Optical fiber sensors for monitoring agricultural drone spraying operations

Spraying is a fundamental agricultural operation, used for the dispersion of both pesticides and fertilisers over trees and crops, directly affecting the volume and quality of agricultural yield; however, spraying is subjected to limitations with respect to safety regulations, water consumption and droplet cloud drift. An emerging agricultural trend is referring to drone spraying operations, offering prominent and unique advantages such as speed of operation, applicability to almost every type of ground and crops, and significant saving in water and pesticides/fertilisers.

A basic issue to be considered during drone spraying for agricultural applications is that of drift, namely, the spatial dispersion of spraying droplets over extended vicinity areas, affecting other crops and fields, as well as, bystanders. There have been few methods for quantifying spraying drift for both ground and drones spraying operations, however, most of them cannot simultaneously combine low cost, reliable results and easy readability by non-specialised personnel.

Herein, we are presenting for the first time a radically new approach in the quantification of spraying drift for agricultural operations, while using optical fiber sensors. Our idea refers to the use of long-period grating (LPG) out-cladding optical fiber sensors, as passive sensing elements, deployed at specific distances away from the drone spraying area, where straying droplets deposited over the optical fiber glass cladding area will modify the spectral response of the LPG. These LPG optical fiber droplet sensing probes will allow the precise monitoring of droplet distribution over given distances, offering high detectivity of few droplet events, low aerodynamic profile for not been affected by wind and drone operation gusts and easy/reliable readability by non-specialised users. Moreover, the same LPG droplet monitoring sensors can be simultaneously been used for monitoring the efficiency of spraying operation, when they are deployed within the foliage of the sprayed trees and on the ground under the crops.

Specialty design, long-length LPGs were inscribed using ultraviolet laser radiation in optical fibers and characterised using dyed water solutions and aerograph nozzle spraying. Our preliminary in-lab investigations have shown promising droplet sensing results, with detectivities of ≤4 droplets/mm2, for typical droplet size ~1.0×10-2mm2, and corresponding LPG strength and wavelength changes of 1.3dB and 65pm, respectively. Field testing for drone spraying of those LPG optical fiber droplet sensing probes is currently under investigations and relevant results will be presented on-site.

This study is carried out in collaboration with the Greek SME IONOS Ltd within the framework of ACTPHAST 4.0 innovation project.

A presentation by Stavros Pissadakis, Director of Research FORTH-IESL, Greece, directing the Photonic Materials and Devices Laboratory.


Question 1: What drives you?
The major drive behind our investigations is the translation of highly performing, cost effective and easily manufactured optical fiber sensing technologies into existing and emerging real field applications, while helping end-users reaching sustainability tangible targets and metrics.

Question 2: Why should the delegate attend your presentation?
Because we have readily adapted a widely used and manifold tested optical fiber sensing platform for efficient operation in a new application field, minimizing technological and cost risks, while helping the end-users accessing vital parameters of their spraying operations.

Question 3: What emerging technologies/trends do you see as having the greatest potential in the short and long run?
Optical fiber sensors can greatly impact Smart Farming practices, offering deployment over a grid, small size and reliable operation. Simple sensing probes such as long-period gratings, Bragg gratings, Fabry-Perot and plasmonic cavities can be the base for developing low cost and technological risk devices for measuring chemical, environmental and operational quantities in the field, helping farm-holders accessing crucial information that has not been available before.

Question 4: What kind of impact do you expect them to have?
We expect to create a direct environmental impact by monitoring the efficiency and drift of drone spraying operations, thus, help minimizing the amount of pesticides/fertilisers and water used during a spraying session, but also reliably probing undesired drift effects. Another significant impact refers to Farming 4.0 agricultural business with an active sustainability strategy, helping them to better measure and report ESG metrics, using reliable, yet cost effective sensing technologies.

Question 5: What are the barriers that might stand in the way?
The LPG optical fiber sensing technology developed still needs some improvements in terms of correlation between droplet drift and optical signal, and interrogation/readout units used.

About Stavros Pissadakis
Stavros Pissadakis (PhD 2000, ORC, Univ. Southampton, UK) is a Director of Research FORTH-IESL, Greece, directing the Photonic Materials and Devices Laboratory. He has contributed several new findings in the field of Photonics, in the domains of Optical Fiber Sensors, Lab-in-a-fiber devices and Optical Materials. He has attracted more than 2ME competitive funds, most of them through industrial contracting. He is Member of the Board of Stakeholders at ETP Photonics21, Member of National Council for Research and Innovation and Senior Member of both OSA and IEEE. He has also been heavily involved in commercialisation strategies for Photonic Technologies through national clusters and platforms. Dr Pissadakis has authored more than 210 high impact journal and international conference publications.

About Foundation for Research and Technology – Hellas (FORTH)
The Foundation for Research and Technology – Hellas (FORTH), established in 1983, is one of the largest research centers in Greece with well organized facilities, highly qualified personnel and a reputation as a top-level research foundation worldwide. The Institute of Electronic Structure and Laser (IESL) aims at performing high quality both fundamental and applied research in specific target areas in the fields of laser science and applications, micro/nano-electronics, polymers and soft matter, and materials science a. IESL has established its strong international presence in these areas occupying a distinct position in the international scientific map. IESL has been a key participant of the Access to Research Infrastructures programme (since 1990 as a Laser facility and now as a facility in Cultural Heritage, Soft Matter and Photonic Science/Technology). A number of important scientific achievements by members of the Institute have led to publications in high impact journals and to international awards and distinctions for excellence to its research personnel.

Stavros Pissadakis is speaker at the 2021 edition of the Smart Farming Conference.

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