[Society of Exploration Geophysicists International Conference on Engineering Geophysics, Al Ain, United Arab Emirates, 15-18 November 2015 - Al Ain, United Arab Emerites (15 November to 18 November)] International Conference on Engineering Geophysics, Al Ain, United Arab Emirates, 15-18 November 2015 - Use of electrical resistivity tomography for mapping the extensions of an existing cavity, a case study from Doha, Qatar