Recent Developments in Weather Radars and Radiosondes2014-06-19

Aki Lilja, Vaisala

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Contents

�About Vaisala

�Recent Developments of Weather Radars

�Recent Developments of Radiosondes

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About Vaisala

� Concentrating on environmental and

industrial measurements

� Customers in 150+ countries

� Americas (39%)

� EMEA (36%)

� APAC (24%)

� Employs 1,500+ professionals

� Offices in 16 countries

� Headquarters in Helsinki

� Net sales 273 MEUR (2013)

� 10.6% allocated to R&D

� Publicly owned

(Helsinki stock exchange)

� Established in 1936 by

professor Vilho Väisälä

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About Vaisala – part 2

� Weather Radars since in 2008

� More than 120 radars sold� all C band� almost all dual polarization� most use magnetron transmitter� main product WRM200

� Radiosondes since 1936

� Largest manufacturer� RS92 radiosonde:

WMO Intercomparison 2010� RS41 radiosonde:

UK Met Office Intercomparison 2014

� main product RS41-SG

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Contents

�About Vaisala

�Recent Developments of Weather Radars

�Recent Developments of Radiosondes

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Why Weather Radars?What are weather radars used for?

� (National/international) maps of precipitation areas

� typically Z in color scale

� Quantitative Precipitation Estimation (QPE)

� mm/h in the grid

� Detection of weather: hail, snow, graupel, squall lines,...

� Wind Profiles over the radar site (when precipitation)

� m/s u,v as the function of h

� Wind shear, tornadoes,...

� Birds (flight hazard), etc. bio

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source: www.fmi.fi

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What is the fundamental limitation for WR detection range?

4/3 Earth radiusmodel applied

4-8 km

12-20 km

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Recent Development:Dual Polarization in Operational Use

1. scattering by both h and v

2. propagation phase lag difference in h and v

3. cross correlation h vs. v voltages

h

v

1. h sees the drop being larger than the same drop seen by v

2. for h there appears to be more water in the volume than for v

3. both h and v see the same individual drops

=> Zh and Zv, ZDR=Zh/ZvZ~D6

=> ΦDP and KDP [deg/km]KDP~D3

=> ρhv

”STAR” mode

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Dual Polarization – So What?

�Better rain ”maps” due to improved clutter filtering (ρhv)

�QPE:R(Z,KDP,ZDR) vs. R(Z)

�Wind phenomena: filtering of moving non-meteorological echoes (e.g. flocks of birds)

� ”HydroClass” hydrometeor classification by direct observation

�Enhanced sensitivity Z detection by correlating h and v voltages (noise cancel)

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Dual Polarization – What is important in the Hardware

� Crucial that antenna looks at the same volume in h and v

� The antenna must not ”mix” signals of the h and v channels:

� ”cross polarization isolation”

� Linear Depolarization Ratio (LDR)

� ”What is the maximum ρhv that your antenna can produce from small drizzle?”

� Good quality dual polarization antenna needs to be designed for the purpose

� WRM200 antenna and cross polarization isolation better than 35 dB

� Every antenna provided with a measurement report

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h

v

”squintangle”

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U.S. development: National Weather Radar Testbed and Phased Array

� U.S. program to create a weather radar antenna that rapidly scans for ”rain maps” and concentrates on severe weather (tornadoes, supercells)

� Stationary antenna consisting of patch antenna elements and electronic beam forming

� Challenges:

� High cost

� Fundamental difficulty in providing high quality dual polarization data

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source: http://www.nssl.noaa.gov/tools/radar/mpar/

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Contents

�About Vaisala

�Recent Developments of Weather Radars

�Recent Developments of Radiosondes

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Why Radiosondes?(”What if I just produce profiles from NWP model”)

�Radiosondes remain the most important surface based dataset for numerical weather prediction model initialization

�Radiosondes provide direct observation of the thermodynamic profile => can make correct conclusions about the atmosphere

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Why Radiosondes?

�Numerical Weather Prediction (NWP) model initialization

� input -> output

�Profiles for (human) forecasting

� thermodynamic profiles

� assessment of model outputs

�Climatology work (GRUAN)

�Atmospheric research

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source: Alfred Wegener Institute www.awi.de

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Important aspects in radiosondes

�SI traceability of the measurements

� also WMO’s added recognition of importance

�Consistency of operations� =ease of use, minimization of

operator errors

�Performance in the atmosphere

� accuracy and precision

� avoidance of ”wet bulb”

� avoidance of heating bias of the sensors (especially UT)

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Recent Development: Vaisala RS41-SG(comparison to Vaisala RS92-SGP)

� Extreme ease of use� Zero-click sounding operation� No desiccants needed in the ground

check device� Power button� Automatic turn-on in the ground check

device� No galvanic ground check connection

(RFID-like wireless used instead)� =Consistent observations

� Improved temperature measurement� Platinum resistor� Improved hydrophobic coating

� Improved humidity measurement� No adjustment based on desiccants� ”Physical zero point” check and residual

adjustment� Integrated temperature sensor to remove

solar bias

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Vaisala Radiosonde RS41-SGPlatinum Resistive Temperature Sensor features very fast response time with small solar radiation error

SI traceable references in calibration

Humidity Sensor element equipped with both heating for deicing and

integrated temperature sensor for solar

radiation error correction.

SI traceable references in calibration

Automatic Sensor Boom Positioning when unwinder is attached to RS41 =

reduction in operator errors

Integrated GPS Antenna = easier handling

Compact Design is easy to handle during launch preparations, designed to

be placed on a table

LED Status Lights clearly indicate when the RS41 is ready to launch = reduction

in operator errors

Wireless Connection and Maintenance-Free Ground Check no need for serial connector

no desiccants!

Ground Check Device RI41 utilizing built-in RS41 references is the

recommended ground check device.

Ozone interface connector, also for other sensors with X-DATA protocol =

“open architecture” for research use

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Thank You!

aki.lilja@vaisala.com