Your search returned the following 3 documents:

3. Improved Approximations for Guarding 1.5-Dimensional Terrains
   Khaled Elbassioni, Erik Krohn, Domagoj Matijevic, Julian Mestre, and Domagoj Severdija
   Algorithmica 60 (2): 451-463, 2011
   
2. Improved Approximation Algorithms for 1.5D Terrain Guarding
   Khaled Elbassioni, Erik Krohn, Domagoj Matijevic, Julián Mestre, and Domagoj Severdija
   In: Proceedings of the 26th International Symposium on Theoretical Aspects of Computer Science (STACS), Freiburg - Germany, 2009, 361-371
   
1. Improved Approximations for Guarding 1.5-Dimensional Terrains
   Khaled M. Elbassioni, Erik Krohn, Domagoj Matijevic, Julián Mestre, and Domagoj Severdija
   Algorithmica Online First: 1-13, 2009