Defining proximal soil sensing

We attempt to define proximal soil sensing (PSS) through a variety of modalities:proximal/remote, in-situ and ex-situ (field and laboratory), non-invasive/intrusive and mobile/stationary. Examples of known combinations of these are given. A narrow definition only considers mobile measurement so it defines PSS as principally a mapping tool. A wider definition of PSS includes in-situ and ex-situ, mobile and stationary field methods and gives more scope for the development of PSS methods