Agroecology 4 min

Keeping a digital eye on crops

Proxy and remote sensing technologies are only one aspect of precision or digital agriculture. They nonetheless play a key role in understanding crops and adjusting cultivation practices. Below is a review of an often little-known tool.

Published on 16 December 2019

illustration Keeping a digital eye on crops

Some fly over seedlings under drone propellers. Others monitor a plot of land, firmly planted in the ground. Others again can be found on machines or tractors and indicate the presence of pests or preside over application rates. Whether in the form of sensors or high resolution cameras, these devices define precision agriculture, which is capable of regulating its action based on the information collected in an area of activity that is inevitably heterogeneous, for it is constantly evolving.  “It started out as a “push” technology, which produced mapping, but did not meet specific demands, Véronique Bellon-Maurel, director of INRAE's NUMM research division and of the #DigitAg institute for the convergence of digital agriculture in Montpellier, points out. “It attracted limited interest in France two decades ago, contrary to the United States and Australia where farmers do not know all their land plots given the extent of farm areas. However, its potential advantages were rapidly identified.”


And first and foremost so by a scientific community that increasingly focuses on the impacts of production on resources and vice versa. For instance at INRAE's EMMAH Joint Research Unit in Avignon, which specializes in the study of the interaction between agricultural practices, water resources and crop conditions, “in other words crop responses to practices and resources, as stated by its director, Stéphane Ruy. “The close observation of what takes place within a plot makes it possible to adjust practices such as fertilization or irrigation based on soil data. Data collection is the key step in a process which is often hastily summarised as remote sensing, which actually brings together several approaches.

A multi-level issue

Our work is based on two major techniques, explains Frédéric Baret, head of the CAPTE1 Mixed Technology Unit within EMMAH. “Satellite remote sensing [cf. Article 6], used every five days, gives an idea of the heterogeneity of a plot, provides knowledge of soil and vegetation conditions, and generates a model-based map, for instance of soil water requirements.” Such high resolution from above is supplemented by the use of centimetric resolution on a daily basis for smaller areas using drones, robots and fixed sensors, depending on the proxy detection method2. “Three types of sensors are in use here”, Frédéric Baret goes on to say. “High resolution cameras will facilitate disease identification. Red-Green-Blue multispectral cameras will make it possible, for instance, to estimate the chlorophyll content of a plant. Finally, the LIDAR3 system, a kind of surface laser scanning process, will produce 3D imagery of the crop.

The work of scientists therefore consists in comparing the models provided by the satellites with the raw observational data collected by the sensors. The decrease in differences between the data produced by both sources opens the way for the regulation of practices via predictive simulations, and the development of scenarios that could lead to better yields along with a lesser ecological footprint. However, given its extreme precision, could proxy-detection or low-attitude remote sensing do without satellite support? “We are faced with a multi-level issue, says Frédéric Baret. “There is a contradiction between high resolution and coverage. One is often observed without the other.” The argument also works the other way around. “Proxy or ground-based remote sensing are best suited to weed control, notes Thierry Caquet, INRAE’s Scientific Director for the Environment. “A weeding robot can be located from space, but not guided. And let’s bear in mind the fact that all these tools must not become “prosthetic techniques”, which separate actors from their purpose.” Human reason is still in command of data and crop treatment.

1 – Acronym for "CAPteurs" (sensors) and "TElédétections" (remote sensing).
2 – The notion of "remote sensing" may apply to drones depending on the resolution and distance of their intervention.
3 – For Light Detection and Ranging

4Scouting Robots: they have a large degree of autonomy as well as a significant detection capacity. The flagship of such prototypes, the Salto jumping robot was developed by the University of Berkeley in California in 2016, and is now used for rescue operations

Read the whole report:

Teledetection par drone
Proxies and remote-sensing
WeedElec, from "haute couture" to cutting-edge weeding
Drone suur parcelle de vigne
Technology has transformed our line of work
Trois jeunes pousses de la précision
Three start-ups in precision agriculture
Satellite detection: from photo to video

Benoit Hervieutranslated by Rebecca James


Thierry CaquetScientific Director EnvironmentINRAE

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