# Presentation: 502355

## High Resolution VIL Algorithm

**James Evans**
**NEXRAD TAC**
**22 MAY 2002**

## Key FAA Systems that Benefitfrom Improved NEXRAD Algorithms

- Integrated Terminal Weather System

- Weather And Radar Processor

- Corridor Integrated Weather System

- Medium Intensity Airport Weather System

## Why VIL vs. Composite Reflectivity?

**Issue is how to characterize storm intensity given values at a number of different altitudes**
**Layer Composite Reflectivity**
**Takes maximum reflectivity from any altitude**
**Vertically Integrated Liquid (VIL)**
**Converts reflectivity at each height to equivalent water mass**
**Determines how much water is being held aloft**
**Argument: this is closely related to strength of updraft**
**Situations where VIL is better**
**“****Bright band”**
**Ground clutter / AP**

## NEXRAD Products Comparison During a Bright Banding Case

**On the left is Composite Reflectivity image, the line shows the location of the NEXRAD cross section (next slide)**
**The center image is the lowest tilt of the NEXRAD and similar to the BRRM product used in the WARP and on ETMS.**
**The image on the right shows NEXRAD based VIL product created by CIWS**

## NEXRAD Cross Section of a Stratiform event

-  **Vertical cross section (RHI) of a Stratiform rain event showing the****  stratified precipitation or “Bright Banding”**

## Why High Resolution VIL (HRVIL) vs. VIL

**VIL an excellent proxy for severe convection**
**Critical flight planning element**
**Even small changes in VIL important**
**Some problems with existing NEXRAD VIL**
**Coarse spatial resolution (4 km)**
**Coarse data level resolution (16 levels)**
**Short range (230 km)**
**MIT/LL FAA solution – HRVIL**
**Polar format VIL maintains inherent radar resolution (1****0**** x 1 km)**
**256 data levels replace 16 data levels**
**Full range (460 km)**
**Key FAA systems will utilize HRVIL**
**CIWS, MIAWS, WARP**
**NCWF, TCWF**

## High Resolution VIL (HRVIL) Computation

**Same basic NEXRAD VIL conversion and integration used**
**Except no lower limit of 18 dBZ**
**All valid range gates contribute**
**HRVIL computed to maximize depiction of structure**
**256 data levels**
**VIL < 1 kg m****-2**** now resolved**
**200 data levels vs. 5 for VIL range of 0-20 kg m****-2**
**Polar output**
**mitigates Cartesian smoothing**
**Full range calculations**
**intended to benefit 2 hour convective forecasts**

## High Resolution VIL Curve Compared to Current VIL Data Levels

**High Resolution VIL Curve Compared to Current VIL Data Levels**

- Current NEXRAD VIL does not resolve VIL below 1 kg m-2

**Notes:**
The form of the curve (linear to about 1 kg m-2, log thereafter) is shown.
253 points of valid digital HRVIL are portrayed.  NEXRAD VIL has 16 data levels at 5 kg m-2 increments.
NEXRAD VIL does not resolve below 1 kg m-2.  Thus, the HRVIL is capable of monitoring incipient growth possibly useful for TCWF.

Color coding is used to relate to the familiar VIP levels.

## Current and High Resolution VIL Comparison 

## HighRes VIL Comparison – Sun strobe

## HighRes VIL Comparison – Bull`s-eye

## High Resolution VIL and ORPG Builds

**Build 2 version provided to the ROC Jan. 31, 2002 for deployment beginning Sept. 30, 2002 **
**Computationally similar to current NEXRAD VIL**
**Polar format and digital representation significantly improve depiction of VIL vs. NEXRAD VIL**
**For Build 3, the algorithm is being retooled to receive DQA algorithm data stream to eliminate contaminated dBZ input**
**Build 3 hand-off to ROC this July**