sarp.snowprofile (version 1.3.2)

computeRTA: Compute Relative Threshold Sum approach (RTA)

Description

The function can compute the RTA index for layers and for interfaces. The calculation follows the example in Monti (2013), referenced below. The six individual relative lemons are computed as follows. To compute the RTA index for layers, the layer properties are combined with the interface properties of the weakest interface below or above the layer. To compute the RTA index for interfaces, the interface properties are combined with the weakest layer properties below or above the interface. The six properties considered in the index are

• grain size, hardness, grain type (layer properties)

• difference of grain sizes and hardness (at the interface)

• depth (at the top interface of the layer)

Instead of implementing a static threshold for the depth weighting, the depth is scaled with a weibull function that is corrected for potential crusts and their stabilizing effects (Monti and Mitterer, personal communication).

Note that due to the crust correction, the results from this function will only be correct if applied to profiles that have not yet been resampled (such as by functions from sarp.snowprofile.alignment: resampleSP, resampleSPpairs, dtw, averageSP).

The RTA index ranges between [0, 1], with the weakest layer/interface euqal to 1. Values > 0.8 indicate layers/interfaces with a poor structural stability.

Usage

computeRTA(x, target = c("interface", "layer"))
# S3 method for snowprofileSet
computeRTA(x, target = c("interface", "layer"))
# S3 method for snowprofile
computeRTA(x, target = c("interface", "layer"))

Value

The input object will be returned with the new layer properties rta/rta_interface describing the RTA index added to the profile layers.

Arguments

x

a snowprofile or snowprofileSet. Profile layer properties must be known for all layers (i.e., no NAs in gtype, hardness, gsize allowed!)

target

Do you want to compute the index for the layers or for the layer interfaces? defaults to both.

Methods (by class)

• computeRTA(snowprofileSet): for snowprofileSets

• computeRTA(snowprofile): for snowprofiles

Author

fherla

References

Monti, F., & Schweizer, J. (2013). A relative difference approach to detect potential weak layers within a snow profile. Proceedings of the 2013 International Snow Science Workshop, Grenoble, France, 339–343. Retrieved from https://arc.lib.montana.edu/snow-science/item.php?id=1861

See Also

computeTSA

Examples

## apply function to snowprofileSet
profileset <- computeRTA(SPgroup)

## apply function to snowprofile and plot output
sp <- computeRTA(SPpairs$B_modeled1)
plot(sp, TempProfile = FALSE, main = "RTA")
lines(sp$layers$rta*5, sp$layers$height - 0.5*sp$layers$thickness, type = "b", xlim = c(0, 5))
lines(sp$layers$rta_interface*5, sp$layers$height, type = "b", xlim = c(0, 5), col = "red")
abline(h = sp$layers$height, lty = "dotted", col = "grey")
abline(v = 0.8*5, lty = "dashed")