There's a running gag at the local polytechnic: All the engineering fields have one thing in common – you measure data, put it into a matrix, calculate its covariance matrix and find the eigenvectors and eigenvalues.

In the case of radio direction finding, PCA allows you to distinguish multiple overlapping signals on the same frequency if they're hitting the antenna array from different directions.

If you have any other interesting applications in your own field, I'd like to hear them, too.