GRLevel3 displays all of the significant Level III radar products for both
legacy and Dual Pol NEXRADs and TDWRs. Due to the mix of legacy, high
resolution, and Dual Pol data streams, GRLevel3 works with *categories* of
products. There are 14 categories:

BR | Base Reflectivity | Reflectivity is one of the fundamental radar products |

BV | Base Velocity | Base Velocity is a fundamental Doppler radar product |

SRV | Storm Relative Velocity | Base Velocity with the storm motion removed |

SW | Spectrum Width | The amount of variability in the base velocity |

ET | Echo Tops | Height of the 18 dbz reflectivity |

VIL | Vertically Integrated Liquid | Estimate of liquid in a vertical column of reflectivity |

OHP | One Hour Precipitation | Estimate of how much rain has fallen in one hour |

STP | Storm Total Precipitation | Estimate of how much rain has fallen in an entire event |

ZDR | Differential Reflectivity | Dual Pol product comparing the horizontal and vertical reflectivity |

CC | Correlation Coefficient | Dual Pol product measuring the variability of echoes |

KDP | Specific Differential Phase | Dual Pol product measuring liquid content in echoes |

HCA | Hydrometeor Classification Algorithm | Dual Pol product estimating the type of echoes |

DOD | One Hour Difference | Dual Pol product showing the difference between Dual Pol and legacy algorithms for One Hour Precipitation |

DSD | Storm Total Difference | Dual Pol product showing the difference between Dual Pol and legacy algorithms for Storm Total Precipitation |

The Dual Pol products are only available on NEXRADs that have been modified to support Dual Polarization.

GRLevel3 always chooses the highest quality product from each category. For example, on a Dual Pol NEXRAD, GRLevel3 displays the Dual Pol version of Storm Total Precipitation instead of the legacy product. Here are the radar products for each category (columns are: AWIPS, resolution, levels, range, name):

**Base Reflectivity (BR):**

NxQ | 1° x 1000 m | 256 | 460 km | Digital Base Reflectivity (up to 6 tilts) |

NxR | 1° x 1000 m | 16 | 230 km | Legacy Resolution Base Reflectivity (4 tilts available) |

NxZ | 1° x 2000 m | 16 | 460 km | Base Reflectivity 248nm |

NCR | 1° x 1000 m | 16 | 230 km | Composite Reflectivity |

NCZ | 1° x 4000 m | 16 | 460 km | Composite Reflectivity 248 nm |

TRx | 1° x 150 m | 256 | 88 km | TDWR Base Reflectivity |

TZL | 1° x 300 m | 256 | 415 km | TDWR Base Reflectivity 223 nm |

**Base Velocity (BV):**

NxU | 1° x 250 m | 256 | 300 km | Digital Base Velocity (up to 6 tilts) |

NxV | 1° x 1000 m | 16 | 230 km | Legacy Base Velocity (4 tilts) |

TVx | 1° x 150 m | 256 | 88 km | TDWR Base Velocity |

**Storm Relative Velocity (SRV):**

XxS | 1° x 250 m | 256 | 300 km | Digital Storm Relative Velocity (GRLevel3-derived) |

NxS | 1° x 1000 m | 16 | 230 km | Legacy Resolution Storm Relative Velocity |

**Echo Tops (ET):**

EET | 1° x 1000 m | 256 | 345 km | High Resolution Digital Echo Tops |

NET | 4 km x 4 km | 16 | 230 km | Legacy Echo Tops |

**Vertically Integrated Liquid (VIL):**

DVL | 1° x 1000 m | 256 | 460 km | High Resolution Digital VIL |

NVL | 4 km x 4 km | 16 | 230 km | Legacy VIL |

**One Hour Precipitation (OHP):**

DAA | 1° x 250 m | 256 | 230 km | Dual Pol One Hour Rainfall |

OHR | 1° x 2000 m | 16 | 230 km | Legacy One Hour Rainfall |

**Storm Total Precipitation (STP):**

DTA | 1° x 250 m | 256 | 230 km | Dual Pol Storm Total Rainfall |

DSP | 1° x 2000 m | 256 | 230 km | Digital Storm Total Rainfall |

OHR | 1° x 2000 m | 16 | 230 km | Legacy One Hour Rainfall |

**Dual Pol-Only Products (ZDR, CC, KDP, HCA, DOD, DSD):**

NxX | 1° x 250 m | 256 | 300 km | Digital ZDR |

NxC | 1° x 250 m | 256 | 300 km | Digital CC |

NxK | 1° x 250 m | 256 | 300 km | Digital KDP |

NxH | 1° x 250 m | 256 | 300 km | Digital HCA |

HHC | 1° x 250 m | 256 | 230 km | Digital Hybrid HCA |

DOD | 1° x 250 m | 256 | 230 km | Digital DP One Hour Difference |

DSD | 1° x 250 m | 256 | 230 km | Digital DP Storm Total Difference |

The Melting Layer (ML) radar product is a series of lines showing the position of the melting layer relative to the radar beam for a given tilt. The melting layer itself is determined by the radar using three methods:

- Automated detection of the melting layer signature in CC and BR (when possible)
- Environmental model data (RAP). The freezing level is the top and the bottom is assumed to be 500 m below
- Manual entry of the melting layer top and bottom

Since the radar beam increases in height with range, the melting layer lines typically form rings around the radar site. These rings are not typically perfect circles due to two factors:

- The melting layer heights can vary around the radar site
- The beam elevation angle varies with azimuth (typically at the start of a tilt)

GRLevel3 only shows a particular tilt of the melting layer when its corresponding graphical radar product is displayed. For example, ML 0.5° only shows up on BR/BV/SRV 0.5°. There are up to four ML lines shown:

Inner Light Gray Ring | Where the beam top enters the Melting Layer |

Inner Solid White Ring | Where the beam center enters the Melting Layer |

Outer Solid White Ring | Where the beam center leaves the Melting Layer |

Outer Light Gray Ring | Where the beam bottom leaves the Melting Layer |

In winter you will sometimes only see the outer ML rings and/or partial ML rings because the bottom of the melting layer is below the radar site itself.