Cotton yield prediction using remote visual and spectral images captured by UAV system

Abstract: Crop yield prediction is helpful for farmers to make reasonable agronomic decisions such as crop insurance, planning of harvest, storage requirement, cash flow budgeting and the determination of input factors. This paper presented an application for cotton yield prediction based on the remote visual and spectral images captured by a UAV (unmanned aerial vehicle) remote sensing system. Field experiments were carried out at a cotton field approximately 5 hm2. Images of the cotton field were captured by the UAV remote sensing system at a 50 m flight height before fully blooming. One RGB panoramic image and one CIR (color-infrared) panoramic image were obtained by stitching the collected partial images with 75% overlap. Yield data with GPS (global position system) information were registered respectively to the RGB and CIR images according to the GCPs (ground control points). Then 3 features including color feature, coverage rate and vegetation index were extracted from the images and used to develop predication models. Color feature was the hue channel in HSV (hue, saturation, value) color model. Coverage rate was calculated by using Excess Green value based on RGB (red, green, blue) color model. Vegetation index was NDVI (normalized difference vegetation index) value usually used to monitor the crop growth. The datasets including yield data and 3 features were randomly divided into training data (90% of raw data) for modeling and test data (10% of raw data) for evaluating the model accuracy. The training data were preprocessed though removing 10% partial outliers based on probability distribution of yield data and being smoothed by mean filter respectively. Then multiple linear regression models were built to predict cotton yield, and parameters of the models were estimated based on the least square method and calculated by SAS software. 3 parameters were used to evaluate the models including P value in F-test statistic, coefficient of determination R2, and MAPE (mean absolute percentage error) between predicted values and the ground truth data in acre area level. The results showed that 7 linear regression models built by 1 variable (color feature, coverage rate or vegetation index), 2 variables (color feature and coverage rate, color feature and vegetation index or coverage rate and vegetation index) and 3 variables (color feature, coverage rate and vegetation index) were all statistically significant at significance level 5%. However, the adequacy of the multiple linear regression model with 3 variables was the best due to the highest R2=0.977 3 compared to other 6 regression models built by 1 variable and 2 variables. So the multiple linear regression model with 3 variables was used to predict yield. And the average MAPEs on the multiple linear regression models built by 3 variables was 4.0% in acre area level. The results from this study indicate that combining visual and spectral features from image sensors can be used effectively to predict yield.