There are many different analysis techniques used in remote sensing, ranging from the simple to complex. In imaging spectrometry, i.e. hyperspectral remote sensing, a common technique is to utilize measured field or laboratory spectra to drive physics-based image classification and material detection algorithms. Here the measured spectra are used as representative examples of the materials and species that are assumed present in the remote sensing scene. Spectral analysis techniques can then be used to ascertain the presence, distribution and abundance of these materials and species throughout an image.
In most cases the best approach is to measure field spectra for a given study area yourself using a field-portable spectrometer; however, the time and cost associated with such fieldwork can oftentimes be prohibitive. Another alternative is to utilize spectral libraries, which contain catalogs of spectra already measured by other researchers.
Below are examples of open access spectral libraries that are readily available online:
- 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 and the USGS 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.
It is doubtless that other spectral libraries exist and that many thousands of additional spectra have been measured for individual research projects. It is expected that more and more of this data will be available online and more uniform collection standards will be adopted, particularly as airborne and space-based hyperspectral sensors continue to become more prevalent.