Photographs in soil survey
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.
