Estimating cabbage physical parameters using remote sensing technology

Remote sensing has long been used as a tool to extract plant growth and yield information for many crops, but little research has been conducted on cabbage (Brassica oleracea var. capitata L.) with this technology. The objective of this study was to evaluate aerial photography and field reflectance spectra for estimating cabbage physical parameters. An experiment was conducted on a cabbage field with 81 experimental plots to which different insecticide treatments were applied. Aerial color-infrared (CIR) photographs were taken from the field shortly before harvest. Meanwhile, field reflectance spectra and four plant physical parameters, including plant diameter, head diameter, plant weight and head weight, were measured from a total of 243 plants (three plants per plot). Plant area and spectral digital values for the near-infrared, red and green bands for each of the 243 plants were extracted from a digitized aerial CIR photograph. Four different vegetation indices, including the normalized difference vegetation index (NDVI), were calculated. Correlation analysis showed that the cabbage physical parameters were significantly related to the photo-derived plant area and spectral variables. Regression analysis showed that head weight was linearly related to plant area with an r2 value of 0.91 and quadratically related to NDVI with an r2 value of 0.66. Stepwise regression performed on cabbage head weight and 601 bands from 400 to 1000 nm in the field reflectance spectra revealed that 71% of the variability in head weight could be explained by eight significant bands in the spectra. As an application example, cabbage yield estimated from photo-derived plant area in each plot was used to compare the differences among 16 treatments. These results indicate that remote sensing can be a useful tool for evaluating cabbage growth and yield variations.