R/ha.R

In sirad: Functions for Calculating Daily Solar Radiation and Evapotranspiration

ha <-
  function(days,lat,lon,extraT=NULL,A=NA,B=NA,Tmax,Tmin) {
    i <- dayOfYear(days)
    latt <- radians(lat)
    if (is.null(extraT)) extraT <- extrat(i=i,lat=latt)$ExtraTerrestrialSolarRadiationDaily
    
    if (is.na(A)) A <- extract(Ha_map, matrix(c(lon,lat),1,2))
    if (is.na(A)) stop("Lat/lon outside the coefficient map!")
    if (is.na(B)) B <- extract(Hb_map, matrix(c(lon,lat),1,2))
    if (is.na(B)) stop("Lat/lon outside the coefficient map!")
    
    ha <- extraT*A*sqrt(Tmax-Tmin)+B
    ha 
  }