Evaluation of the Radiometric Accuracy of Images Obtained by a Sequoia Multispectral Camera

Abstract

Geometric and radiometric corrections of images obtained by remotely piloted aircraft systems (RPAS) are required for the measurement of the spectral reflectance and calculation of vegetation indices. This study aimed to determine which radiometric calibration procedures allow obtaining suborbital images with more accurate reflectance data and spectral indices based on data collected by a Sequoia multispectral camera coupled to a RPAS on black oat cultivations at the flowering stage located in Eldorado do Sul, RS, Brazil. The orthophoto mosaics were processed without and with radiometric corrections by reflectance calibration ground target and/or solar irradiance sensor of the camera, and the radiometric accuracy of these images was evaluated using spectral reflectance ground data collected by the Crop Circle canopy sensor. The results indicated that the use of a reflectance calibration ground target is recommended to increase the radiometric accuracy of photographs even if the Sequoia solar irradiance sensor is employed. The use of the light gray target in the radiometric calibration resulted in orthophotos with the mean square error of reflectance values lower than 0.01 for all the analyzed bands and spectral indices.

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“…The Parrot equipment presents 2 sensors: a multispectral camera and a light sensor to monitor sunlight intensity. The multispectral sensor has four (1.2 megapixels) monochrome cameras: green, red, red edge, near-infrared, and 16 MP RGB [55]. Their RGB and multispectral spatial resolution were of 1.2 cm/px and 3.8 cm/x, respectively [56].…”