proximal sensing is the measurement of attributes of the soil, vine canopy, or fruit using sensors mounted on vehicles or vineyard machinery operating in the vineyard, i.e. the sensor is operated close to the target of interest (cf. remote sensing). Hand-held sensors may also be used but are unlikely to be cost-effective if the intention is to collect sufficient data to produce a map. (See soil mapping.)
Proximal soil sensing is a common application in precision viticulture and provides key data input to zonal viticulture. Electromagnetic induction (EMI) is the most common form of proximal soil sensing and is used to identify variation in soil properties which affect the electrical conductivity of the soil (salinity, soil texture, soil water status), or which are correlated with them. Research has shown that patterns of variation in vine performance often closely mimic patterns of variation in these soil attributes. A possible alternative to EMI sensing is to use electrical resistance tomography (ERT) to measure resistivity. Since resistivity is the inverse of conductivity, the information provided by these two types of sensors is essentially the same. However, the requirement for contact with the soil in the case of ERT, coupled with the much larger size of sensor, tends to make them a poor option in established vineyards or where the soil is stony; EMI instruments are generally smaller and do not require contact with the soil.
