Martian dust storms observations.
 Martian dust storms can occur during the ISO lifetime but cannot
 be predicted with certitude long in advance. The chemistry of the
 Martian atmosphere is bound to be deeply modified then, the
 presence of extensive dust both diffuse and in upper atmospheric
 will affect the radiation reaching the surface and lower layers
 while different models predict heterogeneous chemistry on the
 surfaces of the dust grains. The temperature structure of the
 atmosphere is not well known during these storms, while most
 models predict a global warming during a global storm, locally,
 coolings could occur leading to a modification of the balance of
 water vapour. The Martian chemistry, after the results of the
 Mariner, Mars, Viking and Phobos missions is much more complex
 than what was earlier expected as exemplified by our tentative
 identification of formaldehyde (Korablev et al, 1994).
 The ISO payload presents the best way to monitor it from the
 earth's orbit.
 This proposal asks for a complete Martian scan with all the
 payload using the same survey mode as guaranteed time proposal
 (TDGRAAU_MARS) but on a target of opportunity mode.