Download PDF
Download page Task 3 – Compare Different Datasets..
Task 3 – Compare Different Datasets.
Task 3 will compare precipitation grids from the Lower Mississippi River Forecast Center (LMRFC) and South East River Forecast Center (SERFC). Visually comparing datasets can be useful when multiple sources are available for the same region. For the sake of simplicity, only a single timestep will be used in this initial comparison.
View LMRFC Precipitation.
Create a New Map Window.
Right-Click on the "Pearl-Part A" Session.
From the "Sessions and Maps" option, select "Add Map Window."
Enter the name "LMRFC Precip 1HR" for the new Map Window in the dialog that pops up and press OK.
Right-Click on the TIN node within the "LMRFC Precip 1HR" heading and select "Select DSS paths..."
Make the following DSS file selection:
...\HEC-MetVue_DssDataReader\HEC-MetVue_DssDataReader_Start\Data\DSS\precip.2021.08.dss
Filter the B-Part to "Pearl River" and the F-Part to "LMRFC-QPE."
Select the LMRFC-QPE precipitation grid for 30 August 2021 12:00 by highlighting the pathname within the "Available TINs" window and clicking "Add Sel."
Select "OK" to add the selected data to the map window.
The LMRFC precipitation data for 30 August 2021 12:00 is added to the map window and the basin-average totals are displayed.
Zoom in closer to the Pearl River watershed by expanding the map files, right-clicking on PearlMS.shp and selecting "Zoom to this Map."
Question: What is the basin-average precipitation total for the Upper Pearl Subbasin on 30 August 2021 12:00 (from the LMRFC precipitation grids)?
The LMRFC precipitation grids indicate that the Upper Pearl Subbasin received an average of 0.11 inches (14710 ac-ft) of precipitation on 30 August 2021 at 12:00.
View SERFC Precipitation.
Create a New Map Window.
Right‐Click on the "Pearl-Part A" Session.
From the "Sessions and Maps" option, select Add Map Window.
Enter the name "SERFC Precip 1HR" for the new Map Window in the dialog that pops up and press OK.
Within the "SERFC Precip 1HR" Map Window, right-click on the TIN node and click on "Select DSS paths..."
Make the following DSS file selection:
...\HEC-MetVue_DssDataReader\HEC-MetVue_DssDataReader_Start\Data\DSS\precip.2021.08.dss
Filter the B-Part to "Pearl River" and the F-Part to "SERFC-QPE."
Select the SERFC-QPE precipitation grid for 30 August 2021 12:00 by highlighting the pathname within the "Available TINs" window and clicking "Add Sel."
Select "OK" to add the selected data to the map window.
The SERFC precipitation data for 30 August 2021 12:00 is added to the map window and the basin-average totals are displayed.
Zoom in closer to the Pearl River watershed by right-clicking within the map window → Encompass Data → TIN
Note that the extents of the SERFC precipitation data does not fully cover Pearl River watershed. The western portions of the Middle Pearl-Strong, Middle Pearl-Silver and Bogue Chitto subbasins are not covered as indicated by the dashed red line that was drawn in below:
Dataset extents can be easily visualized by highlighting the Map Panel name ("SERFC Precip 1HR") within the Explorer Window to activate the Properties options. Within the "Map Layers" tab, "Show TIN Grid/Mesh" can be selected to display the mesh that comprises the TIN.
Areas triangulated in green represent areas that contain data Data while areas in blue represent No Data. By displaying the TIN Grid/Mesh, we can more easily see the boundaries of the SERFC dataset.
Question: What is the basin-average precipitation total for the Upper Pearl Subbasin on 30 August 2021 12:00 (from the SERFC precipitation grids)?
The SERFC precipitation grids indicate that the Upper Pearl Subbasin received an average of 0.13 inches (16432 ac-ft) of precipitation on 30 August 2021 at 12:00.
Compare Different Data Sources.
Next, let's compare the extents and volume from the LMRFC and SERFC precipitation grid for the same timestep (30 August 2021 12:00).
Turn off the "Show TIN Grid/Mesh" option and select the "Tile Windows" (
) icon to view all active Map Windows within the "Pearl-Part A" HEC-MetVue session.
Notice that all three map windows are displayed within the "Pearl-Part A" HEC-MetVue session. Since we are only interested in comparing the "LMRFC Precip 1HR" and "SERFC Precip 1HR," we can "close" any extra map windows to simplify the tiled display.
Close Extra Map Windows.
Right-Click on the "LMRFC Precip" map window heading and select "Close Map Window."
The "LMRFC Precip" map window will be removed from within the "Pearl-Part A" session window and its listing will appear greyed-out within the explorer window.
Closing the map window does not delete any of its data or properties, but rather moves it to the background until it is needed again. Map windows can be re-activated by right-clicking the map window heading within the Explorer Window and selecting "Open Map Window."
View Tiled Map Windows.
To re-center the remaining LMRFC and SERFC Comparison map windows, select the "Tile Windows" () icon once again.
The two remaining "Open" map windows will be resized to fill the "Pearl-Part A" session window.
If necessary, zoom in closer to the Pearl River watershed extents to compare differences between the SERFC and LMRFC precipitation datasets.
Both the LMRFC and SERFC precipitation grids for the 30 August 2021 12:00 timestep are now displayed.
Question: What differences do you notice between the two different datasets?
- Recall that the extents of the SERFC data do not cover the full extents of the Pearl River watershed:
- Basin-average values vary between the LMRFC and SERFC data–even in subbasins that are fully covered by both datasets. For example, the "Lower Pearl" subbasin received an average of 0.05 inches (4993 ac-ft) of precipitation within the SERFC dataset and 0.08 inches (7274 ac-ft) within the LMRFC dataset on 30 Aug 2021 12:00.
Now that we've examined the LMRFC and SERFC datasets individually, Task 4 will demonstrate how to temporally combine multiple datasets at once and when it might be useful.