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16th Conference on Air-Sea Interaction 11–15 January 2009, Phoenix, Arizona. Validation of satellite-based estimates of whitecap coverage: Approaches and initial results. Magdalena D. Anguelova, Justin P. Bobak, William E. Asher, David J. Dowgiallo, - PowerPoint PPT Presentation
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Magdalena D. Anguelova,
Justin P. Bobak, William E. Asher, David J. Dowgiallo,
Ben I. Moat, Robin W. Pascal, Margaret J. Yelland
16th Conference on Air-Sea 16th Conference on Air-Sea InteractionInteraction
11–15 January 2009, Phoenix, Arizona Validation of satellite-Validation of satellite-
basedbased
estimates of whitecap estimates of whitecap
coverage: Approaches and coverage: Approaches and
initial resultsinitial results
Naval Research Laboratory, Washington, DCApplied Physics Laboratory, University of Washington, Seattle,
WANational Oceanography Centre, Southampton, UK
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Long-term goalLong-term goalImprove Sea Salt Source Function parameterization by modeling the high variability of whitecap coverage
CSTUdXTuW scur ,,,,,,, uW
STuW s ,,*
or
u – wind speed (u10 or u*?)T – atmospheric stability (= Tair – Tsea)X – wind fetch
d – wind durationUcur – water currentsTs – sea surface temperatureS – salinityCk – concentration, type (k) of surface active materials
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
The first stepThe first step
FrameworkFramework
Improve existing or develop new models; Extensive database: W + various factors; Measurements: W + various factors;
Existing W measurements: Photographs/video images; Insufficient for extensive database;
Alternative approach: From satellites to get global coverage; wide range of meteo & environ conditions;
CSTUdXTUW scur ,,,,,,,Whitecap variability:Whitecap variability:
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Daily map of Daily map of WW
Daily data (swath) for entire 2006, months of 2007 and 2008
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Retrieving W (changes in TB at microwave frequencies): Using parts of WindSat forward model (v.1.9.6) ;
Rough surface emissivity, er ; Atmospheric variables atm. correction;
Foam emissivity model, ef ;
Independent sources for the input variables: TB from WindSat; V, L from SSM/I or TMI; U10 from QuikSCAT, SSM/I, or GDAS; Ts from GDAS; S = 34 psu;
Improvements over the published feasibility study: More physical models for er, ef, and atm. corr.; Independence of the variables; Minimization of errors.
Satellite-based foam Satellite-based foam fraction fraction WW
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
ValidationValidation
Insufficient ground truth values: Data collection:
Slow and expensive; Sporadic and non-systematic;
Limited range of conditions; Fewer in situ-satellite matches in time and space;
Different principles of measurement: Reflectivity in the Visible (photographic/video); Emissivity in the Microwave (radiometer);
Various approaches to circumvent difficulties.
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Validation approachesValidation approaches
Historical database of in situ values; Wind speed formula;Ship-borne measurements;Air-borne measurements.
There are questions and issues
with each approach.
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
In situIn situ historical data by historical data by typetype
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
10 GHz seems good10 GHz seems good
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
All Frequencies, H polAll Frequencies, H pol
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Satellite vs Wind formulaSatellite vs Wind formula
Wsat more uniform by latitude;
High lat higher W.
March, 2007, 0.5 deg x 0.5 deg
Satellite, 18.7 GHz, H pol.
Wind speed formula: Monahan and O’Muircheartaigh,
1980: U10 from QuikSCAT or GDAS; Time/space matched with WindSat;
41.310
61084.3 UW
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Difference mapsDifference mapsWW = = WWsatsat – – WWmodmod
18H10H
+W = 0.041% ; - W = 0.44% +W = 0.61% ; - W = 0.63%
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Experiment HiWASE on Polarfront ship positioned at Station M; UK colleagues: Margaret Yelland, Ben Moat and Robin Pascal; Long-term (Sep 2006 to Sep 2009) measurements of W and other
variables; In situ data for W;
Two cameras, daylight restrictions (Mar-Oct); Photographic data processed at 3 intensity thresholds with AWE
technique; Temporally-averaged values in a time window around or close to
WindSat pass time; The effect of time window (minutes to 3 hours) was investigated;
WindSat data for W: Closest pixel to lat/lon position of each in situ point; WindSat low resolution (50 km x 71 km); Three frequencies (10, 18, and 37 GHz), H pol.; The effect of averaging over NºxNº box (e.g., 1/2ºx1/2º) was
investigated;
In situ data for W; Two cameras, daylight restrictions (Mar-Oct); Photographic data processed at 3 intensity thresholds with AWE
technique; Temporally-averaged values in a time window around or close to
WindSat pass time; The effect of time window (minutes to 3 hours) was investigated;
WindSat data for W: Closest pixel to lat/lon position of each in situ point; WindSat low resolution (50 km x 71 km); Three frequencies (10, 18, and 37 GHz), H pol.; The effect of averaging over NºxNº box (e.g., 1/2ºx1/2º) was
investigated;
PolarfrontPolarfront ship data ship data
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
In situIn situ historical data by historical data by typetype
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
PolarfrontPolarfront to historical to historical in in situsitu
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
WindSat matched to WindSat matched to PolarfrontPolarfront
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
In situIn situ and satellite winds and satellite winds
180-min time window
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
In situIn situ and satellite winds and satellite winds
180-min time window
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
RASSI ExperimentRASSI Experiment RAdiometry and Sea Surface Imagery (2007):
North Atlantic, Gulf of Mexico (Hurricane Dean); High altitude: 6.7 km (20,000 ft); Clear sky to partial cloud cover;
Radiometric measurements: APMIR (Airborne Polarimetric Microwave Imaging Radiometer) Channels available (GHz): 37VH34, 19VH34, 6.6VH,
6.8VH, 7.2VH (some data at channels at 10.7 and 22.235);
Footprint roughly 1x2 km from on 19 and 37 GHz; Video measurements:
High resolution video camera; Field of view of 159 m by 119 m.
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
RASSI ExperimentRASSI Experiment RAdiometry and Sea Surface Imagery (2007):
North Atlantic, Gulf of Mexico (Hurricane Dean); High altitude: 6.7 km (20,000 ft); Clear sky to partial cloud cover;
Radiometric measurements: NRL’s APMIR (Airborne Polarimetric Microwave Imaging
Radiometer) Channels available (GHz): 37VH34, 19VH34, 6.6VH,
6.8VH, 7.2VH (some data at channels at 10.7 and 22.235); Footprint roughly 1x2 km from on 19 and 37 GHz;
Video measurements: High resolution video camera; Field of view of 159 m by 119 m.
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
RASSI ExperimentRASSI Experiment RAdiometry and Sea Surface Imagery (2007):
North Atlantic, Gulf of Mexico (Hurricane Dean); High altitude: 6.7 km (20,000 ft); Clear sky to partial cloud cover;
Radiometric measurements: NRL’s APMIR (Airborne Polarimetric Microwave Imaging
Radiometer) Channels available (GHz): 37VH34, 19VH34, 6.6VH,
6.8VH, 7.2VH (some data at channels at 10.7 and 22.235); Footprint roughly 1x2 km from on 19 and 37 GHz;
Video measurements: UW’s High resolution video camera; Field of view of 159 m by 119 m.
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Hurricane Dean flightHurricane Dean flight
KSYP
#6
#7
#42003
#42055
3FPQ9
#1#2
#3
#4#5
Buoy
Ship
RASSI
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
In situIn situ historical data by historical data by typetype
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
RASSI foam vs historical RASSI foam vs historical in in situ situ
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
RASSI foam vs historical RASSI foam vs historical in in situ situ
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
RASSI vs WindSat pairsRASSI vs WindSat pairs
Wind dependent AB factor Wind dependent AB factor 11 to 15 11 to 15 using Monahan & Woolf using Monahan & Woolf (1989) parameterizations for (1989) parameterizations for A+B and AA+B and A
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
RASSI vs WindSat pairsRASSI vs WindSat pairs
Wind dependent AB factor Wind dependent AB factor 11 to 15 11 to 15 using Monahan & Woolf using Monahan & Woolf (1989) parameterizations for (1989) parameterizations for A+B and AA+B and A
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Difficulties in validating satellite-based foam fraction; Amount of data; Conditions covered; Principle of measurements;
Compensate using different approaches: Historical in situ data; Wind speed formula; Direct validation with APMIR/video data; Direct validation with ship data;
Results: Ball-park in magnitude compared to in situ data; More uniform latitudinally than wind formula; Direct validation shows:
underestimate at low winds and over estimate at high winds; How much of this result is correct?
Future work: More match-ups of in situ and satellite data; Indirect validation (with other variables, not directly W); Tuning of the satellite-based algorithm.
SummarySummary
Compensate using different approaches: Historical in situ data; Wind speed formula; Direct validation with ship-borne photographic data; Direct validation with air-borne video data;
Results: Ball-park in magnitude compared to in situ data; More uniform latitudinally than wind formula; Direct validation shows:
Wsat overestimate at low winds and Relatively good estimate at high winds;
Future work: More match-ups of in situ and satellite data; Indirect validation (with other variables, not directly W); Tuning of the satellite-based algorithm.
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Additional slidesAdditional slides
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Match-up issuesMatch-up issues
Only 4 full swaths: from GDAS, Large temporal
mismatch for other GDAS match-ups;
Chunks of swaths for most passes: due to QuikSCAT passes
CROSSING the WindSAT passes;
Reflects on the number of samples available for low and high latitudes.
Sample count
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Samples available for 1 Samples available for 1 monthmonth
Sample count
High latitudes with high winds are under represented.
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Frequency and polarization Frequency and polarization
dependencedependence Understanding the info
each freq and pol gives for W: Research foam skin depth; The effect of foam
thickness on the skin depth and foam emissivity;
The results could be important for gas exchange (CO2 and other gases);
Combining suitable freqs and pols in one “oceanographically” representative W;
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Compare to Compare to in situin situ A+B data A+B data
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Low freqs close to Low freqs close to in situin situ A+BA+B
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
18 GHz18 GHz Very similar to 23 GHz Atmosphere influence?
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
All frequencies, V polAll frequencies, V pol
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
All Frequencies, H polAll Frequencies, H pol
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
BiasesBiasesPair binned
data;W = Wsat-
Wins;Plot bins with
high count.
Freq (GHz), H pol.61018232337
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Satellite vs Wind formulaSatellite vs Wind formula
March, 2007 0.5 deg x 0.5 deg
Wind speed formula
Satellite, 10.7 GHz, H pol.
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Ship cruisesShip cruises
Two ship cruises in 2006 and 2007 Ian Brooks and Margaret
Yelland, UK: Data for:
Foam fraction – direct validation;
Sea-salt aerosol flux – indirect val.
Matchups with WindSat data Spatial and temporal; Video data availability for
about 10 points; Cruise data still processed
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
In situIn situ and satellite winds and satellite winds (raw)(raw)
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Binned by wind speedBinned by wind speed
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Compare Compare in situin situ – satellite – satellite pairspairs
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Compare Compare in situin situ – satellite – satellite pairspairs
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
RASSI measuring RASSI measuring configurationconfiguration
37 GHz station 2
-87.45
-87.4
-87.35
-87.3
-87.25
-87.2
-87.15
-87.1
-87.05
25.3 25.4 25.5 25.6 25.7
all points
points averaged
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Wind speed conditionsWind speed conditions
4
6
8
10
12
14
16
18
20
0 1 2 3 4 5 6 7 8
Station
Win
d s
pee
d, U
10 (
m/s
)
WindSat
SSMI
QuikSCAT
GDAS
Buoys
Ships
16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al.
Wind vector field during the Wind vector field during the flightflight
12
34
5
67
12
34
5
67
12
34
5
67