Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. Much as the human eye seesvisible light in three bands (red, green, and blue), spectral imaging divides the spectrum into many more bands. This technique of dividing images into bands can be extended beyond the visible.
Engineers build sensors and processing systems to provide such capability for application in agriculture, mineralogy, physics, and surveillance. Hyperspectral sensors look at objects using a vast portion of the electromagnetic spectrum. Certain objects leave unique 'fingerprints' across the electromagnetic spectrum. These 'fingerprints' are known as spectral signatures and enable identification of the materials that make up a scanned object. For example, a spectral signature for oil helps mineralogists find new oil fields.
Hyperspectral remote sensing is used in a wide array of applications. Although originally developed for mining and geology (the ability of hyperspectral imaging to identify various minerals makes it ideal for the mining and oil industries, where it can be used to look for ore and oil),[2][3] it has now spread into fields as widespread as ecology and surveillance, as well as historical manuscript research, such as the imaging of the Archimedes Palimpsest. This technology is continually becoming more available to the public. Organizations such as NASA and the USGS have catalogues of various minerals and their spectral signatures, and have posted them online to make them readily available for researchers.
[edit]Mineralogy
Geological samples, such as drill cores, can be rapidly mapped for nearly all minerals of commercial interest with hyperspectral imaging. Fusion of SWIR and LWIR spectral imaging is standard for the detection of minerals in the feldspar, silica, calcite, garnet, and olivinegroups, as these minerals have their most distinctive and strongestspectral signature in the LWIR regions.[8]
Hyperspectral remote sensing of minerals is well developed. Many minerals can be identified from airborne images, and their relation to the presence of valuable minerals, such as gold and diamonds, is well understood. Currently, progress is towards understanding the relationship between oil and gas leakages from pipelines and natural wells, and their effects on the vegetation and the spectral signatures. Recent work includes the PhD dissertations of Werff[9] and Noomen.[10]
[edit]Surveillance
Hyperspectral surveillance is the implementation of hyperspectral scanning technology for surveillance purposes. Hyperspectral imaging is particularly useful in military surveillance because ofcountermeasures that military entities now take to avoid airborne surveillance. Aerial surveillance was used by French soldiers using tethered balloons to spy on troop movements during the French Revolutionary Wars,[11] and since that time, soldiers have learned not only to hide from the naked eye, but also to mask their heat signatures to blend in to the surroundings and avoid infrared scanning. The idea that drives hyperspectral surveillance is that hyperspectral scanning draws information from such a large portion of the light spectrum that any given object should have a uniquespectral signature in at least a few of the many bands that are scanned. The soldiers from NSWDG who killed Osama bin Laden in May 2011 used this technology while conducting the raid (Operation Neptune's Spear) on Osama bin Laden's compound in Abbottabad,Pakistan.[citation needed][1]
Traditionally, commercially available thermal infrared hyperspectral imaging systems have needed liquid nitrogen or helium cooling, which has made them impractical for most surveillance applications. In 2010, Specim introduced a thermal infrared hyperspectral camera that can be used for outdoor surveillance and UAV applications without an external light source such as the sun or the moon.
[edit]Environment
Most countries require continuous monitoring of emissions produced by coal and oil-fired power plants, municipal and hazardous waste incinerators, cement plants, as well as many other types of industrial sources. This monitoring is usually performed using extractive sampling systems coupled with infrared spectroscopy techniques. Some recent standoff measurements performed allowed the evaluation of the air quality but not many remote independent methods allow for low uncertainty measurements. The Telops Hyper-Cam, an infrared hyperspectral imager, now offers the possibility of obtaining a complete image of emissions resulting from industrial smokestacks from a remote location, without any need for extractive sampling systems. Emission quantification measurements have been achieved with the Hyper-Cam which can now be used to independently, safely and rapidly identify and quantify polluting emissions from a remote location.[17]
[edit]Advantages and disadvantages
The primary advantage to hyperspectral imaging is that, because an entire spectrum is acquired at each point, the operator needs no prior knowledge of the sample, and postprocessing allows all available information from the dataset to be mined. Hyperspectral imaging can also take advantage of the spatial relationships among the different spectra in a neighbourhood, allowing more elaborate spectral-spatial models for a more accurate segmentation and classification of the image.[18]
The primary disadvantages are cost and complexity. Fast computers, sensitive detectors, and large data storage capacities are needed for analyzing hyperspectral data. Significant data storage capacity is necessary since hyperspectral cubes are large, multidimensional datasets, potentially exceeding hundreds of megabytes. All of these factors greatly increase the cost of acquiring and processing hyperspectral data. Also, one of the hurdles researchers have had to face is finding ways to program hyperspectral satellites to sort through data on their own and transmit only the most important images, as both transmission and storage of that much data could prove difficult and costly.[1] As a relatively new analytical technique, the full potential of hyperspectral imaging has not yet been realized.
Virtual Archaeology
Archaeology is no longer just about digging holes. New research, undertaken by a team led by the University of Leeds should revolutionise the effective use of 'state-of-the-art' remote sensing technology such that aerial detection will increase dramatically without physically disturbing cultural heritage sites.
Different deployed platforms. Image re-used under a creative commons share-a-like licence from DARTProject www.dartproject.info.
Dr Ant Beck, research fellow at Leeds and a key member of the Detection of Archaeological Residues using remote sensing Techniques (DART) project has said that 'Our research findings are leading to an improved understanding of detection techniques and in the future our work will enable successful remote sensing surveys to take place in landscapes where at present the physical and environmental factors have been difficult to say the least. This work will transform archaeology by allowing archaeologists a better view of the archaeological residues under the soil without disturbing, and potentially damaging, sites of specific interest."
Initial work has been taking place in Cambridgeshire this year and although it is still at an early stage, initial analysis confirms the hyperspectral images have revealed more and different information than the comparison aerial photographic image.
Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. Much as the human eye sees visible light in three bands (red, green, and blue), spectral imaging divides the spectrum into many more bands, including into the invisible.
Use of wavelengths outside the visible spectrum offer immense potential for archaeological prospection. Initial research has shown that the Near Infra-red region provides the greatest contrast and allows for improved detection of archaeology. The contrast is greater in particular wavebands/lengths (for example at 1156nm which is attributable to lignin in the leaf). This is due to both spectral sensitivity (being able to see the wavelength) and spectral resolution (being able to observe a small enough part of the wavelength to capture the contrast). Dr Ant Beck said 'This is very encouraging. Further analysis should allow us to pinpoint the links between archaeological features, environmental dynamics and crop type leading to improved detection in, what have traditionally been considered, marginal landscapes'.
Aerial prospection has already located more 'sites' than any other technique in the realms of archaeology but this research project will lead to more effective ways of using remote sensing and will improve the future management of archaeological sites.
Resolution comparison. Image re-used under a creative commons share-a-like licence from DARTProject www.dartproject.info.
The challenge to date has been that existing remote sensing techniques have had to cope with the vast differences in the physical, chemical, biological and environmental processes involved in the landscape. This has meant that current detection techniques can be ineffective due to the physical and environmental factors on specific sites and landscapes.
By collaborating with a range of scientific disciplines (geotechnical, remote sensing, plant biology, computer vision) to improve the way we observe and detect buried, and therefore invisible archaeology, the research team are creating a wealth of experience and expertise which will allow archaeologists to use state-of-the-art aerial imaging sensors to detect archaeology that has never been found before.
The Director of the UK AHRC/EPSRC Science and Heritage Programme, Professor May Cassar, said 'The DART project epitomises the strides in interdisciplinary research taking place in heritage science today as a result of funding from the AHRC/EPSRC Science and Heritage Programme. The excitement of this project is due to the exploration and discovery of a new world through the detection of archaeological residues using remote sensing techniques. Without having to turn over a single spade of earth and without disturbing the archaeological record, the wealth of our archaeological past is being revealed.'
The project is Open Science: this means that, where practicable, all science objects (data, algorithms, illustrations etc.) will be made openly available for public re-use and exploitation. By openly sharing journal articles, data, code, online software tools, questions, ideas, and speculations we can open up the scientific process. This has the potential to revolutionise the research process and the way we engage with peers, policy makers and the public.
The research forms part of the co-funded Arts and Humanities Research Council (AHRC)/ Engineering and Physical Sciences Research Council (EPSRC) Science Heritage research programme.
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