A Review Studies on Using Optical Sensors in Agricultural Production MOLNAR-IRIMIE Adrian, Ovidiu RANTA*, Ovidiu MARIAN, Daniel PĂCURAR, Georgiana MARȚIȘ, Sorin STĂNILĂ Faculty of Agriculture, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, 3-5 Calea Manastur, 400372, Cluj-Napoca, Romania Received 2 May 2019; received and revised form 21 May 2019; accepted 25 June 2019 Available online 30 June 2019 Abstract The optical sensors for assessing the condition of crops are based on the analysis of the wavelength of the light reflected by the vegetal mass, i.e. the measurement of the wavelength type and intensity of light reflected back to the sensors. In general, optical sensors are based on the ability of vegetation to reflect incident electromagnetic radiation, which allows for correlation between the qualitative and quantitative data characterizing agricultural crops. Sensors for measuring crop reflectance can be graded by platform, such as: aerial or spacecraft (satellites, aircraft, unmanned aerial vehicles, balloons), field means (hand-held sensors, sensors mounted on agricultural machinery). Keywords: smart agriculture, precision agriculture, optical sensors, remote sensing. 1. Introduction Generally speaking optical sensors are based on the ability of vegetation to reflect incident electromagnetic radiation, which allows for correlation between the qualitative and quantitative data characterizing agricultural crops. Various light wavelength values of different colors can be used to measure the different plant properties. The currently available optical sensors use two or more wavelengths, characteristic of red, green, blue (visible radiation), and near infrared (invisible radiation). For example, green color, which is associated with plant vigor, has a wavelength of around 500 nm. *Corresponding author. Tel: +40-264-596384 Fax: +40-264-593792 E-mail: ovidiu.ranta@usamvcluj.ro It is of interest for infrared radiation with wavelengths near the visible spectrum, namely 0.76- 0.9 μm (near infrared) and 1.55-1.75 μm (short- wavelength infrared).Green plants absorb much of the visible wavelengths, namely blue and red light, but more reflects the wavelengths of green light. Determining the spectral response (the reflection of vegetation) in the wavelength range characteristic of green light is an indicator of the relative amount of chlorophyll in the leaves [1, 3]. Determination of the reflectance in the green spectrum can be used to assess the availability of nitrogen in culture or any parameter or characteristic that causes green color reduction [2]. 2. Discussions To assess the crop status, the Normalized Difference Vegetation Index (NDVI) is used as a statistically significant correlation that has been established between this index and the foliar surface index, i.e. the vegetative development or biomass production.By definition NDVI is calculated with the Available online at http://journals.usamvcluj.ro/index.php/promediu ProEnvironment ProEnvironment 12 (2019) 246-249 246 brought to you by CORE View metadata, citation and similar papers at core.ac.uk