science fora changing world

Merged Aeroradiometric Data for Alaska:

A Web Site for Distribution of Gridded Data and Plot Files

by

R.W. Saltus, F.E. Riggle, B.T. Clark, and P.L. Hill 

Open-File Report 99-0016

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial Standards. Use of 

brand names is for descriptive purposes and does not constitute endorsement by the U.S. Geological Survey.

1999
Abstract

This report is a listing of the primary information pages in the following 

web site:

http://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-99- 

0016/alaskarad.html

This web site describes the results of a USGS project to merge NURE 

aeroradiometric data into consistent 2-km grids spanning the state of 

Alaska. The website allows users to download (via FTP) data files (in 

several formats) and plot files. The anonymous FTP sites are:

ftp://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-99-0016/data.html

and

ftp://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-99-0016/plots.html

Table of Contents 

Pages Content

cover...... Main page - color figure

1-5......... Map information - text and references

6............ Survey index map - color figure

1.......... Data sources - table

8.......... View maps - color figures

9........... FTP available plot files - explanation page

10-13.... FTP available data files - explanation page
Aeroradiometric Map Background

Information

Table of Contents

1. THE NATIONAL URANIUM RESOURCE EVALUATION

2. NURE AERORADIOMETRIC DATA SPECIFICATIONS

3. DATA PROCESSING

4. UTILITY OF AERORADIOMETRIC DATA

5. REFERENCES

THE NATIONAL URANIUM RESOURCE EVALUATION

The National Uranium Resource Evaluation (NURE) program was conducted by 

the U.S. Government between 1974 and 1983. The NURE program was 

administered by the Grand Junction, CO, office of the Department of Energy. The 

program included airborne gamma-ray spectrometry and magnetic data collection 

as well as extensive geochemical sample collection and processing. 

Aeroradiometric and aeromagnetic surveys of 98 1° by 3° quadrangles were flown 

in Alaska between 1975 and 1980. The data were flown in 15 surveys by Texas 

Instruments (T.I.), Lockwood, Kessler, and Bartlett (LKB), and AeroServices 

(Aero) under contract to the U.S. Government. A series of contractor reports 

document the surveys on a quadrangle by quadrangle basis. We list references to 

these reports on the detailed survey index pages accessible through the Survey Irfo 

page.
NURE AERORADIOMETRIC DATA SPECIFICATIONS

The Alaska NURE aeroradiometric surveys were flown with the following 

specifications:

1. Flight height: 400 ft (122 m) above ground.

2. Flight line spacing: 6 mi (10 km).

3. Direction of flight lines: E-W.

The data were measured using sensors containing 30-50 L of thallium activated 

sodium iodide crystals. The data were processed by the contractors to correct for 

aircraft background contamination, cosmic rays, altitude variations, airborne Bi214, and Compton scattering. The sensors were calibrated using test pads 

maintained at Grand Junction, CO, and Lake Mead, AZ. The data are reported in 

four data channels:

1. Total count (energy between 0.4 and 2.8 MeV).

2. Equivalent Uranium (energy between 1.66 and 1.86 MeV) in ppm.

3. Equivalent Thorium (energy between 2.4 and 2.8 MeV) in ppm.

4. Potassium (energy between 1.37 and 1.57 MeV) in percent (%).

Because of the low flight height (400 ft) and relatively wide data spacing (6 mi), 

less than 4% of the ground surface was actually sampled by the measurements in 

the quadrangles surveyed. The measurements typically sample only the upper 2 ft 

(50 cm) of the Earth (Duval and others. 1971).
DATA PROCESSING

The aeroradiometric grids were produced from the raw NURE radiometric data 

tapes as follows:

1. Data were read and reformatted into a standard line format.

2. Data lines with gaps were identified and renumbered.

3. A 3-point median filter was passed over the data (to remove one-point 

spikes).

4. A Gaussian filter was run over the data (to reduce multi-point noise).

5. Data points exceeding minimum and maximum criteria for each channel 

(uranium, thorium, potassium, and total count) were eliminated.

6. 2.5 km grids were constructed from each data channel using the minimum 

curvature gridding algorithm.

This procedure was performed on 6 blocks spanning Alaska. The resulting grids 

were then merged together to produce the final data grids. As part of the merging 

process datum levels were adjusted between surveys to minimize obvious data 

shifts at survey boundaries. This process does not correct for all the discrepancies 

between the surveys. These differences are particularly noticeable in the 

normalized RGB maps because these maps amplify small variations in the data 

values. Care should be taken when interpreting the patterns on these maps to avoid 

attaching geologic significance to boundaries between surveys.
UTILITY OF AERORADIOMETRIC DATA

In addition to directly sensing surface uranium, radiometric data can be used to 

locate intrusive rocks or to map any rock unit with a distinctive radiometric 

signature. Potassium is commonly found in potash feldspars, microcline, and 

orthoclase or in micas such as muscovite and biotite. Uranium and thorium in 

igneous and metamorphic rocks are usually found in accessory minerals such as 

apatite, sphene and zircon or in the rarer allanite, monazite, pyrochlore, thorite, 

uraninite, and xenotime (Hoover and others. 1992). Uranium tends to be highly 

mobile in the near surface whereas thorium is relatively stable. Uranium is 

chemically active over a broad range of temperature and pH and moves readily in 

the groundwater. Thorium is much less soluble than uranium and potassium and 

does not move except by mechanical means such as wind and erosion processes. 

Both thorium and uranium content tend to be greater in felsic rocks and to also 

increase with alkalinity (Hoover and others, 1992).

The ratio between potassium and thorium is rather constant in most rocks, typically 

varying from 0.17 to 0.2 (K/Th in %/ppm, Hoover and others. 1992). Rocks with 

K/Th ratios significantly outside this usual range have been called potassium or 

thorium specialized (Portnov. 1987). Igneous rocks with potassium specialization 

have been related to gold-silver, silver-polymetallic, molybdenum, and bismuth 

deposits. Thorium specialized rocks are identified with tin, tungsten, rare-earth, 

and rare-metal deposits (Portnov. 1987).

Ternary radioelement maps are a useful way to display uranium, thorium, and 

potassium data (Broome and others. 1987). In many cases, particular rock types 

will have characteristic ratios of the three elements and this type of map display 

can highlight useful geologic trends and patterns. In addition to distinguishing 

lithologic variations, because of the contrasting chemical properties of the 

radioactive elements, radiometric data can provide information relevant to 

understanding of various geochemical and physical processes, including alteration 

and weathering (Duval. 1989). Aerotnagnetic maps provide good complementary 

information for use in geologic interpretations.
REFERENCES

Broome, J., Carson, J.M., Grant, J.A., Ford, K.L., 1987, A modified ternary 

radioelement mapping technique and its application to the south coast of 

Newfoundland: Geological Survey of Canada Paper 87-14, 1 sheet, scale 

1:500,000.

Duval, J.S., 1989, Radioactivity and some of its applications in geology, in 

"Proceedings of the Symposium on the Application of geophysics to 

Engineering and Environmental Problems", SAGEEP 89, March 13-16, 

Golden, Colorado, p. 1-61.

Duval, J.S., Cook, B., and Adams, J.A.S., 1971, Circle of investigation of an 

air-borne gamma-ray spectometer: Journal of Geophysical Research, v. 76, 

n. 35, p. 8466-8470.

Hoover, D.B., Reran, W.D., and Hill, P.L., 1992, The geophysical 

expression of selected mineral deposit models: U.S. Geological Survey 

Open-File report 92-557, 129 p.

Portnov, A.M., 1987, Specialization of rocks toward potassium and thorium 

in relation to mineralization: International Geology Review, v. 29, p. 326- 

344.

Riehle, J.R., Fleming, M.D., Molnia, B.F., Dover, J.H., Kelley, J.S., Miller, 

M.L., Nokleberg, W.J., Plafker, George, and Till, A.B., 1996, Digital 

shaded-re lief image of Alaska: U.S. Geological Survey Map 1-2585, 1 sheet 

plus 11 p. text, scale 1:2,500,000.
^USGS

science fora changing world

Aeroradiometric Survey Index Map

Click on a Survey Number in the map below to zoom in and find out more about that survey.

73' 171' 165' ISff 1S3' 147 141'______________ 78'

Index Map of Alaska

NURE Aeroradiometric

Surveys

Data Contractor

-Texas Instruments

- Aero Service

-LKB

170* 136' 162' JSS 154 130'
Alaska NURE Data Table

ID# Name CO Dates Fit Dir Height LnMi Publication

6007

6008

6016

6017

6018

6019

6020

6023

6024

6025

6026

6035

6036

6037

6121

6169

Copper River

Seward-Selawik

Yukon

Bethel

Nunivak Island

Taylor 

Mountains

Nushagak Bay

Cook Inlet

Eastern Alaska

Chugach-Yakutat

Southeastern 

Alaska

Eagle-Talkeetna

Lime Hills-Lake 

Clark

Dillingham

West-Central 

Alaska

Northern Alaska

T.I.

T.I.

T.I.

T.I.

T.I.

T.I.

T.I.

LKB

LKB

LKB

LKB

T.I.

T.I.

T.I.

Aero

Aero

06/75-07/75

06/75-07/75

05/76-08/76

05/76-08/76

05/76-08/76

05/76-08/76

05/76-08/76

06/76-07/77

07/76-08/76

08/76-08/77

08/76-09/77

06/77-09/77

06/77-09/77

06/77-09/77

07/79-09/79

07/80-08/80

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

6 mi.

E-W

E-W

E-W

E-W

E-W

E-W

E-W

E-W

E-W

E-W

E-W

E-W

E-W

E-W

E-W

E-W

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

400 AG

1950

7630

9700

7700

250

1400

1100

5753

4037

3680

7683

12392

2775

1509

13273

8835

GJO-1653

GJO-1653

GJBr-005(77)

GJBr-005(77)

GJBy-005(77)

GJBr-005(77)

GJBr-005(77)

GJBr- 108(78)

GJBr-091(78)

GJB}"- 127(78)

GJB7-048(79)

GJBr-113(78)

GJB7-113(78)

GJB7-113(78)

GJBX-072(80)+

GJBX-295(81)+

Explanation of columns: ID # = Pat Hill survey index number; Name = survey name; CO = contractor; 

Dates = dates flown; Fit = flightline spacing; Dir = flightline direction; Height = flight height above 

ground (ft); LnMi = approximate number of line miles in survey; Publication = NURE report reference 

(see detailed reference lists on individual survey index pages in this report).
ZUSGS

science fora changing vmtt

Aeroradiometric Map Image Thumbnails

Individual Element Maps:

Thorium (Th) II Uranium (U) II Potassium (K)

Ratio Maps:

Uranium over Thorium II Potassium over Thorium

RGB Composite Maps:

Non-Normalized II Normalized
scbnc» 

uses

for a changing world

Get Plots: File Type Explanation

Rick Saltus 

13 August 1998

The following directory contains binary HPGL format plot files for 

aeroradiometric maps that span the state of Alaska. See the web site 

for a look at the maps and more information. These plot files will plot

on plotters such as the HP750. The resulting maps are about 2 ft x 3 ft. 

The maps are at 1:2,500,000 scale.

These plot files have been compressed using the "gzip" public-domain 

utility. Before plotting these files you will need to uncompress them. 

Information on gzip is available at:

http://www.maths.lancs.ac.uk/~smithdml/GNU/GNUWeb/gzip.html 

(unix and PC DOS versions)

http://www.winzip.com/ 

(PC windows version)

http://www.1source.com/tools/compress.html 

(contains link to download Mac gzip)

Listing of plot files:

1. K - Potassium map draped over topography

2. U - Equivalent uranium map draped over topography

3. Th - Equivalent thorium map draped over topography

4. KdivTh - Potassium/Thorium ratio map draped over topography

5. UdivTh - Uranium/Thorium ratio map draped over topography

6. RGB - Ternary radioelement map

7. RGBnorm - Normalized ternary radioelement map draped over topography
ZUSGS

Get Data: File Type Explanation

Rick Saltus 

13 August 1998

The following directory contains ASCII and binary gridded files for 

the Alaska aeroradiometric data. Each data grid is available 

in four different data formats:

1. GeoSoft GXF format (an ASCII grid transfer format)(nure_*.gxf)

2. ER Mapper grid format (a two-part transfer format)(nure_* & nure_*.ers)

3. ARC/INFO grid export format (a binary format)(nure_*.eOO)

4. USGS ODDF grid format (a binary format)(nure_*.gd)

Each of these formats is discussed briefly below.

If none of these formats are directly readable by software on your 

system, then your best bet is probably to write a program to input 

and translate the GXF format. Extensive description of this format 

is given below.

The data grids in this directory have been compressed using the publicdomain "gzip" compression utility. Information on gzip is available at:

http://www.maths.lancs.ac.uk/~smithdml/GNU/GNUWeb/gzip.html 

(unix and PC DOS versions)

http://www.winzip.com/ 

(PC windows version)

http://www.1source.com/tooIs/compress.html 

(contains link to download Mac gzip)

To avoid file name problems on older PC systems, I have replaced the 

original "." in the filenames with an "_" (underscore) character. 

For example:

original filename: nure_k.eOO

changed to: nure_k_eOO

compressed file name: nure_k_eOO.gz

After you transfer and uncompress the files, you should rename them 

to reolace replace the "_" "with a "." aaain.gin

BASIC GRID STATISTICS (All Grids)

Cell Size = 2000.000 meters Data Type: Floating Point

Number of Rows = 855

Number of Columns = 1110

BOUNDARY 

Xmin = -904000.000 meters

10
Xmax = 

Ymin = 

Ymax =

1316000.000 meters

120000.000 meters

1830000.000 meters

COORDINATE SYSTEM DESCRIPTION

Projection 

Units 

Parameters : 

1st standard parallel 

2nd standard parallel 

central meridian 

latitude of projection's 

false easting (meters) 

false northing (meters)

ALBERS 

METERS

origin

Spheroid

55 

65

-151 

55

0 

0 

0 

0 

0. 

0.

CLARKE1866

0.000 

0.000 

0.00 

0.000 

00000 

00000

1. Grid exchange Format (nure_*.gxf)

GXF (Grid exchange File) is a standard ASCII file format for exchanging 

gridded data among different software systems. Software that supports the GXF 

standard will be able to import properly formatted GXF files and export grids 

in GXF format.

Grid Description:

A grid is a rectangular array of points at which single data values define a 

two dimensional function. Grid point locations are related to a Grid 

Coordinate System (GCS), which is a right handed Cartesian system with X and Y 

axis defined by the bottom and left sides of a grid array. The grid point at 

the bottom, left corner of the array is the origin of the GCS. All distances 

are in meters.

GCS coordinates are related to a Base Coordinate System (BCS) through a plane 

translation and rotation. (For these Alaska grids, the base coordinate system 

is the Albers conical equal-area projection with standard parallels of 55 and 

65 degrees, a base latitude of 55 degrees north, a central meridian of 151 

degrees west, a semi-major axis of ellipsoid of 6378206.400 meters, an 

eccentricity of 0.0067686579973.) The origin of the GCS is located at point 

(xO,yO) in the BCS, and the X and Y grid indices are related to BCS units 

through the separation between points in the GCS X and Y directions.

Labeled Data Objects and Comments

A GXF file is an ASCII file made up of a number of labeled data objects and 

comments. Each labeled data object has a label line followed by one or more 

data lines. A label line is identified by a '#' character in the first column 

followed immediately by an upper-case label. The data associated with that 

label are found on one or more lines that follow the label.

Lines

All lines in a GXF file must be less than or equal to 80 characters in length. 

Any lines that are not part of a labeled data object are ignored and can be 

used to place comments within a GXF file. Programs that read GXF files will 

skip such comment lines while they search for the next GXF data object.

GXF Object Definitions

#TITLE

A one line descriptive title of the grid. Some grid formats include textual

descriptions of the grid, and this information can be placed in a #TITLE

11
object.

Default: blank title

#POINTS

The number of points in each grid row (horizontal or vertical as defined by

the #SENSE object).

Default: no default - this object is required.

#ROWS

The number of rows in the grid. A grid row (or vector) is a collection of

consecutive grid points that represent the grid values along a horizontal or

vertical line in the grid. The complete grid is then defined by a consecutive

sequence of grid rows.

Default: no default - this object is required.

#PTSEPARATION

The separation between points in the grid. This should be in Base Coordinate

System units (ground units for geographically based grids).

Default: 1.0

#RWSEPARATION

The separation between rows in the grid. These should be in Base Coordinate

System units (ground units for geographically based grids).

Default: 1.0

#XORIGIN

The X location of the bottom left corner of the grid in the Base Coordinate

System.

Default: 0.0

#YORIGIN

The Y location of the bottom left corner of the grid in the Base Coordinate

System.

Default: 0.0

#ROTATION

The rotation angle of the grid. This is the counter-clockwise angle of the

bottom edge of the grid with respect to the Base Coordinate System X axis.

Rotation only has meaning for Base Coordinate Systems that use the same units

on the X and Y axis.

Default: 0.0

#SENSE

The first point of the first row of the stored grid can be at any corner of 

the grid rectangle, and the grid rows can be run vertically or horizontally. 

The SENSE object defines this storage sense as follows:

±1 first point at bottom left of grid

±2 first point at upper left of grid

±3 first point at upper right of grid

±4 first point at bottom right of grid

A positive SENSE stores rows in a right-handed sense; a negative SENSE stores 

rows in a left-handed sense. This means that if you were standing at the 

first grid point and looking into the grid, the first grid row would extend to 

your right for a right handed grid (positive sense), or to your left for a 

left handed sense (left-handed grid): 

(All grids on this CD have SENSE=+1.) 

Default: 1 (first point at bottom left, rows left to right)

#TRANSFORM

This keyword is followed by two numbers on the same line: SCALE and OFFSET,

which are used to transform the grid data to desired units:

12
Z = G * SCALE + OFFSET

where

Z grid value in the desired unit

G are grid values as specified in the #GRID object

Default: SCALE =1.0, OFFSET =0.0

#DUMMY

The grid must be rectangular (every row must have the same number of points). 

The dummy value defined by this object is used to define blank areas of the 

grid. Any grids that include blank areas must define a dummy value. 

Default: no dummy value.

#GRID

The grid data is listed point by point and row by row. The #GRID object and

data is always the last object in a GXF file.

The first data point is at the location indicated by #SENSE, and is followed

by successive points in that row of points (either horizontal or vertical),

then the points in the next row, and so on. The points in a row can follow on

to the next data line, although each new row must start on a new data line. A

GXF reading program can expect #ROWS of #POINTS for a total of #ROWS time?

#POINTS data values.

Default: none, must be included as the last object in a GXF file.

2. ER Mapper grid format (nure_k & nure_k.ers)

The ER Mapper grid format consists of two files: a binary data file 

(no file suffix) and a ASCII header file (*.ers). These files can 

be read directly by the ER Mapper software or by other packages such 

as ERDAS IMAGINE. Note that the header files refer to the projection 

called "ALINTAK1". This is not a standard ER Mapper projection. To 

register the grid properly within ER Mapper you must create a projection 

entry that corresponds to the parameters listed above for the projection 

of these data.

3. ARC/INFO Grid Export format (nure_k.eOO)

This format is readable by ARC/INFO, ERDAS IMAGINE, and other packages. 

When imported into ARC/INFO, this file will unpack into a directory 

containing all the components of the registered grid coverage.

4. USGS ODDF binary grid format (nure_k.gd)

This is a binary format with an included ASCII header. This format 

is used by the USGS Geophysics Group within the Minerals Program of 

the Geologic Division.

13