water (version 0.5)

momentumRoughnessLength: Calculates Momentum Roughness Length

Description

this function estimates Momentum Roughness Length (Zom) from the average vegetation height around the weather station.

Usage

momentumRoughnessLength(method = "short.crops", LAI, NDVI, albedo, a, b, fLAI.Perrier, h.Perrier, mountainous = FALSE, surface.model)

Arguments

method

method selected to calculate momentum roughness length. Use "short.crops" for short crops methods from Allen et al (2007); "custom" for custom method also in Allen et al (2007); Or "Perrier" to use Perrier equation as in Santos et al (2012) and Pocas et al (2014).

LAI

rasterLayer with Leaf Area Index. See LAI(). Only needed for method = "short.crops"

NDVI

rasterLayer with Normalized Difference Vegetation Index. Only needed for method = "custom"

albedo

broadband surface albedo. See albedo()

a

"a" coefficients for Allen (2007) custom function to estimate Momentum roughness length. Only needed for method = "custom"

b

"b" coefficients for Allen (2007) custom function to estimate Momentum roughness length. Only needed for method = "custom"

fLAI.Perrier

proportion of LAI lying above h/2. Only needed for method = "Perrier"

h.Perrier

crop height in meters. Only needed for method = "Perrier"

mountainous

empirical adjustment for effects of general terrain roughness on momentum and heat transfer. See Allen (2007)

surface.model

surface model with a RasterLayer called "Slope" needed is mountainous = TRUE. See surface.model()

Details

According Allen et al,. 2010 Zom is a measure of the form drag and skin friction for the layer of air that interacts with the surface.

References

R. G. Allen, M. Tasumi, and R. Trezza, "Satellite-based energy balance for mapping evapotranspiration with internalized calibration (METRIC) - Model" Journal of Irrigation and Drainage Engineering, vol. 133, p. 380, 2007

Pocas, I., Paco, T.A., Cunha, M., Andrade, J.A., Silvestre, J., Sousa, A., Santos, F.L., Pereira, L.S., Allen, R.G., 2014. Satellite-based evapotranspiration of a super-intensive olive orchard: Application of METRIC algorithms. Biosystems Engineering 128, 69-81. doi:10.1016/j.biosystemseng.2014.06.019

Santos, C., Lorite, I.J., Allen, R.G., Tasumi, M., 2012. Aerodynamic Parameterization of the Satellite-Based Energy Balance (METRIC) Model for ET Estimation in Rainfed Olive Orchards of Andalusia, Spain. Water Resour Manage 26, 3267-3283. doi:10.1007/s11269-012-0071-8