Using Scatterometers and Radiometers to Estimate Ocean Wind Speeds and Latent Heat Flux Presented by: Brad Matichak April 30, 2008 Based on an article from the Journal of Climate: Sattelite Estimates of Wind Speed and Latent Heat Flux over the Global Oceans by Abderrahim Bentamy, Kristina B. Katsaros, Alberto M. Mestas-Nunez, William M. Drennan, Evan B. Forde, and Herve Roquet

Objectives The satellites being used The satellites being used European Remote Sensing Satellite Scatterometer (ERS-2) European Remote Sensing Satellite Scatterometer (ERS-2) NASA Scatterometer (NSCAT) NASA Scatterometer (NSCAT) Defense Meteorological Satellite Program (DMSP) Radiometers Defense Meteorological Satellite Program (DMSP) Radiometers Alternative methods of measuring wind speeds and latent heat flux Alternative methods of measuring wind speeds and latent heat flux Collecting the data Collecting the data Results/Conclusions Results/Conclusions

European Remote Sensing Scatterometer (ERS-2) Launched on April 21, 1995 Launched on April 21, 1995 Sun-synchronous polar orbit Sun-synchronous polar orbit Height of 780km Height of 780km Inclination of 98.5° Inclination of 98.5° Gives it a visibility of all areas of the Earth Gives it a visibility of all areas of the Earth Period of 100 minutes Period of 100 minutes 35 day repeat cycle 35 day repeat cycle Wind Scatterometer Wind Scatterometer Observes wind speed and direction at the sea surface for climatological datasets and models Observes wind speed and direction at the sea surface for climatological datasets and models

Nasa Scatterometer (NSCAT) Launched on August 16, 1996 abord the Advanced Earth Observing Satellite (ADEOS) Launched on August 16, 1996 abord the Advanced Earth Observing Satellite (ADEOS) Near-polar Sun-synchronous orbit Near-polar Sun-synchronous orbit Height of 800km Height of 800km Inclination of 98.6° Inclination of 98.6° Period of 101 minutes Period of 101 minutes 41 day repeat cycle 41 day repeat cycle Study runs from October 1996-June 1997 while NSCAT was operational Study runs from October 1996-June 1997 while NSCAT was operational

Defense Meteorological Satellite Program Designs, builds, launches, and maintains satellites that monitor meteorological and oceanographic environments Designs, builds, launches, and maintains satellites that monitor meteorological and oceanographic environments Each satellite has a near-polar Sun-synchronous orbit Each satellite has a near-polar Sun-synchronous orbit Height of 830km Height of 830km Period of 101 minutes Period of 101 minutes Study focuses on Special Sensor Microwave Imagers (SSM/I) aboard the F10-F14 satellites Study focuses on Special Sensor Microwave Imagers (SSM/I) aboard the F10-F14 satellites

Real time observations and calculations to compare satellite estimates to Buoy Networks Buoy Networks Observe wind speed and direction, air and sea surface temperatures, and on some, relative humidity Observe wind speed and direction, air and sea surface temperatures, and on some, relative humidity Data collected from three networks Data collected from three networks National Data Buoy Center (NDBC) National Data Buoy Center (NDBC) European Offshore Data Acquisition System (ODAS) European Offshore Data Acquisition System (ODAS) Tropical Atmosphere Ocean (TAO) Tropical Atmosphere Ocean (TAO) Ships Ships Comprehensive Ocean-Atmosphere Data Set (COADS) Comprehensive Ocean-Atmosphere Data Set (COADS) COADS based on quality-controlled marine surface observations from ships COADS based on quality-controlled marine surface observations from ships Also from moored environmental buoys and near-surface measurements from oceanographic profiles Also from moored environmental buoys and near-surface measurements from oceanographic profiles

Observations/Calculations, continued Atmospheric analyses Atmospheric analyses European Centre for Medium-Range Weather Forecasts (ECMWF) European Centre for Medium-Range Weather Forecasts (ECMWF) Analyses of 10-m wind vectors and surface latent heat fluxes Analyses of 10-m wind vectors and surface latent heat fluxes Calculates sea surface values using the SST analysis released daily by NOAA/NCEP Calculates sea surface values using the SST analysis released daily by NOAA/NCEP National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) Used 4 times daily surface wind speed fields and daily averaged latent heat fluxes calculated and given on the NOAA Climate Diagnostic Center Web site Used 4 times daily surface wind speed fields and daily averaged latent heat fluxes calculated and given on the NOAA Climate Diagnostic Center Web site Weekly averages of the ECMWF and NCEP-NCAR wind speeds and latent heat flux fields compiled for comparison with satellite estimates Weekly averages of the ECMWF and NCEP-NCAR wind speeds and latent heat flux fields compiled for comparison with satellite estimates

Collecting Satellite Estimates (Wind Speeds) ERS-2 Scatterometer ERS-2 Scatterometer Measured backscatter from sea surface of a 5.3-GHz elecromagnetic signal emitted at different incidence angles Measured backscatter from sea surface of a 5.3-GHz elecromagnetic signal emitted at different incidence angles 10-m wind speeds derived over one swath 500km wide using ERS-2 backscatter coefficients based on the The Center for Satellite Exploitation and Research (CERSAT) wind algorithm 10-m wind speeds derived over one swath 500km wide using ERS-2 backscatter coefficients based on the The Center for Satellite Exploitation and Research (CERSAT) wind algorithm NSCAT Scatterometer NSCAT Scatterometer Measured backscatter using a 14.1-GHz signal Measured backscatter using a 14.1-GHz signal Wind speed values taken over two swaths 600km wide from the Jet Propulsion Laboratory (JPL) Wind speed values taken over two swaths 600km wide from the Jet Propulsion Laboratory (JPL) SSM/I radiometers on the DMSP F10-F14 Satellites SSM/I radiometers on the DMSP F10-F14 Satellites Measured surface brightness temperatures at frequencies of 19, 22, 37, and 85 GHz respectively Measured surface brightness temperatures at frequencies of 19, 22, 37, and 85 GHz respectively Wind speeds taken over swaths of 1394km width using a modified algorithm that includes a water vapor content correction Wind speeds taken over swaths of 1394km width using a modified algorithm that includes a water vapor content correction All satellite wind fields merged into a single weekly gridded wind field All satellite wind fields merged into a single weekly gridded wind field

Collecting Satellite Estimations (Latent Heat Flux) Uses the following equation: Uses the following equation: Q E = - l ρ C E (Ū a – Ū s )(q a – q s ) Q E = latent heat flux Q E = latent heat flux l = latent heat of evaporation l = latent heat of evaporation ρ = air density ρ = air density C E = bulk transfer coefficient for water vapor (Dalton Number) C E = bulk transfer coefficient for water vapor (Dalton Number) Ū a = surface wind speed at height of 10m Ū a = surface wind speed at height of 10m Ū s = ocean surface speed (set to 0) Ū s = ocean surface speed (set to 0) q a = near-surface air specific humidity q a = near-surface air specific humidity q s = air specific humidity q s = air specific humidity

Latent Heat Flux, continued Errors can occur in wind speed, exchange coefficient, SST, and specific air humidity due to instrumental errors, boundary layer models, sampling schemes, and aliasing problems Errors can occur in wind speed, exchange coefficient, SST, and specific air humidity due to instrumental errors, boundary layer models, sampling schemes, and aliasing problems Assumptions made for calculation: Assumptions made for calculation: 1. SST at a grid point is constant over a day 2. Surface pressure is constant at hPa 3. Air temperature at 10m is 1.25K less than at sea surface As with wind speeds, estimations are collected into weekly averages for comparisons with other observations and calculations As with wind speeds, estimations are collected into weekly averages for comparisons with other observations and calculations

Comparisons/Results

Results, continued Results show a generally good agreement between satellite estimates, buoy and ship data, and atmospheric analyses Results show a generally good agreement between satellite estimates, buoy and ship data, and atmospheric analyses Differences in satellite estimates and ECMWF and NCEP-NCAR calculations suggest satellites may be becoming more accurate than atmospheric analyses Differences in satellite estimates and ECMWF and NCEP-NCAR calculations suggest satellites may be becoming more accurate than atmospheric analyses One error not corrected estimating specific air humidity to neutral stratification One error not corrected estimating specific air humidity to neutral stratification Value of error not expected to be large since winds are neutral and most of the ocean is in near-neutral stratification during the averaging period Value of error not expected to be large since winds are neutral and most of the ocean is in near-neutral stratification during the averaging period

Suggestions for Future Work The source of the error between satellite estimations and the ODAS network needs further research The source of the error between satellite estimations and the ODAS network needs further research Include the stratification correction for specific air humidity to further test satellite accuracies Include the stratification correction for specific air humidity to further test satellite accuracies Including stress, divergence, and curl from the wind field into the estimations of the flux fields Including stress, divergence, and curl from the wind field into the estimations of the flux fields Satellites to be used include QuikSCAT and ADEOS-2 Satellites to be used include QuikSCAT and ADEOS-2

Questions/Comments?