NASA operates a highly modified Douglas DC-8 jetliner as a flying science laboratory. The aircraft, based at the NASA Armstrong Flight Research Center facility in Palmdale, California, is used to collect data for experiments in support of projects serving the world's scientific community, including Antarctic flights as part of Operation IceBridge.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 126.96.36.199.0