Post on 20-Jan-2016
transcript
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