Date: 2023-11-06

# Chlorophyll-a colour scale: the SeaWiFS palette

#### 2023-11-06

We need to plot satellite remote sensing chlorophyll-a data with the NASA palette and a correct scale.

The R package palr contains a function to return the required colours and values, but it contains a large maximum value to account for large possible summary values.

We specify a maximum range on the values, and plot the scale in two different ways.

    maxrange <- c(0.01, 10)
    library(palr)
    pal <- chl_pal(palette = TRUE)

    sb <- which(pal$breaks >= maxrange[1] & pal$breaks <= maxrange[2])

    plot(pal$breaks, col = pal$cols, log = "y", ylim = maxrange)
    ## select values from the NASA legend
    abline(h = c(0.01, 0.03, 0.1, 0.3, 1, 3, 10))

    op <- par(fig = c(0.3, 0.7, 0, 1));
    plot(NA_real_, xlim = c(0, 1), ylim = maxrange, xlab = "", ylab = "", log = "y")
    rasterImage(matrix(rev(pal$cols[sb])), 0, 0.01, 1, 10)
    abline(h = c(0.01, 0.03, 0.1, 0.3, 1, 3, 10))

    par(op)

Compare these plots with the official NASA legend here.

https://oceancolor.gsfc.nasa.gov/l3/