Abstract
Images acquired at a low altitude can be the source of accurate information about various environmental phenomena. Often, however, this information is distorted by various factors, so a correction of the images needs to be performed to recreate the actual reflective properties of the imaged area. Due to the low flight altitude, the correction of images from UAVs (unmanned aerial vehicles) is usually limited to noise reduction and detector errors. The article shows the influence of the Sun position and platform deviation angles on the quality of images obtained by UAVs. Tilting the camera placed on an unmanned platform leads to incorrect exposures of imagery, and the order of this distortion depends on the position of the Sun during imaging. An image can be considered in three-dimensional space, where the x and y coordinates determine the position of the pixel and the third dimension determines its exposure. This assumption is the basis for the proposed method of image exposure compensation. A three-dimensional transformation by rotation is used to determine the adjustment matrix to correct the image quality. The adjustments depend on the angles of the platform and the difference between the direction of flight and the position of the Sun. An additional factor regulates the value of the adjustment depending on the ratio of the pitch and roll angles. The experiments were carried out for two sets of data obtained with different unmanned systems. The correction method used can improve the block exposure by up to 60%. The method gives the best results for simple systems, not equipped with lighting compensation systems.
Highlights
In recent years, the use of imagery from unmanned aerial vehicles (UAV) in many diverse fields of science and technology has been very popular
The proposed approach cannot be separated from other aspects of the radiometric correction process of images acquired by UAVs
The approach proposed here should be considered as only one aspect of the complex process of radiometric correction of images acquired by UAVs
Summary
The use of imagery from unmanned aerial vehicles (UAV) in many diverse fields of science and technology has been very popular. Images from a low altitude can be considered as a source of accurate information about various environmental phenomena, which is why UAVs are often used to monitor agriculture [1], vegetation [2], waters [3], and others. In such works, the main task is to analyze images in order to detect selected phenomena based on a comparison of the spectral properties of the imaged objects. Image correction is necessary to reproduce the actual reflection coefficients of the objects
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