## 3 Problem Identification  
[PERSON] [10] argues that EO has the potential to assess the necessity of developing policy. There are however, few publicly available documented cases describing how remote sensing influenced actual policy development. The detection of the ozone hole is probably the best documented example of EO triggering policy development [11]. Concern about the detrimental effect of chlorofluorocarbons (CFCs) on the ozone layer [12] stimulated the US Congress to commission NASA to develop a sensor (TOMS) to monitor the state of the ozone layer. The sensor, launched in 1978 on-board the NIMBUS satellite, did not report any anomalies until 1986, when NASA confirmed (Figure 2) that the deepening and enlargement of the size of the ozone hole had indeed occurred since the late 1970s [13]. This confirmation, based on re-analysis of the TOMS data, responded to a paper one year earlier, which woke up the world by reporting a steady decline of spring ozone concentrations over one British Antarctic Survey research station [14]. In response to these findings, the 1987 Montreal Protocol [15] prescribed a 50% reduction, and four years later, a complete ban on the use of hard CFCs. Figure 1: Scheme of a policy cycle. Figure 2: Size and depth (Dobson units) of the ozone hole in October of 1979, 1982, and 1985, as detected by TOMS [16]. What was new in the remote sensing data? After all, the British Antarctic Survey reported earlier a reduction in spring ozone concentration over their Antarctic research station. The remote sensing confirmed that this record from a single station was not an anomaly, and revealed the size and depth of the hole more convincingly than an entire array of ground based sensors could. Recognition of environmental problems is frequently confirmed, but rarely initiated by earth observation; other sources of information generally precede quantification by earth observation. For example, the recent remotely sensed detection of increased water turbidity due to dredging (Figure 3) in Northern Poyang Lake, China [17], which was followed by a ban on sand mining, was preceded by reports expressing concern about the impacts of dredging [18,19]. The findings of [PERSON] _et al._[17], however, which quantified the extent of the problem, and which had been communicated to provincial government officials half a year before the ban, probably placed the issue higher on the political agenda. Apart from these examples, few other sources attribute the formulation of environmental policy to remote sensing. Presumably, this is because the diffuse nature of the process leading to policy formulation makes it difficult to assess the precise contribution of EO. Remote sensing contributes, however, increasingly to high level influential policy studies. One example is the FAO's global Forest Resource Assessments [20], which, while based on reports from national forest surveys, have a separate remote sensing survey since the 1990s, as a complement to the main assessment report. Other examples of policy relevant information from EO include the recent assessments of the rate of polar sea ice cover reduction [21] and the melting of the Arctic [22] and Antarctic ice caps and the Third and Fourth Assessment Reports of the Intergovernmental Panel on Climate Change [23,24]. Through these channels, remote sensing contributed without doubt to the development of policies on climate change adaptation and mitigation, deforestation, and trade in forest products. It will be clear that earth observation infrastructure and products, such as satellites, imaging devices, and imagery, are required to enable the support of international policies, and there have been various initiatives to assess the needs and existing capacity.