phytotools (version 1.0)

reflectance: Computes surface reflectance

Description

The fraction of surface reflectance at the air-water interface is calculated as a function of solar zenith angle following Kirk (2011).

Usage

reflectance(date, latitude, longitude, timezone)

Arguments

date

The date and time over which to calculate reflectance. Date and time must be in the ISO format with the timezone set to UTC, see examples.

latitude

Latitude in decimal degrees. Northern hemisphere is positive.

longitude

Longitude in decimal degrees. Eastern hemisphere is positive.

timezone

Time zone, west is negative. See Details.

Value

A two column matrix specifying the decimal day of year and the fraction of surface reflectance.

Details

Timezone refers to hours relative to UTC. There is currently no provision for daylight savings time.

References

Kirk, J.T.O., 2011. Light and photosynthesis in aquatic environments. Cambridge Press.

See Also

incident

Examples

#Calculate surface reflectance in 10 minute increments 
#for Godthabsfjord fjord, Greenland on March 1

#Setup date sequence
date <- seq(ISOdatetime(2013,3,1,0,0,0,tz="UTC"), 
            ISOdatetime(2013,3,2,0,0,0,tz="UTC"),
            by = "10 min")

#Call the function
ref <- reflectance(date,64.20,-51.76,-3)

#Plot data
plot(ref[,1],ref[,2],type="l",xlab="Day of Year",ylab="Surface Reflectance")