hacal: Calibrate Hargreaves model

In sirad: Functions for Calculating Daily Solar Radiation and Evapotranspiration

Description

Function estimates Hargreaves model coefficients 'A' and 'B' based on reference data

Usage

hacal(lat, days, rad_mea, extraT=NULL,tmax, tmin)

Arguments

lat	Latitude in decimal degrees.
days	Vector of class 'Date' of length n.
rad_mea	Vector of length n containing reference (e.g. measured) solar radiation [MJm-2].
extraT	Optional. Vector of length n of extraterrestrial solar radiation [MJm-2]. If 'NULL' then it is calculated by the function. Providing extraterrestrial solar radiation speeds up the computation
tmax	Vector of length n containing daily maximum temperature [C].
tmin	Vector of length n containing daily minumum temperature [C].

Details

Function estimates Hargreaves model coefficients 'A' and 'B' based on reference (e.g. measured) solar radiation data. It performs a linear regression.

Value

Vector of length 3 containing:

Ha	Hargreaves 'A' coefficient
Hb	Hargreaves 'B' coefficient
Hr2	Coefficient of determination of performed linear regression

Author(s)

Jedrzej S. Bojanowski

References

Hargreaves, G.H., Samini, Z.A. 1892. Estimating potential evapotranspiration. J. Irrig. Darin. Eng., ASCE 108 (3), 225-230.

See Also

'ha'

Examples

data(Metdata)
tmax <- Metdata$meteo$TEMP_MAX
tmin <- Metdata$meteo$TEMP_MIN
days <- Metdata$meteo$DAY
lat <- Metdata$LATITUDE
rad_mea <- Metdata$meteo$RAD_MEA
hacal(lat=lat,days=days,rad_mea,extraT=NULL,tmax=tmax, tmin=tmin)

Example output

        Ha         Hb        Hr2 
 0.1732065 -0.1358756  0.8446852 

sirad documentation built on May 2, 2019, 4:41 p.m.