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热红外高光谱遥感影像信息提取方法综述

曹丽琴1, 汪都2, 熊海洋2, 钟燕飞2(1.武汉大学资源与环境学院;2.武汉大学测绘遥感信息工程国家重点实验室)

摘 要
热红外高光谱遥感影像蕴含着丰富的光谱特性和温度信息,能够反映出地物、气体等特有的诊断特征,在矿物识别、环境监测、军事等众多领域发挥着重要作用。然而,由于热红外高光谱观测数据受到地表温度和发射率、大气环境、仪器测量噪声等的共同影响,引起背景噪声与目标信号差异较小、耦合信号无法精确分离等问题,使得热红外高光谱影像信息提取存在巨大的挑战,应用难以有效实施。本文针对热红外高光谱信息提取的研究进展和现存难点,系统梳理热红外高光谱影像信息提取方法,主要包括地表温度和发射率地表参量反演、热红外高光谱混合光谱分解、影像分类及目标探测。并在此基础上,总结现有热红外高光谱信息提取的现状和问题,并展望热红外高光谱遥感影像信息提取未来可能的发展趋势和研究方向。
关键词
A review of information extraction methods from thermal infrared hyperspectral remote sensing images

Cao Liqin, Wang Du1,2, Xiong Haiyang1,2, Zhong Yanfei1,2(1.State Key Laboratory of Information Engineering in Surveying,Mapping,and Remote Sensing,Wuhan University,Wuhan,;2.China)

Abstract
Longwave infrared (LWIR) hyperspectral remote sensing images offer a wealth of spectral information alongside land surface temperature data, rendering them invaluable for discerning solid-phase materials and gases. This capability holds significant implications across diverse domains, including mineral identification, environmental monitoring, and military applications. However, the underlying phenomenology and environmental interactions of emissive regions within the LWIR spectrum significantly diverge from those observed in reflective regions, thereby impacting various facets of thermal infrared (IR) hyperspectral image (HSI) analysis, spanning from sensor design considerations to data exploitation methodologies. Compounding this complexity are the intertwined influences of factors such as land surface temperature, emissivity, atmospheric profiles, and instrumental noise, leading to challenges such as subtle distinctions between background noise and target signals, as well as inaccuracies in signal separation within thermal infrared hyperspectral observation data. Consequently, the effective extraction of thermal infrared hyperspectral image information poses formidable challenges for practical application implementation. In this paper, we systematically review methods for LWIR hyperspectral image information extraction, drawing upon ongoing research progress and addressing prevailing challenges in LIWR hyperspectral remote sensing. Our examination encompasses four primary areas: (1) Land surface temperature and emissivity inversion: LWIR hyperspectral remote sensing serves as a potent tool for large-scale land surface temperature (LST) and land surface emissivity (LSE) monitoring. However, the accurate retrieval of LST and LSE is fraught with complexity owing to their intricate coupling with atmospheric components, as delineated by the radiative transfer equation. To mitigate this ill-posed problem, we discuss two broad approaches: the two-step method and the integration method. The former entails atmospheric compensation (AC) and temperature and emissivity separation (TES), where AC filters out atmospheric influences to isolate ground-leaving radiance from at-sensor radiance. Subsequently, TES methods are employed to estimate LST and LSE. Given the propensity for inaccurate AC to introduce accumulation errors and compromise retrieval accuracy, integration methods capable of simultaneous atmospheric compensation and temperature and emissivity separation are also reviewed, with deep learning-driven methods exemplifying a typical integration approach. (2) LWIR hyperspectral mixed spectral decomposition: Spectral mixture analysis (SMA) involves identifying and extracting endmember spectra in a scene to determine the abundance of each endmember within each pixel. Most applications of LWIR SMA focus on mineral detection and classification. Unlike the reflectance of a mixed pixel, which is defined as a linear combination within the pixel, the emissivity of a mixed pixel is not as straightforward to define because the measured radiance depends on both the emissivity and temperature of each material. The mixed spectral decomposition methods for isothermal and non-isothermal pixels were discussed. When a pixel is isothermal, the isothermal mixture model is identical to the mixture for reflectance after removing the temperature component. However, as a pixel becomes non-isothermal, unmixing methods are necessary to handle the nonlinearity resulting from temperature variations. This paper summarizes all the methods and highlights the challenges associated with SMA in this work. (3) Classification: Classification tasks in the LWIR domain involve successfully modeling and classifying background materials, such as minerals and vegetation mapping. However, the scarcity of prominent spectral features in the LWIR spectrum complicates the remote differentiation of natural land surfaces. For instance, various materials such as paints, water, soil, road surfaces, and vegetation exhibit spectral emissivities ranging between 0.8 and 0.95. Moreover, while there are spectral emissivity variations among different materials, they are less conspicuous compared to the reflective region. Additionally, the uncertainty associated with retrieved emissivity further challenges the classification of different materials. This paper reviews traditional machine learning classification methods, including spectral-based, spatial-based, and spectral-spatial integration-based methods, alongside deep learning approaches, summarizing the advancements in these processing methods. (4) Target detection: Target detection encompasses both solid-phase and gas-phase targets. The algorithms employed for LWIR hyperspectral image (HIS) analysis, similar to those used for visible-near infrared (VNIR) and shortwave infrared (SWIR) HIS, have reached a mature stage and are reviewed in this work, including Matched filter-(MF)-type algorithms, among others. Challenges in target detection mirror those encountered in classification tasks, as spectral emissivities in the LWIR tend to be smaller than the corresponding spectral reflectance variations observed in the reflective region. Consequently, the performance of solid-phase target detection algorithms in real-world applications is impacted, particularly by their sensitivity to target-background model mismatch arising from similar emissivities and other errors. In contrast, gas detection in the LWIR domain relies on selective absorption and emission phenomena, particularly by chemical vapors, which exhibit narrow spectral features. Although gas plumes may span a large number of pixels, their detection depends on factors such as concentration, signature strength, and temperature contrast with the background materials. Consequently, chemical detection applications necessitate rigorous physical processes in both airborne (down-looking) and standoff (side-looking) configurations. In addition to employing strict physical and statistical models, gas detection methodologies are increasingly integrating deep learning models. This trend reflects the recognition of the potential of deep learning in enhancing the capabilities of gas detection algorithms. Our discourse concludes with a discussion on the future trajectory and research direction of thermal infrared hyperspectral remote sensing image information extraction. Despite the continual integration of new technical methodologies such as deep learning, the computational intricacies inherent in LWIR hyperspectral remote sensing underscore the necessity of approaches that combine physical mechanisms with machine learning models. These hybrid methodologies hold promise in addressing the multifaceted challenges associated with LWIR hyperspectral image analysis, thereby paving the way for enhanced information extraction and practical application implementations.
Keywords

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