bcauto {sirad} | R Documentation |
Auto-calibrate Bristow-Campbell model
Description
Function estimates Bristow-Campbell model coefficient 'B' based on auto-calibration procedure
Usage
bcauto(lat,lon,days,extraT=NULL,Tmax,Tmin,tal,BCc=2,
BCb_guess=0.13,epsilon=0.5,perce=NA,dcoast=NA)
Arguments
lat |
Latitude in decimal degrees. |
lon |
Longitude in decimal degrees. |
days |
Vector of class 'Date' of length n. |
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]. |
tal |
Clear sky transmissivity. |
BCc |
Bristow-Campbell model coefficient 'C' usually equaled to 2. |
BCb_guess |
Assumption of Bristow-Campbell coefficient. Default set to 0.13. |
epsilon |
A value of which potential radiation is decreased. See "details". |
perce |
Percent of clear days. In 'NA' then perce is estimated based on the Cloud Fraction Cover map. |
dcoast |
Distance to the coast [km]. |
Details
The auto-calibration method bases on the assumption that on the clear-sky days model should not overpredict potential values. To define those clear-sky days, we estimate daily solar radiation using Bristow and Campbell model with default values of B = 0.13 and tal = 0.72 and we select those days for which estimated daily solar radiation is the closest to the potential values (extraterrestrial*tal). The number of clear-sky days is estimated based on the mean Cloud Fraction Cover map. Next, based on selected clear-sky days, we perform a non-linear least squares regression to derive B coefficient treating potential values decreased by 'epsilon' as a reference solar radiation values. The analysis of auto-calibration results showed clear correlation between optimal 'epsilon' and distance to the coast. We proposed simplified method in which 'epsilon' is equal to 0.1 MJm-2 or to 0.5 MJm-2 when distance to the coast is smaller or bigger than 15 km respectively.
Value
BCb |
Bristow-Campbell 'B' coefficient |
Author(s)
Jedrzej S. Bojanowski
References
Bojanowski, J.S., Donatelli, M., Skidmore, A.K., Vrieling, A., 2013. An auto-calibration procedure for empirical solar radiation models Environmental Modelling and Software 49, 118-128.
See Also
'bc' to use Bristow-Campbell model, and 'bccal' to perform calibration based on reference data.
Examples
data(Metdata)
tmax <- Metdata$meteo$TEMP_MAX
tmin <- Metdata$meteo$TEMP_MIN
days <- Metdata$meteo$DAY
lat <- Metdata$LATITUDE
lon <- Metdata$LONGITUDE
rad_mea <- Metdata$meteo$RAD_MEA
dcoast <- Metdata$DCOAST
bcauto(lat,lon,days,extraT=NULL,tmax,tmin,perce=NA,dcoast)