qrad {Thermimage}

Estimates the area specific heat transfer by radiation (W/m2)

Description

Estimates heat transfer by radiation (W/m2), using the absorbed radiation estimate from qabs() minus emitted radiation from the object surface (determined from thermal image surface temperature estimates). Positive value = heat gain from environment to object. Negative value = heat loss from object to environment.

Usage

qrad(Ts = 30, Ta = 25, Tg = NULL, RH = 0.5, E = 0.96, rho = 0.1, cloud = 0, SE = 0)

Arguments

Ts

Surface temperature (degrees Celsius) of the object. Default value is 30.

Ta

Air temperature (degrees Celsius), or effective atmospheric temperature. Default value is 25.

Tg

Ground temperature (degrees Celsius) to estimate longwave ground radiation. Default value is NULL, since Tg can be estimated from Ta unless otherwise measured.

RH

Relative humidity (fraction 0 to 1). Default value is 0.5. Used in call to Ld() to determine incoming radiation.

E

Emissivity (fraction 0 to 1) of the object absorbing longwave radiation. According to Kirschoff's law, emissivity = absorptivity. Absorptivity is multiplied by the average of the incoming longwave radiation to estimate absorbed radiation.

rho

Reflectivity (fraction 0 to 1) of the object absorbing solar radiation. Used to modify absorbed solar energy. Default is 0.1.

cloud

Fractional cloud cover (fraction from 0 to 1). Used in call to Ld() to determine incoming radiation. Default is 0.

SE

Solar energy (W/m2), usually measured. Default is 100.

Details

Total solar radiation must be supplied at this stage. The calculation here provides the worst case scenario since since no profile/angle metrics are yet taken into account. The animal could change orientation to/away from solar beam.

Author(s)

Glenn J Tattersall

References

Blaxter, 1986. Energy metabolism in animals and man. Cambridge University Press, Cambridge, UK, 340 pp.

See Also

Ld Lu Ld qabs

Examples

## The function is currently defined as
function (Ts = 30, Ta = 25, Tg = NULL, RH = 0.5, E = 0.96, rho = 0.1, 
    cloud = 0, SE = 0) 
{
    qrad <- qabs(Ta = Ta, Tg = Tg, RH = RH, E = E, rho = rho, 
        cloud = cloud, SE = SE) - E * StephBoltz() * (Ts + 273.15)^4
    qrad
  }

# Example:
Ts<-30
Ta<-25
Tg<-28
RH<-0.5
E<-0.96
rho<-0.1
cloud<-0
SE<-100
# qrad should result in a positive gain of heat:
qrad(Ts, Ta, Tg, RH, E, rho, cloud, SE)

# if rho is elevated (i.e. doubles reflectance of solar energy), heat exchange by 
# radiation is reduced
rho<-0.2
qrad(Ts, Ta, Tg, RH, E, rho, cloud, SE)

# But if solar energy = 0, under similar conditions, qrad is negative:
SE<-0
qrad(Ts, Ta, Tg, RH, E, rho, cloud, SE)

# For detailed examples and explanations, see:
# https://github.com/gtatters/Thermimage/blob/master/HeatTransferCalculations.md