aqp (version 2.3.1)

estimateSoilColor: Estimate dry soil colors from moist soil colors and vice versa.

Description

All else equal, soil color will predictably shift in perceived lightness (change in Munsell value) as moisture content changes. Field-described soil colors are typically collected at approximately air dry ("dry") and field capacity ("moist") states. This function estimates "dry" soil colors from "moist" soil colors and vice versa. Two methods are available for estimation, both developed from a national collection of field-described soil colors (approx. 800k horizons). Estimates are only valid for mineral soil material, having Munsell values and chroma < 10. Estimation has a median error rate of approximately (CIE dE2000) 5.

Available Methods:

• "procrustes": soil colors are converted using scale, rotation, and translation parameters in CIELAB color space

• "ols": soil colors are converted using 3 multiple linear regression models (CIELAB coordinates)

This is still a work in progress.

Usage

estimateSoilColor(
  hue,
  value,
  chroma,
  method = c("procrustes", "ols"),
  sourceMoistureState = c("dry", "moist"),
  returnMunsell = TRUE
)

Value

data.frame of estimated colors in Munsell notation. The sigma column contains CIE2000 color contrast metric values describing the perceptual distance between estimated color in CIELAB coordinates and closest Munsell chip.

Arguments

hue

vector of Munsell hue ('10YR', '2.5Y', etc.)

value

vector of Munsell value (2,2.5 2.5, 3, 5, 6, etc.)

chroma

vector of Munsell chroma (2, 3, 4, etc.)

method

character, one of 'procrustes' or 'ols', see details

sourceMoistureState

character, source colors are either 'dry' or 'moist'

returnMunsell

logical, TRUE: return closest Munsell chip, FALSE: return estimated CIELAB coordinates

Author

D.E. Beaudette

Details

For both methods, estimation proceeds as:

• convert Munsell notation to CIELAB color coordinates via munsell2rgb()

• apply rotation or regression model to color coordinates in CIELAB space

• locate closest Munsell chip to resulting CIELAB coordinates via col2munsell()

Estimation of dry from moist soil color state is not guaranteed to be symmetric with estimation of moist from dry.

Scaling, rotation, and translation parameters for shifting between dry <--> moist CIELAB coordinates were determined using vegan::procrustes(). Multiple linear regression models were fit using rms::ols().

Estimation error for both methods, converting from either moisture states is, approximately 5 (CIE dE 2000).

References

J. A. Shields, E. A. Paul, R. J. St. Arnaud, and W. K. Head. 1968. SPECTROPHOTOMETRY MEASUREMENT OF SOIL COLOR AND ITS RELATIONSHIP TO MOISTURE AND ORGANIC MATTER. Canadian Journal of Soil Science. 48(3): 271-280. https://doi.org/10.4141/cjss68-037

Examples

# keep examples from using more than 2 cores
data.table::setDTthreads(Sys.getenv("OMP_THREAD_LIMIT", unset = 2))

estimateSoilColor(hue = '10YR', value = 3, chroma = 3, sourceMoistureState = 'moist')

# estimation is not always symmetric
estimateSoilColor(hue = '10YR', value = 4, chroma = 3, sourceMoistureState = 'dry')

# more examples
estimateSoilColor(hue = '2.5Y', value = 8, chroma = 2, sourceMoistureState = 'dry')
estimateSoilColor(hue = '2.5YR', value = 3, chroma = 4, sourceMoistureState = 'moist')

estimateSoilColor(hue = 'N', value = 2, chroma = 0, sourceMoistureState = 'moist')

estimateSoilColor(hue = '7.5YR', value = 2, chroma = 2, sourceMoistureState = 'moist')

# resulting hue is not always the same
estimateSoilColor(hue = '5G', value = 6, chroma = 6, sourceMoistureState = 'dry')

# return estimated CIELAB coordinates
estimateSoilColor(hue = '5G', value = 6, chroma = 6, sourceMoistureState = 'dry',
 returnMunsell = FALSE)