## 1 Introduction  
Remotely sensed earth observation (EO) has revolutionized our understanding of our dynamic environment. The array of remotely sensed EO techniques expanded in the 1970s when digital satellite borne imagery complemented aerial photography, which had been available since the early 20 th century. Today, the number of EO systems designed to observe and monitor environmental processes is large and continues to grow. Government support for this is strong, as many environmental remote sensing systems are publicly funded, and an increasing number of countries invest in EO infrastructure.  
Environmental concern is a major driver for the public support to earth observation. The reverse is true as well; EO stimulates environmental awareness and concern. In _An Inconvenient Truth_, [PERSON] [1] describes how a single image of the earth, taken in December 1968 by a crew member of the Apollo 8 mission, \"exploded into the consciousness of mankind. In fact, within two years of this picture being taken, the modern environmental movement was born. The Clean Air Act, the Clean Water Act, the Natural Environmental Policy Act, and the first Earth Day all came about within a few years of this picture being seen for the first time\".  
Satellite borne remote sensing and modern environmental policy thus came of age at the same time. The launch of the first Landsat satellite in the early 1970s coincided with the development of the first environmental policies, and the subsequently established environmental protection agencies created the initial demand for environmental EO products.  
Following an increase of Landsat applications in the 1970s, in the early 1980s, the question was raised whether the market could recover the costs of earth observation. The Landsat program, which was commercialized in 1982 (a decision reversed in 1992 for military reasons) resulted in a fall back of the utilization of and the non military societal benefits obtained from remote sensing [2]. Since then, the debate has continued between proponents of commercialization and those arguing that the societal benefits of environmental EO merit continuing public support.  
Commercialization of environmental EO assumes that viable markets exist. The demand for environmental EO, however, depends considerably on policy and market opportunities, and should thus be considered in the context of societal demand and the policies the EO serves. The countries represented in the Group on Earth Observation (GEO) recognized this dependency on societal demand, while agreeing in February 2005 to develop a Global Earth Observation System of Systems (GEOSS). This initiative aims to develop the societal benefits of EO in nine specific benefit areas [3,4].  
A systematic insight in, and awareness of, how remote sensing may contribute to environmental policy can help to enlarge the societal demand for EO applications. However, existing reviews of environmental EO applications are structured according to products, techniques, or benefit areas, rather than the function they have, with respect to the policy they support. In this paper, we review the potential, actual contribution, and limitations of EO from the perspective of their support for environmental policy.