seawinds scatterometer data: characteristics and challenges

SeaWinds Scatterometer Data:Characteristics and Challenges

M. H. FreilichCOAS

8 Feb 2005

OutlineOutline

• What What do scatterometers measure?do scatterometers measure?

• SeaWinds: SeaWinds: Instrument, processing, productsInstrument, processing, products

• Accuracy: Accuracy: The numbersThe numbers

• Challenges:Challenges:

– Coastal measurementsCoastal measurements

– Wind RetrievalWind Retrieval

– Rain/extreme conditionsRain/extreme conditions

What: Interpretation of Scatterometer Wind EstimatesWhat: Interpretation of Scatterometer Wind Estimates

• Scatterometers measure backscatter– From centimetric waves

– Generated (primarily) by wind stress

• Scatterometer winds are “xx km resolution, 10 m neutralstability wind velocity [speed and direction]”– Speed: scalar (spatial) average over the footprint– Direction: direction of the vector (spatial) mean– Essentially instantaneous (backscatter measurements

acquired within minutes)

What: Interpretation (cont.)What: Interpretation (cont.)

• 10 m neutral stability wind????– Wind speed and direction at 10 m height that would

cause the observed surface stress if:– Atmosphere neutrally stratified– Motionless sea surface– No long waves

Kelly et al., GRL, 2001

Chelton, Schlax, Freilich, Milliff, Science, 2004

8/99-7/03 4-year Average Wind Stress Curl

Chelton, Schlax, Freilich, Milliff, Science, 2004

8/99-7/03 4-year Average Wind Stress Curl

QuikSCATQuikSCAT:: Scatterometry BasicsScatterometry Basics

• Active microwave radar–Day and night–Clear-sky and clouds

• Scattering from short waves–“Cats paws”–In equilibrium with wind–Backscatter depends on wind speed, direction

•Multiple measurement angles–Dual scanning pencil beam

•Collocated backscatter measure- ments used to solve for wind speed and direction

NOAA/NESDIS Storm Page (3 views)

Wind Vectors

Ambiguities

o V-pol forward

NRCS

NOAA/NESDIS http://manati.orbit.nesdis.noaa.gov/cgi-bin/qscat_storm.pl

(2 deg grid)

QuikSCATQuikSCAT: : SeaWinds MeasurementsSeaWinds Measurements

SeaWindsSeaWinds: : and Swath Schematic and Swath Schematic

QuikSCATQuikSCAT: : Comparison with NCEP and Comparison with NCEP and ECMWFECMWF

Chelton and Freilich, MWR, 2005

Accuracy: Accuracy: QuikSCAT and NSCAT Buoy ComparisonsQuikSCAT and NSCAT Buoy Comparisons

Chelton and Freilich, MWR, 2005

QuikSCAT/Buoy:QuikSCAT/Buoy: NOFAR swathNOFAR swath

Spd RMS: 1.23 m/sSpd BIAS: 0.13 m/s

3-20 m/s: 19.1 deg (5.2 deg bias)5-20 m/s: 16.0 deg (5.2 deg bias)

3-20 m/s: 25.3 deg (5.0 deg bias)5-20 m/s: 19.6 deg (5.1 deg bias)

L2B vs. DIRTH:L2B vs. DIRTH: Nadir swathNadir swath

3-20 m/s: 19.6 deg (4.7 deg bias)5-20 m/s: 16.3 deg (5.1 deg bias)

3-20 m/s: 23.3 deg (4.7 deg bias)5-20 m/s: 18.6 deg (5.0 deg bias)

3-20 m/s: 23.5 deg (4.7 deg bias)5-20 m/s: 20.7 deg (5.1 deg bias)

3-20 m/s: 27.8 deg (4.7 deg bias)5-20 m/s: 23.0 deg (5.0 deg bias)

QuikSCATQuikSCAT: : Vector Wind AccuracyVector Wind Accuracy

Overall QuikSCAT Accuracy Summary, non-raining

L2B DIRTH Npts Speed rms, bias (m/s) NOFAR 1.23 0.13 1.23 0.17 458512 SWEET 1.21 0.13 1.22 0.17 377257 NADIR 1.33 0.14 1.30 0.18 64705

Dir. sd (deg), [3/5-20] NOFAR 19.1 / 16.0 17.5 / 14.3 458512 SWEET 18.2 / 15.0 17.1 / 13.9 377257 NADIR 23.5 / 20.7 19.7 / 16.3 64705 Ran. Comp. Err. (m/s) (NOFAR/SWEET/NADIR)

1.5 / 1.4 / 1.9 1.4 / 1.3 / 1.6

Bias (m/s) -0.3 -0.3 Gain 1.05 1.05

OutlineOutline

• What What do scatterometers measure?do scatterometers measure?

• SeaWinds: SeaWinds: Instrument, processing, productsInstrument, processing, products

• Accuracy: Accuracy: The numbersThe numbers

• Challenges:Challenges:

– Coastal measurementsCoastal measurements

– Wind RetrievalWind Retrieval

– Rain/extreme conditionsRain/extreme conditions

Temperature Pigment

Summer CZCS Image of US West Coast

Equatorward winds cause coastal upwelling -- Low SST near coast -- High productivity -- Complex air-sea interaction

Temperature Pigment

Effect of 30 km scatterometer land mask

NO accurate wind data over the critical upwelling region

High resolution winds will allow study of air-sea interaction in coastal upwelling areas

25 April 2001

12.5 km Hi-Res “MGDR-slice” Winds12.5 km Hi-Res “MGDR-slice” Winds

• Near-real-time product

• 12.5 km backscatter measurements from QSCAT slices

• “Composite2” processing to yield 4 o per retrieval

• Standard MLE wind retrieval algorithm

• Erroneous wind variability (noise)

• Poor far-swath performance

• Systematic spikes in wind speed histograms

• In the 21st century, why must NOAA provide degraded products?

12.5 km Hi-Res “MGDR-slice” Winds (12.5 km Hi-Res “MGDR-slice” Winds (blueblue))

New12.5 km Hi-Res “Research-Slice” WindsNew12.5 km Hi-Res “Research-Slice” Winds

• Offline (non-real-time) product

• 12.5 km backscatter measurements from QSCAT slices

• No compositing: up to 16 o msmts per retrieval

• Refined MLE wind retrieval algorithm– Cubic spline + log-log wind speed model function interpolation– Improved optimization algorithm for objective

function extrema

• Full 5+ year reprocessing complete

RainRain

• Scatterometer wind measurement assumes:– Power minus noise comes from surface– Surface geometry is caused by wind

• Rain violates the assumptions:– Scattering/attenuation (non-surface)– Rain-induced surface roughness (non-wind)

• Multi-channel radiometers provide (some) independent data– Correction/elimination of rain-contaminated o msmts.– AMSR on ADEOS-2

• QSCAT challenge – combine limited data in unique ways to indicate presence of rain

QuikSCAT Rain DetectionQuikSCAT Rain Detection

• Noise measurements (minus signal) yield estimates of Tb (increases w/ rain rate)

• Rain increases h-pol/v-pol ratio (esp. for low wind speed)

• Rain increases backscatter variability• Tendency for retrieved direction to cross-

track

• NOF (Mears et al.)– Single-parameter, no QSCAT Tb

– Best for low wind speeds (< 15 m/s)

• MUDH (Huddleston and Stiles)– Table lookup, trained vs SSM/I 2 km*mm/hr

– Includes QSCAT Tb

D. G. Long, BYUW. L. Jones, UCF

TbHurricane Floyd

QuikSCAT & Buoy:QuikSCAT & Buoy: Rain (direction distributions)Rain (direction distributions)

WHITE- HURCN FORCE

Rain Contaminated

95 kt max

GALESTORM

HURCN FORCE

Joe Sienkiewicz - MPC

QuikSCAT/Buoy:QuikSCAT/Buoy: Rain vs. non-Rain (dir. edit)Rain vs. non-Rain (dir. edit)

Spd RMS: 4.40 m/sSpd BIAS: 2.58 m/s

Spd RMS: 1.23 m/sSpd BIAS: 0.13 m/s

MISSION MEASUREMENT APPROACH

SWATH (km) DAILY COV.

RES. (km) ACCURACY (wrt buoys)

ERS-1/2 AMI 4/91 – 1/01

C-BAND SCATT. 500 / 41%

50 (~70)

1.4 – 1.7 m/s rms spd

20o rms dir ~2 m/s random comp.

ASCAT/METOP 10/2005

C-BAND SCATT. 2 x 550 / 68% 25 50 Better than ERS

NSCAT 9/96 – 6/97

Ku-BAND SCATT. (fan beam)

2 x 600 / 75%

(12.5) 25 50

1.3 m/s (1-22 m/s) spd

17o

(dir) 1.3 m/s random comp.

SeaWinds/ QuikSCAT 7/99 – present

Ku-BAND SCATT. (dual conical scan)

1600 / 92%

(12.5) 25

1.0 m/s (3-20 m/s) spd

25o

(dir) 0.7/1.5 m/s random comp.

SeaWinds/ ADEOS-2 12/02-10/03

Ku-BAND SCATT. (w/ u-wave Rad.)

1600 / 92%

(12.5) 25

Same as QuikSCAT

WINDSAT/ CORIOLIS 1/03

SINGLE-LOOK POL. RAD.

895 / ~70%

50

1.3 m/s rms spd

23o

(3-20 m/s)

CMIS/NPOESS 2010 ?

SINGLE-LOOK POL. RAD.

1700 / >92%

20

2 m/s or 10-20% spd

20o

?? (5-25 m/s)

PAST/PRESENT FUTURE

QuikSCAT/Buoy:QuikSCAT/Buoy: Rain vs. non-Rain (dir. edit)Rain vs. non-Rain (dir. edit)

Spd RMS: 4.40 m/sSpd BIAS: 2.58 m/s

Spd RMS: 1.23 m/sSpd BIAS: 0.13 m/s

DIRTH:DIRTH: Rain vs. non-Rain (dir. edit)Rain vs. non-Rain (dir. edit)

Spd RMS: 4.46 m/sSpd BIAS: 2.90 m/s

Spd RMS: 1.26 m/sSpd BIAS: 0.19 m/s

DIRTH:DIRTH: Nadir vs. “Sweet” swath (dir. edit.)Nadir vs. “Sweet” swath (dir. edit.)

3-20 m/s: 23.5 deg (4.7 deg bias)5-20 m/s: 20.7 deg (5.1 deg bias)

3-20 m/s: 23.3 deg (4.7 deg bias)5-20 m/s: 18.6 deg (5.0 deg bias)

3-20 m/s: 17.1 deg (5.2 deg bias)5-20 m/s: 13.9 deg (5.1 deg bias)

3-20 m/s: 23.7 deg (5.0 deg bias)5-20 m/s: 18.0 deg (4.9 deg bias)

L2B vs. DIRTH:L2B vs. DIRTH: “Sweet” swath (dir. edit.)“Sweet” swath (dir. edit.)

3-20 m/s: 18.2 deg (5.3 deg bias)5-20 m/s: 15.0 deg (5.2 deg bias)

3-20 m/s: 24.9 deg (5.1 deg bias)5-20 m/s: 19.0 deg (5.1 deg bias)

3-20 m/s: 17.1 deg (5.2 deg bias)5-20 m/s: 13.9 deg (5.1 deg bias)

3-20 m/s: 23.7 deg (5.0 deg bias)5-20 m/s: 18.0 deg (4.9 deg bias)

DIRTH:DIRTH: NOFAR swathNOFAR swath

Spd RMS: 1.23 m/sSpd BIAS: 0.13 m/s 3-20 m/s: 17.5 deg (5.1 deg bias)

5-20 m/s: 14.3 deg (5.1 deg bias)

3-20 m/s: 23.6 deg (4.9 deg bias)5-20 m/s: 18.1 deg (4.9 deg bias)

MUDH Rain Expected Performance vs. SSM/IMUDH Rain Expected Performance vs. SSM/I

Huddleston and Stiles, 2000

QuikSCAT -- Buoy:QuikSCAT -- Buoy: Rain (direction distributions) Rain (direction distributions)

QuikSCAT -- Buoy:QuikSCAT -- Buoy: Rain (speed distributions) Rain (speed distributions)

QuikSCAT:QuikSCAT: Rain Fraction (%) at NDBC LocationsRain Fraction (%) at NDBC Locations

ScatterometryScatterometry: : 2-Look Solutions2-Look Solutions

ScatterometryScatterometry: : 4-Look Solution(s)4-Look Solution(s)

QuikSCATQuikSCAT: : Rain FlagRain Flag

• Absorption and scattering from rain and heavy clouds degrades wind velocity accuracy

• Multi-Dimensional Histogram Rain Flag – Normalized beam difference– Measured speed– MLE misfit– Radiometer mode Tb (H,V)– Table-driven, trained with SSM/I

• ~5% flag rate (approx. 2 km mm/hr)

• Rain-free data has improved quality– 24% speed rms decrease, 3-7 m/s

• Active/Passive environmental retrievals will be possible with SWS and AMSR on ADEOS-II

QuikSCAT Radiometer Mode

• QuikSCAT noise measurements contribute to autonomous rain flag capability

• Careful calibration/analysis allows subtraction of signal energy from 1 MHz bandwidth noise measurements, and interpretation of noise measurements as brightness temperature

• QSCAT radiometer mode data compare well with space/time collocated SSM/I rain rates and water contents D. G. Long, BYU

W. L. Jones, UCF

TbHurricane Floyd

Joe Sienkiewicz, Lead Forecaster, NWS Marine Prediction Center

REMARKS:

262100Z1 POSITION NEAR 21.4N7 130.6E0.

TROPICAL STORM (TS) 20W (PRAPIROON), LOCATED APPROXIMATELY

375 NM SOUTH-SOUTHEAST OF OKINAWA HAS TRACKED NORTH

NORTHWESTWARD AT 20KNOTS OVER THE PAST 6 HOURS. THE WARNING

POSITION IS BASED ON 261730Z9 INFRARED SATELLITE IMAGERY. THE

WARNING INTENSITY IS BASED ON SATELLITE CURRENT INTENSITY

ESTIMATES OF 30 AND 35 KNOTS AND A SHIP REPORT OF 35 KNOTS.

ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS CONVECTION

IS SHEARED 15 NM TO THE NORTH AND EAST OF A PARTIALLY EXPOSED

LOW LEVEL CIRCULATION CENTER (LLCC). IMAGERY ALSO INDICATES

CONVECTION HAS INCREASED IN INTENSITY OVER THE PAST 06 HOURS.

UW-CIMSS ANALYSIS AND THE 200 MB ANALYSIS INDICATE OUTFLOW

ALOFT CONTINUES TO IMPROVE AS THE TROPICAL UPPER-TROPOSPHERIC

TROUGH (TUTT) TO THE WEST CONTINUES TO FILL. A 260916Z4

QUIKSCAT PASS INDICATED A WELL DEFINED LLCC WITH LIGHTER WINDS

AROUND THE CENTER AND STRONGER WINDS ON THE PERIPHERY. THE

SYSTEM IS FORECAST TO TRACK NORTHWESTWARD THROUGH 24 HOURS,

THEN INCREASINGLY WEST-NORTHWESTWARD AS THE SUB-TROPICAL RIDGE

BUILDS IN NORTH OF THE SYSTEM. THE 35 KNOT WIND RADII HAVE BEEN

INCREASED BASED ON THE 260916Z4 QUIKSCAT PASS.

Jeff Hawkins, Naval Research Laboratory, Monterey, CA 93943

QuikSCAT data has become a high priority data set for weather

forecasters

QuikSCAT data is a significant resource for a significant

number of advisories issued

National Weather Service AdvisoryNational Weather Service MeteorologicalData Assimilation Software Display

QuikSCAT:QuikSCAT: Operational ApplicationsOperational Applications

WIND MEASUREMENTSWIND MEASUREMENTS:: Mission SchedulesMission Schedules

99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15

QSCAT SWS/ADEOS-II ERS-2 ASCAT/METOP WINDSAT CMIS/NPOESS

Wind

Roughness

Backscatter/Emission

Roughness

99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15

QSCAT SWS/ADEOS-II SWS/GCOM-B ERS-2 ASCAT/METOP WINDSAT CMIS/NPOESS

WIND MEASUREMENTSWIND MEASUREMENTS: (Wished) : (Wished) Mission SchedulesMission Schedules

Model FunctionModel Function:: Refinement ApproachRefinement Approach

• Objective is to use QSCAT o

measurements

• Exploit unique QSCAT scanning geometry – Single incidence angle for each polarization– Complete range of angular differences (“”) for collocated fore and aft measurements from each beam

• Collocated NCEP, ECMWF provide estimates of directional distributions for each (U) bin

• NCEP and Interim QSCAT data yield estimates of speed (“U”) for each collocated fore-aft pair

Sponsors:

• OPNAV

• N6

• N096

• NPOESS IPO

• Space Test Program

Support Organizations:

• ONR (Executing Agent)

• NRL (Payload)

• Spectrum-Astro (S/C)

Rationale:

• Validate Polarimetric Radiometry From Space to Develop Wind Vector

• Wind Direction is the Number One Unfilled Requirement of N096

• Risk Reduction for NPOESS CMIS

• Benefits:

• 25 km Resolution Wind Vector

• 3x Improvement in Horizontal Resolution for Imagery (vs. SSMI)

• Tactical Downlink to the Fleet

WindSat - Mission DescriptionOverview:• Measure Ocean Surface Wind Speed and Direction• Titan II Launch (03/15/02) on STP’s Coriolis Satellite Bus

Into a Sun-Synchronous Orbit (830 Km, 98.7 deg); 1100 km Forward Swath; 400 km Aft Swath

• 3 Year Mission Supports Calibration, Validation and Operational Users

WindSat on Coriolis

Polarimetric Radiometry

TH

T+45

TV

T-45

Tlc

Trc

Upwelling MicrowaveEmission

rclc

hv

hv

hv

hv

vvhh

vvhh

s

TT

TT

TT

TT

EE

EE

EEEE

EEEE

V

U

Q

I

I4545

*

*

**

**

Im2

Re2

Available from “Dual Polarization” Systems (SSM/I, SSMIS)

New Capability Available from “Polarimetric” Systems(WindSat)

•Emission and Scattering Vary With Wind Vector (speed and direction)

•Wind Direction Dependence Arises From Anisotropic Distribution and Orientation of Wind Driven Waves

•Stokes Vector

•Polarization Properties of Emitted/Scattered Radiation

•Contains Directional Information

•Wind Direction signal is two orders of magnitude smaller than Wind Speed signal

•Two means of measuring

•Correlation of Primary Polarizations

•Direct measure of 45, LHC, RHC

(Wind Speed = 9 m/s; Vertical Lines Identify Upwind Direction)

Tv,

KT

u,

K

T4,

K

V-Polarization H-Polarization

3rd Stokes Parameter 4th Stokes Parameter

Th,

K

Comparison of 37 GHz A/C Data andNRL 2-Scale Model

10.7, 18.7, 37 GHz:

V/H, ±45, LCP/RCP

6.8, 23.8 GHz: V/H

RF

29.6 rpmSpin Rate

350 WattsPower

675 lbs.Weight

8.25 ft.Width

10.5 ft.Height

WindSat Payload Configuration

Reflector Support

Structure

Warm Load

Canister Top Deck and Electronics (Rotating)

Bearing and Power Transfer Assembly (BAPTA)

Launch Locks(4 Places)

Spacecraft Interface

Stationary Deck

Feed Bench

Feed Array

Cold Load

Main ReflectorGPS Antenna

Transition ScheduleSlopes indicate 10-90% need (NPOESS GAP 5b)

CY 99 00 11 12 13 14 15 16 17 1803 08 09 1001 02 0704 05 06

Local Eq

uato

rial C

rossin

g T

ime

Earliest Availability

Projected End of Life based on 50% Need

S/CDeliveries

S/C delivery interval driven by 15 month IAT schedule

MissionSatisfaction

0530

1330

DMSP

WindSat/Coriolis

0730 - 1030

NPOESSC3

POES

EOS-Aqua

NPOESSC2 or C1N’

Earliest Need to back-up launch

F20

NPOESSDMSP

POES

NPP

EOS-Terra

METOP

NPOESSC1 or C2

F16

N

MF17 F19F15

F18

L (15)

(Slide from NPOESS Climate brief, 1/25/01)

Model FunctionModel Function:: Refinement ApproachRefinement Approach

• Objective is to use QSCAT o

measurements

• Exploit unique QSCAT scanning geometry – Single incidence angle for each polarization– Complete range of angular differences (“”) for collocated fore and aft measurements from each beam

• Collocated NCEP, ECMWF provide estimates of directional distributions for each (U) bin

• NCEP and Interim QSCAT data yield estimates of speed (“U”) for each collocated fore-aft pair