A simplified empirical line calibration method for sUAS-based remote sensing

The use of small unmanned aircraft systems (sUAS) to acquire very high resolution multispectral imagery has attracted growing attention recently; however, no feasible and convenient radiometric calibration method has been specifically developed for sUAS remote sensing. In this research we used a modified color infrared (CIR) digital single-lens reflex (DSLR) camera as the sensor and the DJI S800 hexacopter sUAS as the platform to collect imagery. Results show that the relationship between image raw digital numbers (DNs) and the natural logarithm of measured surface reflectance is linear and the y-intercept of the linear equation can be interpreted as the minimal surface reflectance that can be detected by each sensor waveband. The empirical line calibration equation for every single band image can be built using the v-intercept as one data point, and the natural log-transformed measured reflectance and image DNs of a gray calibration target as another point in the coordinate system. Image raw DNs are therefore converted to reflectance using the calibration equation. The Mann-Whitney U test results suggest that the difference between the measured and predicted reflectance values of thirteen tallgrass sampling quadrats is not statistically significant. The method theory developed in this study can be effectively employed for other sUAS-based remote sensing applications.