Drone-Based Hyperspectral and Thermal Imagery for Quantifying Upland Rice Productivity and Water Use Efficiency after Biochar Application

Abstract

Miniature hyperspectral and thermal cameras onboard lightweight unmanned aerial vehicles (UAV) bring new opportunities for monitoring land surface variables at unprecedented fine spatial resolution with acceptable accuracy. This research applies hyperspectral and thermal imagery from a drone to quantify upland rice productivity and water use efficiency (WUE) after biochar application in Costa Rica. The field flights were conducted over two experimental groups with bamboo biochar (BC1) and sugarcane biochar (BC2) amendments and one control (C) group without biochar application. Rice canopy biophysical variables were estimated by inverting a canopy radiative transfer model on hyperspectral reflectance. Variations in gross primary productivity (GPP) and WUE across treatments were estimated using light-use efficiency and WUE models respectively from the normalized difference vegetation index (NDVI), canopy chlorophyll content (CCC), and evapotranspiration rate. We found that GPP was increased by 41.9 ± 3.4% in BC1 and 17.5 ± 3.4% in BC2 versus C, which may be explained by higher soil moisture after biochar application, and consequently significantly higher WUEs by 40.8 ± 3.5% in BC1 and 13.4 ± 3.5% in BC2 compared to C. This study demonstrated the use of hyperspectral and thermal imagery from a drone to quantify biochar effects on dry cropland by integrating ground measurements and physical models.

Effect of the Shadow Pixels on Evapotranspiration Inversion of Vineyard: A High-Resolution UAV-Based and Ground-Based Remote Sensing Measurements

“…Surprisingly, the shadow detection process had a positive influence on the quantification of vineyard evapotranspiration, with the accuracy of ET being improved by 4.59-6.82%. Simultaneously, our results demonstrate that the spatial heterogeneity of ET can be seen in the vineyard (Figure 9), with the grapes being comparable to other crops such as peaches and nectarines that are grown in orchards [19] and upland rice [51]. Moreover, the mean evaporation and transpiration fluxes were 238.05 and 208.79 W m −2 , respectively, and crop transpiration accounted for 46.7% of evapotranspiration.…”

Canopy Temperature Is Regulated by Ecosystem Structural Traits and Captures the Ecohydrologic Dynamics of a Semiarid Mixed Conifer Forest Site

“…Thermal sensors placed on UAS represent an opportunity to fill this gap that provides a lower‐cost approach to meet the critical requirements of spatial, spectral, and temporal resolutions (Berni et al., 2009). Although thermal UAS platforms have been used to assess vegetation water stress (Jin et al., 2021; Zhang et al., 2019), studies integrating satellite and UAS thermal data to assess diurnal vegetation water stress are currently lacking.…”

Investigating the impacts of biochar on water fluxes in a rice experiment in the dry corridor of Central America, Costa Rica

“…Instead, the suction lysimeters and soil moisture sensors considered in this study provide a similar and a rather small sampling or sensor footprint. While in‐situ sensors provided useful insights on the temporal variably of different variables and differences within and between treatments, the informative value is spatially rather limited when compared with the remotely sensed spatial data presented by Jin et al (2021). Therefore, future studies should combine spatial sparse but high temporal in situ sensors with spatial snapshot multisensory information (hyperspectral and thermal imagery) obtained for example from unmanned aerial vehicles to estimate the gross primary productivity and water use efficiency allowing to investigate the effect of biochar at the field scale where management decisions are made (Jin et al, 2021).…”

“…Thus, the BC2 soil likely had relatively larger macropores that could have increased the connectivity of the 20 cm soil layer where biochar was applied with deeper soil layers. high temporal in situ sensors with spatial snapshot multisensory information (hyperspectral and thermal imagery) obtained for example from unmanned aerial vehicles to estimate the gross primary productivity and water use efficiency allowing to investigate the effect of biochar at the field scale where management decisions are made (Jin et al, 2021).…”

“…Although the experimental design was somewhat unbalanced (different size of BC1 and C compared to BC2 and different biochar typology and age), which could be problematic when studying the effect of biochar on yield, the random and multiple plant sampling within each plot likely minimizes boundary effects or design effects relevant for our results.Instead, the suction lysimeters and soil moisture sensors considered in this study provide a similar and a rather small sampling or sensor footprint. While in-situ sensors provided useful insights on the temporal variably of different variables and differences within and between treatments, the informative value is spatially rather limited when compared with the remotely sensed spatial data presented byJin et al (2021). Therefore, future studies should combine spatial sparse butF I G U R E 8 The dual isotope space with the isotopic composition of irrigation (down facing triangle), mobile soil water collected at 15 cm (SW 15 , diamond) and 40 cm (SW 40 , cross) and groundwater (upward facing triangle).…”