A precise gravimetric geoid model in a mountainous area with scarce gravity data : a case study in central TurkeyAbbak, Ramazan Alpay; Sjöberg, Lars E.; Ellmann, Artu; Ustun, AydinStudia geophysica et geodaetica2012 / p. 909-927 : illhttps://link.springer.com/article/10.1007/s11200-011-9001-0