Dual Polarization radar data.

Updated Nov 06 2007

http://www-sdd.fsl.noaa.gov/~ramer/noaa/dualPol/dualPol.html

During the OB8.3 time frame dual polarization radar data will become available. Briefly, this involves alternating between sending vertically and horizontally polarized pulses. Whereas employing doppler allows the radar to be sensitive to the motion of the targets, employing dual polarization allows the radar to be sensitive to the shape of the targets. The biggest impacts of this technology will be improved values for accumulated precipitation, improved hail detection, and improved detection of non-meteorological targets.

It has now come to the point where GSD has received meteorologically reasonable sample data for just about everything; the latest sample data received was a meaningful differential reflectivity example. Besides that, the only thing GSD is waiting on is an initial list of levels for VB cappis.

Digital Precip Rate.

The conversion from the two byte values in the product to the one byte image counts is completely adaptable outside of code. This example is linear to 8in/hr, and logarithmic from there up to the maximum possible value.

Differential Reflectivity.

Melting Layer.

Here we have the melting layer on top of a hydro class image. The categories are distinguished by line pattern. This has been prototyped such that the line patterns and legend text are arbitrarily configurable.

Hydrometeor Class.

We can also display a Hybrid Hydro Class sample product; it looks extremely similar. Note that the sample string is now a more detailed description than what appears on the color bar.

A segregated User Selectable Precip.

Correlation Coefficient.

Specific Differential Phase.

What follows is the current prototype for including these products in the menus, based on requirements agreed upon to date. This has recently been updated to include three letter identifiers for most dual pol entries and a reordered precip menu..

Note the addition of a new submenu entitled Dual Pol Prods, and that some dual polarization products have been added to the Precip submenu; both of these menus have been torn away. Also note that the Dual Pol precipitation products can be found both on the Precip submenu and in a precipitation product area on the Dual Pol Prods menu. No code had to be written to allow this; the default AWIPS menuing software already supports this. An analogous approach could easily be taken with the proposed melting layer contours; posting them both in the Dual Pol Prods submenu and in the Graphics submenu.

This latest screen shot, which has some new OB8.2 layouts merged in, points out that the top level menu for individual radars are getting very long; it may be worth considering pushing some stuff down a level. The best suggestion I could offer would be to leave only the one or two most used radar applications on the top level, and put the rest in a new Radar Applications sub menu. Also, maybe this is a mistaken assumption, but over time, has not the usage of the 4 bit SRM dropped off in favor of the 8 bit SRM? If true, we could consider pushing all the Z/SRM4 combo selectors off the top level menu and into the Z/SRM4 tilts submenu. These two steps, taken together, could free up enough space such that there would be room on the top level menu for two or three key dual polarization products. If we were to follow up on this approach, we would have to get more people involved than those that typically take part in our dual polarization requirements meetings.

The following screen shot shows the layout of the proposed menus for the Diff Refl, Melting Layer and Dual Pol 4 Panel sub menus:

Note that the four panels, instead of being for 4 different tilts, are for one specific tilt. By tilt, here we actually refer to a range of tilts, as has been the case for all elevation based products since OB3. As this prototype is currently configured, the individual panels in each simple four panel display will contain the following: base reflectivity, differential reflectivity, correlation coefficient, and hydrometeor classification. In the combo four panel, the individual panels will contain the following: base reflectivity/base velocity combo, differential reflectivity/SRM combo, specific differential phase/storm total precip combo, and correlation coefficient/hydrometeor classification combo. Since each of these four panels is tilt specific, there is also an All Tilts version of the four panel, as there is all other tilt based dual polarization products. Note that there is also (shown in the very first screen shot) a non-tilt based four panel focused on precipitation products. Be aware that the specifc contents of these four panels are easily configurable in tables; no code specifies this layout. Thus, the details can be easily changed later.

A recent addition to this prototype menu layout for dual polarization data are selectors that give direct access to the 4 bit versions of these products. The previously shown default selectors, like most other AWIPS radar data selectors, automatically provide the user with whatever is the highest spatial and bit depth resolution available. The screen shot that follows shows the updated layout of the 4bit/Legacy Prods submenu with a new section for dual polarization products.

On June 19, GSD also received some initial information about desired color tables. This next set of screen shots show the four bit versions of these tables as in the requirements document to date, followed by a first prototype of ramped versions of these tables suitable for the display of 8 bit data. Note that the first screen shot shows a proposed menu layout within the Image Controls dialog for selecting these color tables. The product used to show the color tables is an arbitrary 4 bit reflectivity product; the reader should not assume that this means that these tables cannot be used with dual pol data. The 8 bit tables have the same color as the 4 bit tables at counts of 0, 16, 32, etc.

The reader will also note that no 8 bit version for the Hydrometeor Class color table has been prototyped. Since the Hydrometeor Class is a pure enumeration rather than a conservative field, there are some details to work out before attempting to create a color table for the 8 bit Hydrometeor Class; a straightforward ramping will not be sufficient.

Volume Browser Access.

We now have prototyped volume browser access for all the three dimensional data sets associated with the dual polarization data. The screen shot that follows shows the updated VB Other field submenu, where all the radar fields are placed, on top of a cross section of correlation coefficient and radar tilt angle.

This next screen shot shows a 700mb CAPPI of the hydrometeor class done from the volume brower. Note that a means has been found to label the color bar and drive the sampling with strings rather than pure numbers; previously the only VB display type capable of handling enumerations was a field of icons. Also note that no interpolation is done between the classes, which is not desired for an enumerated data type.