You need to know what you're looking for to begin with. Alejandro is working closely with his Army counterpart, Cindy Swim, of the Edgewood Research, Development, and Engineering Center, and they have divided between them the chemical systems for air and ground platforms to test a variety of new laser sources, detectors, and platform designs. The reflected signal is analyzed, and, based on the spectral modulation of the beam, operators can deduce what portions of the spectrum were differentially absorbed or scattered by airborne elements, in what quantity, and, therefore, the type of chemical. DIAL is seen as the surgeon among the doctors, revealing detailed information on chemical or biologic constituents, although usually at the cost of range. Another challenge to remote laser sensing is posed by water in the atmosphere.
Chemicals generally absorb more light in the UV and IR than in the visible.
Unfortunately, water also absorbs light and is always present in the atmosphere in greater or lesser degrees. Water does not present a problem in two specific spectral ranges, however. There are many different ways to skin that cat, and each has advantages and disadvantages. The FAL was initially designed by Raytheon as part of a mobile chemical detection system with a specified range of 10 km. It also is capable of predicting the surface contamination after the attack.