aral {gamair}

Aral sea remote sensed chlorophyll data

Description

SeaWifs satellite chlorophyll measurements for the 38th 8-day observation period of the year in the Aral sea, averaged over 1998-2002, along with an Aral sea boundary file.

Usage

data(aral)
data(aral.bnd)

Format

The aral data frame has the following columns

lon

longitude of pixel or boundary vertex.

lat

latitude of pixel or boundary vertex.

chl

chlorophyll measurement

exra

The highest rainfall observed in any 12 hour period in that year, in mm.

Details

Trying to smooth the data with a conventional smoother, such as a thin plate spline, leads to linkage between the two arms of the sea, which is clearly an artefact. A soap film smoother avoids this problem.

Source

https://seawifs.gsfc.nasa.gov/

Examples

require(gamair);require(mgcv)
data(aral); data(aral.bnd)

## define some knots...
knt <- list(lon=c(58.55,59.09,59.36,59.64,59.91,60.18,58.27,58.55,59.09,
59.36,59.64,59.91,60.18,60.45,58.27,58.55,58.82,59.09,59.36,59.64,59.91,
60.18,60.45,58.27,58.55,59.36,59.64,59.91,60.18,58.55,59.36,59.64,59.91,
60.18,58.55,58.82,59.36,59.64,59.91,60.18,60.45,58.82,59.09,59.64,59.91,
60.18,59.64),
lat=c(44.27,44.27,44.27,44.27,44.27,44.27,44.55,44.55,44.55,44.55,44.55,
44.55,44.55,44.55,44.82,44.82,44.82,44.82,44.82,44.82,44.82,44.82,44.82,
45.09,45.09,45.09,45.09,45.09,45.09,45.36,45.36,45.36,45.36,45.36,45.64,
45.64,45.64,45.64,45.64,45.64,45.64,45.91,45.91,45.91,45.91,45.91,46.18))

## fit soap film...
b <-  gam(chl~s(lon,lat,k=30,bs="so",xt=list(bnd=list(aral.bnd),
                nmax=150)),knots=knt,data=aral)

## plot results...
plot(b)