Author Contributions
Conceptualization, F.H.H., M.J.W., M.J.H. and A.B.R.; data curation, F.H.H., M.C. and A.B.R.; methodology, F.H.H and M.J.W. and A.B.R.; resources, M.J.W., M.J.H. and A.B.R; software, F.H.H; supervision, M.J.W., M.J.H. and A.B.R; validation, F.H.H; visualization, F.H.H; writing—original draft, F.H.H; writing—review and editing, F.H.H., M.J.W., M.J.H. and A.B.R.
Figure 1.
Flow chart of key processing steps used to convert raw images to reflectance images. The blue circles indicate inputs, green squares indicate processing steps and yellow squares derived products.
Figure 1.
Flow chart of key processing steps used to convert raw images to reflectance images. The blue circles indicate inputs, green squares indicate processing steps and yellow squares derived products.
Figure 2.
Relative Spectral response of the two Sony cameras used in this study. Vertical dotted line indicates the 830 nm blocking filter present in the adapted Sony NIR camera.
Figure 2.
Relative Spectral response of the two Sony cameras used in this study. Vertical dotted line indicates the 830 nm blocking filter present in the adapted Sony NIR camera.
Figure 3.
Linear relationships and R2 between camera exposure settings, (a) aperture and (b) ISO, and image digital numbers. For (a) Aperture, f-numbers have been converted from ‘stops’ to aperture diameter via 1/f-stop2.
Figure 3.
Linear relationships and R2 between camera exposure settings, (a) aperture and (b) ISO, and image digital numbers. For (a) Aperture, f-numbers have been converted from ‘stops’ to aperture diameter via 1/f-stop2.
Figure 4.
The input NIR image (left), generated vignetting filter (middle) and vignetting corrected image (right).
Figure 4.
The input NIR image (left), generated vignetting filter (middle) and vignetting corrected image (right).
Figure 5.
Results of relationships between exposure and vignetting corrected image DNs and Tec5 spectrometer reflectance in wavebands (a) Blue, (b) Green, (c) Red and (d) Near Infrared (NIR). All camera bands show strong linear agreements with Tec5 reflectance. Measurements of five black, grey and white spectral reflectance targets were used for this.
Figure 5.
Results of relationships between exposure and vignetting corrected image DNs and Tec5 spectrometer reflectance in wavebands (a) Blue, (b) Green, (c) Red and (d) Near Infrared (NIR). All camera bands show strong linear agreements with Tec5 reflectance. Measurements of five black, grey and white spectral reflectance targets were used for this.
Figure 6.
Example image of an RGB image of wheat trial plots and right the ExGR mask output. In the ExGR mask, white represents green classified pixels and black non-green pixels. Imagery is from the 21 June 2017 UAV data collection campaign.
Figure 6.
Example image of an RGB image of wheat trial plots and right the ExGR mask output. In the ExGR mask, white represents green classified pixels and black non-green pixels. Imagery is from the 21 June 2017 UAV data collection campaign.
Figure 7.
Assessment of the cumulative influence of correction steps on the precision of scaled mean plot measurements in the Red band. Scaled reflectance for (a) Raw, (b) Irradiance, (c) Exposure and (d) Vignetting corrected images are compared to scaled COTS camera convolved Tec5 measurements of mean plot reflectance. The dashed line represents the 1:1 line.
Figure 7.
Assessment of the cumulative influence of correction steps on the precision of scaled mean plot measurements in the Red band. Scaled reflectance for (a) Raw, (b) Irradiance, (c) Exposure and (d) Vignetting corrected images are compared to scaled COTS camera convolved Tec5 measurements of mean plot reflectance. The dashed line represents the 1:1 line.
Figure 8.
Assessment of the cumulative influence of correction steps on the precision of scaled mean plot measurements in the NIR band. Scaled reflectance for (a) Raw, (b) Irradiance, (c) Exposure and (d) Vignetting corrected images are compared to scaled COTS camera convolved Tec5 measurements of mean plot reflectance. The dashed line represents the 1:1 line.
Figure 8.
Assessment of the cumulative influence of correction steps on the precision of scaled mean plot measurements in the NIR band. Scaled reflectance for (a) Raw, (b) Irradiance, (c) Exposure and (d) Vignetting corrected images are compared to scaled COTS camera convolved Tec5 measurements of mean plot reflectance. The dashed line represents the 1:1 line.
Figure 9.
Assessment of the cumulative influence of radiometric corrections applied to COTS camera-derived NDVI. Results for (a) Raw, (b) Irradiance, (c) Exposure and (d) Vignetting corrected NDVI are compared to scaled COTS camera convolved Tec5 measurements of mean plot NDVI. Dashed line indicates the 1:1 line.
Figure 9.
Assessment of the cumulative influence of radiometric corrections applied to COTS camera-derived NDVI. Results for (a) Raw, (b) Irradiance, (c) Exposure and (d) Vignetting corrected NDVI are compared to scaled COTS camera convolved Tec5 measurements of mean plot NDVI. Dashed line indicates the 1:1 line.
Figure 10.
Exposure value for the RGB and NIR cameras over the duration of a flight showing the cameras adjusting exposure independently. Data is from the flight on 21 June 2017.
Figure 10.
Exposure value for the RGB and NIR cameras over the duration of a flight showing the cameras adjusting exposure independently. Data is from the flight on 21 June 2017.
Figure 11.
Accuracy assessments of blue band reflectance for three dates. Tec5 reflectance is convolved to the spectral response of the COTS cameras for comparison. The points are coloured based on nitrogen treatment applied to the plot. Standard deviation of reflectance measured by the COTS cameras is presented by vertical error bars. The dashed line represents the 1:1 line.
Figure 11.
Accuracy assessments of blue band reflectance for three dates. Tec5 reflectance is convolved to the spectral response of the COTS cameras for comparison. The points are coloured based on nitrogen treatment applied to the plot. Standard deviation of reflectance measured by the COTS cameras is presented by vertical error bars. The dashed line represents the 1:1 line.
Figure 12.
Accuracy assessments of green band reflectance for three dates. Tec5 reflectance is convolved to the spectral response of the COTS cameras for comparison. The points are coloured based on nitrogen treatment applied to the plot. Standard deviation of reflectance measured by the COTS cameras is presented by vertical error bars. The dashed line represents the 1:1 line.
Figure 12.
Accuracy assessments of green band reflectance for three dates. Tec5 reflectance is convolved to the spectral response of the COTS cameras for comparison. The points are coloured based on nitrogen treatment applied to the plot. Standard deviation of reflectance measured by the COTS cameras is presented by vertical error bars. The dashed line represents the 1:1 line.
Figure 13.
Accuracy assessments of red band reflectance for three dates. Tec5 reflectance is convolved to the spectral response of the COTS cameras for comparison. The points are coloured based on nitrogen treatment applied to the plot. Standard deviation of reflectance measured by the COTS cameras is presented by vertical error bars. The dashed line represents the 1:1 line.
Figure 13.
Accuracy assessments of red band reflectance for three dates. Tec5 reflectance is convolved to the spectral response of the COTS cameras for comparison. The points are coloured based on nitrogen treatment applied to the plot. Standard deviation of reflectance measured by the COTS cameras is presented by vertical error bars. The dashed line represents the 1:1 line.
Figure 14.
Accuracy assessments of NIR band reflectance for three dates. Tec5 reflectance is convolved to the spectral response of the COTS cameras for comparison. The points are coloured based on nitrogen treatment applied to the plot. Standard deviation of reflectance measured by the COTS cameras is presented by vertical error bars. The dashed line represents the 1:1 line.
Figure 14.
Accuracy assessments of NIR band reflectance for three dates. Tec5 reflectance is convolved to the spectral response of the COTS cameras for comparison. The points are coloured based on nitrogen treatment applied to the plot. Standard deviation of reflectance measured by the COTS cameras is presented by vertical error bars. The dashed line represents the 1:1 line.
Figure 15.
Accuracy assessments COTS camera-derived NDVI for three dates. The points are coloured based on nitrogen treatment applied to the plot. Standard deviation of reflectance measured by the COTS cameras is presented by vertical error bars. The dashed line represents the 1:1 line.
Figure 15.
Accuracy assessments COTS camera-derived NDVI for three dates. The points are coloured based on nitrogen treatment applied to the plot. Standard deviation of reflectance measured by the COTS cameras is presented by vertical error bars. The dashed line represents the 1:1 line.
Figure 16.
Comparison of accuracies achieved by COTS (blue) cameras and Parrot Sequoia (red) in (a) green, (b) red and (c) NIR reflectance and (d) NDVI. Comparisons are made against Tec5 measure reflectances and NDVI. Reflectance was measured from both cameras on the same date (21 June 2017), whilst Tec5 measurements were collected two days later. The dashed line represents the 1:1 line.
Figure 16.
Comparison of accuracies achieved by COTS (blue) cameras and Parrot Sequoia (red) in (a) green, (b) red and (c) NIR reflectance and (d) NDVI. Comparisons are made against Tec5 measure reflectances and NDVI. Reflectance was measured from both cameras on the same date (21 June 2017), whilst Tec5 measurements were collected two days later. The dashed line represents the 1:1 line.
Figure 17.
Example subset of NDVI orthomosaics from three dates—27 March 2017 (left), 18 May 2017 (middle), 21 June 2017 (right). Orthomosaics highlight the spatial variability of NDVI both between and within plots.
Figure 17.
Example subset of NDVI orthomosaics from three dates—27 March 2017 (left), 18 May 2017 (middle), 21 June 2017 (right). Orthomosaics highlight the spatial variability of NDVI both between and within plots.
Figure 18.
Temporal trends of ten wheat cultivars grown under four different nitrogen treatments for: (a) the standard unmasked mean NDVI; (b) mean NDVI derived from ExGR masked plots to remove the influence of background soil; (c) displaying temporal differences between masked and unmasked NDVI results; (d) percentage green pixel as calculated from the ExGR masks. Nitrogen application dates and quantities for the N2, N3 and N4 treatments are presented by the vertical lines. All data represent the means of three replicates.
Figure 18.
Temporal trends of ten wheat cultivars grown under four different nitrogen treatments for: (a) the standard unmasked mean NDVI; (b) mean NDVI derived from ExGR masked plots to remove the influence of background soil; (c) displaying temporal differences between masked and unmasked NDVI results; (d) percentage green pixel as calculated from the ExGR masks. Nitrogen application dates and quantities for the N2, N3 and N4 treatments are presented by the vertical lines. All data represent the means of three replicates.
Table 1.
Details of the four nitrogen treatments applied to the diversity field experiment for 2017.
Table 1.
Details of the four nitrogen treatments applied to the diversity field experiment for 2017.
Treatment Code | Total Nitrogen Application (kg N ha−1) | Application Date | Nitrogen Applied (kg n ha−1) |
---|
N1 | 0 | - | 0 |
| | - | 0 |
| | - | 0 |
N2 | 100 | 15/03/2017 | 50 |
| | 05/04/2017 | 50 |
| | 09/05/2017 | 0 |
N3 | 200 | 15/03/2017 | 50 |
| | 05/04/2017 | 100 |
| | 09/05/2017 | 50 |
N4 | 350 | 15/03/2017 | 50 |
| | 05/04/2017 | 250 |
| | 09/05/2017 | 50 |
Table 2.
Spectral sensitivities for the Parrot Sequoia’s four spectral bands.
Table 2.
Spectral sensitivities for the Parrot Sequoia’s four spectral bands.
Camera Channel | Wavelength Range (nm) |
---|
Green | 530–570 |
Red | 640–680 |
Red Edge | 730–740 |
NIR | 770–810 |
Table 3.
Sony α5100 camera band sensitivities. Sensitivities were measured using a double monochromator fitted with an integrating sphere.
Table 3.
Sony α5100 camera band sensitivities. Sensitivities were measured using a double monochromator fitted with an integrating sphere.
Model | Channel | Wavelength Range (nm) |
---|
“RGB” Camera | Red | 580–660 |
| Green | 420–610 |
| Blue | 410–540 |
“NIR” Camera | NIR (blue channel) | 800–900 |
Table 4.
Details of DCRAW settings used to convert images from raw to Tagged Image File Format (TIFF).
Table 4.
Details of DCRAW settings used to convert images from raw to Tagged Image File Format (TIFF).
DCRAW Command | Action |
---|
–v | Print verbose messages |
–6 | Write 16bit |
–W | No automatic image brightening |
–g 1 1 | Apply unadjusted gamma curve |
–T | Write Tiff format |
–r 1 1 1 1 | Set unadjusted white balance |
–t 0 | Do not rotate image |
–q 0 | Apply linear demosaicing |
–o 0 | Raw output colour space |
–K darkimage.pgm | Apply dark image correction using file specified |
Table 5.
Calibration equations for each of the four camera bands. Equations were derived from comparison of camera and Tec5 measurements of five reference targets.
Table 5.
Calibration equations for each of the four camera bands. Equations were derived from comparison of camera and Tec5 measurements of five reference targets.
Camera and Band | Calibration Equation |
---|
RGB-Blue | |
RGB-Green | |
RGB-Red | |
NIR-Blue | |
Table 6.
Processing settings for Agisoft Photoscan. The same settings were used for all Orthomosaics generated.
Table 6.
Processing settings for Agisoft Photoscan. The same settings were used for all Orthomosaics generated.
Processing Step | Setting |
---|
Align photos | High |
Generate dense point cloud | Medium |
Generate mesh | High |
Generate orthomosaic | Disabled |