As with the GRIDCART keyword described above, the order of cards within the GRIDPOLR subpathway is not important, as long as all inputs for a particular network are contiguous and start with the STA secondary keyword and end with the END secondary keyword. It is not even required that all ELEV cards be contiguous, although the input file will be more readable if a logical order is followed. The network ID is also not required to appear on each runstream image (except for the STA card). The model assumes the previous ID if none is entered, similar to the use of continuation cards for pathway and keywords.
The following example of the GRIDPOLR keyword generates a receptor network consisting of 180 receptor points on five concentric distance rings centered on an assumed default origin of (0.,0.). The receptor locations are placed along 36 direction radials, beginning with 10. degrees and incrementing by 10. degrees in a clockwise fashion.
Another example is provided showing the use of a non‑zero origin, discrete direction radials and the specification of elevated terrain and flagpole receptor heights:
As with the GRIDCART keyword described above, the user has the option of specifying the radial number (e.g. 1, 2, 3, etc.) on the ELEV and FLAG inputs, or the actual direction associated with each radial.
For purposes of model calculations, all receptor locations, including those specified as polar, are stored in the model arrays as x, y and z coordinates and flagpole heights. For the purposes of reporting the results by receptor in the main print file, the tables are labeled with the polar inputs, i.e., directions and distances.
3.4.2 Using Multiple Receptor Networks
For some modeling applications, the user may need a fairly coarsely spaced network covering a large area to identify the area of significant impacts for a plant, and a denser network covering a smaller area to identify the maximum impacts. To accommodate this modeling need, the ISC models allow the user to specify multiple receptor networks in a single model run. The user can define either Cartesian grid networks or polar networks, or both. With the use of the ORIG option in the GRIDPOLR keyword, the user can easily place a receptor network centered on the facility being permitted, and also place a network centered on another background source known to be a significant contributor to high concentrations. Alternatively, the polar network may be centered on a receptor location of special concern, such as a nearby Class I area.
As noted in the introduction to this section (3.4), the model initially allows up to 5 receptor networks in a single run. This limit can be changed by modifying the Fortran PARAMETER statement and recompiling the model. The variables that define each array, e.g., the distances and directions for a polar network, are stored in arrays, so that results can be presented for each network separately in the main output file of the model. Thus, increasing the number of networks allowed will increase the amount of memory needed to run the model, although the increase is relatively small. There are also limits on the number of distances or directions (or the number of x‑points and the number of y‑points for Cartesian grids) that can be specified for each network. These are initially set to 50 distances or x‑points and 50 directions or y‑points. These limits are also controlled by Fortran PARAMETER statements, and may be modified. More information on controlling the storage limits of the models is provided in Section 4.2.2.
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