# Converting analog interpretive data to digital formats for use in database and GIS applications.

### James G. Flocks

## Key Words: Sediment core description sheet, seismic profile interpretation, digitize, spreadsheet

## Abstract

There is a growing need by researchers and managers for comprehensive
and unified nationwide datasets of scientific data. These datasets must
be in a digital format that is easily accessible using database and GIS
applications, providing the user with access to a wide variety of
current and historical information. Although most data currently being
collected by scientists are already in a digital format, there is still
a large repository of information in the literature and paper archive.
Converting this information into a format accessible by computer
applications is typically very difficult and can result in loss of data.
However, since scientific data are commonly collected in a repetitious,
concise matter (i.e., forms, tables, graphs, etc.), these data can be
recovered digitally by using a conversion process that relates the
position of an attribute in two-dimensional space to the information
that the attribute signifies. For example, if a table contains a certain
piece of information in a specific row and column, then the space that
the row and column occupies becomes an index of that information. An
index key is used to identify the relation between the physical location
of the attribute and the information the attribute contains. The
conversion process can be achieved rapidly, easily and inexpensively
using widely available digitizing and spreadsheet software, and simple
programming code.

In the geological sciences, sedimentary character is commonly
interpreted from geophysical profiles and descriptions of sediment
cores. In the field and laboratory, these interpretations were typically
transcribed to paper. The information from these paper archives is still
relevant and increasingly important to scientists, engineers and
managers to understand geologic processes affecting our environment.
Direct scanning of this information produces a raster facsimile of the
data, which allows it to be linked to the electronic world. But true
integration of the content with database and GIS software as point,
vector or text information is commonly lost. Sediment core descriptions
and interpretation of geophysical profiles are usually portrayed as
lines, curves, symbols and text information. They have vertical and
horizontal dimensions associated with depth, category, time, or
geographic position. These dimensions are displayed in consistent
positions, which can be digitized and converted to a digital format,
such as a spreadsheet. Once this data is in a digital, tabulated form it
can easily be made available to a wide variety of imaging and data
manipulation software for compilation and world-wide dissemination.

## Introduction

In the geological sciences subsurface features are typically
characterized using sediment sampling and geophysical techniques. Data
generated from these techniques, as well as interpretations of the data,
are commonly documented on paper copies. Two examples of paper copies
commonly found in research institutions are sediment core description
sheets and seismic profiles.

Increasingly, such data is both generated and represented in digital
format. The obvious advantage is that the data can then be directly
utilized by computer applications to facilitate interpretation and
accessibility. However, an abundant amount of data is still being
generated or currently exists as archived paper copies. In many cases
generating hard copies of interpretative data is still an important and
practical part of the analytical process. Computer software has replaced
the colored pencil during visual interpretations of seismic profiles,
but transcribing visual descriptions of sediment cores directly into a
computer is not a practical option to standardized paper templates when
working in a core-archive laboratory. Furthermore, paper copies resolve
potential difficulties with incompatible or out-dated computer file
formats when archiving interpretative data. So the need still exists to
convert this data to a digital format; often a difficult task that can
result in loss of data. For example, direct digital scanning of the
paper copies can produce raster facsimiles of the data, but this seldom
provides any quantitative information.

Since a paper copy of any image is essentially a two-dimensional
representation, quantitative representations of digitally scanned paper
copies can be retained if the scans are subsequently referenced in the
two-dimensional plane and this reference is retained in the digital
format. A commonly used example of this method is geo-referenced raster
images of topographic maps. The maps have been digitally scanned and
converted to a format where the constraints of the map (i.e. latitude
and longitude) are retained in the digital file (e.g. GEO-TIFF). This
reference information can then be accessed by GIS applications and
projected over the entire surface of the map. However, vector
information that is visually evident on the original map; roads, rivers,
etc., require further digitization if they are to be used quantitatively
as database layers.

This report presents methods of digitizing paper copies of two specific,
commonly used analog representations of geologic data: core description
sheets and seismic profiles. The reader should be familiar with these
two data formats. Examples of their use can be found widely in coastal
stratigraphic studies (Suter and others, 1991; Kindinger and others,
2001). Digitizing converts the information they contain into
two-dimensional (X,Y) space. Computer programs can then identify the x-y
relationship and extract the associated information as well as
incorporate data that otherwise would be lost during other data entry
methods. The extracted information is then converted to a tabulated
digital format for use in database and GIS applications. Batch mode
processing allows for rapid analysis of numerous sheets or profiles,
thereby increasing the speed at which the data can be converted.

Interpretations of data in geologic applications are commonly expressed
in a consistent format that is familiar to the user and allows for
correlation across various geologic investigations. For example,
description of sediment cores are often rendered to a form sheet that
has various fields necessary to adequately describe most sedimentary
characteristics: texture, physical properties, depositional parameters,
etc. (Fig. 1). In geophysical surveys, persistent amplitude peaks across
a profile may represent stratigraphic boundaries and are commonly mapped
using line drawings directly on the printed profile (Fig. 2). These
paper copies make it easy to produce rapid and direct interpretations of
the geologic data. The hard-copies also provide a stable archive of both
the original data and the interpretations. However, the data is
available only on-hand, and digitization of the data is required not
only to disseminate the information but also to spatially reference the
data so that subsurface interpretations can be mapped. Currently,
digitizing paper copies is not only time-intensive, but is often
selective of the type of data that is retained. For example, information
from core description sheets are often hand-typed into a tabulated
format, where the rows represent depth or thickness of the stratigraphic
unit being described and the columns contain the text from the
description part of the sheet (Fig. 1 (C)). Semi-quantitative
information such as observed sand percentages are not included unless it
is estimated during data entry from the sand-percent curve (Fig. 1 (B))
and included into a column. With seismic profiles, interpretations can
be redrawn using computer applications, but because the profiles are
commonly very long in one dimension, the extent that is redrawn is often
limited. Also, the geographic reference of the profile is seldom
retained.

![](media/image1.png){width="7.677083333333333in"
height="7.798611111111111in"}

Figure 1. Example portion of core description sheet shows how attributes
pertaining to sediment core are described. Data is entered as symbols,
curves or text.

![](media/image2.png){width="7.6097222222222225in" height="5.89375in"}

Figure 2. Example of a seismic profile with line-drawing
interpretations, illustrating the digitizing process (A, B).
Three-dimensional block diagram of digitized output from multiple line
interpretations (C).

Although core description sheets and analog seismic profiles represent
different kinds of data, they have a common fundamental relation:
two-dimensional representations of data. This does not exclude
three-dimensional information or other attributes such as text
descriptions, it means simply that since they exist on a two dimensional
surface, every attribute can be represented with an x and y distance
from an origin, regardless of the attribute. The x, y position becomes a
place-marker for the attribute, reducing it to a numerical array that
can be reconstructed according to a key that outlines the relation. For
example, a core description sheet may contain a column that represents
the amount of shell material down-core (Fig. 1(A)). Variations in shell
content are represented by filling-in the column semi-quantitatively, so
that more fill in the column represents increased shell content. This
diagram can be expressed as two x-y expressions: the shell percent (x)
versus core depth (y); and the column position (x,y) on the paper. Thus,
even though the shell content on a core description sheet is not
represented numerically, the shell percent relative to core depth can
still be recovered by knowing how far from an origin (i.e. the edge of
the description area) the shell percent column exists.

On paper copies of seismic profile data, the amplitude traces are
overlain by navigational fixes and shot numbers at set intervals (Fig.
2(A)). The distance to these navigational fixes on the paper can be
measured, so that geographic relationships can be tagged to
interpretations on the profile. Likewise, stratigraphic depth can be
calculated relative to the vertical position (y) of the interpretation
on the paper. The following sections describe the processes to convert
these analog formats to digital files. Although mechanically similar,
for clarity the methods for converting analog core description sheets
and seismic profile data will be described separately.

## Methods

### Sediment core description sheets

Direct sampling of the subsurface is the only way to positively identify
geologic characteristics such as stratigraphic horizons, textural
variability or trace element distributions. Sediment sampling is also
used in conjunction with geophysical measurements to ground truth or
confirm the geophysical data, which provides a wider spatial coverage. A
common method to portray the information acquired from sediment cores is
to describe the core-section using specific physical and textural
attributes: sand/silt/clay ratios, massive versus laminated
stratification, etc. These attributes are estimated, or measured, by the
geologist and transcribed onto a form sheet that contains spaces where
the presence and magnitude of each attribute down-core can be displayed
(Fig. 1). The forms also often contain fields where the visual
descriptions of the sediments can be included using commonly accepted
terminology, providing a fairly comprehensive description of the
sediment core. These form sheets, called core description sheets,
provide the basic sedimentologic parameters required to adequately
characterize the geology of a study area, and are fairly consistent
among research institutions. As a result, core descriptions can be
readily utilized for correlations between different data sets and by
different research projects.

A common method for converting core description sheets into a digital
format involves typing the text descriptions into a spreadsheet, with
stratigraphic intervals representing the rows of the spreadsheet. For
example, a sediment core from the marine environment may contain 130
centimeters of gray silt containing shells, burrows and organic material
(Fig. 1(C)). In a spreadsheet this information may be transcribed as one
row containing the stratigraphic interval (0-130cm), a midpoint (65cm)
and the subsequent text descriptions (gray silt with shells\...).
Although converting this information to a spreadsheet has tremendous
potential over the hard copy, a lot of information recorded on the core
description sheet has not been retained. Additionally, the constituents
within the stratigraphic unit are either tied to the unit thickness or
are averaged to a single midpoint, losing the higher resolution
variations recorded in the hard copy. Spreadsheet data for use in GIS
and database applications often contain incremented rows of a constant
value, every centimeter for example. This requires that the data from
the core description sheet be integrated in user specified intervals
(i.e. 1 cm) across the stratigraphic interval, for better correlation
with conventional database structure (Fig. 3).

![](media/image3.png){width="6.551388888888889in"
height="8.315277777777778in"}

Figure 3. Example spreadsheet output after core sheet from Figure 1 has
been digitized. Columns on core description sheet that do not contain
data have been omitted. Various sections of the core are shown, gaps are
represented by black circles. Stratigraphic units are integrated across
user-defined intervals (1 cm). Section (B) shows how the text
description portion is displayed in the output file. Section (C) shows
how the header information is displayed in the output file. Since the
header information pertains to the whole core, output is repeated for
each interval.

### Sediment Cores - Data input

The information on core description sheets can be divided into four
basic formats: symbols, curves, sections (intervals), and text. The
first column in Figure 1 shows sedimentary structures and associated
features represented by standard classification symbols. The "%sand"
column shows examples of curve data, where a line represents percentage
of constituent. The column from left to right indicates increasing
percent range. The "color" column in the figure shows how a section of
the core may be referred to without a quantitative attribute, in this
case the whole core is included as "grey clay to tan sand". This format
is often used in the "samples" section of core description sheet to show
which intervals of core have been sampled for analysis. Finally, the
text on the right side of the figure is a common way to include
observations of stratigraphic units (Fig. 1(C)). The data from the core
description sheets will be digitized and processed according to these
four format types.

The process begins by using a standard digitizer tablet to calibrate the
area being analyzed on the core descriptions sheet (Fig. 4(A)). Software
that receives the signal from the tablet and outputs x,y positions as an
ASCII file is necessary. Similarly, the core description sheets can be
digitized on a computer by first generating raster images of the sheets
and using a digitizing software that outputs x,y positions in ASCII
format. Tablets have been found to be quicker and more comfortable for
the user when doing large batch jobs, however, whether a sheet is
digitized on a tablet or computer screen is not important as long as the
output data is the same. The horizontal (x) direction of the sheet is
arbitrary or could be dependant on the resolution of the tablet. The
vertical (y) direction can be equal to the maximum penetration depth of
the sediment core. This will facilitate processing of the downcore
information without requiring an extra conversion formula. Assuming that
a collection of core description sheets have the same layout, a index
table can be developed by the user that describes the range from an
origin (i.e. the left edge of the core description sheet) that each
attribute column occupies (Fig. 5). Included on this index table is a
keyword of what each column represents, this description is usually at
the top of each column on the core description sheet. The index table
also includes a keyword designating whether the attribute is a curve,
symbol or text; this determines which processing routine will be used.
The actual digitizing process involves reducing the information on the
sheet to x,y values, as shown in Figure 6. Once presence and magnitude
of an attribute has been established, the information can be recorded
versus depth where they occur. For example, if a core description sheet
depicts the presence of shell material from 0 to 130 cm core depth, the
abundance profile of this parameter can be recorded as x and y values
relative to an origin (Fig. 4(B)). Data that is not represented as a
percentage is recorded only by the top and bottom of distribution (Fig.
4(C)). All of the non-text attributes on the sheet can be recorded in
this fashion, converting the text and symbol descriptions requires extra
referencing.

![](media/image4.png){width="6.321527777777778in"
height="5.514583333333333in"}

Figure 4. Expanded section of core description sheet from figure 1
showing area being digitized (A). Columns are recognized by their
distance (x-value) from origin, vertical dimension (y) is either core
length or depth of core penetration relative to a datum. Curve
attributes are digitized along their outer edge (B). Symbols and text
are digitized according to their distribution (C).

start 0 nodata x-beds

clay 99.808 symbol deformed_beds

silt 128.330 colcurve planar_beds

fine_sand 156.521 colcurve lenticular_beds

med_sand 185.071 colcurve organics

coarse_sand 212.728 colcurve sand

granule 242.172 colcurve burrows

blank 270.846 interval shell_fragments

interval 308.588 curve gray

sand% 365.975 curve tan

silt% 423.359 curve brown

color 461.796 interval black

deformation 488.817 curve

bed_thickness 518.567 curve

%shell 545.433 curve

%organic 574.822 curve

%bioturb 604.764 curve

wavy 631.537 curve

flaser 659.110 curve

lenticular 688.072 curve

cross_bed 714.806 curve

massive_bed 744.359 curve

inclined_bed 772.441 curve

horiz_lam 801.307 curve

blank2 829.705 curve

grain_size 857.333 interval

heavy_minerals 885.636 interval

micro_fossils 914.433 interval

radio 943.770 interval

radio2 972.458 interval

photo 1000.00 interval

text text

Figure 5. Numbers in index table are distance from origin of columns on
the core description sheet. Text attributes are indicated by x-distance
\> 1000. Rightmost column are the attributes listed on the symbol menu
(see Fig. 6(C)).

![](media/image5.png){width="6.448611111111111in"
height="6.268055555555556in"}

Figure 6. Overlay of digitized points (black diamonds) onto the core
description sheet, showing how the information is reduced to points. The
text information on the right-hand side of the sheet is accounted for
using column descriptions and the symbol menu (A), using depth intervals
of the stratigraphic unit (shown as points with dash circles). Digitized
points with dash squares show how symbol data is rendered. Unused
columns can be re-designated to include applicable attributes (B). A
symbol key can be added to digitize commonly used symbols or colors (C).
Columns are delimited by digitizing a point within the column, but above
the top of the sediment core (E).

Typing the text descriptions into a spreadsheet can be a tedious
process. This step can be avoided since most of the relevant information
in the text description can also be described using the other attributes
on the core description sheet. For example, in figure 1(C), the first
130 cm of the core is described as "massive grey silt with abundant
shell and organics". This description can be represented by existing
fields on the core description sheet that reiterate the text statement.
Note that most of the descriptors in the sentence already have columns
on the sheet that reflect downcore presence and magnitude. Thus, the
above description would be digitized as: \"0, 130, massive, grey, silt,
shell, organics\" (Fig. 6(A)). The extent and magnitudes of these
constituents within the unit is already recorded using their respective
profiles. Depth (y) ranges for each text description, commonly
stratigraphic units, is recorded by designating a column on the core
description sheet to be used as depth. When the processing program
detects the x-values for the depth column, it knows that a core depth
interval is being defined. Until a new core depth interval is defined it
will assume that all the text attributes being digitized pertain to that
stratigraphic unit. The program will then loop through the user-defined
intervals and list text attributes repetitively until a new text
description occurs. This will retain the text information with all the
other attributes and force the text descriptions of the core description
sheet to conform to spreadsheet requirements, which most database
applications recognize. Additional fields can be added in specific
locations on the sheet to further capture text information not
represented by columns. For example, note that this core description
sheet does not have fields corresponding to specific sediment colors.
Blank columns or non-used fields can be adopted to include common
descriptors such as "grey", "tan", or "contact" (Fig. 6(B)).
Additionally, a symbol menu can be developed and attached to the sheets
during the digitizing process (Fig. 6(C)). Attaching text descriptors to
the symbol menu, however, should be minimized. The advantage to
restricting text descriptions to existing (and a few extra user defined)
fields on the core description sheets is that the terminology becomes
standardized for all the cores described using the specific core
description form. This way, interpretations from any sediment core
survey that used the specific core sheet shown in figure 6 will have the
same text descriptors, this can increase the correlation potential
between cores even if they are from different projects or were described
by different interpreters. If additional columns are to be used for text
descriptors, their listing is required in the index table (Fig. 5). A
set of index tables can be collected that describe different core
description forms, or modifications to the same form. The user will be
prompted to select the specific index table during the next step of this
process.

### 

### Sediment cores - Recognizing the attributes

At this point the type of data on the form is irrelevant. It is the key
sheet that establishes the link between the digitized values and the
form attributes. Since the key sheet is customized for each style of
core description form, it is not necessary to modify the processing
program when different core description forms are encountered. The key
sheet only picks one x-value for each attribute on the core description
sheet (Fig. 4). However, since the attributes occupy space (i.e.
columns), it is necessary to pick one edge or a midpoint of the
attribute space. In this process, the right edge of the attribute column
describes the x-value of that attribute. So that:

*Attribute = Attribute (x-value) -- Previous attribute (x-value)*

For curves, such as shell percent (Fig. 1(A)), the left edge of the
column equals zero percent presence of attribute and the right edge
equals 100 percent. Thus, the percentage of attribute per core depth
interval can be calculated as:

*Attribute percent (y) = (Attribute (x-value) -- X~n-1~) / (X~n~ --
X~n-1~)*

Where: *Attribute (x-value) = x-value of digitized point*

All of the non-text attributes are digitized as x-y values, the computer
program uses the above formulas and the index table to identify the
attributes by their x-value, calculate percent abundance and output the
values relative to core depth (Fig. 3).

Since the attribute percentages are recorded per user-defined core
interval (y), x-values for each core interval needs to be determined. It
would be very difficult to digitize a point for each y-interval.
Typically points are digitized only where there are inflection points in
the data. For example, if a core contains sand only between 130 and 230
cm core depth, one might digitize the zero percentage above 130 cm, and
then follow the sand percentage curve, digitizing where the curve
deviates from a straight line (Fig. 7(D)). Since these digitized points
do not correspond to any consistent core interval, it is necessary to
interpolate x-values at the core intervals in between digitized values.
This is accomplished by considering the vertical (y) distance between
digitized points and integrating an x-value depending on the x-values at
the digitized points:

*X value (n) = ((X value (dig1) -- X value (dig0)) \* (Y value (n) -- Y
value (dig0)) / (Y value (dig1) -- Y value (dig0))*

Where dig0 and dig1 represent the previous and subsequent digitized
points, respectively, around the core interval for which an x value is
being interpreted. The processing program will perform a rolling loop to
calculate an x value for every down core interval, throughout the length
of the core. This process provides a greater detail of information than
that obtained by constraining the core description to just stratigraphic
units.

![](media/image6.png){width="7.588888888888889in"
height="8.261805555555556in"}

Figure 7. Output-flow of sand percent curve from points digitized from
profile (A), raw x,y digitizer-output values (B), conversion to depth
versus sand percent (C) and resulting sand percent plot (D). Latitudinal
and longitudinal slices through a 3-dimensional model of a 3 km^2^ sand
deposit (E), extending 5 meters below the sea floor. The image was
generated from the digitized and gridded output of the observed sand
percent of 15 sediment cores, integrated at 1 cm intervals.

The attributes can be determined only by comparing the x-value from the
index table to the digitized x-values. This may create a problem if
there is any deviation from the defined columns, say if a point in the
shell percent column is inadvertently digitized slightly left of the
column (i.e. \< 0%), or if there are any distortions between the
facsimilies of the sheets being digitized. This problem can be avoided
by incorporating variable margins to the attribute constraints. The
index table defines where the percent-shell attribute begins and ends on
the core description sheet, but the processing program can apply a
certain amount of leniency to those x-values. As an example, if there is
no shell material between 130cm and 230cm in the core (Fig. 4(B)), the
user may digitize down the zero percent line (left most portion of
shell% column). While doing this, it would be easy to "miss" the line
and digitize a point in the previous column, which on this particular
core description sheet describes bed thickness. The processing program
would then interpret this digitized value to refer to a bed thickness
attribute. However, if the computer program were to incorporate a 'slop'
range about the column constraints, then any point within this range
could be included with the appropriate attribute values. The discrepancy
can then being converted to 0% or 100% depending on which side of the
column it occurred. Alternatively, if each column were clearly
identified at the onset of digitizing, then points beyond the column
range can be set to the range. For example, if the first digitized point
for each column was set squarely in the middle of the column, but out of
the actual core depth range, then this point could be used as an
indicator of which column the subsequent points pertain to (Fig. 6(E)).
Thus, points digitized to the left of the column in this set would be
interpreted as 0% percent and those to the right as 100%. Such
refinements in the program allows for flexibility and improved
efficiency in converting large amounts of data.

### 

### Cores - Further refinements

The processing program prompts the user for the sediment core
identification number and retains it as the output file name. The rest
of the header information (elevation, location, etc.) will need to be
incorporated into the output dataset. This will either be done by hand,
or if this data already exists in a digital file a further processing
step occurs where this file is accessed and the data extracted using a
"find" routine that locates the core identification number. Since this
type of information commonly already exists in a digital format within
metadata or navigation data sets, the information should be compiled for
each sediment core survey into one large spreadsheet for easy access by
the processing program. The end of the spreadsheet table shown in Figure
3 shows how the header data from the core description sheet was included
for each user-defined interval in the output file.

Multiple core description sheets can be digitized at one session. If the
sheets do not each occupy the same physical space on the paper, for
example if the sheets are photocopies and the images move around on the
pages, then a three point calibration will be necessary prior to
digitizing each page. This calibration can be avoided if the area to be
digitized is outlined on a clear plastic overlay. This template can then
be attached to the digitizing tablet and each core description sheet can
be placed under the overlay in the proper position. This template can be
used only in the situation where all of the sheets are pre-printed
original forms; photocopies of an original form may produce distortions
and unreliable results. If this is the case, then three-point
calibrations must be preformed prior to digitizing each core.

Once numerous core description sheets have been digitized, the digital
files can be batch-processed by the processing program to greatly
increase conversion speed. Once the conversions have finished, macro
routines can be called up to graph the output data. This will allow the
user to compare the computed values to the actual core description sheet
(Fig. 7 (A & D)). Finally, the output of the data can be customized to
fit database requirements, such as specific field positions of
attributes within a spreadsheet.

### Seismic profile interpretations

Seismic profiles are commonly used to map stratigraphic horizons across
a study area. These horizons are identified as laterally continuous
amplitude peaks on the profiles. Commonly, the stratigraphy is
represented by delineating these consistent acoustic reflections on the
profile and converting depth of the reflection from two-way travel time
(seconds) to depth (i.e. meters) (Fig. 2). Geographic fixes, tied to the
seismic profile by shot and/or time, are recorded with the data so that
position of the profiles can be determined (Fig. 2(A)). Complex computer
programs allow the geologist to perform this task completely in a
digital format, automatically keeping the interpretations geo-referenced
and computing spatial extents such as unit volumes. However, a large
portion of this data still exists as hard copies. In this case,
stratigraphic interpretation is typically drawn onto the profile, thus
it becomes necessary to convert the interpretations to a digital format
so that they can be geo-referenced, correlated to data from neighboring
profiles, or perform other spatial computations. This can be
accomplished by using a digitizing table to digitize the interpreted
horizons, reducing the data to x-y values that correspond to distance
along the profile and acoustic depth in milliseconds (Fig. 2(B)).

### Seismic profiles -- Data input

Seismic profiles are annotated with navigational fixes that correspond
to geographic positions recorded concurrently by global positioning
systems (GPS). Since these navigation fixes occupy a space on the
profile (Fig. 2(A)) they can be digitized to return an x-value relative
to an origin on the paper. Every point on an interpreted horizon can
then be assigned a geographic position relative to its neighboring time
fixes, as a ratio of the respective x-positions:

*Gx(n) = Gx~TF1~ - (((X~TF1~ - X(n)) / (X~TF1~ - X~TF0~)) \* (Gx~TF1~ -
Gx~TF0~))*

Where:

*Gx = geographic position in the x direction (i.e. longitude)*

*X = x distance on paper*

*TF0, TF1 = neighboring (previous and next, respectively) navigational
fixes about digitized point (n)*

The geographic-y direction (i.e. latitude) is calculated at the same
time using the same equation. The x-values prior to conversion are
arbitrary. The vertical (y) positions on the profiles correspond to
depth in milliseconds, also annotated on the profiles. Since it is
useful for the user to monitor their progress on a computer screen as
they digitize, it is convenient to assign x-values the same physical
dimension as the depth. This distance will be dropped during the
conversion of x-distance to geographical positions, but at the time of
digitizing will keep the x/y ratio close to one, so that the horizons
can be seen on the computer screen rather than some highly skewed
rendering.

Paper copies of seismic profiles are typically rolls or folded volumes
that can be meters in length. Digitizing interpretations on these
profiles are managed by digitizing the interpreted horizons in sections
that occupy the width of the digitizing table. Before each section is
digitized, three points on the paper are referenced and their x, y
values are inserted into the digital file. This referencing later allows
the conversion program to sort the sections based on their x-values and
then align the profiles relative to depth (y), producing continuous
output of values where the interpreted horizons occur.

### 

### Seismic profiles - Converting the interpretations

The process first involves developing a key that correlates the
digitized points to geographic positions. This process is accomplished
by digitizing the time fixes on the profile (Fig. 2(A) green circles).
When the x-values for the time fixes are known, they can be compared to
a navigation file by their time stamp to determine their corresponding
geographic reference. The horizons on the seismic profile are then
digitized, producing distance (x) and depth (y) values (Fig. 8). The
processing program then loops through the navigational time fixes and
gathers the digitized points from the horizons that occur between the
current and previous navigational time fix, based on their respective
distance (x) value (Fig. 2(B)). Using the formula listed above,
geographic positions are then interpolated for every digitized point
between the navigational time fixes. This allows for a very
high-resolution representation of the interpreted horizon that can be
imported into GIS programs for correlation between neighboring seismic
profiles, as well as subsequent gridding of distribution and depth (Fig.
2(C)), or calculating spatial parameters such as isopachs.

![](media/image7.png){width="3.161111111111111in"
height="4.634722222222222in"}

Figure 8. Example of output from digitized seismic profile. First
section (-\>shot01) contains x and y values, respectively, of time fixes
from profile (see Fig. 2(A)). X-values are distance from origin in
arbitrary units, y-values are depth in milliseconds. Next section
(-\>seaf01) begins digitized output of first interpreted line (brown
line in Fig. 2 (B)). Multiple lines can be included in each file and are
indicated by a user-defined attribute name preceded by a \"-\>\".

### 

### Programming

The digitizing program is a commercial product that registers a tablet,
table or computer monitor over a user defined range. To provide the
proper output format, the digitizing software must be able to produces
an ASCII File output of x,y locations. This is a very basic function
that most cartographic or CAD digitizing software packages are capable
of, the least complicated software available is recommended. Consult the
software manual for directions on how to achieve the desired output;
some additional editing may be necessary to produce the format needed by
the processing program. During the development of this process, Didger
©\* software by Golden Software ©\* and Digitize ©\* by Waccom ©\* were
used. If a digitizing tablet is not available, a raster facsimile of the
core description sheet can be digitized directly from the computer
monitor, using specific software that provides x,y coordinates in an
ASCII format. The processing program is necessary to convert the x-y
values generated by the digitizing program to interpreted values as
defined in the index table. The routine is essentially nested loops that
use incremented intervals to cycle through the digitized x-values from
the input files and compare the values to neighboring x-values assigned
to the core description attributes or navigation time stamps. When the
x-values compare, the program assigns the attributes associated with the
key sheet, or geographic fixes associated with the navigation time
stamps to the digitized x value. The y-values correspond to either core
depth or depth in seismic profile, this value is converted to
appropriate distance values (i.e. milliseconds to meters) and carried
through to the output dataset. While the programs are iterating through
their routines, the output data is being generated and written to a
tabulated ASCII file. The output files contain all of the input
information and their corresponding interpolated x-relationships, such
as constituent percentages for the core descriptions (Fig. 3) or
geographic positions of the interpreted stratigraphic horizons (Fig. 8).
These output files are then ready for the next step of data processing
using GIS or database applications.

The processing program to convert the core description sheet data used
for this report was written in Visual Basic as a Microsoft Excel ©
Macro. As such it is transferable across platforms and can run on any
computer that contains Microsoft Excel ©. The macro and directions for
it's use are available as a USGS Open-File report (Flocks, 2004). The
dig_out files need not be Excel spreadsheets, as long as they are
tab-delimited ASCII text files. The format requirements of the dig_out
files can be modified in the conversion program. Output is an Excel
spreadsheet.

The seismic profile processing program was written in FORTRAN, and
requires a FORTRAN compiler to run. However, the equations outlined in
this report are basic arithmetic equations that can be included into any
computing language, the rest of the program is simply file reading and
iteration routines. And as these processing programs are run after the
digitizing procedure, they need not be associated with the digitizing
software. During the use of the digitizing program for seismic
interpretations, the horizon names should be relevant to the interpreted
horizons to avoid confusion during batch processing of multiple files or
lines.

## Acknowledgements

This work is the result of an identified need to convert analog data
into a digital format for use in database applications, specifically
usSEABED, and for regional programs such as the National Marine
Aggregate Resource Assessment. The author would like to acknowledge J.
Kindinger and J. Williams for their persistence in resolving this issue,
and their support and review of this publication. The comments of J.
Reid, C. Jenkins and M. Kulp improved the processing output, and C.
Dreher and N. Ferina were instrumental in the digitizing process. Core
descriptions from the University of New Orleans Department of Geology
and Geophysics were used as templates to generate the processing code
for the down-core digitizing system, A. Peters provided the description
for the sheet used in this paper.

The use of trade, product, and firm names used in this publication are
for descriptive purposes only and in no way imply endorsement by the U.
S. Government. The U.S. Geological Survey prepares this information \"as
is\" for its own purposes and this information may not be suitable for
other purposes. This report has not been reviewed for conformity with U.
S. Geological Survey editorial standards.

## References

Flocks, J., 2004, Directions for converting analog sediment core
description sheets and seismic profile interpretations to digital,
spreadsheet format: USGS Open File Report, *in review*, 17p.

Kindinger, J., Flocks, J., Kulp, M., Penland, S., and Britsch, L, 2001,
Sand resources, regional geology, and coastal processes for the
restoration of the Barataria Barrier shoreline: USGS Open File Report,
01-384, 69 p.

Suter, J., Penland, S., and Ramsey, K., 1991, Nearshore sand resources
of the Mississippi River delta plain: Marsh Island to Sandy Point,
Louisiana Coastal Geology Technical Report, No. 8, 129 p.