what are the different possible ways to generate target dictionary ?

My project is based on target detection in hyperspectral images,here I am in need of target dictionary for detecting target.I created dictionary by selecting 20 target pixels from the input image and store its value(spectral signature) and named it as target dictionary.My professor told me its very childish,so please suggest me different possible ways of creating it.If u told me to download the target spectral signature from net kindly specify the link below. Thank you in advance..