1. What is the purpose of airborne hyperspectral imaging?
Any material that is detectable either directly or indirectly based on its spectral features, can be mapped with an airborne hyperspectral camera. The point of airborne hyperspectral imaging is in creating a material map of the study area, land or water surface. Taking the sensor in the air gives you a vantage point to search these materials, plant species etc. from the much larger area than what is immediately visible on the ground – easily hundreds of square kilometers at the time, only limited by altitude and time spent flying. While airborne sensors usually create detailed geometric models (LiDAR) or imagery for human interpretation (multispectral cameras, SAR), hyperspectral sensors create data which is analysed into a thematic map of material features. Imagine that – you can be kilometers up in the air, speeding hundreds of kilometers per hour, and still create an exact map of materials, minerals or plant species at your survey area. No other passive imaging technology can do that!
2. How does it differ from multispectral airborne imaging?
“Multispectral” is one of the most confused and misused umbrella terms used in remote sensing. Multispectral imagers typically have 3-5 broad bands with gaps in between, depending on which applications the multispectral imager is built for. Let’s remember that even normal digital camera found from every smartphone, is multispectral imager with 3 spectral bands. Thus, multispectral can mean almost anything from general consumer camera to an application specific imager.
By definition, hyperspectral imaging collects hundreds of contiguous, narrow spectral bands. This means that there are no “gaps” between the bands. Hyperspectral means far more, more narrow bands than multispectral imaging.
Resulting differences for a user are threefold. With hyperspectral imager, you can differentiate material (minerals, plants etc) of much smaller spectral difference, thanks to much higher spectral fidelity. To put it in layman’s terms, with multispectral imager you can – for example – tell if the area has vegetation or not. With hyperspectral imager, you can tell which species the vegetation consists of, and moreover, if those plants are suffering a stress, and at best what is the cause of the stress. Multispectral imaging may be enough to tell asphalt apart from gravel or concrete, but in order to tell how old the asphalt is and what is its material composition, you need more and narrower bands provided by the hyperspectral imager. Only hyperspectral imager can tell apart minerals that are important for geologists, but which exhibit so minute spectral differences that multispectral imager is unable to tell them apart. There are many of such minerals!
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