slide 1 German Aerospace CenterMicrowaves and Radar Institute Extraction of clear-air wind Dr. Thomas Börner DLR Oberpfaffenhofen Microwaves and Radar Institute D Weßling

slide 2 German Aerospace CenterMicrowaves and Radar Institute Outline Introduction to clear air data Purpose of this study Possible parameters for DLR's POLDIRAD Analysis of the data set, results Conclusions

slide 3 German Aerospace CenterMicrowaves and Radar Institute Introduction to clear air data In Europe, weather radar is primarily used to measure precipitation over large areas. Wind measurements are a secondary benefit, not seen as the primary role.  Quality of wind data is usually less than optimal! Reason: low power and lack of sensitivity Clear air echoes detectable at max. ranges: km. Exact cause is still subject to speculation. Evidence suggests: insects and birds! High Z DR values: 5-10 dB. Best performance during summer until autumn.

slide 4 German Aerospace CenterMicrowaves and Radar Institute Purpose of this study Original intention: search for new possibilities of processing the data to increase the quality of clear air wind measurements. Problem: during summer there was still no unprocessed (raw) data available, only final products. Workaround: collect data with as many different sensor setup parameters (PRF, resolution, etc.) as possible.  Find the best combination for clear air measurements!

slide 5 German Aerospace CenterMicrowaves and Radar Institute Possible parameters for DLR's POLDIRAD PRF: 400 Hz, 800 Hz, 1200 Hz Pulse length: 1 µs, 2 µs (only for PRF = 400 Hz) Resolution (bin length): 150 m, 300 m Number of samples per bin: 32, 64, 128 Elevation: any angle, chosen 1° and 2°  Total of 48 possible combinations!

slide 6 German Aerospace CenterMicrowaves and Radar Institute Z – PRF behavior (300 m, 1 µs, 128 samp.) 400 Hz 800 Hz 1200 Hz

slide 7 German Aerospace CenterMicrowaves and Radar Institute V – PRF behavior (300 m, 1 µs, 128 samp.) 400 Hz 800 Hz 1200 Hz

slide 8 German Aerospace CenterMicrowaves and Radar Institute Z – samp. behavior (300 m, 1 µs, 1200 Hz) 32 samples 64 samples 128 samples

slide 9 German Aerospace CenterMicrowaves and Radar Institute V – samp. behavior (300 m, 1 µs, 1200 Hz) 32 samples 64 samples 128 samples

slide 10 German Aerospace CenterMicrowaves and Radar Institute V – res. behavior (1200 Hz, 1 µs, 128 samp.) 150 m300 m

slide 11 German Aerospace CenterMicrowaves and Radar Institute V – elev. behavior (1200 Hz, 1 µs, 128 samp.) 1°2°

slide 12 German Aerospace CenterMicrowaves and Radar Institute Scanning Time The total time to scan one full PPI increases for –lower PRF –higher number of samples –higher resolution –higher pulse length  important if the weather situation changes rapidly (or if there are strong local turbulences) and has to be scanned in short intervals.

slide 13 German Aerospace CenterMicrowaves and Radar Institute “Quality” or Accuracy Insects and birds can develop considerable speeds relative to the wind, which add to the measured radial wind velocities!  Insects:up to 6 m/s.  Birds:up to 15 m/s. Clear air wind velocities have therefore to be handled with care. However, polarimetric signatures of these objects can help in the areas of entomology and ornithology in order to track and also classify aerial plankton.

slide 14 German Aerospace CenterMicrowaves and Radar Institute Conclusions Best combination of parameters: –PRF: 1200 Hz –number of samples: 128 –resolution: 150 m –pulse length: N/A –elevation: as close to the ground as possible If time is of concern, the recommendation is to reduce the resolution and/or the number of samples.