 m was chosen for the survey. In other words, the survey was carried out with the aircraft flying along lines only 25 m apart until it covered the area. This is at the limit of current technology, and as a result the spatial resolution (or ‘sharpness’) of the images in this report is unusually high.
The survey results indicated that there are some higher levels of radioactivity in the Sleisbeck survey area. The airborne survey indicated that these areas of higher activity appear confined to the abandoned Sleisbeck mine, probably associated with the pit area and low grade ore overburden dumps. It is recommended that these areas of higher activity indicated by the airborne survey be visited on the ground and field-verified with a ground-based gamma spectrometer. The airborne gamma survey was found to provide an overview of radiological issues around the Sleisbeck mine area, confirmed that the higher levels are confined to historical mining areas, and, highlighted the priority areas for further ground-truthing, should this be required.
This Internal Report should be cited as follows:
Pfitzner K, Ryan B & Martin P 2003. Airborne gamma survey of the Sleisbeck mine area. Internal Report 400, January, Supervising Scientist, Darwin. Unpublished paper.
ii
Airborne gamma survey of the Sleisbeck mine area
K Pfitzner, B Ryan & P Martin
1 Introduction Small uranium mines, a mill, and prospects operated in the upper South Alligator River valley from 1956 to 1964 when contemporary environmental rehabilitation legislation did not exist. When mining ceased, the sites were abandoned with no attempt at rehabilitation for minimisation of environmental impacts. A number of field investigations and a hazard reduction program have occurred since mining ceased. In August 2000, Project 1125 ‘Airborne gamma survey of the upper South Alligator River valley’ (file ref SG2000/0144) commenced in order to provide remotely sensed data and images giving information on the state of abandoned uranium mine sites in the upper South Alligator Valley. The project was designed to provide remotely sensed data, including interpretation, to help Parks North in their planning process for rehabilitation of the abandoned uranium mines in the valley, as well as rehabilitation of tailings in the vicinity of Rockhole Mine Creek. Results of this project are outlined in a number of reports (Pfitzner & Martin 2000, Pfitzner et al 2001a, Pfitzner et al 2001b, and, Bollhöfer et al 2001, Pfitzner & Martin 2002).
The airborne gamma survey of the upper South Alligator River valley area highlighted the higher regions of eU and was found to be a time and cost effective method for providing an overview of radiological anomalies due to historical mining activities in the area, and, in determining the location for ground-based studies. As a result of the upper South Alligator River valley study, another airborne gamma survey was commissioned over the abandoned Sleisbeck mine in 2002. Parks North and eriss jointly funded the acquisition of both the upper South Alligator River valley and Sleisbeck airborne gamma datasets.
This report outlines the preliminary results of the Sleisbeck survey. A brief overview of the airborne gamma survey, including a description of the aircraft and survey equipment, follows. A full description of the survey equipment, raw data formats, and the processing steps undertaken by UTS Geophysics prior to receiving the data, are described in the appendix. Examples of the imagery obtained, particularly for the eU channel of the radiometric data, are illustrated. Finally, because field based validations and further interpretations have not yet been performed, the issue of ancillary information and an appropriate disclaimer to be embedded on images passed on to parties other than eriss are discussed.
Future reports may further detail the radiometric, magnetic and elevation data, and possibly other remotely sensed data sets should they become available, as well as field validations should they be required.
2 Airborne gamma survey – overview
2.1 Acquisition parameters In July 2002, UTS Geophysics conducted a low-level airborne geophysical survey over the abandoned Sleisbeck mine. The survey commenced and was completed on the 30th July 2002. The area surveyed was approximately 125 km south of Jabiru in the Northern Territory.
1
The survey was flown using the AGD84 coordinate system, Universal Transverse Mercator projection, derived from the Australian Geodetic Datum. The survey area was contained within Zone 53 with a central meridian of 135 degrees. The survey coordinates are as follows:
263050 8477960
268850 8475020
267900 8473150
262100 8476090
A subset of the STOW 1: 100 000 topographic map illustrates the survey area (figure 1) in relation to Coronation Hill. Figure 2 highlights the topographic map covering the Sleisbeck survey area, marking the abandoned Sleisbeck mine, the old Sleisbeck airstrip and part of the Katherine River (running through the SE edge of the survey area).
The survey resulted in the collection of airborne radiometric data (eU, eTh, K and Total Count measures), magnetic, and digital elevation data.
The geophysical data was collected along 25 m spaced flight lines, with 250 m tie line spacing. An Exploranium GR820 spectrometer was used, characterised by 48 litre detector volume, with sampling at 1 second. The altitude readings were collected with radar altimeter, at a reported accuracy of 0.3 m, resolution of 0.1 m and sampling rate at 0.1 seconds. A total of 650 line km of data were collected. The appendix outlines the UTS Geophysics Airborne System in detail.
3 Site description Sleisbeck was a minor uranium mine in the valley area, differing markedly from the other mines of the region in that it lies away from the Palette Fault, and is hosted by Kapalga Formation, in a wide variety of lithologies (Stuart-Smith et al 1988).
The Sleisbeck mine workings consist of an open pit approximately 100 m x 30 m in dimensions. A 5 m high wall with exposed uranium mineralisation is located on the eastern side of the pit, which retains water throughout the year. The exposed uranium mineralisation is largely confined to a small (~1.5 m x 4 m) hollow in the wall, and can be reasonably accessed only by boat from the water side. There are three major dumps approximately 100 m to the western side of the pit, which appear to contain overburden and low grade uranium ore. These dumps are ~0.5 m high and are spread over an area ~20 m x ~80 m.
In 1997 a preliminary radiological survey was conducted by eriss at the request of Parks North Australia and Internal Report 284 was produced (Tims & Ryan 1998). The 1997 gamma survey readings from the Sleisbeck Mine workings, including the pit and the three dumps of overburden and low grade ore, are reported in table 4 of this report. Readings were made ~5 m from the pit entrance and along the pit walls. Measurements made along the pit walls were made with the detector tubes mounted vertically, ~1 m from the face of the wall. Background level measurements were made ~1 m above the water surface. All technical details of the instruments and methods used are available in Internal Report 284 (Tims & Ryan 1998).
2
• Coronation Hill
0 5kilometres Sleisbeck survey area
Figure 1 Location of the Sleisbeck survey area
0 1
Airstrip
Katherine River
kilometres N
Figure 2 Topographical subset of the Survey Area
3
4 Image display procedures 4.1 Basic data import and image display All data supplied by UTS Geophysics was in ERMapper format. Further processing was performed in ENVI image processing software. The K, eTh, eU, total count (TC), and digital terrain data was imported into ENVI software as floating point data. Files were then masked to ignore the default null value allowing the collection of image based statistics. The map attributes and image coordinates were then manually entered based on the header information. The files were then reprojected to UTM GDA94 Zone 53.
To aid interpretation, a digital 1:100 000 topographic map covering the Stow Map sheet was acquired. The map sheet was subset to cover the same region as the airborne survey region, rectified and reprojected to UTM GDA94 Zone 53 for correlation with the airborne survey data.
The K, eTh, eU, TC and DEM data were displayed as greyscale images, and as a colour composite K, eTh, eU (RGB). A more detailed analysis of the U channel was performed as it is of prime importance for characterising elevated U levels. The eU channel was displayed as a ‘rainbow colour table’ and contrast stretched to emphasise the higher counts. Basic statistics were generated from the U channel data and used as a threshold into ten class ranges (counts/second) highlighting sources of varying levels of higher counts areas. The ten classes of counts greater than 200 counts/s were used as a threshold and overlaid on the topographic subset in order to allow spatial association with the general land features. Field spectrometer measurements (1997), located in geographic coordinates (AGD66) were converted to UTM GDA94 coordinates so that the field-based locations recorded in 1997 could be spatially associated with the 2002 airborne results.
5 Results Figures 3–6 illustrate the eU, eTh, eK, and, TC images respectively, displayed as grey scale without any data manipulation. Figure 7 illustrates the digital terrain image, displayed as grey scale without any data manipulation. In all cases, the lighter the greyscale tone, the higher the digital number and the darker the grey scale tone, the lower the digital number. Figure 8 illustrates K, eTh and eU as a RGB colour composite.
Figure 9 illustrates the eU channel displayed with a rainbow colour table, where red colours illustrate the highest digital numbers and the lightest shade of blue represents the lowest digital numbers. By applying a contrast stretch (figure 10) to the rainbow colour table, the higher counts/s are emphasised and a greater portion of the scene is represented as blue. Basic statistics were generated from the eU channel data and are outlined in table 2. These values are in counts/s, as supplied by UTS Geophysics.
The range of digital numbers in the eU channel greater than 200 counts/s were used as a threshold into ranges of 200 counts/s. Ten classes resulted, highlighting the sources of varying levels of higher counts. Table 3 illustrates the ranges used in the threshold (counts/s), the colour assigned, and the number of pixels associated with the particular threshold. Figure 11 illustrates these ranges, with counts less than 200 being displayed as grey scale. Counts greater than 200 counts/s at 200 count/s intervals were used as a threshold and overlaid on the topographic subset in order to allow spatial association with the general land features (figure 12). Figure 13 highlights a subset of the higher count intervals with GDA94 map coordinates. Table 4 outlines field-based spectrometer readings recorded in 1997, describing terrestrial gamma dose rates at Sleisbeck mine site (the coordinates obtained from the 1997 survey were reprojected to UTM GDA94). Figure 14 maps the location of these field-based readings with the airborne derived counts displayed over the pit area.
4
Figure 3 Greyscale eU Channel, as received from UTS Geophysics. UTM GDA94 grid has been added, based on digital image coordinates.
Figure 4 Greyscale eTh Channel, as received from UTS Geophysics. UTM GDA94 grid has been added, based on digital image coordinates.
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Figure 5 Greyscale K Channel, as received from UTS Geophysics. UTM GDA94 grid has been added, based on digital image coordinates.
Figure 6 Greyscale Total Count, as received from UTS Geophysics UTM GDA94 grid has been added, based on digital image coordinates.
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Figure 7 Greyscale Digital Terrain, as received from UTS Geophysics. UTM GDA94 grid has been added, based on digital image coordinates.
Figure 8 K, eTh, eU (RGB) colour combination. UTM GDA94 grid has been added, based on digital image coordinates.
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Figure 9 eU Channel – Rainbow Colour Table
Figure 10 eU Channel – Rainbow Colour Table, with contrast stretch
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Table 2 Basic statistics from the U channel (counts per second)
Minimum number Maximum number Mean value Standard Deviation
17 2182.4 34.1 63.2
Table 3 U Channel thresholds associated with figures 9 and 10
Digital Number Range Colour assigned Number of pixels (counts/second)
2000-2183 Red 3
1800-2000 Orange 9
1600-1800 Yellow 48
1400-1600 Green 69
1200-1400 Cyan 88
1000-1200 Blue 112
800-1000 Purple 117
600-800 Magenta 160
400-600 Orchid 263
200-400 Violet 1367
2000-2183 1800-2000 1600-1800 1400-1600 1200-1400 1000-1200 800-1000 600-800 400-600 200-400
Figure 11 U Channel threshold of highest counts/s, with values of less than 200 counts/s displayed as grey scale
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2000-2183 1800-2000 1600-1800 1400-1600 1200-1400 1000-1200
800-1000 600-800 400-600 200-400
Figure 12 Topographical data with eU channel highest counts/s overlaid. The extent of the airborne survey is shown by the black box.
263
500
2637
50
2640
00
2642
50
2645
00
2647
50
2650
00
2652
50
2655
00
2657
50
2660
00
2662
50
8476250
8476000
8475750
8475500
8475250
8475000
2000-2183 1800-2000 1600-1800 Figure 13 Subset over the Sleisbeck pit areas of eU channel counts > 200 counts/s 1400-1600 1200-1400 with GDA94 coordinates 1000-1200 800-1000 600-800 400-600 200-400
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Table 4 Terrestrial gamma dose rate at Sleisbeck mine site, May 1997
Location Coordinates (AGD66) Coordinates (GDA94) Counts·s-1 Dose Rate (µGy·hr -1)
1. Access area to pit S 13° 46.823 ’ E 132° 49.550 ’ 265067.23 8475657.66 5.7 ~0.28
(~5 m from the water)
2. Pit wall hot spot S 13° 46.826 ’ E 132° 49.540 ’ 265049.25 8475651.96 585.6 ~38
(~1 m from the wall)
3. Waste rock stockpile site 1
S 13° 46.864 ’ E 132° 49.516 ’ 265006.62 8475581.49 19.0 ~1.0
4. Waste rock stockpile site 2
S 13° 46.844 ’ E 132° 49.502 ’ 264981.05 8475618.15 12.7 ~0.6
5. Waste rock stockpile site 3
S 13° 46.839 ’ E 132° 49.453 ’ 264892.63 8475626.57 134.6 ~9
6. Waste rock stockpile site 4
S 13° 46.835 ’ E 132° 49.456 ’ 264897.98 8475633.99 23.9 ~1.4
264700 264800 264900 265000 265100 265200 265300
# # # #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
# # # # # # # # # # # 1800-2000 # # # # # # # # # # # # 8475800 8475800 # # # # # # # # # # # # # # 1600-1800
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# # # # # # # # # # # # # # # # # # # # # # # # # # # 600-800 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #♦# # # # # 1 400-600 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # 200-400 # # # # # # # # # # # # # # # # # # # # # # # #♦2 # # # # # # # # # # # # # # # # # #♦6 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # ♦5 ♦4 8475600 8475600 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
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# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # 8475500 8475500 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
8475400 8475400 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
# # # # # # # # # # # # # # # # # # # # # # # # # # # ♦1997 field
# # # # # # # # # # # # # # # # locations
# # # # # # # # 2000-2183
8475300 8475300 # # # # # #
# # #
264700 264800 264900 265000 265100 265200 265300
Figure 14 Subset over the Sleisbeck pit areas (counts > 200 counts/s eU channel) with location of 1997 field-based spectrometer readings
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6 Discussion The eU channel (figure 3) highlighted the historical Sleisbeck mining area as higher count rates. This was also the case for the K channel, but not the eTh channel. This implies that the uranium mineralisation is associated with an elevated potassium content, but not an elevated thorium content.
In all airborne gamma images (figures 3–6), the Katherine River is characterised by low count rates. This is because water absorbs gamma rays, leading to a reduction in the signal received by the detector in the aircraft. Hence the gamma signal will be low where there is freestanding water such as in a river, billabong or pond. In the eTh image, a black area (i.e. low count rates) is located at the Sleisbeck site, and this presumably represents the water body in the pit. This feature is not as obvious in the eU and K channel images, however this is because of the strong eU and K signals from the pit walls and surrounding areas. Since the detector is not collimated, when the aircraft is flying over the water body it is still detecting some gamma rays from the surrounding areas. Nevertheless, in figures 11–14 it can be seen that the eU signal is depressed over the actual pit water body relative to the surrounding areas.
In the eTh channel, small creek channels are relatively high. This implies that the creek sediments have an elevated thorium content, and the higher signal probably shows sediment depositional zones. The RGB image (figure 8) shows these elevated eTh areas as green. Figure 8 shows high regions of eU as blue (surrounding pit area), while pink areas correspond to regions dominated by K with some eTh contribution, white areas are high in all channels, and dark areas (such as the Katherine River) have low count rates in all channels.
An area corresponding to the geological unit ‘Qa’ (silt, sand, gravel and clay) to the NW of the upper reach of the Katherine River shows relatively high count rates. Like the eU channel, the eTh channel (figure 4) highlighted the same ‘Qa’ area to the NW of the upper reach of the Katherine River as high count rates.
The highest counts in the TC image (figure 6) correspond to the Sleisbeck mining areas along with the Qa area to the NW of the upper Reach of the Katherine River (as with the eU and eTh channels).
Figure 9 illustrates the eU channel displayed with a Rainbow colour table, where red colours are greater than yellow, which are greater than green. Dark blue areas correspond to the lower count rates. Essentially figure 9 shows the same information as figure 3 (greyscale), although in colour. Figure 10 displays a contrast stretch image to the Rainbow Colour table that utilises the full dynamic range of the colour display. With the contrast stretch applied, it is clear that the abandoned Sleisbeck area shows the highest count rates. eU count rates range from 17 – 2182 counts/s (table 2). Using 200 counts/s intervals above 200 counts/s of the eU channel highlighted the source of higher count rates (figure 11), which are clearly associated with the abandoned Sleisbeck mine (figures 12 and 13).
The external gamma radiation measurements for the 1997 survey are illustrated in table 4. The following is quoted from Tims and Ryan (1997), and summarises the gamma dose rate measurements at the site:
The gamma radiation dose rate in the over burden dump area is typically <1 µGy·h-1 (1990 survey), slightly above the natural background rate for the region, which is ~0.2-0.5 µGy·h-1. The two low grade ore dumps alongside the over burden give readings that are somewhat higher, typically ~1-2 µGy·h-1; however there are some small, isolated regions present on these dumps which produce recordings of up to 10 µGy·h-1.
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The highest gamma dose rate found at the site was in the hollow part of the vertical wall on the eastern side of the pit, with recordings between 40 and 50 µGy·h-1. Accordingly, count periods of 100 s duration were used at this part of the wall. The dose rate at the surface of the pit water is ~1–2 µGy·h-1 and a pit water sample collected in the 1990 survey was mildly radioactive.
It should be noted that the gamma dose rate measured at the surface of the pit water is not due to the radioactivity in the water. Rather, it is primarily due to the radioactivity in the pit walls.
Figures 10−13 show five areas away from the Sleisbeck pit where there is a somewhat elevated eU signal. It would be prudent to investigate these spots on the ground to determine whether any human activities have given rise to these signals, and hence whether any rehabilitation effort would be desirable.
Figure 14 maps the converted (UTM GDA94) location coordinates obtained during the 1997 field survey on a subset of the airborne gamma survey Sleisbeck pit area (counts > 200 counts/s of the eU channel). It should be noted that these GPS readings were recorded in 1997 when the accuracy of hand-held GPS were much poorer than current signals obtainable, due to random selective interference. Considering this, together with the airborne survey highlighting areas of higher count rates that have not yet been field-verified, it would be useful to revisit the Sleisbeck area and perform ground-based gamma readings over the higher count areas indicated from the airborne survey.
7 Conclusions The airborne gamma data provided synoptic coverage of the Sleisbeck area providing a cost and time effective method for detailing radiological issues over a large area (compared to attempting to characterise the area with ground-based studies alone). The airborne gamma survey of the Sleisbeck area was found to be particularly useful for highlighting regions of higher count rates. The survey results indicated that there are some higher levels of radioactivity in the Sleisbeck survey area. These appear confined primarily to the abandoned Sleisbeck mine pit area, although there are five other sites in the near vicinity with somewhat elevated eU signals. There is no evidence of a strong eU signal leading away from the pit indicating no extensive deposition of eroded mine material detected within the creek systems in the survey area. Rather, the sediments in the creek systems seem to be characterised by an elevated thorium content, this probably being a natural phenomenon.
To determine the exact landform features associated with regions of higher count rates indicated from the airborne gamma survey, ground-based gamma readings at selected locations based on the airborne survey results are recommended, in association with accurate GPS readings.
8 Disclaimer requirements As these data have only recently been received, and because no further interpretations or validations including field work have been performed, it was considered essential to make known the limitations of the survey data until any such validation has been performed. Maps should read ‘Preliminary Results’, accompanied by ancillary information in the bottom right corner. This information may read:
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Radiometrics Spectrometer: Explorium GR-820 Detector Volume: 48 l Flight line Spacing: 25 m Recording Interval: 1.0 second or 25 m Sensor Height: 45 m Survey Date: July 2002 Survey flown by: UTS Geophysics Coordinate System: UTM GDA94 Zone 53
Preliminary results of airborne survey These preliminary data have been provided for information only, and should not be used for the estimation of actual soil concentrations or dose rates at specific locations.
Further interpretations and validations to follow.
Not for publication. Commonwealth of Australia
The information above and within this report should draw the attention of the data receiver to a number of cautionary points. These are summarised below.
• The detector is not collimated to receive counts from a particular direction. The recorded gamma rays may come from any direction. Count rates will be higher where the crystal is closest to the source of counts.
• Flight lines are nominally parallel at 25 m distance from each other, but in practice operational restrictions mean that the aircraft will stray from its intended line.
• The recording interval for each reading was 1 second. In this time the aircraft flies a nominal 25 m along the flight line. However, aircraft speed will vary over the course of the flight.
• The aircraft height is nominally 25 m but the aircraft cannot maintain this height over the whole survey, particularly in hilly country.
• From the above points, it follows that the counts received by the detector will not be from an exact 25 m x 25 m footprint. Rather, the detection efficiency will vary over the nominal footprint, and a proportion of the signal received comes from outside this area. This proportion will vary depending upon the actual aircraft height and geographic location at the time.
• Within a 25 m x 25 m ‘footprint’ area, it may be that a particular area has a much elevated concentration of the radionuclide of interest compared with the average over the rest of the area. If this elevated area does not cover the whole footprint, it should be noted that the count rate recorded in the imagery will be an average of these levels to provide a single digital number. It should also be noted that the raw counts have then been interpolated, and in this case, the smallest element size is 10 m on the imagery. For these reasons, relationships with actual soil concentrations in specific locations should not be used for direct correlation with airborne results.
• Count rates will vary exponentially with the depth of the source below the soil surface.
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• The signal is reduced with increasing soil moisture. The presence of water bodies will reduce the signal dramatically; for example, the presence of the Katherine River may be seen on some of the figures as a line of low count rate (e.g. see figure 9).
• The so-called ‘U’ signal does not in fact represent directly a signal from the element uranium. In general, it can be best thought of as indicating the presence of Ra-226 (radium-226) in the soil (Ra-226 is one of the radioactive progeny of U-238). This point is especially important in the present survey because of the possible presence of uranium mill tailings in the area covered by the survey. It follows that the so-called ‘U’ signal in this survey should not be taken to be a measure of concentrations of the element uranium.
• The detector volume for the radiometrics was a 50 litre crystal, whereas commonly a 33 litre crystal is used for radiometric surveys. The larger crystal was chosen to maximise the counts received.
• Whilst every care is taken to ensure the accuracy of products produced from these surveys, eriss makes no representations or warranties about accuracy, reliability, completeness or suitability for any particular purpose and disclaims all responsibility and liability until such validations and further interpretations are complete.
From these points, it follows that the airborne results should be used only as an indicator of relative differences in count rates averaged over broad areas until ground truthing and further validations and interpretations have been completed.
Nevertheless, the initial preliminary results (see figures 10–14) are encouraging and the authors are confident that these data provide useful information.
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9 Appendix The appendix describes the airborne system including details of the survey parameters (9.1), the data preprocessing performed by UTS Geophysics (9.2), and, the received survey data formats (9.3).
9.1 UTS Geophysics Airborne System The following information was supplied by UTS Geophysics and relates to the system for acquiring detailed airborne, radiometric and digital elevation.
The UTS navigation flight control computer, data acquisition system, and geophysical sensors were installed into a specialised geophysical survey aircraft. The list of geophysical and navigation equipment used for the survey is as follows:
• FU24-954 fixed wing survey aircraft
• UTS flight planning and survey navigation system
• UTS high speed digital data acquisition system
• Novatel 3951R, 12 channel precision navigation GPS
• Satellite transmitted differential GPS correction receiver
• UTS LCD pilot navigation display and external track guidance display
• UTS post mission data verification and processing system
• Bendix King KRA-405 radar altimeter
According to UTS Geophysics, the fixed wing survey aircraft has the following characteristics:
• Cruise speed 105 Kn
• Survey speed 100 Kn
• Stall speed 45 Kn
• Range 970 Km
• Endurance (no reserves) 5.6 hours
• Fuel tank capacity 490 litres
• Engine type Single engine, Lycoming, IO-720
• Fuel type AV-GAS
Magnetic Data Acquisition Equipment, as used by UTS Geophysics, is as follows:
• UTS tail stinger magnetometer installation
• Scintrex Cesium vapour CS-2 total field magnetometer
• Fluxgate three component vector magnetometer
• RMS Aeromagnetic Automatic Digital Compensator (AADC II)
• Diurnal monitoring magnetometer (Scintrex Envimag)
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Radiometric Data Acquisition Equipment, as used by UTS Geophysics, is as follows:
• Exploranium GR-820 gamma ray spectrometer
• Exploranium gamma ray detectors
• Barometric altimeter (height and pressure measurements)
• Temperature and humidity sensor
According to UTS Geophysics, survey data positioning and flight line navigation was derived using real-time differential GPS (Global Positioning System). Navigation was through an electronic pilot navigation system providing computer controlled digital navigation instrumentation mounted in the cockpit as well as an externally mounted track guidance system. GPS derived positions were used to provide both aircraft navigation and survey data location information.
The GPS systems, as used by UTS Geophysics, for the survey were as follows:
• Aircraft GPS model Novatel 3951R
• GPS satellite tracking channels 12 parallel
• Typical differentially corrected accuracy 2-3 m (horizontal) 5-7 m (vertical)
• Real-time differential service RACAL Landstar
Accurate survey heights above the terrain were measured using a King radar altimeter installed in the aircraft. The height of each survey data point was measured by the radar altimeter and stored by the UTS data acquisition system. The altitude acquisition equipment, as used by UTS Geophysics, is as follows:
• Radar altimeter King KRA-405, twin antenna altimeter
• Accuracy 0.3 metres
• Resolution 0.1 metres
• Range 0–500 metres
• Sample rate 0.1 Seconds (10Hz)
The installation platform used for the acquisition of magnetic data was a tail mounted stinger. This stinger system was constructed of carbon fibre and designed for maximum rigidity and stability. Both the total and field magnetometer and three component vector magnetometer were located within the tail stinger. Total field magnetic data readings for the survey were made using a Scrintrex Cesium Vapour CS-2 Magnetometer. This precision sensor, as used by UTS Geophysics, has the following specifications:
• Model Scintrex Cesium Vapour CS-2 magnetometer
• Sample Rate 0.1 seconds (10Hz)
• Resolution 0.001nT
• Operating Range 15 000nT to 100 000nT
• Temperature Range -20°C to +50°C
According to UTS Geophysics, at the start of the survey, the system was calibrated for reduction of magnetic heading error. The heading and manoeuvre effects of the aircraft on the magnetic data were removed using a RMS Automatic Airborne Digital Compensator
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(AADC II). Calibration of the aircraft heading effects were measured by flying a series of pitch, roll and yaw manoeuvres at high altitude while monitoring changes in the three axis magnetometer and the effect on total field readings. A 26 term model of the aircraft magnetic noise covering permanent induced and eddy current fields was determined. These coefficients were then applied to the data collected during the survey in real-time. UTS static compensation techniques were also employed to reduce the initial magnetic effects of the aircraft upon the survey data. According to UTS Geophysics, a base station magnetometer was located in a low gradient area beyond the region of influence by any man made interference to monitor diurnal variations during the survey. The diurnal base station magnetometerwas located 1km north of Jabiru airport for the survey period.
The specifications for the magnetometer, as used by UTS Geophysics, are as follows:
• Model Scintrex Envimag
• Resolution 0.1 nT
• Sampling Interval 5 seconds (0.2Hz)
• Operating range 20 000nT to 90 000nT
• Temperature -20°C to + 50°C
An Air DB barometric altimeter was installed in the aircraft so as to record and monitor barometric height and pressure. The data was recorded at 0.10 second intervals and used for the reduction of the radiometric data. The barometric altimeter acquisition equipment, as used by UTS Geophysics, is as follows:
• Model Air DB barometric altimeter
• Accuracy 2 metres
• Height resolution 0.1 metres
• Height range 0–3500 metres
• Maximum operating pressure 1300 mb
• Pressure resolution 0.01 mb
• Sample rate 10 Hz
Temperature and Humidity measurements were made during the survey at a sample rate of 10Hz. Ambient temperature was measured with a resolution of 0.1 degree Celsius and ambient humidity to a resolution of 0.1 percent.
The gamma ray spectrometer used for the survey was capable of recording 256 channels and was self stabilising in order to minimise spectral drift. The detectors used contain thallium activated sodium iodide crystals. Thorium, cesium and uranium source measurements were made each survey day to monitor system resolution and sensitivity. A calibration line was also flown at the start and end of each survey day to monitor ground moisture levels and system performance. The radiometric data acquisition, as used by UTS Geophysics, is as follows:
• Spectrometer model Exploranium GR820
• Detector volume 48 litres
• Sample rate 1 Hz
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9.1.2 Details of survey parameters The survey data acquisition specifications were with line spacing of 25 m, line direction of 117-297, tie line spacing of 250 m, and, tie line direction of 027-207. The total number of line kilometres of survey data collected over the survey area was 650 km. Sensor height was at 40 m, which, according to UTS Geophysics may vary where topographic relief or laws pertaining to built up areas do not allow this altitude to be maintained, or where the safety of the aircraft and equipment is endangered. table 1 summarises the flight logs for the survey area flown:
Table 9.1 Survey Flight Summary
Flight date Flight No
Survey details Lines Flown Line km Flown
30/07/02 01 Traverse Lines 100010-100700 70 452
02 Traverse Lines 100710-100850, 100140100180
15 98
T1 Tie Lines 190010-190260 26 55
TOTAL 602
9.2 Data processing procedures performed by UTS Geophysics prior to survey data delivery
9.2.1 Magnetic data processing The processing of the raw magnetic data performed by UTS geophysics can be summarised as follows:
• Raw data loaded from field tapes and trimmed to the correct survey boundary extents
• System parallax was removed using corrections measured by the acquisition system
• Diurnal base station data was loaded, checked and suitably filtered for correction of the aircraft magnetic data
• Filtered diurnal measurements were subtracted from the diurnal base field and the residual corrections applied to the survey data by synchronising the diurnal data time and the aircraft survey time
• Regional magnetic gradient was subtracted from the survey data by application of the IGRF model extrapolated to the date of the survey and interpolated on the survey position
• Data corrected to remove any residual parallax errors
• Tie line levelling was applied to the parallax corrected data by measuring tie line crossover points with the survey traverse line data
• Final microlevelling techniques were then applied to the tie line levelled data to remove minor residual variations in profile intensities
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9.2.2 Radiometric data processing The processing of the raw radiometric data performed by UTS geophysics can be summarised as follows:
• Raw data loaded from field tapes and trimmed to the correct survey boundary extents
• System parallax was removed using corrections measured by the acquisition system
• Statistical noise reduction of the 256 channel data was performed using the Maximum Noise Fraction (MNF) method
• Principal component transformation of the noise-whitened data performed
• Signal-rich components were retained and spectral data reconstructed without the noise fraction
• Channels 30-250 only are noise-cleaned, as these contain the regions of interest
• Energy peaks between the potassium and thorium peaks were recalibrated from the noise-cleaned 256 channel measurements
• 256 channel data was windowed to the 5 primary channels of total count, potassium, uranium, thorium, and low-energy uranium
• Dead time corrections applied
• Cosmic and aircraft background corrections applied
• Radon background removal performed using the Minty Spectral Ratio method
• Spectral stripping was applied to the windowed data
• Radar altimeter was corrected to standard temperature and pressure
• Height corrections based on the STP radar altimeter were then performed to remove and altitude variation effects from the data
• Corrected count rate data was then converted to ground concentrations for potassium, thorium and uranium
• Microlevelling of the total count, potassium, thorium and uranium data was applied to remove and minor residual variations in profile intensities
For further information refer to the ‘Logistics Report for a Detailed Airborne Magnetic, Radiometric and Digital Elevation Survey for the Jabiru Project carried out on behalf of eriss by UTS Geophysics, Job #A513’ held in the eriss library. For UTS contact details refer to:
Head Office UTS Geophysics Fauntleroy Avenue, Perth Airport REDCLIFFE WA 6104 Tel: +61 8 9479 4232; Fax: +61 8 9479 7361
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9.3 Survey data received The data received was written to CD and contained magnetics, radiometrics and Digital Terrain data in the following formats:
File Name File Format
a51301k Potassium counts
a5130k.ers Ermapper gridded data header file
A51301r.hdr Radiometric header file
A51301r.ldt Located digital data file
A51301raw_256.dfn Raw 256 channel data
A51301raw_256.ldt Located raw 256 channel data
a51301tc Total count data
a51301tc.ers Ermapper gridded data header file
a51301.th Thorium counts
a51301th.ers Ermapper gridded data header file
a51301u Uranium counts
a51301u.ers Ermapper gridded data header file
a51301m Magnetic data
a51301m.ers Ermapper gridded data header file
a51301m.hdr magnetic header file
a51301m.ldt Located digital data file
a51301dt Digital terrain data
a51301dt.ers Ermapper gridded data header file
a51301dt.hdr Digital terrain header file
a51301dt.ltd Located digital data file
Ermapper gridded data header files information included the following information:
Radiometric data Elevation data
Coordinate System UTM UTM
Projection Type Projection Type AGD84 AGD84
Data Type ieee4bytereal ieee4bytereal
# of lines 521 867
# of pixels 741 1234
Value Counts per second Metres
x dimension 10 m 6 m
y dimension 10 m 6 m
Beginning easting 261795 261797
Beginning northing 8478205 8478199
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References Bollhöfer A, Ryan B, Pfitzner K & Martin P 2002. A radiation dose estimate for visitors of
the South Alligator River Valley from remnants of uranium mining and milling activities. Internal Report 386, Supervising Scientist, Darwin. Unpublished paper.
Pfitzner K & Martin P 2000. Airborne gamma survey of the South Alligator River valley: First report. Internal Report 353, Supervising Scientist, Darwin. Unpublished paper.
Pfitzner K, Martin P & Ryan B 2001a. Airborne gamma survey of the upper South Alligator River valley: Second Report. Internal Report 377, Supervising Scientist, Darwin. Unpublished paper.
Pfitzner K, Ryan B, Bollhöfer & Martin P 2001b. Airborne gamma survey of the upper South Alligator River valley: Third Report. Internal Report 383, Supervising Scientist, Darwin. Unpublished paper.
Pfitzner K & Martin P 2002. Mapping the upper South Alligator River valley area using integrated datasets. Australasian Remote Sensing and Photogrammetric Conference, Brisbane, 2-4th September 2002.
Stuart-Smith P G, Needham RS, & Bagas L 1988. 1:100 000 Geological Map Commentary STOW REGION Northern Territory, Northern Territory Geological Survey. Australian Government Publishing Service, Canberra, pp30.
Tims S & Ryan B 1998. Radiation surveys of El Sherana camp site and Sleisbeck pit and waste rock piles. Internal report 284, Supervising Scientist, Canberra. Unpublished paper.
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