Proposal for an Embedded System Architecture Using a GNDVI Algorithm to Support UAV-Based Agrochemical Spraying.

An important area in precision agriculture is related to the efficient use of chemicals applied onto fields. Efforts have been made to diminish their use, aiming at cost reduction and fewer chemical residues in the final agricultural products. The use of unmanned aerial vehicles (UAVs) presents itself as an attractive and cheap alternative for spraying pesticides and fertilizers compared to conventional mass spraying performed by ordinary manned aircraft. Besides being cheaper than manned aircraft, small UAVs are capable of performing fine-grained instead of the mass spraying. Observing this improved method, this paper reports the design of an embedded real-time UAV spraying control system supported by onboard image processing. The proposal uses a normalized difference vegetation index (NDVI) algorithm to detect the exact locations in which the chemicals are needed. Using this information, the automated spraying control system performs punctual applications while the UAV navigates over the crops. The system architecture is designed to run on low-cost hardware, which demands an efficient NDVI algorithm. The experiments were conducted using Raspberry Pi 3 as the embedded hardware. First, experiments in a laboratory were conducted in which the algorithm was proved to be correct and efficient. Then, field tests in real conditions were conducted for validation purposes. These validation tests were performed in an agronomic research station with the Raspberry hardware integrated into a UAV flying over a field of crops. The average CPU usage was about 20% while memory consumption was about 70 MB for high definition images, with 4% CPU usage and 20.3 MB RAM being observed for low-resolution images. The average current measured to execute the proposed algorithm was 0.11 A. The obtained results prove that the proposed solution is efficient in terms of processing and energy consumption when used in embedded hardware and provides measurements which are coherent with the commercial GreenSeeker equipment.

Nitrogen management in wheat based on the normalized difference vegetation index (NDVI) / Manejo do nitrogênio em trigo baseado no índice de vegetação por diferença normalizada (NDVI)

ABSTRACT: Biomass production and nitrogen (N) accumulated in wheat shoots may be used for quantifying optimal topdressing nitrogen doses. The objective of this study was to develop and validate models for estimating the amount of biomass and nitrogen accumulated in shoots and the N topdressing dose of maximum technical efficiency in wheat using the normalized difference vegetation index (NDVI) measured by an active optical canopy sensor. Field experiments were carried out in two years and treatments consisted of N doses applied at plant emergence and as topdressing. NDVI, shoot biomass and N accumulated in shoots at the growth stage of six fully expanded leaves and grain yield were evaluated, being determined the topdressing N dose of maximum technical efficiency (DMTE). The NDVI was positively correlated to shoot biomass and N content in shoots and models for the relationship between these variables were developed and validated. The DMTE was negatively correlated with the NDVI value evaluated at the moment of N topdressing application. Thus, NDVI evaluation by an active optical canopy sensor can be used for nitrogen fertilization in variable rate, allowing the adjustment of applied N doses in different areas within a field.

RESUMO: A produção de biomassa e o conteúdo de nitrogênio (N) acumulado na parte aérea de trigo podem ser utilizados na quantificação da dose ótima de N em cobertura. O objetivo deste estudo foi desenvolver e validar modelos para a estimativa das quantidades de biomassa e nitrogênio acumulado na parte aérea e a dose de máxima eficiência técnica de N em cobertura em trigo utilizando o Índice de vegetação por diferença normalizada (NDVI) medido por sensor óptico ativo de dossel. Experimentos foram conduzidos a campo, em dois anos, e os tratamentos constaram de doses de N aplicadas na emergência das plantas e em cobertura. Foram avaliados o NDVI, a biomassa e a quantidade de N acumulada na parte aérea no estádio de seis folhas completamente expandidas e o rendimento de grãos, sendo determinada a dose de máxima eficiência técnica de N em cobertura (DMET). O NDVI apresentou correlação positiva com a biomassa e quantidade de N acumulada na parte aérea e modelos para as relações entre estas variáveis foram propostos e validados. A DMET correlacionou-se negativamente com o valor de NDVI avaliado no momento da aplicação de nitrogênio em cobertura. Assim, a avaliação do NDVI por sensor óptico ativo de dossel pode ser utilizada para a adubação nitrogenada em taxa variável, permitindo o ajuste da dose de N aplicada em diferentes locais da lavoura.

Variabilidade espacial da produtividade de milho irrigado e sua correlação com variáveis explicativas de planta / Spatial variability of grain yield of irrigated corn and its correlation with explanatory plant variables

RESUMO: Em decorrência da instabilidade da produtividade das principais culturas associada ao déficit hídrico, tem se tornado cada vez mais frequente a necessidade do uso de tecnologias como a irrigação e a agricultura de precisão (AP). O presente trabalho objetivou avaliar a variabilidade espacial da produtividade de grãos de milho e sua correlação com variáveis explicativas de planta em área irrigada. O estudo foi conduzido nas safras agrícolas 2010/2011 e 2011/2012, em área de 35ha, manejada em sistema plantio direto e irrigação por pivô central. Os componentes de produtividade e a produtividade de grãos foram avaliados seguindo uma malha amostral de 100x100m. A produtividade de grãos e a maior parte dos componentes de produtividade apresentaram baixa dispersão dos dados, condicionando a normalidade dos dados. A produtividade de grãos, mesmo com a irrigação, apresentou elevada variabilidade espacial. Na análise de trilha, verificaram-se altos coeficientes de determinação dos componentes de produtividade com a produtividade de grãos.

ABSTRACT: Due to yield instability of main crops associated to drought, the use of technologies such irrigation and precision agriculture (PA) have been recently adopted in large scale. This study had the objective to assess the spatial variability of corn yield and its correlation with explanatory plant variables in an irrigated field. The study was carried out during the growing seasons 2010/2011 and 2011/2012, in an area of 35ha managed under no-till and center-pivot irrigation. Corn yield and yield components were evaluated following a sampling grid of 100x100m. Grain yield and most yield components showed low dispersion data, resulting in data normality. Even under irrigation, corn yield showed high spatial variability. In path analysis, it was found high determination coefficients of corn yield with yield components.

Resistência de espécies arbóreas submetidas a extremos climáticos de geada em diferentes sistemas agroflorestais / Resistance of arboreal species submitted to extreme frost in different agroforestry systems

O presente trabalho teve como objetivo avaliar a resposta das espécies arbóreas Schizolobium parahyba (Vell.) Blake (guapuruvu), Mimosa scabrella Benth. (bracatinga), Peltophorum dubium (Spr.) Taubert (canafístula), Parapiptadenia rigida (Benth.) Brenan (angico-vermelho) e o híbrido Eucalyptus urophylla S.T. Blake x Eucalyptus grandis Hill ex Maiden (eucalipto) em consórcio com a cana-de-açúcar (Saccharum spp.) em dois arranjos de sistemas agroflorestais (faixa - 3x3m + 12m e linha - 6x1,5m) submetidos a extremos climáticos de geada, na região Noroeste do Rio Grande do Sul. Os danos (resistência á geada) foram avaliados segundo o sistema de notas utilizado por HIGA et al. (2000) no qual atribuiu-se uma nota de 0 a 10 conforme a intensidade do dano na planta. Para os graus de resistência à geada, adaptou-se metodologia utilizada por CARVALHO (1981), a qual também é em função da intensidade do dano na planta. Diante da condição de geada estudada, observa-se que os diferentes arranjos de sistemas agroflorestais afetam a resistência da espécie guapuruvu, sendo sensível no sistema agroflorestal faixa e moderadamente tolerante no sistema linha. Em ambos os sistemas, as espécies angico-vermelho, bracatinga e eucalipto mostram-se resistentes, enquanto que a canafístula demonstra ser tolerante.

The present research had the aim to evaluate the answers of the arboreal species Schizolobium parahyba (Vell.) Blake (guapuruvu), Mimosa scabrella Benth. (bracatinga), Peltophorum dubium (Spr.) Taubert (canafístula), Parapiptadenia rigida (Benth.) Brenan (angico-vermelho) and the hybrid Eucalyptus urophylla S.T. Blake x Eucalyptus grandis Hill ex Maiden (eucalipto) in consortium with sugar cane (Saccharum spp.) in two agroforestry arrangement systems (strip - 3x3m + 12m and line - 6x1,5m) submitted to climatic extreme frost conditions, in the Northwest of Rio Grande do Sul. The damages (resistance to frost) were appraised according to the system of notes used by HIGA et al. (2000) in which a note from 0 to 10 was attributed according to the intensity of the damage to the plant. For the resistance degrees to frost, it was adapted the methodology used by CARVALHO (1981), which is also in function of the intensity of the damage to the plant. Upon the frost condition studied, it was observed that the results demonstrated that different of agroforest system arrangements damaged the resistance of the guapuruvu specie, being sensitive in the agroforest system strip and moderatelly tolerant in the system line. In both systems, the species angico-vermelho, bracatinga e eucalipto showed resistance, while the canafístula demonstrated to be tolerant.