Point vs. VAD scans for complex terrain

G. D. Emmitt and C. O’HandleyWG SBLWDestin, FL

January 27-30, 2009

Overview The conical scan is the traditional pattern used to obtain vertical profiles of the wind field with an airborne Doppler wind lidar. Nadir or zenith pointing scanning wedges are ideal for this type of scan.

A bi-axis scanner has been operated on a Navy Twin Otter for more than 6 years and was installed on a Navy P3 for use in a field experiment to study typhoons.

The bi-axis scanner enables a broad range of scanning patterns. A subset of the possible patterns is critical to obtaining useful wind profiles in the presence of complex terrain or small (~ 100's of meters) organized atmospheric structures (rolls, updrafts, waves, etc).

Several scanning strategies have been tested in flights over the Monterey Peninsula and within tropical cyclones. Combined with Google Earth (on-board) and satellite imagery overlays, new realtime adaptive scanning algorithms are being developed and tested.

TODWLscanner

STV

Particleprobes

SurfaceTemperatureSensor

The instrument

• 2µm coherent detection (CTI MAG1A)• 2 mJ ; 500 Hz• 10 cm two axis scanner, side door mounted• GUI with realtime instrument control and data

display• Range: .3 – 21km depending upon aerosols• Accuracy: < .10 m/s in three components• Weight: 700lb Power: 700 W

Scanning options

• Nadir step-stare conical (3 – 12 positions) for vertical profiles for u, v, w & aerosols

• Zenith step-stare (u, v, w)• Forward sweeping (prospecting for OLEs and

shear layers ahead of aircraft• Nadir point scans (u,v,w) in complex terrain

and organized flows (e.g. OLEs)

0 1000 2000 3000 4000 5000 6000EAST/W EST D ISTAN C E (M )

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SC AN PATTER N FO R "PO IN T SC AN "3 C O M PLETE SC AN SG S: 64 M /S , H T: 1950 M , D W ELL: 2 SECBLAC K: 1200 MR ED : 750 MBLU E: 300 M

FLIG H T TR ACK

0 1000 2000 3000 4000 5000 6000EAST/W EST D ISTAN C E (M )

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SC AN PATTER N FO R "VAD "2 C O M PLETE SC AN SG S: 64 M /S , H T: 1950 M , D W ELL: 2 SECBLAC K: 1200 MR ED : 750 MBLU E: 300 M

FLIG H T TR ACK

Ridge and Valley

-45000 -44000 -43000 -42000 -41000 -40000

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15000SCAN C O VERAG ERED : VADS 10 - 13, F ILE 1226 (SW TR ACK)BLACK: PO INT, 1241 (NE TR ACK)LO S 'S EN D AT 950 M M SL

POINT

Speed Comparison Over High Complex Terrain

Valley Floor

-54000 -53000 -52000 -51000 -50000 -49000

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6000SCAN C O VER AG ER ED : VAD S 4 - 6 , F ILE 1231 (SW TR AC K)BLACK: PO IN T, 1237 (N E TRAC K)LO S 'S END AT 150 M M SL

Speed comparisons over valley floor

POINT

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STAR TIN G PO IN T(A IR C R AFT LO C ATIO N )

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SAM PLE PO IN T SC AN G EO M ETR Y

FLIG HT TRACK

Acknowledgements

• Most of our research on profiling in complex terrain and the implications to model validation/initialization has been funded under an SBIR through the Army Research Office (Dr. Walter Bach).

• Additional funds were provided by the Integrated Program Office of NPOESS (Dr. Stephen Mango)