Towards a Framework for Noctilucent Cloud Analysis

Puneet Sharma,Peter Dalin,Ingrid Mann

doi:10.3390/rs11232743

Puneet Sharma, Peter Dalin + Show 1 more

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https://doi.org/10.3390/rs11232743

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Abstract

In this paper, we present a framework to study the spatial structure of noctilucent clouds formed by ice particles in the upper atmosphere at mid and high latitudes during summer. We studied noctilucent cloud activity in optical images taken from three different locations and under different atmospheric conditions. In order to identify and distinguish noctilucent cloud activity from other objects in the scene, we employed linear discriminant analysis (LDA) with feature vectors ranging from simple metrics to higher-order local autocorrelation (HLAC), and histogram of oriented gradients (HOG). Finally, we propose a convolutional neural networks (CNN)-based method for the detection of noctilucent clouds. The results clearly indicate that the CNN-based approach outperforms the LDA-based methods used in this article. Furthermore, we outline suggestions for future research directions to establish a framework that can be used for synchronizing the optical observations from ground-based camera systems with echoes measured with radar systems like EISCAT in order to obtain independent additional information on the ice clouds.

Highlights

Noctilucent clouds (NLC) that can be seen by the naked eye and polar mesospheric summer echoes (PMSE) observed with radar display the complex dynamics of the atmosphere at approximately 80 to 90 km height [1]
Our results indicate that the performance of the convolutional neural networks (CNN)-based approach exceeds that of the linear discriminant analysis (LDA) based approaches used in this paper
We outline a framework to study noctilucent cloud activity for an image dataset associated with three different locations and different atmospheric conditions

Summary

Introduction

Noctilucent clouds (NLC) that can be seen by the naked eye and polar mesospheric summer echoes (PMSE) observed with radar display the complex dynamics of the atmosphere at approximately 80 to 90 km height [1]. PMSE and NLC display wavy structures (as shown Figure 1) around the summer mesopause, a region that is highly dynamical with turbulent vortices and waves of scales from a few km to several thousand km Analysis of these structures in the upper Earth atmosphere gives us information on the dynamics in this region. The time-series analyses of satellite observations in combination with model calculations indicate that the cloud frequencies are influenced by factors like stratospheric temperature, volcanic activity, and solar cycle [8,9]. In this context the comparison of NLC and PMSE will improve the understanding of their formation processes

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