¥It is important to use correlations, not covariances, if variables are measured in
different units (pressure, temperature) to avoid
effects of arbitrary scaling
¥Most geoscience applications only use one type of variable – choice
between covariance and correlation depends whether it is
desirable for all variables (spatial locations) to have
the same weight or allow those with greater
variances to have an increased chance of dominating the
first few PCs