# Ten Years of Experience with Scientific TerraSAR-X Data Utilization
## 3 Results
### Proposal Analysis Overview
#### Cryosphere  
The influence of climate and the climate variability on ice- and snow-covered areas of the Earth (see Figure 6) is investigated by 17 percent of the proposals. Almost 50 percent concentrate on the observation of ice caps and glaciers including monitoring of glacier outlines [82] and their spatiotemporal variability [83; 84] and, changing of calving rates at the shore line [85]. The major application field, however, is the determination of the glacier flow velocity [86; 87], an essential factor for the assessment and understanding of mountain [88; 89; 90], rock [91] and polar glacier dynamics. The latter is often combined with the determination of the glacier's grounding line [92; 93]. TerraSAR-X data are used to monitor the collapse of ice shelves [94; 95; 96] and to investigate their internal and basal structure [97].  
Figure 6: Thematic fields of cryosphere-related TerraSAR-X proposals, sorted by frequency, addressing polar and mountain glaciers, snow, permafrost, sea-, lake- and river-ice.  
Mapping of snow-covered areas is a key aspect of 28 percent of the cryosphere proposals. A detailed knowledge of snow-covered areas, snow height [98] and the structure and physical properties of the snow pack [99] are important for many applications such as water supply, flood and avalanche risk prediction, weather forecast as well as the understanding of climate change in the long term. Not only snow cover over land is observed but also its impact on sea ice cover and breakup dynamics [100].  
About 27 percent of the proposals monitor the river and lake ice phenology [101; 102; 103; 104; 105]. Water resource distribution and accessibility, the use of frozen rivers and lakes for travel and transportation purposes as well as an improved hydropower management are some of the motivations for research. Additionally, thermokarst lakes are key elements of the permafrost landscape. With permafrost thawing and associated greenhouse gas production limited to the period of unfrozen lakes, the ice phenology can be regarded as an indicator for climate change.  
Permafrost research is focus of 16 percent of the proposals. This ecosystem faces dramatic changes caused by climate warming and increasing human activities in the Arctic. TerraSAR-X data are used to determine the thickness [103] of the so-called active layer, the soil above the permafrost where most of the ecological, hydrological and biological activities take place. The seasonal thawing and refreezing of the active layer causes surface deformations, posing a challenge for infrastructure and engineering [104]. Also surface changes of the permafrost landscape [105; 106] and arctic wetlands [107] as well as the erosion of permafrost coastlines and riverbanks [108] are monitored.  
The retreat of sea ice in the Arctic is a clear indicator and a visible sign of global warming. The determination of the sea ice thickness [109], composition and extent [110; 111] as well as iceberg monitoring [112] provides essential information for operational ice services as well as the modelling of the interaction between the polar oceans and the atmosphere. Information derived from TerraSAR-X data about the sea ice state and in particular the dynamic processes forcing the sea ice breakup are used for ice breaker support [113; 114]. Also, the formation and dynamics of polynysa, which are persistent areas of open water even during the polar winter, are monitored [115]. Sea-ice related issues are investigated by 13 percent of the cryosphere proposals.  
TerraSAR-X data are mainly used for mapping purposes. Apart from that, the derivation of glacier flow velocity and velocity change is significant. About a third of the cryosphere proposals address this issue. Here, both interferometric and feature tracking techniques are applied. The latter especially benefits from the high spatial resolution of TerraSAR-X. For 18 percent of the proposals, polarimetric data are requested.