# Review of Works Combining GNSS and InSAR in Europe
## 3 Temporal and Spatial Distribution of Scientific Production in Europe  
### Spatial Distribution  
A total of 191 scientific contributions, among which 12 were about the theorical combination of GNSS and InSAR data and 179 focused on the combined techniques, were collected and analyzed considering all European mainlands. Spatially, not all countries have been the subject of combined GNSS and InSAR studies (considering DInSAR or MTInSAR approaches). In fact, 15 European nations, in addition to Gibraltar, Andorra, San Marino, and Vatican City, are not represented by publications regarding the GNSS and InSAR data combination (Figure 1). The higher number of publications have focused on Italy, with 47 contributions divided into 36 journal articles (e.g., [17; 27; 38; 39; 40; 41; 42; 43]), 4 book chapters [44; 45; 46], and 7 conference proceedings [47; 48; 49; 50; 51; 52]. This number of contributions, which is much higher than that collected for all the other countries, can be justified when considering the high number of geohazards affecting the territory, e.g., landslide events, subsidence phenomena, geothermal processes and mining activities, and the higher use of InSAR within the Italian scientific community.  
After Italy, the other nations most represented are as follows: (i) Spain, with 14 articles in peer-reviewed journals (e.g., [53; 54; 55; 56; 57]) and 3 congress proceedings [58; 59; 60] for a total a 17 scientific contributions; (ii) Germany, with a total number of 15 scientific publications equally divided into various scientific journals (e.g., [61; 62; 63; 64]) and conference proceedings (e.g., [65; 66]); (iii) Portugal, with 8 peer-reviewed scientific articles (e.g., [67; 31; 68]), 1 book chapter [69], and 3 conference paper (e.g., [70]), and Iceland, represented by 11 contributions in peer-reviewed journals (e.g., [71; 72; 73]) and only 1 conference abstract [74], for a total of 12 scientific contribution for both countries; (iv) Norway, with 8 contributions in scientific international journals (e.g., [75; 22; 76; 77]), 2 book chapters of peer-reviewed journals [78; 79], and only 1 proceedings abstract for a conference [80]; and (v) Greece, equally divided in 5 peer-reviewed journal articles (e.g., [81; 82; 83]) and 5 abstracts for congresses or meetings (e.g., [84; 85; 86]), for a total contribution of 10. It has to be considered that, for the Germany, 11 scientific contributions, i.e., 6 articles published in international peer-reviewed journals and 5 abstracts for congresses refer to the Upper Rhine Graben Area, were focused on the boundary between France and Germany. To avoid repeated counting, it was decided prior to processing to assign all the contributions about the Upper Rhine Graben Area to Germany.  
Following the classification, Netherlands is represented by 8 scientific works equally divided into international journal articles and conference papers. Switzerland and Romania provided 7 scientific contributions, 4 peer-reviewed articles, and 3 meeting proceedings, and 5 publications in international journals and 2 extended abstracts, respectively. The United Kingdom is named in 6 scientific works, of which 1 involves the Scotland territory, divided into 4 international peer-reviewed journals and 2 conference proceedings, while France only includes 3 scientific international articles and 1 conference abstract.  
Albania (1 article published in international journal and 1 congress abstract), Lithuania (1 publication in scientific per-reviewed journal and 1 congress abstract), and Slovakia and Malta (two scientific peer-reviewed journals) were represented by 2 scientific contributions, while Liechtenstein, Hungary, Czech Republic, and Cyprus were closely ranked, with only one scientific work.