WMO/ASEAN Training Workshop on Weather Radar …...Bangkok, Thailand, 5-13 February 2018 WMO/ASEAN...

Bangkok, Thailand, 5-13 February 2018

WMO/ASEAN Training Workshop on Weather Radar Data Quality and Standardization

4. Weather radar Data Quality Control4.1 Calibration4.2 Noise reduction

6, 7 February 2018

Masahito ISHIHARAFormer Meteorologist/Researcher of Japan Meteorological AgencyFormer Professor of Kyoto University

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4. Weather radar Data Quality Control4.1 Calibrationa. Calibration for radar equipment

was lectured by Mr. Inoue in the Session 2 “Weather Radar Maintenance”.

b. Calibration for quantitative Precipitation Estimationwill be lectured by Mr. Sakanashi in the Session 7.3 “QPE & QPF”.

4.2 Noise reductiona. Noises (Error sources) on weather radar observationb. Necessity and methods of noise reduction in weather radar

observationWill be lectured by Mr. Yamauchi and Mr. Hotta in the Session 5 “Hands-on Training on Weather Radar QC”.

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Error sources on weather radar observation

Source: Guide to Meteorological Instruments and Methods of Observation, 2014, WMO3



Ground clutter

4

Most troublesome noise against weather radars

Power linesMountainsBuildings

Mt. Fuji Radar (1964-1999) at the elevation of 3,770 m C-band Radar of JMA Meteorological Research Institute

Ground clutter observed Mt. Radar



5

Rain echoes

Rain echoes

Rain & ground echoes

Sig

nal i

nten

sity

(dB

)Ground clutter remover

- Non-coherent MTI for non-Doppler radars -

Original signal X(t) X(t-Td)Delay Td

Ground-removed signal Y(t)Non-Filtered Filtered

Y(t) fluctuating components of X(t)

X(t) Original signal



6

Ground clutter remover- Coherent MTI for Doppler radars -

Received signal

Continuous signal

Transmitting pulse Amplifying

Amplifying & to Intermedium frequency

Phase detector

In-phase channel signal (I)

Quadrature-phase channel signal (Q)

distance distance

Time series of I & Q complex signal

Fourier transform

Doppler velocity Doppler velocity

Ground echo

Weather echoGround echo is removed

Coherent MTI



7

Ground clutter remover- Coherent MTI for Doppler radars -

Weather echoGround echo

Original Doppler velocity

spectrum

Noise

Removing components around 0 m/s

Linear Compensation of the removal

area

Final spectrum

Power line towers



Sea clutter

8

Sea

Elevated radar

Low-elevation angle beam

Ground clutter

Sea clutter

Typhoon echoes

Mt. Fuji Radar (1964-1999)

Scattered by sea waves and sea water spray



Sea clutter

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• In windy situations, the sea spray may be observed at low elevation angles.

Elevation angle 0.1deg Elevation angle 0.2deg Elevation angle 0.6deg

Elevation angle 0.1deg

2011/08/04Typhoon MUIFA (1011)

2011/08/04Typhoon MUIFA (1011)

Okinawa radar

Calm day



Bright band

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Melting layer

0℃

Snow with water coat

Completely melted

Liquid raindrop

Snowflakes and/or ice particles

+4 ℃Apparently larger particles

Reflectivity



Bright band

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Vertical cross-section

5km

10km

15km

Reflectivity factor 7.0deg

JMA Shizuoka radar

50km

Vertical cross-section a tropical squall line (Houze, 1977)



Precipitation aloft

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Reflectivity at the level of 6 km Cross section A - B



Side lobe

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Source: Guide to Meteorological Instruments and Methods of Observation, 2014, WMO

- Antenna pattern of a parabolic antenna -

Source: Radar for meteorologist : Rinehart, 1999



Side lobe echo

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- Pseudo weather echo coming rom hails -

JMA Kushiro Radar 14:28 LST 28 June 2006 Uchida et al. (2010)

Hail echo

Side-lobe echo from hails

Side-lobeSide-lobe

Main-lobe

Beam patter of JMA Kushiro Radar



Second trip echo

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Rmax = C / 2PRFRmax :Maximum range C: Light speed (3 x 106 km)PRF: Pulse repetition Frequency

2Rmax

Rmax : Normal maximum range

1st trip echo

2nd trip echo

• 1st trip echo: true echo in the maximum range

• 2nd trip echo: false echo out of the maximum range

Radar


Intense tall convection



Three-body scatter spike due to hails

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（Wilson and Reum 1988)

Intense target for radars: hails

<1>

<2>

<3>

Flare echo

Side lobe echo

Flare echo

Hails



Artificial non-precipitation target: - air planes, chaff, wind turbine, sky lift -

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Natural non-precipitation target: - birds -

18http://www.weather.gov/images/bgm/research/birds1997/fig2a1.jpg

http://www.weather.gov/images/bgm/research/birds1997/fig2a1.jpg



Natural non-precipitation target: - volcano ash -

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Source: NNN

Source: JMA図３．層状エコーと噴煙エコーが混在する事例

（2011/02/14 05:00-10新燃岳噴火）左：3 km CAPPI，右：A-B間鉛直断面

A B

10km9876543210A

B



Beam blockage due to mountains/buildings

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No blockagePartial blockage

Full blockage

rk 0.2-L1.0-22

e

6222t

3

rg1010

r 2log 1024D |K| h G P P

θπ

Partial blockage of a radar beam makes reduction of beam width 𝜃 ,and then leads the fault reflectivity measurement.

Reduced due to blockages



Lack of beam filling

21Source: Guide to Meteorological Instruments and Methods of Observation, 2014, WMO

Ratio of accumulated precipitation amount<Rain-gauge/Radar (dB)>



Anomalous propagation: super-refraction, ducting

2222

Causes of inversion layer○ Cold air advection near the surface○ Night cooling of the surface○ Down motion of air-mass○ Passage of a weather front○ Fog layer

Standard propagation path

Anomalous propagation paths

The propagation passage is greatly changed by certain causes; mainly by inversion layers near the surface and anomalous vertical profile of the refractive index of the air.⇒ Radio waves propagate and finally hit the surface. ⇒ Radio waves are trapped in the layer and propagate longer distance.

AP echo observed by Sapporo radarSep. 8, 2011 16:50(JST)



Electromagnetic interference

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Interference with another rotating radar Interference with continuous radio waves



Interference with Radio Local Area Networks (RLANs)

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Interference with Radio Local Area Networks (RLANs)

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Electromagnetic interference from other radars or devices, such as Radio Local Area Networks (RLANs), is becoming increasingly significant, requiring substantial diligence to protect against it. Interference among adjacent radars is mitigated through the use of slightly different frequencies (but still in the same band) with appropriate filters on the transmitter and receiver. There may be occasional interference from airborne and ground-based C band radars using the same frequency.Use of the electromagnetic spectrum is determined by agreement and managed through the International Telecommunication Union. At the World Radiocommunication Conference 2003, the C band frequencies were opened up to the telecommunication industry on a regulated secondary non-interfering non-licensed basis to be shared with the meteorological community. In order to be non-interfering, the RLAN devices are supposed to implement Dynamic Frequency Selection, which is designed to vacate a C band channel if a weather radar is detected. However, the algorithms used to detect the weather radar are not sufficient to prevent interference before they vacate the channel. The Doppler spectra of RLAN signals appear as white noise and can be removed with adaptive noise techniques. However, they increase the noise level and reduce the sensitivity of the weather radar where the RLAN is detected. WMO has issued guidance statements relating to the co-use of the C band frequencies.




SimplifiedRadio Regulations of International Telecommunication Union

(RR ITU) around C-band weather radars

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• Radio LANs must monitor weather radar signal at the first one minute of their operation.• If weather radar signal is received during their operation, radio LANs must shift their

frequency bands.

Radiolocation station

Mobile station Mobile station Mobile station

Marine/aviation radar

Radio LANs Radio LANs

JAPAN

RR Region 3

Weather radar



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Thank you

Masahito [email protected]

mailto:[email protected]

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WMO/ASEAN Training Workshop on Weather Radar …...Bangkok, Thailand, 5-13 February 2018 WMO/ASEAN...

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