SYSTEMS PERFORMANCE AND STABILITY ANALYSISAND OPERATING STRATEGIES ON TURKISH RADAR NETWORK

by Aytaç HAZERTurkish State Meteorological Service

Electronic Observing Systems DivisionKütükcü Alibey Cad. No:4 06120 Kalaba-Ankara-TURKEY

Tel:+90-312-302 27 86Fax:+90-312-361 23 53

e-mail: ahazer@meteor.gov.tr

ABSTRACT

Turkish State Meteorological Service (TSMS) has been operating 4 Doppler

Meteorological weather radars. Three of them were installed 2003 and are single

polarization radars. Other one is polarimetric radar installed in 1999. It is being planned to

equip whole Turkey with weather radars.

To maintain radars without any problem, institutes must carry out maintenance

strategy. Maintenance works for Weather Radars on Türkiye is done by TSMS’s Radar

Maintenance Unit which has three electronic engineers, two mechanical engineers and

one electronic technician.

Maintenance works can be separated by two. These are Corrective Maintenance

and Preventive Maintenance.

Corrective maintenance is done when some failures or errors occurs both in

hardware and software. On the contrary, Preventive Maintenance must be done

periodically by well trained and talented maintenance people

Operating strategy is quite important manner for nowcasting and for also lifetime of

radars. For example, some bad scanning strategies can decrease lifetime of radars.

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SYSTEM PERFORMANCE AND STABILITY ANALYSIS

All components of single radar must be followed periodically and stability analysis

must be performed to get good system performance. All sub-components of major

components have to operate in some certain limits and must not exceed these limits.

When some parameters exceed the boundary levels, maintenance people research that

where this problem is originating. After that faulty part has to be replaced or the parameter

which has abnormal situation must be adjusted by some electronic devices.

Maintenance team is performing four major maintenance works for stability analysis:

1) Antenna Controls

2) Receiver(RX) Measurements

3) Transmitter(TX) Measurements

4) General System Checks

Antenna Controls

Basically, for an antenna, it is important to follow antenna position both in azimuth

(AZ) and in elevation (EL), antenna velocity and acceleration and deceleration of antenna

whether the antenna is going to place we requested, is moving at the speed of our request

and with acceleration we permit.

We want radar to reach a position in certain limits. There is a formula defined about

error.

Error=answer (read on the ant. utility)-measured value at antenna scale.

Error must not exceed 0,1° both in AZ and in EL. If it exceeds the limits it must be

adjusted by changing dip switch positions or by software or mechanically.

Figure below is representing four year analysis of these errors.

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Figure: Errors at positioning the antenna.

For control of velocity of antenna, we are measuring the time for a 360° rotation.

This is 30 second for 12°/sec velocity and 15 second for 24°/sec velocity.

Figure: Time for 12°/sec

speed among the years.

Figure: Time for 24°/sec

speed among the years.

Acceleration and deceleration analysis is being done by a special software.

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Receiver (RX) MeasurementsIn RX, coherency of some special oscillators’ frequency and stability of these

oscillators’ power levels are very important. We have COHO and STALO oscillators.

COHOs must be 0,00 ±1 dBm and STALO must be 15,00 ±3 dBm.

Fig: COHO levels.

Figure: STALO level

Very important another thing is RX gain which must be constant in linear region. RX

gain must be in the range of 33,5-35,5dB.

Figure: RX Gain.

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Because the Exciter RF signal which goes to the TX is provided by RX, Exciter RF

needs to be minimum 20dBm.

BIT RF has very important role about BITE system.

Transmitter (TX) Measurements

As everybody knows, there are so many important components at the transmitter

such as Focus coil, heater, klystron, modulator, ion pump, High voltage power

supply(HVPS), HVPS regulator, blowers, i.e. All of them must be very stable. Most

important parameters are klystron pulse current, transmitting power, transmitting RF

frequency, Pulse Repetition Frequency (PRF), Pulse Width, heater current and voltage,

focus coil current and voltage, ion pump coil current and voltage, RF drive power, High

voltage power supply(HVPS) voltage, HVPS regulator voltage, HV and Heater time etc.

When calculating duty cycle factor you have to know PW and PRF. Figure below

shows how the PW and PRF are stable.

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Figure: Pulse width

measurements.

Figure: PRF measurements

There are three important parameters, first is heater current and voltage where

klystron needs heating, second is focus coil voltage and current for the purpose of

focusing electrons inside the klystron and last one is ion pump current and voltage to make

de-ionization inside the klystron.

Figure: Focus Coil Current and Voltage

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Figure: Heater current and voltage.

Figure: Ion pump current and voltage.

Figure: HV and Heater Time Figure: Reference Voltage

Figure: HVPS and HVPS Regulator.

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Figure: Klystron Pulse Current

Figure: Transmitting RF Power

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The transmitting signal has to have some certain characteristics. For

example, PW must be 0,5sec., signal waveform must be rectangular, peak

power of transmitting RF signal must be minimum 250kW which equals to 84dBm,

Pulse repetition time 1000Hz and transmitting frequency must be 5625MHz.

Some graphics for those parameters are shown below.

Figure: Transmitting RF Frequency, RF driving power and TX RF power.

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General System Checks

These are related directly to the system performance. This means, if there become

misunderstanding with radar, in the future, maybe you will not understand anything from

radar. Then we have to perform some system performance tests.

In our radar network, we are performing two tests.

1) dBZ level check

2) Sun tracking

dBZ level check

Depending on the radar constant, when we apply some test signal, we have to see

some dBZ level on the Ascope. When we apply some certain frequency, because radar

constant is not changing for a single radar, we have to get some constant dBz values.

Of course, there can be some tolerable errors. Error can be defined as follows:

Error = Measured value on the Ascope Unit – Calculated Value

This error must be in the range of ± 1dB. If this is out of the range, we have to

perform ZAUTO procedure.

Sun Track

If we have true time on the radar workstations, with a software, system knows

where the sun is. When we run the program, antenna starts to follow antenna. Sun sends

some sun beam to every direction. Antenna must receive the whole sun beam. When

antenna sees the sun without any error, signal level is high. If there is some error, signal

level becomes less.

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OPERATING STRATEGIES

Scanning strategy (operating strategy) is very important part of this work. Radars must have our own scanning strategies. These scanning procedures must work without any straining the radar.

G e n e r a l l y

Turn Severe Weather

Activate the Operational Mode by Automatic Switching

G e n e r a l l y

Turn Severe Weather

Activate the Operational Mode by Automatic Switching

Clear Air Mode

This task is preferred when significant precipitation is not estimated in the radar coverage. It uses a long pulse and the radar is operated at a relatively slow scan rate that allows the sampling of five contiguous elevation angles (0.5° to 4.5°) in a period of 10 minutes. When a radar system detects precipitation of a specified intensity and extent (30 dBZ), it automatically switches from Clear Air to the Precipitation Mode by using Automatic Mode Switch Menu for two plans.

Precipitation Mode

This is the standard mode of operation whenever precipitation is first detected. When the weather conditions turn severe, the Precipitation Mode can be activated. The Precipitation Mode provides a faster scan rate to monitor a larger volume of space in a shorter time.

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Clear Air ModeTask Schedular Name:

CLEAR

1 TASK Configuration: RAIN

SCAN STRATEGY PLAN 1

Precipitation ModeTask Schedular Name:

PRECIPITATION

3 TASK Configurations:SURVEILLANCE

MONITOR (A,B,C)RHI (Optional)

Clear Air ModeTask Schedular Name:

CLEAR

1 TASK Configuration: SURVEILLANCE

SCAN STRATEGY PLAN 2

Precipitation ModeTask Schedular Name:

PRECIPITATION

3 TASK Configurations:SURVEILLANCE

MONITOR (A,B,C)RHI (Optional)

This permits the tracking of rapidly moving meteorological phenomena found in convective weather patterns. This mode is characterized by the use of a narrow pulse width at both high and low PRFs. It consists of the Surveillance Task with Monitor Task. In Addition, a RHI Task can be scheduled for observing storm structure in detail, especially for storms close to the radar (max range 120 km).

SURVEILLANCE Task Configuration

It is used to generate PPI at a single elevation close to zero for long range weather monitoring (Elevation Angle:0.5°, Max Range:300 km, Pulse Width:2).PPI, is the fastest of all radar products and therefore suitable for studying the fast-developing mesoscale storms.

RAIN Task Configuration

 Elevation Angles (°)  0.5, 1.5, 2.5, 3.5, 4.5 Resolution (°)  1.0 Pulse Width (usec)  2.00 Scan Speed (°/sec)  12.00 Data  T, Z, V, W Samples  55 Number of Bins  1200 Bin Spacing (m)  250.0 Max Range (km)  300.0 PRF (Hz)  500-375 Unambiguous Velocity (m/s) 20 (4:3) Processing  PPP

 Data Quality Thresholding  T: LOG, Z: LOG&CSR, V:SQI&CSR, W: SIG&SQI&LOG

 LOG (dB)  0.8 SIG (dB)  10 CSR (dB)  18 SQI  0.4 Speckle  Z on, V on

Product ListPPI(Z) (300 km, 0.5°),PPI(Z,V,W) (120 km, 0.5°),CAPPI(Z,V,W,R)(120 km, CAPPI Height:10 km)MAX(Z,R)(150 km, 0-15 km)WIND(120 km, 2,3,5 km.)SRI(300 km )VIL(300 km, 20 km)WARN precipitation Surveillance Detection (It warns during the occurrence of precipitation by using VIL product).

MONITOR Task Configuration

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(Hybrid Task)

 Elevation Angles (°)  0.5-45.0 (16 angles) Resolution (°)  1.0 Pulse Width (usec)  1.00 Scan Speed (°/sec)  12.00, 24.00, 24.00 Data  T, Z, V, W Samples  64, 32, 32 Number of Bins  1200 Bin Spacing (m)  250.0 Max Range (km)  120.0 PRF (Hz)  1200-900 Unambiguous Velocity (m/s)  48 (4:3) Processing  RPHASE

 Data Quality Thresholding T: LOG, Z: LOG&CSR, V:SQI&CSR, W: SIG&SQI&LOG

 LOG (dB)  0.8 SIG (dB)  10 CSR (dB)  18 SQI  0.4 Speckle  Z on, V on

Product ListWARNHail Detection, Flash Flood Warning, Severe Storm Detection and Lightning Hazard.

CONCLUSION:

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To maintain the radars efficiently and to get bigger MTBF (mean time between

failures) Stability analysis and system performance check and also scanning strategies

(operating strategies) is very important.

To increase the life time of radar, institutes must apply maintenance strategies

very well. This will not be only useful at the time you found failure situation, also will be

very useful at the future.

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