Create Final FFMP Shapefiles

Author:        Paul Jendrowski

Organization:  NOAA, National Weather Service, Blacksburg, VA

email:         paul.jendrowski@noaa.gov

This process creates the final basin and bin shapefiles to be used with FFMP. FFMP requires a polygon shapefile to define the basins and a point shapefile that represents the center point of each 1 degree by 1 km DHR data point. The basin shapefile must contain a field named [Pfaf_id] that contains a unique Pfafstetter ID for each basin. The bin shapefile must contain a point for each 1 degree by 1 km radar bin in the DHR product and contain a field named [Pfaf_id] that identifies the basin the bin maps to.

The basin shapefile must be processed so there are no basins without bins and all basins meet a minimum area threshold. Removing the small basins is required to minimize FFMP CPU usage as much as possible and to ensure all basins can be resolved on the D2D display. The bins shapefile must be processed to include the [Pfaf_id] value corresponding to the basin the bin is within.

There are two aspects of the radar coverage that also need to be considered:

1. The maximum range from the radar reasonable precipitation estimates can be derived. This maximum range is highly site specific and is based on radar site elevation, terrain blockage and precipitation climatology. The maximum range is estimated from experience using the radar's precipitation products and is not a predefined setting on the WSR-88D. Basins beyond the maximum range should be deleted to eliminate computations in areas where good precipitation estimates can not be generated. This can be done automatically in the "Merge By Bin" function by first selecting bins less than the maximum range threshold.
2. Only bins that are not blocked should be mapped to the basins. Since FFMP calculates area averaged accumulation, known bin locations that have invalid data due to ground clutter or beam blockage should not be used in the calculations to avoid biasing the basin accumulation.

1. Merge Basins Without bins

1. The view should contain your edited basin polygon shapefile, streamlink theme and a point theme of the radar bins. It is recommended that all three themes are visible in the view. The basin shapefile is your local customized version. The Bins shapefile should be a copy of the original bins shapefile (kxxx_bins.*) from the original FFMP basins CD. This file will be edited during this step.
2. Make the Bins theme active and clear the selection. If you wish to use a maximum range threshold, perform the following:
1. Query on the bins theme: ([Range_km] < xxx) using "New Set", where xxx is the maximum range threshold.
3. On the View, make the Bins theme and the basin theme both active.
4. From the Bsn-Tools menu, select "Merge By Bin".
1. Name the new file "wsbin.shp".
   
2. Answer "Yes" to prompts to recompute area.
3. During the final merging step, the view may be automatically zoomed to selected features (via " Merge w/Next Downstream "). You will be prompted on whether to merge all the indicated basins together. Examine the selected features and determine if the indicated basins should be merged. If you answer no (i.e. you want to merge the basins in a different way to better match the radar coverage), you will have to manually merge these basins later.
5. Clear the selection on the bins theme.
6. Check to make sure all basins have a bin:
1. Make the new merged theme (wsbin.shp) the active theme.
2. Query ([has_bin] = 0) using "New Set".
3. If any basins are selected, you must examine each selected basin and merge it with an upstream or downstream basin that has a bin using the "Merge Basins" function on the Bsn-Tools menu. Then redo this "Merge Basins Without Bins" step using the new merged theme.
7. If all basins now have bins, clean up unneeded tables and themes. A temporary theme "Merged1" may have been added to the view; this theme can be deleted. Proceed on to the next step.

2. Merge Small Basins

1. Make the new merged theme (wsbin.shp) the active theme.
2. From the Bsn-Tools menu, select "Merge By Area".
1. Enter your minimum area threshold in square miles. This generally should be somewhere between 1.0 and 2.0 sq mi. Make sure this threshold is smaller than the area of any basins you have manually split or urban areas you may have created.
2. Name the new file "wsarea.shp".
3. Make the new merged theme (wsarea.shp) the active theme.
4. Query ([Area_sq_mi] < X) using "New Set", where X is the threshold area used above.
5. Examine any selected basins and determine if any further action is needed. Most of the selected basins will be outlet basins ([Parent_id] = 0) and can probably be deleted (Bsn-Tools menu, "Delete Basins"). Otherwise, merge these basins by selecting an upstream or downstream basin to merge with and use the "Merge Basins" function.
6. At this point, all basins should have bins and be greater than the minimum area threshold.
7. Clean up unneeded tables and proceed on to the next step.

3. Map Bins to Basins

1. Make both the Bins theme and the basins theme (wsarea.shp) active.
2. Click on the "Open Theme Table" button to open the attribute tables for both themes.
3. In both tables, select the [Shape] field.
4. With both tables open, make the Bins theme table the active window and click on the "Join" button. This will perform a spatial join and add the basin attributes to the Bins theme attribute table.
5. From the Table menu, select "Start Editing".
6. Make the [Pfaf_id] field the active field.
1. Click the "Calculate" button.
2. Double click on the [Pfaf_orig] field so [Pfaf_orig] appears in the lower left part of the Calculate window.
3. Click the "OK" button. This will set the [Pfaf_id] field to the values in the [Pfaf_orig] field.
4. From the Table menu, select "Remove All Joins".
7. Return to the View with the Bins theme and make the Bins theme the active theme.
1. Select bins that should be excluded from FFMP calculations (known ground clutter areas and blockage areas). For blockage areas which are generally wedges, use queries to select specific azimuth and range sectors and use "Add to Set" in the Query Builder window.
2. Click on the "Open Theme Table" button to open the attribute table for the Bin theme.
3. Make the [Pfaf_id] field the active field.
4. Click the "Calculate" button.
5. Enter 2 double quotes "" to reset the [Pfaf_id] to a null string.
6. Click the "OK" button.
8. From the Table menu, select "Stop Editing" and save the edits.
9. Clean up unneeded tables.

4. Set "Pfaf_id" field in basin shapefile

1. Make the basin theme (wsarea.shp) the active theme.
2. Click the open theme table button.
3. From the Table menu, select "Properties"
4. In field [Pfaf_orig], type in the Alias column "Pfaf_id".
5. Return to the view.
6. Make the basin theme (wsarea.shp) the active theme.
7. Clear any selection on the theme.
8. From the Theme menu, select "Convert to Shapefile".
9. Enter "kxxx_aggr_basins.shp" for the new name replacing "kxxx" with the appropriate radar ID.
10. Remove the "Pfaf_id" alias from the basin theme attribute table.
11. Clean up unneeded tables and themes.

• kxxx_bins.shp
• kxxx_bins.shx
• kxxx_bins.dbf
• kxxx_aggr_basins.shp
• kxxx_aggr_basins.shx
• kxxx_aggr_basins.dbf

• kxxx_bins.shp
• kxxx_aggr_basins.shp