Proximal sensing refers to measurements using sensors in close proximity to the object of interest (Adamchuk et al. 2018). Proximal crop sensors are used to collect information about a growing crop and can be mounted on the ground, handheld or borne by vehicles such as tractors or robots. Remote sensing involves the measurement of crop properties often with similar equipment as used in proximal sensing, but from a greater distance, using satellites, airplanes or unmanned aerial vehicles (UAVs, drones). The latter may also be used at short distances. At the other end of the spatial scale, there are sensors that can be used very close to, or in contact with, plant parts. Hence, there is a wide range of different types of sensors and scales on which they are used. Different sensors can also be used in combination, e.g. a proximal sensor can be used to calibrate data collected by remote sensing (Fig. 1).