Tomographic reconstruction using 4 views and tunable diode laser

Abstract

Called the 'Reduced Back Projection' technique(or RBP), this new method is an improvement on existing tomographic reconstruction techniques in the field of laser diagnostics on a combustor exhaust. The highlight of this technique is the use of only FOUR views to create a planar reconstruction from path averaged data which is obtained from water absorption spectroscopy in the IR region near 1373nm. Water sensitive wavelengths are generated by using a Tunable Diode laser working in the IR region. For the purpose of this paper, work is done on a plane in the exhaust of a burner perpendicular to the flame direction. The geometry of the burner decides the distribution of water molecules in the interrogation plane. This technique is based on the back projection method but has been extensively modified and improved to work with just four views instead of the hundred or so views used in medical tomography. Simulations have been run to check the working of the new technique and compared with other current methods in tomography (SART, back projection, etc..). Preliminary experimentation over a simple two burner geometry has been performed. In both simulation and experiment, the RBP technique has yielded better results than existing methods by virtue of the new method being able to capture features where the other methods have failed. Thus, RBP can be applied to situations where resources, time and spatial constraints exist.