FIGURE 4.1 Overview of National Aeronautics and Space Administration (NASA) Earth Observing satellites in operation during IPY. Many sensors carried on these platforms were supported either in full, or in part, by international partners. SOURCE: NASA.

Satellite development and launch is a lengthy process, typically extending over a period of 5 to over 10 years. Thus, by the time the planning of IPY was completed, it was too late to develop and launch satellite systems with a specific IPY focus. Optimization of deployment of satellite-based remote sensing systems related to any broad-based observational program requires that the general program outline and requirements be established well in advance of the actual initiation of the program and be transmitted to the agencies involved in satellite operations. For example, discussions that ultimately led to the ICESat satellite dated back as far as 1979 (Science and Applications Working Group, 1979) (launch date was January 12, 2003). On the other hand, the occurrence and urgency of the IPY strengthened the voice of the polar research community in achieving a rapid recovery from the failed launch of CryoSat-1 in 2005 with the successful launch of CryoSat-2 in 2009.

Satellite observations of the polar regions face several challenges not encountered in lower latitudes. Foremost among these challenges is the lack of data centered on the poles, which arises because Earth observing satellites rarely pass directly over the poles. Rotation of the satellite can avoid this data gap, but this is rarely done; one exception was the Radarsat-1 satellite, which was rotated once on-orbit to obtain synthetic aperture radar (SAR) images of the entire Antarctic ice sheet. These data provide long-term time series of ice sheet changes.

The long periods of darkness and regions of extensive cloud cover, which preclude observations

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