Air Coverage Test with SCANTER 4002 at Horns Rev Wind Farm I and II

Transcription

1 Air Coverage Test with SCANTER 4002 at Horns Rev Wind Farm I and II Abstract The challenges of aircraft detection in the area of wind farms are addressed. Detection and tracking capabilities of the SCANTER 4002 are demonstrated by showing test results in different conditions and for different target types. Axel C.K.Thomsen, Michael A. Riis, Ole Marqversen Terma A/S, Hovmarken 4, 8520 Lystrup, Denmark Contact mail: akt@terma.com, mar@terma.com or oem@terma.com are based on MTI and Normal radar video, but the postprocessing is configured differently, optimized for detection of the different target types. As a consequence, the processed air targets video can also include small distinctive target that usually is present in the normal radar video only. I. INTRODUCTION The emerging issues for air coverage close to and above wind farms can be addressed from different viewpoints. Most papers address the possible problems regarding air coverage at wind farms. This paper describes the obtained test results of an 'off the shelf solution'. Various incorporated options are described and the corresponding results are shown. The requirements for inter-turbine detectability and the obtained specification of SCANTER 4002 are discussed in detail in [1]. The requirements for inter-turbine detectability regard: Azimuth antenna resolution Range resolution CFAR processing Instantaneous linear dynamic range Adaptive sensitivity control Pulse compression range side lobes Azimuth antenna side lobes MTI/MTD suppression of clutter between turbines Tracking algorithms not seduced by turbines To summarize, the stated requirements in [1] are met very well by SCANTER II. RADAR CONFIGURATION The radar set-up includes a SCANTER 4002 (Figure 2) and a 15 Large Aperture Antenna (Figure 1), both produced by Terma A/S in Denmark. SCANTER 4002 is the latest version of the off-the-shelf product series of SCANTER 4000, now operating worldwide from Greenland and Antarctica to the tropics of Asia. The SCANTER 4002 radar sensor is an X- band, 2D, fully coherent pulse compression radar providing both MTI and Normal radar (Non-MTI) video simultaneously. This enables a high level of situational awareness and support multiple concurrently operational needs e.g. air surveillance, helicopter control, surface surveillance and Search and Rescue. The SCANTER 4002 generates both network video and plot/tracks to be overlayed on the video. The plot/tracks can be distributed according to the ASTERIX format. Two types of video output are generated in parallel: Processed air targets video and Processed surface target video. Both video types A full resolution attenuation map can be included in the processing. The map blanks each individually video cell if applied and can be set to include stationary targets as wind turbines. Fig LACP-C-39 Large Aperture Antenna with Cosecantly Squared Elevation pattern and circular polarization. Fig. 2 SCANTER 4002 Air cooled transceiver rack. Tracking of different target types is obtained by using a number of tracking lines, as shown in Figure 3, each optimized for the different target types and based on different video types. Tracking lines 1 and 2 are fed with Processed air

2 targets video, while tracking lines 3 through 6 are fed with Processed surface target video. The output of all track lines are correlated and evaluated based on quality. Radar video of the test is recorded at three levels, as shown in Figure 4. This makes it possible to replay the tests with different options and settings applied in the processing and tracking, e.g. to optimize for specific site requirements. III. TEST SITE CONFIGURATION The radar antenna was installed on top of two standard ISO containers to provide an elevation of 12m ASL as shown in Figure 5. The radar transceiver, antenna control unit and remaining equipment were installed in one of the containers. The antenna was operating at 15rpm. The radar antenna has direct view to both Horns Rev I and II with a distance of 15km to the nearest turbine of Horns Rev I. Horns Rev I was established in 2002 and contains 80 2MW turbines producing 160MW in total. Horns Rev II was established in 2009 and contains MW turbines producing 209MW in total. At the time of establishments both wind farms were the world s largest off-shore wind farms. Figure 6 shows the view of a part of Horns Rev I and Figure 7 shows a map of the location. Processed air and surface radar video Transceiver User input Control, monitoring and map data Video to LAN converter Slow air tacker Fast air tracker General purpose tracker Slow small target tracker Fast small target tracker Helicopter tracker TL1 TL2 TL3 TL4 TL5 TL6 Correlation and combination Video Distribution & Tracking VDT IP network Fig. 3 Parallel tracking lines in the Terma VDT (Video Distribution and Tracking) unit. ADC 20GB/min TerRes (Terma Recorder) Pre-Processing Post-Processing Video Distribution ~60MB/min 4x4k Video (Terma Video Server) Fig. 5 Test site at Blaavand ( N E) with Blaavand Lighthouse in the background. and tracking PPI Display ~2MB/min Screen Dumps (PC) Fig. 4 Processing and video recording. Fig. 6 View from the test site container in the direction of Horns Rev I.

3 Fig. 9 Target of opportunity, Sikorsky S-92 Fig. 7 Map overview of the test area. (Source: Radar clear view sector marked with red. IV. TEST TARGETS The primary controlled test target was a small general aviation aircraft, a Grumman GA-7, as seen in Figure 8. This aircraft has been used at several factory acceptance tests of SCANTER 4000 products where its radar cross section has been measured to be between 1 and 4 square meters depending of the aspect angle. The target was equipped with GPS-logging for precise registration of its position. Targets of opportunity were mostly helicopters of the type Sikorsky S-92 (see Figure 9) used for transportation between Esbjerg and the Danish oil fields in the North Sea. V. TEST SCENARIO The controlled aircraft was scheduled to pass the two wind farms in different directions, different heights, different speeds and different weather conditions. The flight directions were guided during the test by commands from the radar control office at the test site. Flight levels of 2500, 5000 and was planed and flight directions in 3 different angles to the lattice structure of the wind farm were planed including turns above the wind farm. The test was scheduled to take place over sufficient days to have different weather conditions. The weather conditions of the first test day, March 29 th 2011, were wind from west 5-10m/s and no rain. On the second day, March 31 st, the wind was from south 10-15m/s and showers with rain rate up to 6mm/h. The GPS logged flight path from the March 29 th is shown in Figure 11 and from March 31 st in Figure 12. No controlled surface targets were included in the test, but the service vessel for Horns Rev Wind Farm I (HR I) was identified and is shown in Figure 10. Fig. 8 Controlled test target Grumman GA-7 with call-sign OY-GAT. Fig. 10 Service vessel for HR I.

4 Flight Level and Speed, Marts 31st Fig. 11 Flight path of the controlled aircraft on March 29 th. 0 15:00:00 15:30:00 16:00:00 16:30:00 Time Fig. 14 Speed (pink in knt) and altitude (blue in FL =100ft) of the controlled aircraft on March 31 st. VI. TEST RESULTS Due to the extensive test and the levels of data recorded, the data volume is extremely large. The ability to reprocess the recordings with different parameters also makes it possible to further optimize the radar and tracking algorithm for this application. Presently, this report will only show examples of the results with the radar processing in its default configuration chosen doing the test. The shown results are based on screen dumps directly stored doing the test. Fig. 12 Flight path of the controlled aircraft on March 31 st. The logged speed and height are shown in Figures 13 and 14 for the two days. Height is shown in Flight-Levels (in hundreds of feets) and speed is shown in knots Flight Level and Speed, Marts 29th The CFAR processing excludes the wind turbines from the statistics. This is required to avoid desensitization and shown in Figure 15 by the receiver noise floor. A special option makes it possible to show CFAR processed video without applying a threshold. Attenuation of the noise-floor shows a lower gain caused by the CFAR processing. At the top-view of Figure 15 the turbines are included in the CFAR statistics and on the bottom-view the turbines are excluded. The flat noise floor in between the turbines at the bottom view shows that the CFAR processing does not introduce desensitization in the area of the wind farm. Good receiver sensitivity can also be seen in Figure 16 where a bird is detected on the backside (top left) of the wind farm :30:00 12:00:00 12:30:00 13:00:00 13:30:00 Time Fig. 13 Speed (pink in knt) and altitude (blue in FL =100ft) of the controlled aircraft on March 29 th.

5 video of the controlled test target passing in FL25 in clear conditions with the attenuation map applied. Again the trails of the target show very few coincidence of paint from the target merging residues of paints from the turbines and track is maintained doing the pass. Figure 18 shows a similar passing just in a direction closer to the line of wind turbines. Again the track is maintained doing the pass. Fig. 15 CFAR gained video without a threshold applied to shown the receiver noise level. The wind turbines are included in the CFAR statistics on the top picture and excluded in the lower picture. Bird Fig. 17 Processed air target video of OY-GAT passing HR1 in FL25 with the attenuation map applied. The red trails of the wind turbines are from before the attenuation map was turned on. Fig. 16 Processed air target video with combined MTI and normal radar video of OY-GAT in FL25. In air processed video normal radar video of point targets can be added or not. Figure 16 shows the combined air video of HR I with the controlled test target OY-GAT passing in FL25 in clear conditions. As seen, inter-turbine detectability makes it possible to get very few lags of plots and tracking is maintained doing the passing. Figure 17 shows the air target Fig. 18 Processed air target video of OY-GAT passing HR1 in FL25 with the attenuation map applied.

6 Figure 19 shows the rain condition doing the test shown in Figure 20. Here the test target OY-GAT passes HR I in FL30. Track is maintained even though the target almost merges with a turbine in azimuth at the shown scan. Fig. 21 Processed air target video of OY-GAT passing HR2 in FL50 in heavy rain condition with the attenuation map applied. Video before attenuation map is turned on is shown in the red trails. Fig. 19 Non-CFAR ed normal radar video to show rain condition doing the test March 30 th. Helicopter Fig. 22 Processed air target video with combined MTI and normal radar video of a helicopter S-92 passing HR II in clear condition. The test target OY-GAT is approaching HR II from east. Service vessel Fig. 20 Processed air target video with combined MTI and normal radar video of OY-GAT in FL30 passing HR I in heavy rain condition. Figure 21 shows the test target passes HR II in FL 50 in heavy rain condition. As seen the track is maintained even though the detectability is lower due to the heavy rain and the elevated target position. Figure 22 shows a non-controlled helicopter passing HR II. It was confirmed to be a Sikorsky S-92. Figure 23 shows a service vessel, as shown in Figure 10, sailing between the turbines of HR I in heavy rain. Fig. 23 Service vessel inside HR I in heavy rain condition.

7 VII. CONCLUSIONS This test shows that the requirements needed to get aircraft detectability in the area and vicinity of wind farms are met by SCANTER The tests have been performed on a small aircraft in different weather conditions, different target altitude and with different target maneuverings. The test also shows that SCANTER 4002 is able to maintain tracks of the test target in the different conditions and with different processing enabled. Further off-line processing of the recordings will be used to document the processing and tracking performance for this application. However, the direct test results of the test confirms that the specified requirements are met and that the off-the-shelf product SCANTER 4002 can be used for air surveillance close to, in-between and above wind farms. ACKNOWLEDGEMENT Acknowledgement to all our colleagues who have participated in the development of SCANTER 4000 product series and Large Aperture antennas. REFERENCES [1] A.Thomsen et al, Air Traffic Control at Wind Farms with TERMA SCANTER 4000/5000, Proceedings of 2011 IEEE Radar Conference, Kansas City, USA, May 2011.