optimization of the operation strategy and parameters … · optimization of the operation strategy...

ERAD 2012 - THE SEVENTH EUROPEAN CONFERENCE ON RADAR IN METEOROLOGY AND HYDROLOGY

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Optimization of the operation strategy and

parameters of Euskalmet weather radar

Maruri M.1,2, Hernaez I.4, Aranda JA3, Gaztelumendi S1,2

1.-Basque Meteorology Agency (EUSKALMET). Parque tecnológico de Álava. Avda. Albert Einstein 44 Ed. 6 Of. 303, 01510 Miñano, Álava, Spain. [email protected]

2.-TECNALIA, Meteo Unit. Parque tecnológico de Álava. Avda. Albert Einstein 44 Ed. 6 Of. 303, 01510 Miñano, Álava, Spain. [email protected]

3.-Basque Government, Department of the Interior, Directorate of Emergencies and Meteorology. C/ Portal de Foronda 41, 01010 Vitoria-Gasteiz, Álava, Spain

4.- Adasa Sistemas, Environmental Quality Division. C/ José Agustín Goytisolo 30-32, 08908, L’Hospitalet de Llobregat, Barcelona, Spain

(Dated: 30 May 2012)

Presenting author

Name

1. Introduction

Since its installation in 2005 (Aranda et al, 2006), the operation of the polarimetric doppler C-band weather radar of the

Basque meteorological agency (Euskalmet) has suffered several changes if compared to the original configuration

(Gaztelumendi et al, 2006). The optimization strategy is explained in this paper.

In many cases, this type of weather radar has a potential which is often far from being completely used (Meischnner et al,

1997). The motivation of the work is an interest on improving the operation of the system, taking into account the complexity

of the installation, the topography of the Basque Country and the study/analysis of the historical data set on episodes of

severe weather with high probability of flooding.

In addition, in recent years there is an increasing social demand of information of short-term potential risks caused by

weather. The Department of the Interior, specifically the Directorate of Emergencies and Meteorology (DAEM), assumes this

responsibility in the Basque Country. A special effort has been made on improving the radar's ability to describe dangerous

situations in three main most populated areas, Bilbao, San Sebastián and Gasteiz, (NEXRAD, 2005).

Although the operation at the time of installation was defined according to standards to provide a quality database as

complete as possible, the daily experience and knowledge of our system and its capabilities to describe weather has led to an

optimization process that is described in this paper. This work could be extrapolated to other systems operating in complex

terrain, regardless if they are new or not. These operating systems have great technological capabilities (Doviak et Zrnic,

1984) to be discovered with experience and with the help of the manufacturer (Rainbow, 2005). The operation is always

dynamic and should be open to improvements.

2. Description of the system

The Euskalmet polarimetric weather radar is sited on top of a mountain of 1221.2 m height ASL. Despite it is a

polarimetric radar, the signal processor only allows recording differential reflectivity. This is a limitation in comparison with

the operational possibilities that offer conventional polarimetric radars. The main technological features that describe the

system are: 0.7º 3dB beam width, 6m diameter parabolic reflector, ASPEN digital signal processor and Version 5 of the

Gematronik software Rainbow.

The scan strategy is repeated in a 10 minutes loop. During this period the following scans are performed:

1. A 300 km range volumetric scan, with a radial resolution of 1 km, in order to get a first look of the weather situation. The

recorded variables are Z (corrected reflectivity) and ZDR (differential reflectivity).

2. A 100 km range volumetric scan, with a radial resolution of 250 m, in order to have a more detailed view of the Basque

country. In this scan Doppler information (V and W) is collected together with Z and ZDR.

3. Two elevation scans, both of them oriented to the west (NW and SW respectively). The definition of the azimuths was

based on the climatology of the region (circulation makes most phenomena come from the west), the storm surveillance

necessities, the topographic blockages and the aim of completing the meteorological information of the volumetric scans in

the most populated area next to the coast. In this scans Z, ZDR, V and W are also collected.


Fig. 1. Diagram showing the location of the radar (K) and the three main cities (Bilbao, San Sebastian and Vitoria). The

shadowed area represents the 100 km range and the black lines the azimuths of the elevation scans.

3. Methodology

The methodology is based on the study of the system's ability to describe different weather conditions and on daily data

monitoring. Deep analyses of the meteorological episodes address to necessary improvements that affect the coverage and

therefore the quality of the raw data. The monitoring reveals the weaknesses of the operation, which leads to the design of

further improvements. All of these changes are focused on obtaining a better database and on improving the stability of the

system and therefore the availability of raw data.

The methodology considers all the incidences registered in the monitoring task and the analysis of meteorological episodes

from the first and a half year of operation, where the maintenance was performed by the manufacturer.

1) Detect problems in operation

The study of data availability, system monitoring (system logs) and routine visual inspection of the data reveal recurring

problems. The correlation between data availability and the incidences that appear in the BiTE (Built-in Test Equipment)

logs is studied.

The methodology looks for an answer associated to each data file lost. If the cause is recurrent or if it is related to a critical

element of the system, then a solution is proposed. In general, the study of the possible causes presents alternatives and new

procedures for monitoring the system that enable better preventive maintenance.

2) Detect weaknesses in the database

This work considers different weather conditions, both clear air (under different temperature profiles) and precipitation

(under different types of precipitation), in order to detect weaknesses in the meteorological description of these situations and

to make improvements that can be applied to the system in operation. The errors are cataloged together with the

meteorological situations. An analysis of the degradation of the data is reported for further studies.

3.1 Operating parameters

The operating parameters are classified into different levels depending on their proximity to the system itself. We work

with them both independently and globally to evaluate potential interactions that may lead to conflict.


Operating parameters associated to the coverage and the quality of the database.

-Geometry of the system. The study focuses on identifying the optimum elevations that allow a better coverage of a region

with a very complex topography. Previous studies of the propagation of the beam over a digital terrain map have been

considered. To reduce scan time and to improve the stability, an optimal range is defined for each elevation.

-Quality parameters associated with the raw data. A revision of the quality parameters of the system has been done

(manual), focusing on the CCOR thresholding, the signal quality index (SQI) and the LOG threshold.

-Parameters to improve system stability. On one hand, the study of the availability of data shows repeated patterns of data

loss. Most of them were associated to the server instability caused by an increase in the internal memory consumption.

Thus, the scan strategy needed more idle time between consecutive loops, especially when calibration programs such as

Zero Check (average noise measurement) or the Single Point Calibration (calibration of the reception chain) are applied,

because they require 40 to 60 seconds.

-Identification of operation incompatibilities in the system. This part of the study was carried during a testing period itself.

We proceeded to review the system and the procedures available to filter common errors such as second trips. At this

point, the system presents incompatibilities between ZDR and some quality procedures. Besides, it is not possible to

collect ZDR an uncorrected Z simultaneously.

Operating parameters at product level.

Each product is defined with a set of input parameters (meteorological and non meteorological). The effort has been made

on generating the best possible product, considering our geometry, the radar location and the typical observable weather

phenomena. Special care has been taken in order not to make changes that may destabilize the system due to the processing

work required.

Operating parameters at application level.

New mechanisms to adapt the raw or processed data to warning and alarm systems have been developed.

All these modifications were tested under non-critical weather conditions before being introduced into regular operation. It

is crucial to check the system stability before bringing on any of the proposed changes.

Other problems of availability, such as those related to communications, are not taken into account in this work, as it is

considered to be outside the system operation. However, those communication problems must be considered for regular

operation because a lack of data can cause problems in the generation of real time products, and it can also affect decision

making in critical situations.

4. Results and discussion

On the one hand system geometry is modified according to simulations that determine the radar coverage of the lower

heights in the region. This shows improvements on the coverage of the three most populated areas. On the other hand the

work takes into account possible data post-processing which can take advantage of an enhanced geometry, especially when

applied to improvements in data quality of those areas partially blocked. Geometry is a key element for good data in weather

radar. In our system elevations near zero or even negative are used. They are useful both to monitor and strengthen the

information on the coastal areas, since the system is located at an altitude of 1221.2 meters (see Table 1).

Scan geometry

Scan Before After

V-300km 0, 0.5, 1, 2, 3 (5 elevations) 0, 0.5, 1, 2.5 (4 elevations)

V-100km -1, -0.5, 0.5, 1.5, 2.7, 4.1, 5.8, 7.8, 10.1, 12.9,

16.2, 20, 24.6, 35 (14 elevations)

-0.5, 0, 0.5, 1, 1.5, 2.7, 4.1, 5.8, 7.8, 10.1,

12.9, 16.2, 20, 24.6, 35 (15 elevations)

E-NW -1 to 50 -1 to 50

E-SW -1 to 50 -1 to 50

Table 1. Comparison of the previous and the current scan geometries.

The current operating parameters are listed below (see Table 2 and Table 3). Some of them are common for the different

elevations, whereas others change depending on the elevation. These changing parameters are mainly based on range

necessities (shorter range is needed for higher elevations) and filters (less restrictive filters are used in higher elevations).


Volumetric Scan 300 km

Nº Elevation

(º) DopplerF

1 0 12

2 0,5 12

3 1 11

4 2,5 10

Common operational parameters

Range (km) 300

Radial Resolution (km) 1

Radial Samples 4

PRF 375

Pulse Long

A. Speed (m/s) 18

Ray Samples 21

Angular Resolution (º) 1

CSR 30

SQI 0,3

LOG 2

Speckle Yes

Table 2. Operating parameters of the 300 km range volume scan.

Volumetric Scan 100 km

Nº Elevation (º) Range (km) PRF Doppler

F

A. Speed (m/s)

1 -0,5 100 900 / 675 10 16 Common operational parameters

2 0 100 750 / 600 11 14 Radial Resol. (km) 0,25

3 0,5 100 750 / 600 11 14 Radial Samples 4

4 1 100 750 / 600 10 14 Pulse Short

5 1,5 100 750 / 600 10 14 Ray Samples 13

6 2,7 100 900 / 675 8 16 Angular Resolution (º) 1

7 4,1 100 900 / 675 8 16 CSR 30

8 5,8 100 900 / 675 8 16 SQI 0,3

9 7,8 100 900 / 675 8 16 LOG 2

10 10,1 100 900 / 675 8 16 Speckle Yes

11 12,9 87,3 900 / 675 8 16

12 16,2 68,8 1100 / 825 7 21

13 20 54,9 1100 / 825 7 21

14 24,6 43,7 1100 / 825 7 21

15 35 28,6 1100 / 825 7 21

Table 3. Operating parameters of the 100 km range volume scan.

The lowest elevations of the volumetric scans have been changed to meet a better resolution of the lower layers. In

addition, some of them are similar in both scans to allow better correlations. In relation with this, the azimuth step of both

volume scans has been set to 1º, what provides an easier manipulation of the raw data.

The quality parameters (SQI, CSR, LOG, Speckle remover) are set according to the recommendation of the manufacturer

and other experiences reflected on bibliography. To enhance the clutter correction, the application of a dynamic clutter

(Hernaez et al.) map based on the statistical behaviour of the clutter and on the simulation of the propagation is under study.

The depth of the doppler filters was increased in order to remove the clutter remaining in the lower elevations, specially

that in the 0.5 degree elevation, which is used for surveillance and QPE. These filters are stronger for lower elevations,

because they are more affected by clutter.

For the PRFs two main reasons have been considered. The first condition is to reduce the effect of the second trip echoes

by an increase on the frequency. Another condition is to reduce the scan time for a better stability the system, what can be

done also by increasing the frequency. This last idea can also be improved with shorter ranges for higher elevations that meet

the tropopause, because a higher PRF can be used.


At this point we have studied the most common mistakes and possible improvements through the operation.

Calibration techniques, monitoring tools and other issues

The main objective was to optimize the time of the scans to achieve a reduction of the instabilities of the system. Many

conflicts were detected between the scan strategy and the calibration procedures such as Single Point Calibration (SPC) and

Zero Check. The range reduction in those elevations crossing the tropopause reduces time in the volumetric scans and

therefore increases the stability of the system.

In order to be closer to the system and to facilitate the real time monitoring, several proprietary tools have been developed

for an enhanced system check. They use the information provided by the BiTE sensors which can be correlated with the

behaviour of the radar data acquisition chain.

a) b)

Fig. 2. Outputs (a) DRX voltages and temperatures and b) TX power, current and temperature) of the system monitoring tools developed.

Fig. 3. Sun ZDR Monitoring. Large differences caused by an increase in the temperature of the radar can be seen.

Fig. 4. Visual inspection of ZDR before and after SPC


5. Conclusion

Generally, in conventional weather radar, any lack of information in the database must be studied. Besides, the analysis of

the performance of the weather radar in different meteorological episodes is good to identify the limitations of the system. It

becomes even more necessary in radar sites covering a complex terrain.

It is also important to maintain the stability of the system since every non-data bin or a poor quality data set can be very

expensive, talking in terms of flooding or other severe weather episode. The behaviour of the stability variables over time

should be controlled as a measure of the necessity of a preventive maintenance. Monitoring “log system files” and reported

suspicious behaviour has been very useful to detect problems at early stages. In this regard, additional tools have been

developed to monitor the system, some of which are presented in this paper. Quality parameters should be reviewed from

time to time to see if they can be modified for an improvement in the data quality.

The optimal operation of a polarimetric radar in complex terrain is not a task that must be done once, but regular reviews

should be established.

Currently many efforts are being made to incorporate new procedures to improve product quality and therefore the

precipitation estimates (QPE). These procedures are as important as the operational parameters. Many of them must be

adapted depending on the weather radar under study.

Optimizing the operating parameters is not an easy work and it has many interactions. The final decision must be a

compromise between the different points of view, and flexible enough to be changed over time.

Acknowledgment

We would like to thank the Directorate of Emergencies and Meteorology of the Basque Government for its support.

We would like to thank the University of the Basque Country and the group of remote sensing of the school of engineering

for the propagation simulations.

References

Aranda J.A., Morais A., 2006: The new weather-radar of the Basque meteorology agency (Euskalmet): site selection, construction and

installation. 4th European Conference on Radar in Meteorology and Hydrology, Barcelona (Spain)

Gaztelumendi S., Egaña J., Gelpi I.R., Otxoa de Alda K., Maruri M., Hernandez R., 2006: The new radar of Basque meteorology Agency:

Configuration and some considerations for its operative use. 4th European Conference on Radar in Meteorology and Hydrology, Barcelona (Spain)

Meischnner P., Collier C, Illingworth A., Joss J. Randeu W, (1997). “Advanced Weather Radar Systems in Europe: The Cost 75 Action”

Vol 78, No 7, July 1997, pp 1411-1430. Bulletin of the American Meteorological Society

Doviak R.J., Zrnić D.S., 1984: Doppler radar and weather observations. Academic Press, USA

Committee to assess NEXRAD Flash Flood Forecasting Capabilities at Suphur Mountain California, 2005: Flash Flood Forecasting Over

Complex Terrain: With an Assessment of the Sulphur Mountain NEXRAD in Southern California. National Research Council flash, National Academies Press (USA)

Hernaez I., Maruri M., Lopez J., 2012: Adaptive clutter filtering using statistical radar data and atmospheric propagation conditions. 7th

European Conference on Radar in Meteorology and Hydrology, Toulouse (France)

Selex-Gematronik, 2005a. “Rainbow® User guide” Release 5.090.

Selex-Gematronik, 2005b. “Rainbow® Quick guide” Release 5.090.

Selex-Gematronik, 2005c. “Rainbow® Products & Algorithms” Release 5.090

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