A transit time ultrasonic flowmeter is a very accurate tool to measure the volumetric flowrate of a fluid flowing in a pipe. To estimate the flowrate, the fluid velocity averaged over the cross-section of the pipe has to be estimated from the fluid velocities averaged over the paths of the flowmeter. That is the reason why the velocity profile of the fluid, which depends on not only the Reynolds number but also on the upstream and downstream pipe configuration, is of great interest in transit time flowmetering. In this work, we propose to reconstruct the fluid velocity profile by using the measures of an 18 paths flowmeter measures to offer an in situ diagnostic tool of the flow. We first test tomography methods: filtered back-projection and then an iterative one, the algebraic reconstruction technique (ART). These methods are not really appropriate to our context of incomplete data. We have previously [Mandard, E, et al., 2005] defined a theoretical parametric model of the velocity profile which allows to in situ detect and characterize the asymmetry of the flow. We defined in this work a new parametric model which has a flowrate function of the asymmetry of the profile. It also has the advantage of determining the parameters of the symmetric term of the model in taking into account the asymmetric part of the profile. This new profile is a promising way in increasing the accuracy of the flowmeter in disturbed flow condition by taking into account the additional information provided by the velocity profile reconstruction