Temporal Variability in Active Reflectance Sensor-Measured Ndvi in Soybean and Wheat Crops

Beneduzzi, Humberto Martins; Souza, Eduardo Godoy de; Bazzi, Claudio; Schenatto, Kelyn

doi:10.1590/1809-4430-eng.agric.v37n4p771-781/2017

Cited by 9 publications

(14 citation statements)

References 21 publications

(24 reference statements)

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“…The values for solar radiation during the readings at three heights (0.8, 1.0, and 1.2 m) ( Figures 3b, 3d, 3f, 3h, and 3j) show a greater variation of amplitude and were smaller during the first hours of the morning and the end of the afternoon; visually, however, it can be seen that these values were not significantly different among sensor heights. When the radiation readings were compared to the NDVI readings (Figures 3a, 3c, 3e, 3g and 3i), the NDVI showed inverse behavior compared to the radiation; that is, the higher the incidence of solar radiation the lower the NDVI, which was a result similar to that found by Souza et al (2010), Rahman et al (2015), and Beneduzzi et al (2017). An exception was stage 8 wheat, which was probably due to cloud cover.…”

Section: Resultssupporting

confidence: 61%

“…The sensor performs ten (10) readings per second, and 100 readings per position were performed, and the mean was calculated. Several authors, such as Souza et al (2010) and Beneduzzi et al (2017) have already observed the effect of the reading time of an active reflectance sensor. Therefore, is decided to perform readings during the day, from 7 am to 7 pm with a 30minute interval between the readings, for a total of 25 samples for each position.…”

Section: Methodsmentioning

confidence: 99%

“…However, varying the angle, provided no evident improvement of the performance of NDVI and SR as predictors of the biomass and grain yield. Beneduzzi et al (2017) investigated the temporal variability of NDVI measured by a GreenSeeker in both soybean and wheat crops. The NDVI data were collected using a GreenSeeker sensor every 15 minutes for 12 or 14 consecutive hours.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Height, Tilt and Twist Angles of an Active Reflectance Sensor on Ndvi Measurements

et al. 2019

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The application of nitrogen (N) fertilizer is complex and expensive, so its correct management has financial and environmental benefits. The use of optical proximity sensors is a promising technique. However, the movement of the agricultural machinery or of the person carrying the sensor will result in height differences and/or different tilt and twist angles with respect to the canopy. We considered whether these variations would affect the reflectance measurement. In this study, we took normalized difference vegetation index (NDVI) readings of a wheat canopy, to which 90 kg ha-1 of urea had been applied in stage 5, and observed the NDVI in stages 6, 8 and 10.5. We also tested soybeans, to which 90 kg ha-1 of urea had been applied in stage R1, and took NDVI readings in stages R2 and R5. Our goal was to study the effects of the position of an active reflectance sensor (GreenSeeker) on the NDVI index at different heights and at different angles to the canopy. We observed that the height of the sensor affected the NDVI depending on the stage of the plant and that angles up to 15° of the sensor did not directly affect the readings.

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Section: Resultssupporting

confidence: 61%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effect of Height, Tilt and Twist Angles of an Active Reflectance Sensor on Ndvi Measurements

et al. 2019

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“…Further study to characterize view angle effects at the scale of forest canopies may benefit from alternative sensor placement. In this study, the Unispec-DC instrument was placed on the south side of the tower, preventing observation of the hot spot where view angle effects on reflectance and spectral indices are most severe (Beneduzzi et al, 2017;Gamon et al, 2006). The hot spot, or 10.1029/2020JG005774…”

Section: Discussionmentioning

confidence: 99%

The Response of Spectral Vegetation Indices and Solar‐Induced Fluorescence to Changes in Illumination Intensity and Geometry in the Days Surrounding the 2017 North American Solar Eclipse

et al. 2020

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Remote sensing is a key method for advancing our understanding of global photosynthesis and is thus critical to understanding terrestrial carbon uptake and climate change. Increasingly sophisticated spectral indices including solar-induced florescence (SIF) and the photochemical reflectance index (PRI) are considered good proxies of canopy structure, biochemistry, and physiology. However, the relative influences of illumination intensity and angle on these measures are difficult to unravel, particularly at the scale of whole forest canopies. We exploit the solar dimming during the 2017 North American solar eclipse as well as a clear day before and cloudy day after the day of the eclipse. This novel approach allows us to assess changes in spectral vegetation indices due to illumination intensity independent of changes in illumination angle. Physiologically relevant spectral indices were most affected by dimming, with illumination level explaining 97% of variability in SIF and 99% of variability in PRI during the eclipse. The spectral change in reflectance through the eclipse period revealed changes in PRI were driven by reflectance differences at the 570 nm reference band rather than at the 531 nm signal band associated with xanthophyll pigment interconversions. This study refines our interpretation of vegetation properties from space with implications for our interpretation of signals related to terrestrial photosynthesis derived from sensors spanning a range of illumination conditions and angles.

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“…The sensor was mounted on a telescoping handheld pole and held horizontally above the canopy while measuring. Measurements were taken within 2 h from local solar noon to minimize influences by solar irradiation differences [35]. For T. cordata, due to stem length increases, measurements with the GreenSeeker were only possible in 2016.…”

Section: Optical Measurements At Canopy Levelmentioning

confidence: 99%

Application of Proximal Optical Sensors to Fine-Tune Nitrogen Fertilization: Opportunities for Woody Ornamentals.

Bracke

Elsen²,

Adriaenssens³

et al. 2019

Agronomy

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Today, high amounts of residual nitrogen are regularly being reported in the open field production of hardy nursery stock. In some cases, excessive fertilizers or side-dressings are applied when circumstances are not favorable for uptake. Aquatic as well as terrestrial ecosystems are sensitive to enrichment with nutrients, but growers also benefit when losses are avoided. In this study, the potential of proximal optical sensors to optimize nitrogen fertilization was investigated in four woody species: Acer pseudoplatanus L., Ligustrum ovalifolium Hassk., Prunus laurocerasus 'Rotundifolia' L. and Tilia cordata Mill. For three consecutive growing seasons, plants were grown under three different fertilization levels to generate different nitrogen contents. Plant growth and nitrogen uptake were monitored regularly and combined with sensor measurements including Soil Plant Analysis Development (SPAD), Dualex and GreenSeeker. Here, we show that optical sensors at the leaf level have good potential for assisting growers in the sustainable management of their nursery fields, especially if leaf mass per area is included. Nevertheless, care should be taken when plants with different leaf characteristics (e.g., wax-layer, color, and leaf thickness) are measured. When all measuring years were considered, high correlations (R 2 ≥ 0.80) were found between area-based foliar nitrogen content and its non-destructive proxy (i.e., chlorophyll)measured by Dualex or SPAD. Based on our results, we recommend a relative rather than absolute approach at the nursery level, as the number of species and cultivars produced is very diverse. Hence, knowledge of absolute threshold values is scarce. In this relative approach, a saturation index was calculated based on the sensor measurements of plants grown in a reference plot with an ample nitrogen supply.Agronomy 2019, 9, 408 2 of 24 crop and soil type. Farmers are encouraged to apply well-considered nitrogen fertilization. However, high amounts of residual nitrogen are regularly being reported for the open field production of ornamental trees and shrubs. Opposed reasons are an incorrect nitrogen fertilization strategy and a mismatch between timing of N fertilization and N uptake by plants [2].Despite diverse research on fertilizer rates in woody ornamentals, there is a lot of variation in recommended fertilizer use. Some authors report little or no effect of fertilizers on ornamental plant quality (e.g., height and length) [3,4], others do find effects [5,6], and others report mixed results depending on the species [7]. According to Rose, suggested annual N rates vary between 48 and 287 kg N ha −1 [8]. The author emphasized that these rates are based on research from the 1950s to the 1970s when maximizing the fertilizer response was the primary goal and other parameters such as soil N content, yield potential and field history were not taken into account. This is indeed very important for open field production with big differences in soil organic matter content, soil type, water availability,...

show abstract

Temporal Variability in Active Reflectance Sensor-Measured Ndvi in Soybean and Wheat Crops

Cited by 9 publications

References 21 publications

Effect of Height, Tilt and Twist Angles of an Active Reflectance Sensor on Ndvi Measurements

Effect of Height, Tilt and Twist Angles of an Active Reflectance Sensor on Ndvi Measurements

The Response of Spectral Vegetation Indices and Solar‐Induced Fluorescence to Changes in Illumination Intensity and Geometry in the Days Surrounding the 2017 North American Solar Eclipse

Application of Proximal Optical Sensors to Fine-Tune Nitrogen Fertilization: Opportunities for Woody Ornamentals.

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