Spectrometers acquire spectrum data at a single point or pixel (Figure 2a) for applications such as chemical analysis, pharmaceutical identification, vegetation growth monitoring, and forensic detection of harmful substances. Imaging Spectrometers
shown in FIG 1. acquire a spectrum at a pixel, over a line, or across an entire plane to produce a three dimensional virtual cube of spectral information as shown in Figures 2b and 2c. click figures to enlarge
. A typical eight-megapixel digital camera produces 24,000,000 bytes of information. The same eight-megapixel image with 2048 spectra per pixel and two bytes per spectra, will produce 32,768,000,000 bytes of information. That is over 1300 times more information per image. This data can be stored, processed, visualized, analyzed, and compared with massive categorized databases for identification of known substances over large areas. See Spectra Insight Software
for examples. Databases available to the public include:
- The USGS Spectral Library
- The ASTER Spectral Library hosted by the Jet Propulsion Laboratory (JPL), contains a compilation of three other libraries, the Johns Hopkins University Spectral Library, the JPL Spectral Library. The ASTER library currently contains over 2400 spectra and can be ordered in its entirety via CD-ROM or users can also search, graph and download individual spectra online.
- The SPECCHIO Spectral Library is an online database maintained by the Remote Sensing Laboratories in the Department of Geography at University of Zurich. Once users have registered with the system to create an account, the SPECCHIO library can be accessed remotely over the internet or alternatively downloaded and installed on a local system. The library is designed specifically for community data sharing, and thus users can both download existing data and upload new spectra.
- The Vegetation Spectral Library was developed by the Systems Ecology Laboratory at the University of Texas at El Paso with support from the National Science Foundation. In addition to options to search, view and download spectra, this library also helpfully includes photographs of the actual species and materials from which the data was measured. Registered users can also help contribute data to further expand the archive.
- The ASU Spectral Library is hosted by the Mars Space Flight Facility at Arizona State University, and contains thermal emission spectra for numerous geologic materials. While the library is designed to support research on Mars, the spectra are also applicable to research closer to home here on Earth.
- The Jet Propulsion Laboratory is currently building the HyspIRI Ecosystem Spectral Library. This library is still in its development phase, and hence contains only a limited number of spectra at this time. Nonetheless, it is expected to grow, since the library was created as a centralized resource for the imaging spectrometry community to contribute and share spectral measurements.