Results of First Flight Tests of the WSRA

Wide Swath Radar Altimeter

Ivan PopStefanija popstefanija@prosensing.com ProSensing Inc. 107 Sunderland Rd. Amherst, MA 01002 USA,

63rd Interdepartmental Hurricane Conference

Peter BlackNRL/SAIC Inc.7 Grace Hopper Ave.Monterey, CA 93943

Edward J. WalshNASA Goddard Space Flight Center, Greenbelt, MD  20771

April 29, 2008 28th Conference on Hurricanes and Tropical Meteorology 2

Operational SRA Why?

Mapping ocean wave height (surface topography) within the inner core of hurricanes

Measurement of directional ocean wave spectra

Real-time reporting of 12-foot seas radius

Improved forecasting of hurricane development

NASA’s SRA prototype has demonstrated instrument feasibility NASA’s SRA prototype has demonstrated instrument feasibility and data product utility and data product utility operational SRA on multiple aircraft operational SRA on multiple aircraft will provide routine data to enhance hurricane forecastingwill provide routine data to enhance hurricane forecasting

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Who can benefit?

NOAA Tropical Prediction Center / National Hurricane Center

Fulfilling operational requirements for wave height and extent of 12 foot sea height radius

National Centers for Environmental Prediction

Development of comprehensive Hurricane Weather Research and Forecasting (HWRF) model SRA data used for modeling of the wave field and surface roughness

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Baseline Technology

Prototype Scanning Radar Altimeter (SRA) was funded through NASA’s Advanced Application Flight Experiment (AAFE) program since 1973

SRA prototype has flown on NOAA’s WP-3D aircraft in every hurricane season since 1998 [retired 2005]

NASA has developed a comprehensive SRA processing software: Transforms wave topography data into

directional ocean wave spectra Extracts pertinent wave information Transmits wave information to the NHC

in real-time

SRA prototype specifications

-1 KW Klystron transmitter

-36 GHz operating frequency

-Mechanically scanned offset reflector antenna (1.5º beam width )

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Features and Benefits of Operational SRA

Feature Benefits

Digital beamforming antenna

Lightweight microstrip design, no moving parts, same beam width at a lower frequency, increased reliability, wing pod installation

Lower operating frequency

Lower attenuation from rain, Availability of COTS components, expanded range of operation, lower system cost

Solid state transmitter Lightweight, long operational life time increased reliability, lower cost

Digital receiver/high performance processor

Improved data quality,more range scans per second

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Reduced Operating FrequencyAttenuation rate in rain drops by a factor of 5

Prototype 36 GHz SRA had frequent data loss due to rain attenuation. This problem is greatly reduced at 16 GHz.

Comparison of minimum detectable ocean surface radar cross section for prototype 36 GHz SRA and 16.15 GHz SRA in heavy rain (25 mm/hour).

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Technology Description:

Digital beam forming antenna Microstrip planar antenna array Comprised of 62 sequentially sampled

subarrays Size: 30 in x 30 in x 2 in

Transmitter 20 W solid-state transmitter pulse compression processing compression ratio of 1000:1 (at a flight

altitude of 500 m) to over 6000:1 (at a flight altitude of 3 km)

effective peak power of the proposed system is 10-60 kW

Digital Receiver SRA DAQ Hardware: Echotek ECDR-2-

12210-PMC 210 digitizer embedded in a single board dual core Pentium processor

Data collection during the 2008 Hurricane Season In the months of August

and September of 2008 ProSensing operated and collected data with WSRA on six missions.

WSRA data was collected over a wide range of ocean surface conditions: from calm seas up to CAT 3 hurricanes.

Storm Name Takeoff Date/Time UTC

Duration (hrs)

Data Collected

Test Flight ( )

05AUG08 / 14:00 3 250GB

Tropical Storm Fay 18AUG08 / 00:00 8 325GBHurricane Gustav CAT 1

01SEP08 / 08:00 8 350GB

Hurricane Ike CAT2 and CAT3

10SEP08 / 08:00 8 425GB11SEP08 / 08:00 8 420GB12SEP08 / 08:00 8 470GB

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WSRA data processing algorithm

Sequential transmission and collection of raw I&Q data for each of 62 antenna array elements.

Performing de-chirping FFT on each of the 62 I&Q vectors. Averaging coherently subsequent frames of 62 vectors with the coherent

integration time equivalent of the antenna traveling a distance of about 60 cm.

Multiplying the data with correction coefficients. Performing the digital beam forming FFT at each range gate. Calculating the magnitude (power) for the each beam return. Figure 15 shows

the radar return for one beam at nadir. This creates a “frame”. Averaging frames together to reduce signal fading. The averaging was set to

generate 10 averaged frames per second.

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WSRA Data Quality

WSRA has expanded the operational range of the measurement conditions over the retired NASA prototype SRA

WSRA has obtained usable signal from a significantly higher altitudes (12,500 feet vs 5,000 feet).

WSRA signal was not significantly attenuated even under high rain rate conditions often found in hurricanes.

WSRA has demonstrated its capability to measure ocean wave spectra under a variety of wind conditions.

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