Dual Pol Product Loading and Analysis
D2D (Base Data, HC, Precip, ML)
FSI (Base Data, HC)
D2D vs FSI
When Dual Pol is fielded there is a turnkey script that will make Dual Pol data available from the D2D menus. In the Dual Pol Primer module WES case we have turned on the new radar menus. All Dual Pol products are available from the new menus in D2D.
Loading Dual Pol data in D2D can be done in similar ways as with non Dual Pol data (e.g. individual products from a product menu, four panels, all tilts), however, the greater number of products raises new challenges for quick analysis. In OB9, the Panel Combo Rotate capability was implemented to allow up to 8 products loaded in a four panel with keyboard shortcuts. A few new menus leverage this enhanced capability to support effective Dual Pol analysis. For example, the All tilts base data menu item loads an 8 product 4panel all tilts that can be used to toggle between any of the 8 products with simultaneous cursor readout of all products. The new multi-product menus are an important starting point for learning how to analyze Dual Pol data, but the opportunity exists for you to design new product combinations tailored to unique radar analysis tasks.
One fundamental issue in analyzing Dual Pol data is the strong sensitivity of Dual Pol variables to phase change and the thermodynamic environment. D2D provides unique ways of incorporating thermodynamic data into analysis of Dual Pol data with the Std Env Data Packages and Popup SkewT. The Std Env Data Packages allow cursor sampling of environmental data with the radar data, as well as plotting of environmental variables in the planes of the radar tilts. The Popup SkewT provides an additional way to visualize the height of the radar data on a SkewT. Integrating the environmental analysis tools with the new multi product displays optimally leverages the strengths of D2D in analyzing Dual Pol data.
D2D also has the capability to generate vertical cross sections and CAPPIs (height or temperature based levels/layers) using the Volume Browser, but these products do not update by themselves, and they are not dynamic as in FSI. Because of these limitations, they are not included in the discussion below.
The following sections document how to load Dual Pol data in D2D for analysis. Section 1 focuses on D2D. Section 2 focuses on FSI, and Section 3 compares the strengths and limitations of D2D and FSI for analyzing Dual Pol data.
1a. D2D Base Data Analysis
To analyze Dual Pol base data (ZDR, CC, and KDP) you can load each product individually from the Best Res Base Products section located in each radar's main menu.
To load multiple base products go to a particular radar's menu, and under the 4-Panel Z+SRM/ZDR+V/KDP+HC/CC+SW section, select the appropriate menu item (e.g. All Tilts base data).
These menu items will load a four panel with Z/SRM in the upper left quadrant, ZDR/V in the upper right quadrant, KDP/HC in the lower left quadrant, and CC/SW in the lower right quadrant. Primary Dual Pol base data analysis is best accomplished using the All Tilts base data menu item (4panel all tilts with 8 products loaded), though you may use the single tilts (e.g. 0.5 base data) for longer time duration loops. Use the 1-8 keyboard shortcuts on the upper left part of your keyboard to switch between products:
- Keyboard shortcuts
- 1 - Z (Reflectivity)
- 2 - ZDR (Differential Reflectivity)
- 3 - CC (Correlation Coefficient)
- 4 - KDP (Specific Differential Phase)
- 5 - SRM (Storm-Relative Motion)
- 6 - V (Velocity)
- 7 - SW (Spectrum Width)
- 8 - HC (Hydrometeor Classification)
To load four panel displays containing mutliple elevation angles of the same product, go to a radar's menu, and select the four panel pullout menu. Then click on the desired set of four panels:
Low resolution versions of the Dual Pol products will be nationally collected and distributed via the Radar Poroduct Central Collection Dissemination Service along with the other basic radar products. While analysis at the forecast office will mostly utilize the high resolution products, you may need to load the low resolution version of the prodocts. To load the low resolution products, go to a particular radar's menu, and select the 4 Bit/Legacy Prods pullout menu. Then select the Dual Pol product desired under the Dual Polarization section:
1b. D2D Hydrometeor Classification Algorithm Analysis
To load HC output by itself, go to a particular radar's menu, and select the Derived Products pullout menu. Under the Reflectivity Based section, select the Hydrometeor Classification (HC) pullout menu to select the desired tilt(s).
To load HC output with mutliple Dual Pol base data products, go to a particular radar's menu, and under the 4-Panel Z/ZDR/HC+KDP/CC section select the appropriate menu (e.g. All Tilts HC analysis):
These menu items will load a four panel with Z in the upper left quadrant, ZDR in the upper right quadrant, HC/KDP with Melting Level overlaid in the lower left quadrant, and CC in the lower right quadrant. Interrogating HC output is best accomplished using the All Tilts HC analysis menu item. Use the 1-5 keyboard shortcuts on the upper left part of your keyboard to switch between products:
1c. D2D Precipitation Accumulation Analysis
D2D is the only place to view Dual Pol precipitation products (not available in FSI). To load Dual Pol precipitation data (STA, OHA, DAA, DPR, HHC, DUA, DSD, DOD), you need to go under a radar's menu to the Precip pullout menu:
The Dual Pol precip products and displays available are:
1d. Melting Layer
The ML product can be used to identify the Melting Layer used in the HC Hydrometeor Classification algorithm. While manual identification of the melting layer using CC, ZDR, and Z is the best way to identify the melting level, interrogating the ML product can provide insight into how the simple algorithm approximation impacts the HC product (remember ML only uses 4 to 10 degree slices directly over the radar to determine 1 value that it applies to the whole radar domain). ML can only be viewed in D2D, and it is not available in FSI. To access the Melting Layer product, you need to go under a radar's menu to the Algorithm Overlays pullout menu. Then select the Melting Layer (ML) pullout menu and the desired ML product:
FSI supports viewing ZDR, CC, and KDP Dual Pol base data products as well as HC Dual Pol algorithm products. In FSI two of the products are labeled differently than in D2D. CC is labeled RhoHV (research convention), and HC is labeled HCA. All other Dual Pol products (e.g. precip products, HHC, ML, etc) are not displayable in FSI.
Because Dual Pol variables have a strong sensitivity to hydrometeor phase, the data have a distinct vertical structure due to the vertical temperature structure of the environment. Thus, the dynamical vertical cross sections in FSI provide a unique way to interrogate Dual Pol base data and algorithm data. The most recent "virtual volume scan" can introduce ambiguity in the vertical cross sections and CAPPIs, however, as with non Dual Pol products. The following sections document how to load Dual Pol data in FSI for base data and algorithm analysis.
2a. FSI Base Data Analysis
FSI displays the three main base data products: ZDR, CC, and KDP, though CC is labeled as RhoHV (research convention). The main changes in FSI for loading Dual Pol data are the new keyboard shortcuts.
- Keyboard shortcuts (different from D2D)
- 1 or "Z" - Z
- 2 or "V" - V
- 3 or "S" - SRM
- 4 or "W" -SW
- 5 or "D" - ZDR
- 6 or "O" - RhoHV (aka CC)
- 7 or "K" - KDP
- 8 or "H" - HCA (aka HC)
2b. FSI Hydrometeor Classification Algorithm Analysis
To toggle to HC use the "8" key or "H" key.
The raw HC data is stored as an integer value, and this value is correlated with the appropriate hydrometeor classification in the display. One limitation of FSI is that the cursor readout displays the integer value (e.g. 10) rather than the category (e.g. hail):
In creating the volumetric data, FSI interpolates the Hydrometeor Classification algorithm output using the integers representing the class. For example, halfway between two data points of Biological (1) and Ice Crystals (3) the interpolation algorithm would assign it a value of 2 (Ground Clutter), which is not meaningful:
Thus, you may see artificial HC data in the vertical cross section and CAPPI panels when interpolation is turned on. In the following image note how the interpolation between beams aloft artificially inserts all the categories between dry snow (DS) and hail (HA), including green (heavy rain) at 37 Kft!
So when evaluating HC data in FSI, you may want to keep interpolation off to avoid interpolation artifacts. This makes pattern matching more difficult when there are lots of gaps between beams, however. If you leave interpolation on when viewing HC data in FSI, you will need to mentally filter the interpolated noise.
3. D2D/FSI Dual Pol Strengths and Limitations
When it comes to analyzing Dual Pol data, D2D and FSI each have unique strengths and limitations. Some of these existed prior to Dual Pol, and some are new, coincident with the new Dual Pol capabilities. For optimal analysis of Dual Pol data consider using each application as appropriate.
- D2D Dual Pol Strengths
- Quick access to all base data products
- Integrates radar data with thermodynamic data
- Load with LAPS or other Std Env Data Pkgs
- Cursor sample temperature or overlay isotherms on radar tilts to interpret hydrometeor phase
- Load with popup SkewT to visualize freezing level (0 C) and supercooled liquid (~ -20C)
- Integrates well with other D2D capabilities (maps, WarnGen, etc)
- D2D Dual Pol Limitations
- Vertical cross sections in the D2D Volume Browser are not dynamic like FSI
- CAPPIs in the D2D Volume Browser are not dynamic like FSI
- FSI Dual Pol Strengths
- Dynamic vertical cross sections
- Dynamic CAPPIs
- FSI Dual Pol Limitations
- Only view ZDR, CC, KDP, and HC products...no display of precip products or ML product
- No thermodynamic data integration in displays
- Interpolation of HC data can introduce artifacts in the vertical cross section and CAPPIs
- Virtual volume scan can introduce artifacts in the vertical cross sections and CAPPIs
- Cursor sampling of HC displays integer of hydro classification rather than name
- Cities display slows down workstation
- Must choose between accuracy of cursor sampling position versus workstation performance