VELMAP New Features

First arrival and reflection picking for 3C data: The Time Picker now allows the user to pick both first break and reflection travel times.  There is a selector switch to identify which travel times are currently being picked: P for first breaks, R1 for the first reflector, R2 for the second reflector, etc.  You can switch between events at any time.  The same automatic and manual picking modes are available for all events and all picks are saved as they are made.  When exporting picks you can choose to export first breaks only, reflection times only or both together.  Travel time files containing only first breaks will have file type .tt.  Travel time files containing reflections or reflections and first breaks will have file type .ttm.

Time Picker projects can be built for either single or multi-component VSP surveys.  For multi-component surveys you will need to know if the input SEGY data is in component or shot order.  Otherwise, building multi-component projects is identical building to single component projects.  You can pick on any component.  Only one component at a time is displayed and View can be used to switch from one component to another.  A single set of picks is stored for the project and all picks will be displayed on whichever component is currently displayed.

Reflection or joint first-arrival and reflection tomography: There are now three travel time tomography options available for inverting 2D velocity models.  First-arrival tomography inverts the first breaks.  Reflection tomography inverts the travel times from a single or multiple reflectors.  Joint first-arrival and reflection tomography combines the two methods.  Travel times for all three methods can be generated in Time Picker.

Reflection and joint tomography require an initial reflector in addition to the initial velocity model and the travel times.  The initial reflector can be generated in Travel Time module after creating a velocity model.  It requires a velocity model to generate a reflector file.  Both tomography methods will adjust the velocity model and the reflector shape to give the best fit for the travel times.  The user can control the relative weight given to the change in velocities and the change in reflector shape with the Reflector-Velocity Trade-Off Control. 

Fixing a user-defined area in model during tomography:  In some areas in the velocity model for VSP images, it cannot be reconstructed from VSP data alone.  For example, the areas above the top receiver, VSP raypaths are nearly vertical, and there is no vertical resolving capability.  But one can use a model derived from a surface seismic image and fix the area during VSP tomography.

In Grid Model, users can use the mouse cursor to highlight the areas that remained unchanged during tomography and save a layer file with the information.  When applying for the option of fixing layers, tomography will request the input of this layer file.

Wave-equation migration for PS conversions:  In addition to the PP Reflection migration, you can now perform PS Reflection migration for converted reflections.  A user specified constant Vp/Vs ratio is assumed for the shear waves.  No other additional parameters are required.