# Presentation: 408869

## Hydrometeorology and Polarimetric Radar 

- How can Polarimetric radar aid in flash flood forecasting?

- James J. Stagliano, Jr.1, James L. Alford1, Dean Nelson1, J. William Conway2,
- Barbara Gibson3 and Don Hyde3

- 1Enterprise Electronics Corporation
- 2Weather Decision Technologies
- 3Choctawhatchee, Pea and Yellow Rivers Watershed Authority

## Slide 2

## Outline

- Failure of Radar
- Promise of Polarimetric Weather Radar
- Choctawhatchee, Pea, Yellow Rivers Watershed
- EEC Polarimetric Weather Radar
- Conclusion

## Failure of Radar

- Numerous meteorological and physical effects limit accurate rainfall estimation
- Marshall – Palmer (Z-R) Relationship
- Different DSD  Varies from event to event
- Different DSD  Varies within precipitation event
- Mie Resonance Effects
- Hail Contamination
- Beam Blockage
- Attenuation
- Nonuniform beam filling
- Height Above Ground
- Wind dispersion
- Precipitation Type (Melting Layer)

## Failure of Radar to Deliver

## Radar – Precipitation Estimation

- Rainfall Estimates given by Marshall-Palmer Relationship
- Dependent on sixth power of diameter

| Drop Size | Quantity | Z | Water Volume |
| --- | --- | --- | --- |
| 1 mm | 4096 | 36 dBZ | 17,160 mm3 |
| 4 mm | 1 | 36 dBZ | 270 mm3 |

- A factor of 63 difference

## Radar – Drop Size Distribution

- Similar Reflectivity, Different Drop Size Distributions

## Scattering

## Precipitation Scattering

- Assumption is all scattering is Rayleigh
- True for S band
- Not true for C and X band (Ryzhkov, 2005)

**C-band:**
- 	** = 5.33 cm
- 	Mie ~ 4.5 mm 

**X-band:**
- 	** = 3.0 cm
- 	Mie ~ 2.5 mm 

## Polarimetric Weather Radar

- Transmits microwave energy in both horizontal and vertical polarizations
- Able to measure entire scattering matrix
- Much more information of scattering medium
- Standard Base Moments: ZH, VH, WH
- Polarimetric Base Moments : ZDR, DP, HV, LDR
- Estimate the average Drop Size Density
- Identify average particle shape  Hydrometeor Classification
- Immunity from beam blockage
- Variables change due to rainfall  Much better rainfall estimations

## Conventional Weather Radar

## Polarimetric Radar

- And Vertical Pulse

## Polarimetric Weather Radar

*Enhanced SIDPOL**TM** *
*(2 Patents Granted to EEC)*

## Vertical cross-sections of radar variables and results of classification.

- NCAR Spol radar. August 14, 1998. Florida

**LR** – light rain, **MR** – moderate rain, **HR** – heavy rain, **LD** – large drops, **R/H** – rain / hail mixture, **GSH** – graupel / small hail, **HA** – hail, **DS** – dry snow, **WS** – wet snow, **IH** – horizontally oriented crystals, **IV** – vertically oriented crystals

## Polarimetric Weather Radar

- Raindrops are oblate spheroids
-  Horizontal Returns greater than vertical returns
-  Phase shift in horizontal is more than in vertical
-  DP increases with range through rain

## Polarimetric Rainrate

- (Doviak and Zrnic, 1993)

## Polarimetric RainRate (KDP)

- Specific Differential Propagation Phase

-  Independent of receiver/transmitter calibration
-  Independent of attenuation
-  Less sensitive to variations of size distributions (compared to Z)
-  Immune to particle beam blocking
-  Unbiased if rain is mixed with spherical hail
-  Noisy at low rainrates

## Radar RainRate

- Marshall - Palmer

- KDP

- Zh - ZDR

- KDP - ZDR

## Polarimetric Radar vs. Gauge

- (Bringi and Chandrasekar, 2001)

## Polarimetric Weather RadarRainfall Measurements

**“****Traditional” R(Z) estimate**

**Polarimetric R(K****DP****) estimate**

## Polarimetric Radar and Rainfall

- One hour point measurements: Radar estimates vs. gages

## Areal Mean Rain Rate Bias

- Hail

## Slide 23

## Choctawhatchee, Pea, Yellow Rivers WatershedHistory

- 1990 – Watershed Authorities created throughout state
- After devastating Elba Flash Floods
- CPYRWA only active authority
- SE AL only region in the state with extensive data on its water resources and needs
- Initially just Choctawhatchee – Pea Rivers
- Started with 3 rain gauges
- 1994 - COE Installed Network of Stage and Rain Gauges
- 1997 – Yellow River Added
- 1998 – Major Flood
- 2005 – Conecuh River under consideration

## Choctawhatchee, Pea, Yellow Rivers Watershed

## Slide 26

## EEC C-Band Polarimetric Radar

- Transmitter
- 1 MW
- Split between channels
- 500 kW per channel
- Magnetron
- Coherent on Receive
- PW 0.4, 0.8, 2.0 s
- PRF 300 – 2000 Hz
- EDRP-9 Signal Processor
**	****Intermediate Frequency   60.00 MHz**
**	****Digitization rate****	****           80 MHz**
**	****Linear dynamic range      >100 dB**
**	****Minimum discernable signal    <110 dB**
**	****Clutter suppression   >50 dB**
**	****Range resolution****	****     >45 meters**
**	****PRF****	****	****     <250 Hz to >1300 Hz**
**	****Phase noise****	****     <-53 dBc integrated over the ****	****	****     Nyquist co-interval**

-  Greatly Improved Accuracy
- Precipitation Estimates Improved Up to 40%
- SidPolTM Radar is Now a True Hydrological Instrument
- Better Clutter Identification and Elimination
- True Precipitation Classification
- Ice
- Snow
- Hail
- Liquid Rain

## Slide 28

## EEC C-Band Polarimetric Radar 

- 2 Installed
- UK Met (250 kW)
- EEC (1 MW)
- 2 more installations this year
- Valpraiso University (Indiana, USA) (1 MW)
- Austria (250 kW)

## Hydrological Modelling - HDSS

- QPE-SUMS
- Multiple sensor integration for quantitative precipitation estimation
- Accurate estimates of rainfall
- Basin accumulation to forecast flood risk

## Alabama Consortium

- Statewide Consortium
-  Universities
- University of South Alabama
- University of Alabama - Huntsville
- Auburn University
- University of Alabama - Tuscaloosa
- Federal Agencies
- NASA
- State Agencies
- Watershed Management Authorities
- State EMA
- Local Agencies
- County EMA’s
- Local First Responders
- EEC

## Integration Research Laboratory

- Fully integrated and operational hydrometeorological forecasting center
- Located at EEC
- Operational testbed for new technology
- Data freely shared with consortium partners

- All data streams integrated
- Satellite
- Radar
- AWS sensors
- NWP
- Integration
- Sensors
- Software
- Communications
- Training
-  Evaluation
- Sensors
- Software
- Communications

## Future Work

- Tropical
- Convective
- Hail shafts
- Large Drops
- More attenuation
- Hurricanes
- Run-off Modeling
- AL Network
- Hurricane Dissipation

- ExtraTropical
- Stratiform
- Brightband
- Smaller Drops
- Snow / Ice
- Run-off Modeling

**South Alabama**

**Valpariso, Indiana**