At
JPL, Chahine initially studied
shock waves generated by space capsules reentering the Earth atmosphere. He then worked on methods to derive atmospheric temperature and composition information from radiation received remotely from instruments in space. He developed a
relaxation method for exact inverse solution of the
radiative transfer equation, and applied it successfully to derive Earth atmospheric temperature and water vapor profiles. He also used the method to derive atmospheric temperature and composition profiles for the atmospheres of
Venus,
Mars and
Jupiter. Chahine and colleagues extended his method to include complementary information from Earth-orbiting
infrared and microwave sounder instruments, accounting for the presence of clouds, to produce the first maps of
global surface temperature from space. The AIRS instrument was formally selected as part of the
Earth Observing System (EOS) in 1988, and was launched on the second EOS platform, the Aqua satellite, in 2002. A major advance using AIRS data was Chahine's derivation of atmospheric
carbon dioxide () in the mid-troposphere. Chahine produced the first satellite-derived global map of atmospheric , while animations of several years of data displayed the global distributions of both the seasonal cycle and the long-term upward trend in atmospheric . The science data products from AIRS were widely praised. The current generation of European meteorological satellites now host an AIRS-like sounder, the
Infrared Atmospheric Sounding Interferometer; while a similar instrument, the
Cross-track Infrared Sounder, was launched in 2011 aboard
NASA's new
Suomi NPP satellite, the forerunner of the next-generation of U.S. weather satellites. In 1989 Chahine became the first chairman of the Science Steering Group of the
World Climate Research Program's
Global Energy and Water Cycle Experiment (GEWEX). He served in this role until 1999, during which time the steering group established important connections amongst the international GEWEX community, bringing together satellite-based data collection and climate modeling. == Honors ==