A technique is presented for rapidly producing unstructured finite element meshes in support of large- scale remote sensing simulations. These tetrahedral meshes typically have more than one million elements and more than 250 thousand nodes, and allow for arbitrary placement of objects into the domain. Open-source mesh generation packages are used in conjunction with a tetrahedra element smoothing operation to achieve the desired final meshes. Meshes can be reproduced in less than 30 minutes on a Cray XT3 architecture.