Essential changes and novels in version 3.2 pertain to implementation of (1) viewing and editing a model, (2) system's framework and (3) traveltime curve inversion. In those three areas, functionality has been expanded or efficiency increased and the user interface improved. All bugs and errors discovered have been eliminated or corrected.
1. Comparing velocity distributions
The new utility Velocity Comparator allows comparing two-dimensional velocity distributions stored in any two m-nodes of any two XTomo-LM 3 projects. Velocity functions are compared at nodes of an orthogonal grid on a rectangle domain common for both models. Result of comparison is represented as a color map and in numeric form. The utility lets the user track velocity changes in the course of interpretation.
2. Editing velocity
2.1. In-place Velocity Editor. To change velocity in a selected domain, one invokes the Editing Velocity dialog with a number of editing options. In version 3.2, a new option is added to the list. It enables the user to define velocity in a vertical strip as the power function of depth. Such approximation is often used in modeling. For editing intricate velocity distributions, the dialog is sometimes quite inconvenient. For example, if one needs to modify velocity in a set of isolated blocks of cells, one has to invoke the dialog for each block using the only option of all its machinery. To make the work easier, the In-place Velocity Editor has been introduced. It looks like a small window floating over the model image. With its controls, one can perform basic editing operations and switch freely to the main window for magnifying the image, making a new selection or viewing velocity range and its average in a selected area (this is a new feature) and so on. Another new option is selecting a subgrid in a dialog by specifying ordinal numbers of the bounding columns and rows.
2.2. Replacing velocity. After grid deformation, velocity stays attached to grid cells, not to depth. To restore velocity-depth dependence (if necessary), one has to apply the Replace Velocity command. It replaces the current velocity function with the one from another m-node in which the grid has the same verticals. In version 3.2, the operation has been extended. First, restrictions on the source grid are lifted. Second, the source velocity function can be taken from a VC file. Such file stores a velocity column set. In both cases the source velocity is redefined at nodes of the current grid. This feature can be applied, in particular, when initial velocity is computed by inversion of diving wave traveltime curves. The inversion result is stored just in a VC file. In the previous version, this file can be used only for creation the starting model of a new project. Now it can be used as a source for replacing velocity in any m-node of the current project.
2.3. Copying velocity. In version 3.2, one can copy velocity distribution from a selected subset of the model to another subset of the same form. One points to the destination by double-clicking a cell that unambiguously defines the target subgrid.
2.4. Eliminating "black cells". A grid cell is painted black when its velocity is beyond the range stored as a project property in Project Manager. When velocity is edited in Model Editor, velocity values going beyond that range are automatically replaced by the nearest range limit. But if velocity is borrowed from an external source (as in 2.2), or after tomographic refinement, black cells may appear. Black cells signal data error to the user, so they must be removed. Model editor offers a new command to do that.
2.5. Velocity profiles and velocity columns. When vertical or horizontal velocity profile was plotted, the piecewise-linear velocity representation of V(*, z) or V(x, *) was used. Now one can choose between piecewise-linear representation and step function representation. The context menu of the profile drawing pad is used as a switch. Similarly, any velocity column the user is about to import into the system, can be interpreted in two ways. In version 3.2 whenever model velocity is changed by import of velocity column(s), the user can select how to treat the column(s): as step functions or as piecewise linear function. (Step function models a layer-cake on a half-space, while piecewise linear function defines continuous velocity distribution in a layer).
3. Editing model geometry
XTomo-LM works with curvilinear grids. Changing grid geometry is carried out by modifying shape of one or several h-lines, typically those representing seismic horizons. A set of curves defining model geometry is called model wireframe. Model wireframe is stored in a text file of the MG format. When a project is created, its starting model can be created by import of a model wireframe, but there were no adequate tool for creating and editing wireframes in versions 2 and 3, though such tool would be an important means of modeling. The new utility MG File Editor or UMG, for short, has been added to XTomo-LM 3.2 to deal with all issues of creating, editing and storing wireframes, in particular, grid h-lines. The utility is launched from the Project Manager's Tools menu.
4. Model Editor's user interface
Despite expanded functionality, Model Editor's user interface has been significantly simplified. Commands related to model top line and seismic horizons are excluded from module's menus. Now, an object of an operation is determined automatically. The old Curve Editor is replaced with H-Line Editor which is UMG run in special mode. Thus, the unified user interface for dealing with model geometry is provided.
5.1. Creating projects. Now this important task is in competence of the New Project Creator module (NPC) which is launched by Project manager. The main NPC window is designed in the way to minimize difference from the old dialog. However, the second tab differs considerably to reflect the new conception of numeric representation explained in the next paragraph.
5.2. Spatial resolution and numeric formats. In the new version, approach to computational accuracy is essentially simplified. Spatial resolution of objects is defined by size of starting model and bit width of real number representation in a computer. Resolution defines accuracy of decimal approximation of real numbers and, hence, numeric formats which are offered as the defaults. Notions of computational and physical resolutions are no longer in use. Old XTomo-LM 3 projects are smoothly included in the new conception.
5.3. Viewing models of other projects. In previous versions, one could simultaneously view models in any m-nodes of the currently opened project. Starting from version 3.2, the same is true for any m-node of any project in the current working folder. To view a model from a foreign project, one applies the new View Model command of the project list context menu. Comparison of models and velocities (see section 1) is especially important for projects based on the same field data to implement alternative approaches to interpretation.
5.4. Copying of an o-node of Processing Tree. In the new version, the two-step copy-paste operation of copying o-node's content can be performed much easier – by dragging the o-node and dropping it on the target m-node.
A very special and rare error has been discovered in implementation of that operation. We have to go into some detail. Suppose that model has a curved top line T. Let an o-node O1 created for model M1 is to be copied to m-node M2. Suppose that receiver R is located at the cross point of T with vertical V. Let in model M2 vertical V is deleted before copying O1 to M2. Then, after copying, R may prove to be hanging well above T. Indeed, if V' and V" are the neighboring verticals, then the new T segment between V' and V" can lie either below or above the old segment [V', V, V"] depending on T shape. If R is above T, then there will be no rays coming to T in the forward problem solution. In the new version, this error is corrected: all "hanging" sources or receivers are landed on T, if the user does not mind. If he or she does, copying is canceled.
5.5. Active module list. This list is withdrawn from the Project Manager main window. Now it is invoked as a separate window by a command of the Tools menu. It contains all currently running modules that are launched directly by Project Manager (not those started by other modules). Description of modules has been improved, functionality kept. In particular, one can close any active module or abort it, if it is hung. The change is caused by technical necessity.
5.6. New use of SRT Port. Now SRT port can be used for observation data exchange between different projects. The new Processing Tree menu command copies Ray Catalog content from an o- or f-node to a new SRT Port database. After that, it can be used as a new data source for any project. In the new version, SRT port is two-level data warehouse: it contains a set of data stores in which databases lies. The existing databases are placed in special data store named .Main. New data stores are created by the user when necessary.
6. Reflection and refraction TX-curve inversion
The improved inversion algorithms are used in version 3.2. They are more robust and efficient. Some errors are corrected. A new module for crude estimation of reflector position at source points is added. Now the Horizons Previewer module can be launched straight from Processing Tree menu. Examples of building horizons are now supplied as a set of M- and I-projects (see next section).
7. Sample projects and documentation
The product is supplied with several sample projects. Their aim is to demonstrate work with XTomo-LM, in general, and in getting solution to some problems of layer model interpretation, in particular. The sample projects use systematically some of the new tools added in version 3.2. Processing Tree nodes of each sample project contain explaining comments. Information on installation and use of the sample can be found in the documentation (section Examples of chapter TX-curve inversion).
The documentation describes the software of version 3.2 with new modules and last changes. In the course of development, some of the base XTomo-LM conceptions have been refined, so the user, even the advanced one, is strongly recommended to look through the following chapters: Introduction, Model, TX-curve Inversion, Utilities and also topics Creating projects, Processing tree, Ray Catalog: Populating. The chapter TX-curve Inversion is written anew to match last versions of the inversion algorithms.