Satellites gave us some of the most powerful images of the tsunami, showing the scope of the disaster and the scale of the damage, and have proven crucial in the recovery and reconstruction process. Some of the satellite photos came from government agencies, while others came from commercial outfits. They are not a replacement for on-the-ground work, but are terrific information resources for those trying to carry out humanitarian relief in times of crisis.
Satellite information is available for humanitarian efforts in part due to an international agreement specifically calling on nations operating satellites to help in the case of an event such as the December 26 tsunami. The agreement is the "Charter On Cooperation To Achieve The Coordinated Use Of Space Facilities In The Event Of Natural Or Technological Disasters," more generally known as the International Charter: Space and Major Disasters (ICSMD). A "natural or technological disaster" -- defined in the charter as a situation of great distress involving loss of human life or large-scale damage to property, caused by a natural phenomenon, such as a cyclone, tornado, earthquake, volcanic eruption, flood or forest fire, or by a technological accident, such as pollution by hydrocarbons, toxic or radioactive substances -- allows signatory countries to request special access to relevant satellite information archives, live data, telecommunications, and broadcast facilities from other signatory nations.
While the December 26 tsunami was by far its most visible activation, the charter has been triggered numerous times in recent years, and as recently as yesterday due to hurricane-force winds hitting Sweden. Six space agencies currently offer their resources through the charter: the European Space Agency (ESA), the separate French space agency (CNES), the Canadian Space Agency (CSA), the Indian Space Research Organisation (ISRO), the US National Oceanic and Atmospheric Agency (NOAA), and Argentina's Comisión Nacional de Actividades Espaciales (CONAE). Russia, China, Japan and Brazil are notably absent.
The Charter website has a nicely-produced pamphlet (PDF) describing the organization and its function.
But satellite information shouldn't just be available in times of disaster. UNOSAT, formed in 2002, is a UN consortium of governments and private companies working with ICSMD to provide broader availability of satellite images and data for humanitarian purposes. (This ReliefWeb newsletter from March of 2003 goes over some of the rationales and applications of UNOSAT.)
Outside of UN auspices, Respond is a newly-formed European consortium of government and private organizations offering global mapping services, from satellites to GIS data, for use by humanitarian agencies dealing with crises ranging from slow-moving famines to sudden earthquakes. Respond intends to provide maps of all sorts as well as alert and communication services. Although Respond is still in its early stages, it is already actively providing extensive mapping and GIS data for tsunami reconstruction efforts and (as we mentioned in December) humanitarian relief in Darfur.