generated within R

Calibration of the CR-410

1. power on the unit, and press the 'Cal' button
2. place the unit on the white standard calibration tile

PAM clustering of mean subsoil color (horizon thickness-weighted) for 170 pedons.

Moist colors in the L*U*V* color space (629 horizons).

Premise

Soil color generally varies in a predictable pattern with depth according to surface vegetation, clay mineralogy and parent material. Highly contrasting parent geology influences soil color within Pinnacles via four main processes:

1. Original color of parent material
   sedimentary sources: grey, yellow, white
   granitic sources: yellow to orange
   volcanic sources: pink, orange, white, green
2. Landscape age
   older landscapes generally have redder hues (Fe-expression) from longer chemical weathering
3. Particle size distribution of parent material and the resulting field capacity of a soil formed from it
   coarse textures result in lower field capacities, limiting vegetation growth and subsequent accumulation of organic matter in the surface horizons
4. Weathering rate of parent material
   sedimentary materials derived from granitic sources (grey to yellow hues) have high levels of quartz and are therefore less susceptible to chemical weathering than volcanic rocks (redder hues)

Common soil colors plotted in the L*U*V color space.

Figure 1: Munsell color chips.

Figure 2: Common soil colors.

Figure 3: Commom soil colors in RGB.

Figure 4: Soil colors in multiple color spaces

Figure 5: Soil profile colors.

The Munsell color system was designed as a series of discrete color chips which closely approximation to the color sensitivity of the human eye. The description of color via three variables tied to perceptible properties (hue, value, and chroma) under a standardized illuminant (sunlight on a clear day) makes the Munsell system a good choice for recording and interpreting soil color data. However, numerical analysis of colors encoded in the Munsell system is difficult because they are from a discrete set of color chips and referenced by values that include both letters and numbers. Rossel et. al. (2006) give a good background on various color space models and their relative usefulness in the realm of soil science. The conversion of Munsell soil colors to RGB triplets, suitable for displaying on a computer screen or printing, is made complicated by the numerous operations involved in converting between color spaces. Figure 1 shows all possible (both real and unreal) Munsell color chips in the L*U*V color space. Figure 2 shows some of the common soil color chips in the same color space. Figures 2 through 5 depict common soil colors in the RGB color space, visualized both in R and POVRAY. Example R code on the conversion is given below.