# Light absorption by the water column

### Description

The absorption of light by water is highly dependent on the wavelength, this dataset gives the absorption coefficients from 200 to 700 nm.

### Usage

1 |

### Format

A data.frame with 2 columns:

- lambda
wavelength in nm

- abs
absorption coefficient in 1/cm

### Source

Data were compiled by Palmeira (2007) from the cited references.

The example section allows to reproduce the left part of figure 2.7 from Palmeira (2007):

### References

Palmeira, L. (2007) *Analyse et modélisation des dépendances entre
sites voisins dans l'évolution des séquences d'ADN*, PhD thesis,
Université Claude Bernard - Lyon I.

Litjens R. A., Quickenden T. I. and Freeman C. G. (1999). Visible and
near-ultraviolet absorption spectrum of liquid water. *Applied Optics*,
**38**:1216-1223.

Quickenden T. I. & Irvin J. A. (1980). The ultraviolet absorption spectrum
of liquid water. *The Journal of Chemical Physics*, **72**:4416-4428.

`citation("seqinr")`

### Examples

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 | ```
data(waterabs)
d <- 100*seq(from = 0, to = 150, by = 1) # depth in cm
lambda <- waterabs$lambda # wavelength in nm
abs <- waterabs$absorption # absorption coefficient cm-1
#
# Smooth signal with cubic splines
#
tmp <- spline(lambda, abs, n = 255)
lambda <- tmp$x
abs <- tmp$y
zun <- sapply(abs,function(x) 10^(-x*d))
z <- sapply(nrow(zun):1, function(x) zun[x,])
#
# Set up world coordinates:
#
plot.new()
plot.window(xlim = range(lambda), ylim = range(d), xaxs = "i", yaxs = "i")
#
# Annotate:
#
title(ylab = 'Depth under water surface (m)', xlab = "Wavelength (nm)",
main = "Light absorption by the water column")
axis(2 , at = seq(0, 15000, l = 7),
labels = rev(c("0","25","50","75","100","125","150")), las = 1)
axis(1,at=(3:6)*100,labels= TRUE)
#
# Show me rainbow colors:
#
alpha <- 1
coul=c(rep(rgb(1,1,1, alpha = alpha), 181),
rev(hsv(h=seq(0,5/6,l=320),alpha = alpha)))
rect(seq(200,699), 0, seq(201,700), 15000 , col = coul, border = coul)
#
# Grey scale:
#
ngris <- 5
image(x = lambda, y = d, z = z, col = rgb(1:ngris, 1:ngris, 1:ngris, alpha = 0.7*(ngris:1),
max = ngris),
axes = F, add = TRUE,
breaks = seq(from = min(z), to = max(z), length = ngris + 1))
#
# Contour lines:
#
contour(x = lambda, y = d, z = z, add = TRUE, drawlabels = TRUE,labcex= 0.75,
col='black',
levels = seq(from = min(z), to = max(z), length = ngris + 1))
box()
``` |