Photographs
are a significant component of soil survey data collection and documentation.
They can illustrate important things about an individual soil or a soil catena
in soil survey reports, scientific journals, textbooks, and periodicals. They
can be included in any electronic presentation of soil survey data to end
users.
Good
photographs provide records and reference sources of basic soil information.
Taking photographs needs to be planned early in the soil survey.
Features such as buildings, rivers, roads, railroads, lakes, and field boundaries, and many kinds of vegetation can be recognized on aerial photographs and serve as location aids.
Cultural features commonly are the easiest features to recognize
on aerial photos, but they generally do not coincide precisely with differences
in soils, except in areas with significant anthropogenic alteration or human
interference.
Relief
can be perceived by stereoscopic study. Relief features are helpful in locating
many soil boundaries on the map.
Topographic maps also provide insight to relief, slope, and aspect. Relief also identifies many kinds of landforms commonly related to kinds of soil. Many landforms (e.g., terraces, flood plains, sand dunes, kames, and eskers) can be identified and delineated reliably according to their shapes, relative heights, and slopes. Their relationship to streams and other landforms provides additional clues.
The soil scientist must understand geomorphology to take full advantage
of photo interpretation.
Accurate
soil maps cannot be produced solely by interpretation of aerial photographs.
Time and place influence the clues visible on the photographs.
Human
activities have changed patterns of vegetation and confounded their
relationships to soil patterns. The clues must be correlated with soil
attributes and verified in the field.
At
the end of this article, you should be able to understand;
· The
importance of use of photos in soil survey and mapping
· What
aerial photography is all about
· Types
of photographs in soil survey and mapping
Important Facts to Know
·
Photographs are a viable mapping base in soil survey.
·
Aerial Photography provides important clues about kinds of soil from the shape
and color of the surface and the vegetation.
·
The relationships between patterns of soil and patterns of images on
photographs for an area can be determined. These relationships can be used to
predict the location of soil boundaries and the kinds of soil within them.
·
The soil scientist must understand geomorphology to take full advantage of
photo interpretation.
Photographs
Aerial
photographs were used as the mapping base in most soil survey areas in the
United States during the 20th century. Conventional panchromatic (black and
white) photography, color photography, and infrared photography were used for
remote sensing and as base maps for the soil survey.
Information
on the applicability of each type of base map and how the older map products
were used is covered in the 1993 Soil Survey Manual (Soil Survey Staff, 1993).
Even
in the current digital age, the use of aerial photographs remains an effective
means of mapping soils in areas where suitable digital imagery and data layers
or the required skills, resources, or support for digital mapping techniques
are not available.
Aerial photographs are still a viable mapping base in soil survey. They provide important clues about kinds of soil from the shape and color of the surface and the vegetation.
The relationships between
patterns of soil and patterns of images on photographs for an area can be
determined. These relationships can be used to predict the location of soil
boundaries and the kinds of soil within them.
Aerial
photographs using spectral bands not visible to the eye, such as color
infrared, enable subtle differences in plant communities to be observed.
Other spectral bands in the infrared are useful in distinguishing differences in mineralogy and moisture on the soil surface and also have better cloud penetration.
These data must be interpreted by relating the visual pattern on
the photographs to soil characteristics found by inspection on the ground.
Read: Types of Soil: Characteristics and Importance
Contemporary Approach
Digital
imagery has replaced photographs as the mapping base in 21st century soil
survey.
The
ability to overlay multiple imagery resources for comparisons, the ability to
quickly adjust scale, and the use of raster-based soil maps have increased the
speed of delivering soil survey products as well as the variety of products
available.
Customized
soil survey products are enhanced by the choice of background imagery (e.g.,
color imagery and topographic imagery) used to display soil survey information.
Uses of Photos and Imageries
1.
Photographs that include a scale are useful in estimating volume, area, or size
distribution.
2.
The comparison of coarse fragments in a soil against photographs of known
quantities of coarse fragments improves the reliability of estimates.
3.
Similar photographic standards can be used to estimate volume or size of
nodules and concretions, mottles, roots, pores, and rock fragments.
4.
Photographic standards can be used in estimating area or the special
arrangement of surface features and land use.
Equipment for Field Use to obtain good photos
1. A good-quality camera is
important in obtaining high-quality photos
Digital cameras are the general norm today. A digital camera allows the image file, along with its respective metadata, to be stored in a database file system for later use.
The camera needs to provide resolution greater than 8 megapixels (at
least 16 megapixels is preferred) to produce high-quality images. The ability
to vary the aperture and exposure time settings is desirable. Many of the
larger point-and-shoot cameras and 35-mm single-lens reflex digital cameras are
adequate.
2. A tripod is generally
necessary
Especially
at shutter speeds below 1/50 second. It reduces camera movement and enables the
photographer to concentrate on composition and focus. A flash is needed in some
poorly lighted situations or to eliminate shadows.
3. A scale that indicates
horizon depth or thickness is important
A
scale that does not contrast greatly with the soil, such as an unvarnished and
unpainted wood rule or a brown or khaki colored cloth tape that is 5 cm by 2 m
works well. Large black or yellow figures at 50-cm intervals, large ticks at
10-cm intervals, and small ticks at 5- cm intervals complete the scale. A
perfectly vertical scale increases the quality of the photo, in contrast to a
tilted scale.
4. A small spatula, kitchen
fork
Or
narrow-bladed knife is useful in dressing the soil profile. Paint brushes of
various widths and a tire pump can help clean dust from peds. A sprayer can be
used to moisten the profile when necessary before a snapshot is taken.
Photographing Soil Profiles
To
be able to obtain high-quality photographs of soil profiles, careful planning
is essential. The procedure for photographing soil profiles are as follows:
1. Good Exposure to source
of light
A
representative site is selected on a vertical cut face or in an area where a
pit can be dug large enough for adequate lighting of all horizons and for the
camera to be 1.5 to 2.5 m from the profile. The pit or cut face should be
oriented so that the maximum amount of light will strike the prepared face at
the proper angle when photographed. Better images are generally obtained when
the soil profile is either in full sun or full shade. Subtle differences in
soil color are often more apparent on cloudy days than in full sun. Direct exposure
to full sunlight often results in a washed out image.
2. Significant contrast in
structure and colour of horizons
The
profile needs to be properly prepared to bring out significant contrast in
structure and color between the soil horizons. Beginning at the top, fragments
of the soil can be broken off with a spatula, kitchen fork, or small knife to
eliminate digging marks and expose the natural soil structure. Dust and small
fragments can be brushed or blown away. Moistening the whole profile or part of
it with a hand sprayer helps to obtain uniform moisture content and contrast.
3. Capture several shots
varying aperture settings
Every
profile should be photographed three or four times with different aperture
settings, angles of light, and exposure times.
4. Use notes to describe
the profiles and locations clearly
Notes
should be made immediately after each photograph is taken to record location
and date, complete description of the subject, time of day, amount and angle of
light, camera setting, method of preparing the profile, and other facts that
are not evident in the photograph. Besides increasing the ways the photograph
can be used, good notes provide information for improving technique. If
possible, a landscape photograph should accompany the soil profile photograph.
Photographing Landscapes
Landscape
photographs illustrate important relationships between soils and geomorphology,
vegetation, land use as well as management. They should be clear and in sharp
focus and have good contrast. Photographs representative of the area being
mapped are the most useful.
Procedures that will ensure
quality landscape photographing include the following:
1. Lighting: The most important thing in landscape photography is lighting. The best pictures are made at the time of day and during the time of year when the sun lights the scene from the side.
The shadows created by these lighting separate parts of the landscape and give the picture depth. If the sun is at a low angle to the horizon, shadows are generally amplified and give an image more contrast and depth. Photographs taken at midday or with direct front lighting can lack tonal gradation and, therefore, appear flat.
Photographs taken on overcast days can
have the same problem. A small aperture should be used to gain maximum depth of
focus.
2. The photo composition: A good photograph has only one primary point of interest. Objects that clutter the photograph (e.g., utility poles, poorly maintained roads and fences, signs, and vehicles) detract from the main subject.
The point of interest should not be in the center of the photograph. The “rule of thirds” for composition is useful when looking at the scene through the viewfinder.
The image area can be
visualized as divided into thirds both horizontally and vertically. The center
of interest should be one of the four points where these lines intersect.
3.
Sky should make up less than one-third of the image
4.
The camera should be kept level with the horizon.
5.
Landscape photographs should be taken from a variety of angles (e.g., from a
kneeling position, on a ladder, on top of a car or low building, etc.).
Close-up Photography
Many
soil features, such as peds, pores, roots, rock fragments, krotovinas,
redoximorphic features, concretions, and organisms, can be photographed at
close range. The minimum focusing distance for most cameras used in the field
allows small features to be photographed.
Many cameras have a built-in macro focus feature that enables focusing within a few inches. Macro lenses are available for most 35-mm cameras. Close-up attachments for conventional lenses are also available.
As with landscape photography, the
lighting angle is important. Direct front lighting tends to blend texture,
separation, and contrast in the photograph.
Photographing
clay films and other minute soil features requires special equipment and
techniques of photomicrography that are outside the range of this manual.
Metadata
For
each photograph, metadata should be recorded, including:
a. The date of the photo,
b. The geographic location,
c. A description (caption) of what the image is intended to show,
d. And a reference to the map unit(s) and e. soil components of the area.
Read: Kinds of Soil Surveys
Conclusion on Photographs in soil survey
They
can be included in any electronic presentation of soil survey data to end users.
Good photographs provide records and reference sources of basic soil
information. Taking photographs needs to be planned early in the soil survey.
Features such as buildings, rivers, roads, railroads, lakes, and field boundaries, and many kinds of vegetation can be recognized on aerial photographs and serve as location aids.
Cultural features commonly are the easiest features to recognize
on aerial photos, but they generally do not coincide precisely with differences
in soils, except in areas with significant anthropogenic alteration or human
interference.
Digital imagery has replaced photographs as the mapping base in 21st century soil survey. The ability to overlay multiple imagery resources for comparisons, the ability to quickly adjust scale, and the use of raster-based soil maps have increased the speed of delivering soil survey products as well as the variety of products available.
Customized soil survey products are enhanced by the
choice of background imagery (e.g., color imagery and topographic imagery) used
to display soil survey information.
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