# Presentation: 473835

## Optimization, Use and Future Development of the Doppler Lidar at the Hong Kong International Airport

- Robert M. Banta, Lisa S. Darby and W. Alan Brewer
*NOAA/ETL, Boulder, Colorado, U.S.A.*
- Collaborators:  C.M. Shun, C.M. Cheng, B.L. Choy,
- O. Lee, S.T. Chan, S.Y. Lau
*HKO, Hong Kong*

## ...

## Doppler lidar

- Scanning system – maps Doppler velocity field (radial winds)
- Aerosols are the scatterers
- Only real-time system currently capable of real-time detection of wind shear

- Characterization of CTI system:
- Δ r ~ 100 m
- Rmax  ~ 8.5 km
- Effective prf ~ 10 Hz
- Vprec ~ 0.5 m s-1  (1 kt)

## Needs fulfilled by Doppler lidar

- Objective 1:  ***Detection*** – the Doppler lidar is sensitive enough to see abrupt changes in glide-path wind speed: relate to what airplanes experience
- Objective 2:  ***Characterization*** of meteorological conditions – monitor flow features seen by Doppler lidar (e.g., terrain forced) and relate to occurrences of shear/turbulence
- Objective 3:  ***Bust post analysis***

## Existing instrumentation at HKIA

- AWS network
- Radar wind profilers
- Terminal Doppler Weather Radar (TDWR)
- Rawinsonde
- Turbulence/wind shear algorithm

## Slide 6

## Existing instrumentation at HKIA

- AWS network
- Radar wind profilers
- Terminal Doppler Weather Radar (TDWR)
- Rawinsonde
- Turbulence/wind shear algorithm

## Meteorological conditions producing shear and turbulence:  “Manual Rules”

- ‘Spring rules’ – Peak wind shear season (March)
- Easterly through southerly flow
- Gap flow
- Southwesterly flow
- Northerly flow
- Tropical cyclone, thunderstorm
- “Sea breeze” front
- Low-level jet

## Gap flow case: 21 Feb 2003

- Weak synoptic post-frontal easterly flow at low levels
- Inversion below 900 m ASL
- Light southeasterly flow in vicinity of
- 	Hong Kong
- Stronger ridge-top and gap flows over Lantau Island

## AWS

## 0000 UTC

- 21 Feb 2003

- 1200 UTC
- 21 Feb 2003

- Hong Kong soundings

## Jump-like feature to lee of gap

## Slide 13

## 1o Degree PPI

- 1o Degree PPI

## 1o Degree PPI

- 1o Degree PPI

## Tung Chung RHI

- Tung Chung RHI

## Tung Chung RHI

- Tung Chung RHI

## +20 knot change in headwind reported 12 minutes before this scan

## 07L-25L RHI

- 07L-25L RHI

- 07L

- 25L

- Light-to-moderate turbulence reported 21 minutes before this scan

- Sham Wat outflow

## Slide 20

## Features 

- Features
- transient

- 2040:10 UTC

- 2053:41 UTC

- 2044:55 UTC

## Slide 22

## Minimum Doppler lidar requirements

- Need to:
- Detect potentially hazardous wind shear
- Characterize meteorological conditions leading to wind shear
*Detection* = fast, frequent scan sequence
*Characterization* = wider coverage to document flow features and evolution
- Maximum range of at least 3 nm from end of runway   *(4-5 nm desirable)*

## With current Doppler lidar spec’s

- With 50-shot averaging -
- Typical sequence of scans needed for Detection plus Characterization has a 5 minute cycle time
*5 minutes is too long for adequate wind shear detection!*
- Tried 25-shot averaging –
- too fast for current processor
- loss of range (500 – 1000 m)

## Doppler lidar – critical component of wind shear detection system

- In case primary lidar needs maintenance, a backup lidar is required
- When not serving as the backup lidar, secondary lidar coordinated with primary lidar will cover both detection and characterization functions (overall detection rate will be enhanced)
- Primary and backup lidars would be near tower (center of airport)
- No routine coverage beyond 3 nm
- Not well aligned with glide paths

## Optimum system without compromise

- Additional lidars at end of each runway
- To provide coverage beyond the required *minimum* of 3 nm beyond the runway
- Better alignment with glide paths
- Lidar on NW corner of airport
- Surveillance of Sham Wat outflow
- Extended coverage of 07L glide path
- Lidar – Fire Station near south runway – monitor 07R departures (to east)

## Hong Kong International Airport

## Optimum Doppler lidar coverage

- Successfully accomplish all lidar objectives
- Detection – rapid scanning available along all glide paths
- Characterization – comprehensive scanning of wind features impacting the airport
- Post-analysis of busts – extended scanning schedules possible for improvement of wind shear detection algorithm
- Objectives 1, 2 & 3 only marginally attainable with two lidars

## Outstanding items on optimization

- Detection – rapid vertical slice scanning sequence over glide path for verification
- Explore removal of blanked sectors, including below 0o elevation (revisit eye-safety issue)

## Rapid-scan RHI method:  Shallow-angle RHI scans that intersect each glide path at 1, 2, and 3 nm’s.  Last week, scans were implemented that cover 1 and 3 nm of the glide paths.

- 1247 UTC and 1248 UTC, reports of
- wind shear, loss of 20 knots, 07L
- These four scans took 10 seconds to take,
- and document the winds along 07L and 07R
- during the time of wind shear reports

## Summary of recommendations	

- Toward fully-automated wind shear detection system
- Try 25-pulse averaging to decrease frequency of scan cycle (repeat time), but currently not feasible due to system constraints
- Use RHI scans for shear detection (rapid scan), pilot ‘training’
- Revisit eye-safety/blanked area issues
- New scanning strategy/schedule
*Continue to discuss – establish scanning strategy for spring*
- Meteorological sampling
- Explore using pressure difference across Lantau Island
- Upstream profiler on Cheung Chau – *support*
- Cable car – thermodynamic information

## Summary (con’t)

- Immediate issues – show that minute-to-minute detection possible
- Verification! – calibration between lidar and aircraft
- Robustness of system
- Future:  Multiple lidars to achieve all objectives