Audio on a mobile device can be used to form low-resolution 3D images. The resolution of audio ranging and imaging is heavily limited by bandwidth. Here is an attempt to increase the resolution through continuous basis pursuit, a grid-less sparse algorithm. Comparison of backprojection, basis-pursuit denoising, and continuous basis pursuit shown.
Open access PDF: http://www.cv-foundation.org//openaccess/content_iccv_2015_workshops/w18/papers/Bedri_Exploring_the_Resolution_ICCV_2015_paper.pdf