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 Interaction 11–15 January 2009, Phoenix, Arizona Validation of satellite-based estimates of whitecap coverage: Approaches and initial results Validation of satellite-based estimates of whitecap coverage: Approaches and initial results Naval Research Laboratory, Washington, DC Applied Physics Laboratory, University of Washington, Seattle, WA National Oceanography Centre, Southampton, UK

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Long-term goal Improve Sea Salt Source Function parameterization by modeling the high variability of whitecap coverage or u – wind speed (u 10 or u * ?)  T – atmospheric stability (= T air – T sea ) X – wind fetch d – wind duration U cur – water currents T s – sea surface temperature S – salinity C k – concentration, type (k) of surface active materials

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. The first step Framework  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; Whitecap variability:

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Daily map of W 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 T B at microwave frequencies):  Using parts of WindSat forward model (v.1.9.6) ;  Rough surface emissivity, e r ;  Atmospheric variables  atm. correction;  Foam emissivity model, e f ;  Independent sources for the input variables:  T B from WindSat;  V, L from SSM/I or TMI;  U 10 from QuikSCAT, SSM/I, or GDAS;  T s from GDAS;  S = 34 psu;  Improvements over the published feasibility study:  More physical models for e r, e f, and atm. corr.;  Independence of the variables;  Minimization of errors. Satellite-based foam fraction W

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Validation  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 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 situ historical data by type

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. 10 GHz seems good

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. All Frequencies, H pol

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Satellite vs Wind formula  W sat 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:  U 10 from QuikSCAT or GDAS;  Time/space matched with WindSat;

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Difference maps  W = W sat – W mod 18H 10H +  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; Polarfront ship data

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. In situ historical data by type

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Polarfront to historical in situ

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. WindSat matched to Polarfront

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. In situ and satellite winds 180-min time window

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. In situ and satellite winds 180-min time window

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. RASSI 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 );  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 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 );  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 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 );  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 flight KSYP #6 #7 #42003 # FPQ9 #1 #2 #3 #4 #5 Buoy Ship RASSI

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. In situ historical data by type

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. RASSI foam vs historical in situ

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. RASSI foam vs historical in situ

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. RASSI vs WindSat pairs Wind dependent AB factor 11 to 15 using Monahan & Woolf (1989) parameterizations for A+B and A

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. RASSI vs WindSat pairs Wind dependent AB factor 11 to 15 using Monahan & Woolf (1989) parameterizations for A+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. Summary  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:  W sat 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 slides

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Match-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 month Sample count  High latitudes with high winds are under represented.

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Frequency and polarization dependence  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 (CO 2 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 in situ A+B data

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Low freqs close to in situ A+B

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. 18 GHz  Very similar to 23 GHz  Atmosphere influence?

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. All frequencies, V pol

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. All Frequencies, H pol

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Biases  Pair binned data;   W = W sat -W ins ;  Plot bins with high count. Freq (GHz), H pol

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Satellite vs Wind formula March, 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 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 situ and satellite winds (raw)

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Binned by wind speed

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Compare in situ – satellite pairs

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Compare in situ – satellite pairs

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. RASSI measuring configuration

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Wind speed conditions

16th Air-Sea Interaction Conference, 14 January, 2009, Anguelova et al. Wind vector field during the flight