Table 2.
The application and limitations of imaging techniques for plant phenotyping under different growing environments [23,41].
| Imaging Techniques | Growing Environment | Applications | Limitations |
|---|---|---|---|
| Visible imaging | Controlled environment | Growth dynamics, Shoot biomass, Yield traits, Panicle traits, Root architecture, Imbibition and germination rates, leaf morphology, seedling vigor, coleoptile length and biomass at anthesis, seed morphology, root architecture | Only provides plant physiological information |
| Field | Imaging canopy cover and canopy colour; colour information can be used for green indices; the use of 3D stereo reconstruction from multiple cameras or viewpoints allows the estimation of canopy architecture parameters | No spectral calibration; Only relative measurement; shadows and sunlight can result in under or over exposure and limit automatically processing image | |
| Fluorescence imaging | Controlled environment | Photosynthetic status, indirect measurement of biotic or abiotic | Difficult to analysis complicated whole-shoot of non-rosette species; pre-acclimation conditions required |
| Field | Photosynthetic status, indirect measurement of biotic or abiotic stress | Difficult to measure at the canopy scale, because of the small signal to noise ratio, though laser-induced fluorescence transients can extend the range available, while soar-induced fluorescence can be used remotely | |
| Thermal imaging | Controlled environment | Surface temperature; stomatal conductance water stress induced by biotic or abiotic factors | Imaging sensor calibration and atmospheric correction are often required; sound physics-based results interpretation needed |
| Field | Stomatal conductance; water stress induced by biotic or abiotic factors | Imaging sensor calibration and atmospheric correction are often required; Changes in ambient conditions lead to changes in canopy temperature, making a comparison through time difficult, necessitating the use of reference. Difficult to separate soil temperature from plant temperature in sparse canopies, limiting the automation of image processing. | |
| Imaging spectroscopy | Controlled environment | water content composition parameters for seeds; leaf area index; Leaf and canopy health status; panicle health status; leaf growth; Coverage density | Sensor calibration required; cost, large image data sets for hyperspectral imaging, complex data interpretation |
| Field | Biochemical composition of the leaf or canopy; pigment concentration; water content; indirect measurement of biotic or abiotic stress; canopy architecture, LAI or NDVI | Sensor calibration required; changes in ambient light conditions influence signal and need frequent white reference calibration; canopy structure and camera geometries or sun angle influence signal. Data management is challenging | |
| LIDAR | Controlled environment | Canopy height and canopy architecture; estimation of LAI; volume and biomass; reflectance from the laser can be used for retrieving spectral information | Specific illumination required for some laser scanning instruments |
| Field | Canopy height and canopy architecture; estimation of LAI; volume and biomass; reflectance from the laser can be used for retrieving spectral information | Integration or synchronization with GPS and encoder position systems is required for georeferencing |