Abstract

Imaging from low altitudes is nowadays commonly used in remote sensing and photogrammetry. More and more often, in addition to acquiring images in the visible range, images in other spectral ranges, e.g., near infrared (NIR), are also recorded. During low-altitude photogrammetric studies, small-format images of large coverage along and across the flight route are acquired that provide information about the imaged objects. The novelty presented in this research is the use of the modified method of the dark-object subtraction technique correction with a modified Walthall’s model for correction of images obtained from a low altitude. The basic versions of these models have often been used to radiometric correction of satellite imagery and classic aerial images. However, with the increasing popularity of imaging from low altitude (in particular in the NIR range), it has also become necessary to perform radiometric correction for this type of images. The radiometric correction of images acquired from low altitudes is important from the point of view of eliminating disturbances which might reduce the capabilities of image interpretation. The radiometric correction of images acquired from low altitudes should take into account the influence of the atmosphere but also the geometry of illumination, which is described by the bidirectional reflectance distribution function (BRDF). This paper presents a method of radiometric correction for unmanned aerial vehicle (UAV) NIR images. The study presents a method of low-altitude image acquisition and a fusion of the method of the dark-object subtraction technique correction with a modified Walthall’s model. The proposed solution performs the radiometric correction of images acquired in the NIR range with the root mean square error (RMSE) value not exceeding 10% with respect to the original images. The obtained results confirm that the proposed method will provide effective compensation of radiometric disturbances in UAV images.

Highlights

  • The determination of the radiometric quality of images acquired from low altitudes using the bidirectional reflectance distribution function (BRDF) is a challenge in remote sensing and digital-image processing

  • In order to prove the efficiency of the developed radiometric correction method, additional comparison analyses were conducted for near infrared (NIR) images acquired from low altitudes for a sample of 898 images obtained within a measurement campaign in October 2017

  • The paper presents the results of research concerning the method of radiometric correction and its assessment for NIR images acquired from low altitudes

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Summary

Introduction

The determination of the radiometric quality of images acquired from low altitudes using the bidirectional reflectance distribution function (BRDF) is a challenge in remote sensing and digital-image processing. Radiometric corrections were performed mainly on satellite-imagery data and classical aerial images. It is one of the most important issues in modern photogrammetry and remote sensing, especially in its many practical applications related to the natural environment. The radiometric quality of images acquired from low altitudes or the impact of the BRDF on UAV image-brightness distribution has not been considered in a broader sense, until now. It has been mentioned in References [1,2]. The other group of semiempirical corrections takes into account the most important radiometric effects like the BRDF or models of the atmosphere [5]

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