Media absorbency determination

A method for estimating a quantity of sample material borne by an absorptive substrate, the method comprising:

• prior to absorption of a sample by the substrate, directing a first radiation onto the substrate, the first radiation being configured to interact with the substrate to an extent relative to anisotropy of the substrate, and measuring interaction of the first radiation with the substrate at a plurality of measurement sites of the substrate to obtain a first radiation interaction measurement;
• applying a sample to the substrate to cause absorption of sample material into the substrate at at least one of the measurement sites;
• after absorption of the sample by the substrate, directing a second radiation onto the substrate, the second radiation being configured to interact with the substrate and to interact with the absorbed sample borne by the substrate to an extent relative to anisotropy of the substrate and the absorbed sample, and measuring interaction of the radiation with the substrate and sample at the plurality of measurement sites of the substrate to obtain a second radiation interaction measurement;
• and
• comparing the first radiation interaction measurement with the second radiation interaction measurement to estimate a quantity of sample material borne by the substrate.