Soil reflectance and physiochemical properties of soils (781701)

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By Eric R. Stoner

The general objective is to define quantitatively the relationships between soil reflectance and physiochemical properties of soils of significance to agriculture and engineering.

Additional materials available

Version 1.0 - published on 30 Apr 2015 doi:10.4231/R7QR4V2H - cite this Archived on 25 Oct 2016

Licensed under CC0 1.0 Universal

Description

Objective:

The general objective is to define quantitatively the relationships between soil reflectance and physiochemical properties of soils of significance to agriculture and engineering. Selection of soil samples with a wide rangeof important soil characteristics by statistical stratification of continental United States climatic zones permits the evaluation of climatic and genetic effects on the relationships between multispectral reflectance and these soil properties. A further objective is to define the relationships sufficiently to design further research to quantify the contributions which different soil components make to the multispectral characteristics of specific soils.

Method:

Because of the need to provide a uniform moisture condition for spectroradiometric analysis of the prepared soil samples, a procedure was chosen which creates a one-tenth bar soil moisturetension on all the soil samples (3,5). Two asbestos tension tables were constructed and a 100 cm column of water was established to create a soil moisture tension for up to 56 soil samples at one time. Sample holders were designed and constructed of plastic rings 2 cm deep by 10 cm in diameter with 60 mesh brass strainer cloth stretched taut and fastened in a countersunk groove in one end. Sample holders were painted with non-reflecting black paint to reduce unwanted reflection external to the target of interest. After saturation of the soil filled, leveled sample holders for about four hours, the samples were placed on the tension tables for 24 hours in order to reach equilibrium. The one-tenth bar moisture tension was desirable mainly for the ease with which large numbers of samples could be prepared at uniform moisture characteristics. Shortly after placement of each sample holder on the sample table of the reflectometer for spectral readings, a portion of the sample was transferred to a moisture tin, weighed, dried in a forced air oven at 105 C, weighed again, and moisture content reported as percentage of oven dry weight.

Quantification of Soil Properties

Modern soil classification systems emphasize the importance of information about the quantitative compositions of soils. In order to differentiate among soil groups, it is necessary to rely on laboratory measurements of selected soil properties. Physical, chemical, and engineering determinations of most soil properties follow well established procedures of laboratory analyses. Certain of these soil properties are selected as diagnostic criteria in the soil classification process, based on their importance in understanding the genesis of the soil. By a procedure of empirical correlation, critical limits between sets of soils are established, designed to reflect the influence of the soil forming factors of climate, parent material, relief, biological activity, and time.

Quantitative measurements of soil spectral properties have become available as a diagnostic tool for the soil scientist with the advent of such instruments as the Exotech Model 20C spectroradiometer. However, the climatic and genetic effects on the relationships between measured spectral properties and specific chemical, physical, and biological properties of the soil are not well understood. Whereas soil color is used as diagnostic criterion in the U.S. Soil Taxonomy (7), the determination of soil color by comparison with a color chart continues to be a rather nonquantitative and subject procedure. Spectral characterization of soil "color" by means of quantitative spectroradiometric measurements may add to the precision with which soils can be differentiated. With this increased precision of soil spectral characterization, the relationships with the more important diagnostic soil characteristics or qualities that are not so easily and accurately observed may be better understood.

EXPERIMENTAL APPROACH

Stratification and Sampling

Approximately 250 soils, representing a statistical sampling of the more than 10,000 soil series in the United States were selected for this investigation. Selections were made from a list of the more than 1300 Benchmark soil series representing those soils with a large geographic extent and whose broad range of characteristics renders these soils so widely applicable for study. Stratification of soil sampling was based on series type location within climatic zones. Climatic strata included the frigid, mesic, thermic, and hyperthermic soil temperature regimes as defined by the U.S. Soil Taxonomy (2,6,7) as well as the perhumid, humid, subhumid, semiarid, and arid moisture regions as identified by Thornthwaite's 1948 Moisture Index (8). A random selection procedure was used within each stratified climatic zone to select a number of soils series approximately in proportion to the geographic extent of that region. Resulting sample distribution by climatic region for the soils actually received is shown in Table 1. Considerations were also made to include soils which represent the major parent material categories and the ten soils orders of the U.S. Soil Taxonomy (7). Table 2 presents the distribution of the Benchmark soil series on-hand according to soil parent material. As can be seen in Table 3, the distribution to Benchmark soils used for this study is very similar to the areal extent of the nine soil orders found in the continental United States (Oxisols being absent in the contiguous states).

The test took place in 1978.

The supporting docs include a brief summary of used instruments, a wavelength table (Wavelength_ASCII.txt), reflectance note and reflectance tables (ReflectanceTable206.txt and ReflectanceTableMulti.txt), and file format description (ExperimentDataFormat3.txt). The format description file is in ASCII format in lines of 80 characters.

This research dataset is part the Field Research Data Library that consists of over 200,000 spectral observations of soils and vegetation that have been collected since 1972 till 1991 as part of the research focused on vegetation and soils at the Laboratory for Applications of Remote Sensing (LARS) located at the Purdue University.

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Notes

  • Location: LARS Optical Lab, West Lafayette, IN
  • County: Tippecanoe
  • Latitude/Longitude: 0402500N 0865500W
  • Illumination: GE-DXW Lamp
  • Spectrometer: Exotech 20C-SW
  • Wavelength Range: 0.40-2.40 um
  • Experiment Type: Soils - Soil
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