A comparative study on monitoring leaf-scale wheat aphids using pushbroom imaging and non-imaging ASD field spectrometers

Present paper provides information on comparing the spectral characteristics of leaf-scale wheat aphids using simultaneously the imaging Pushbroom Imaging Spectrometer (PIS) and non-imaging ASD (Analytical Spectral Devices) Fieldspec-FR2500 field spectrometer. Comparative results indicated that the PIS proved superior to the ASD in spectral resolution and sampling interval, but it was inferior in spectral range and field of view (FOV). Moreover, corresponding spectral properties were fairly similar including reflectance, spectral difference and change rate and the sensitive bands and spectral ranges. Spectral curves from both devices showed the typical reflectance properties of green vegetation: green peak at 550 nm, red valley at 680 nm and high near-infrared reflectance at 780 nm. However, the specific reflectance values appeared different for four damage levels (Normal, Light, Moderate & Serious). The maximum and minimum reflectance values were respectively 41.18% and 2.36% for the PIS, while they were 40.32% and 1.51% for the ASD, respectively. Specifically, in the wavelength range of 400-900 nm, they were similar in the spectral difference and change rate. The maximum values were respectively 14.8% and 14.0 % for the PIS, and they were 8.7% and 20.3% for the ASD, respectively. Additionally, continuum removal was used to compare the selection of sensitive bands and ranges, which were 500 nm and 663 nm, 430-530 nm and 550-690 nm for the ASD, while they were 504 nm and 681 nm, 430-530 nm and 550-730 nm for the PIS, respectively. Finally, using the high spatial resolution PIS image, environment for visualizing images (ENVI-EX) was also used to extract aphids. Overall accuracy attained was thus 97%. This study can explore further investigations in precision agriculture using near-ground imaging spectrometers.