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Dear Afeworki Welday, thank you for your message.
You are correct that most spaceborne and airborne hyperspectral sensors operate in the visible-near-infrared (VNIR) and shortwave infrared (SWIR) wavelength ranges. The inclusion of thermal infrared (TIR) wavelengths in hyperspectral sensors can indeed provide valuable information for various applications, including mineral mapping.
There are a few reasons why TIR wavelengths are not commonly incorporated into hyperspectral satellite missions:
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Technical challenges: Capturing TIR data from space presents certain technical challenges. TIR wavelengths correspond to longer wavelengths (typically beyond 3 micrometers), which require specific sensor designs and technologies that can operate effectively in this range. Developing and calibrating TIR hyperspectral sensors for spaceborne missions can be more complex and costly compared to VNIR-SWIR sensors.
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Atmospheric interference: The Earth’s atmosphere absorbs and emits TIR radiation, which poses challenges for remote sensing in this range. Water vapor and other atmospheric constituents can significantly affect TIR measurements, making it more difficult to accurately retrieve surface information. Extensive atmospheric correction techniques are required to account for these effects, and these corrections can introduce additional uncertainties in the data.
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Application focus: While TIR wavelengths are valuable for certain applications such as mineral mapping, they may not be the primary focus of many hyperspectral missions. Hyperspectral sensors are designed to address a wide range of applications, including vegetation analysis, urban mapping, coastal monitoring, and more. The VNIR-SWIR range covers many spectral features relevant to these applications, and the design of hyperspectral sensors often prioritizes these spectral regions.
That being said, there are some upcoming hyperspectral missions that incorporat TIR wavelengths in their concept such as SGB by NASA.
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