Direct wave travel time linear interpolation algorithm
Huang Yi-jian1, Zhu Guang-ming1, Guo Min2
1. College of Geology Engineering and Geomatics, Chang'an University, Xi'an City, Shaanxi Province, 710054, China;
2. Geophysical Technology Research Centre, BGP Inc. of CNPC, Zhuozhou City, Hebei Province, 072751, China
Abstract:At first in this paper the direct wave travel time LTI algorithm was briefly introduced, then the reason for the algorithm's calculation results to involve non-direct wave travel time was analyzed, so a new algorithm to calculate the direct wave travel time was realized by controlling ray's direction. The calculation steps for the direct wave travel time are almost the same as the steps for the first break travel time LTI algorithm except the two different aspects as below. The first aspect is the different initial value for the travel time, for the nodes other than the source point, a value which is larger than the value of the first break travel time at the node was assigned in first break travel time LTI algorithm, while a value which is larger than the value of the direct weave travel time at the node was assigned in direct wave travel time LTI algorithm, the other different aspect exists in the process of refreshing the travel time for the nodes, that is once wave ray was found propagating from low velocity layer to high velocity layer, then the travel time for the wave ray would be ignored in the next calculations. Calculation example for horizontal layer velocity model and multi-layer model with rugged velocity subsurface show that the direct wave travel time LTI iterative algorithm is sample but effective, reflection ray tracing calculation example demonstrated that large angle reflection wave ray tracing can be conducted by using the algorithm.