Using Scatterometers and Radiometers to Estimate Ocean Wind Speeds and Latent Heat Flux Presented by: Brad Matichak April 30, 2008 Based on an article.

Using Scatterometers and Using Scatterometers and Radiometers to Estimate Radiometers to Estimate Ocean Wind Speeds and Ocean Wind Speeds and

Latent Heat FluxLatent Heat Flux

Presented by:Presented by:

Brad MatichakBrad Matichak

April 30, 2008April 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

ObjectivesObjectives The satellites being usedThe satellites being used

European Remote Sensing Satellite Scatterometer European Remote Sensing Satellite Scatterometer (ERS-2)(ERS-2)

NASA Scatterometer (NSCAT)NASA Scatterometer (NSCAT) Defense Meteorological Satellite Program (DMSP) Defense Meteorological Satellite Program (DMSP)

RadiometersRadiometers

Alternative methods of measuring wind speeds Alternative methods of measuring wind speeds and latent heat fluxand latent heat flux

Collecting the dataCollecting the data Results/ConclusionsResults/Conclusions

European Remote Sensing European Remote Sensing Scatterometer (ERS-2)Scatterometer (ERS-2)

Launched on April 21, 1995Launched on April 21, 1995 Sun-synchronous polar orbitSun-synchronous polar orbit Height of 780kmHeight of 780km Inclination of 98.5Inclination of 98.5°°

Gives it a visibility of all areas of the Gives it a visibility of all areas of the EarthEarth

Period of 100 minutesPeriod of 100 minutes 35 day repeat cycle35 day repeat cycle Wind ScatterometerWind Scatterometer

Observes wind speed and direction at Observes wind speed and direction at the sea surface for climatological the sea surface for climatological datasets and modelsdatasets and models

Nasa Scatterometer (NSCAT)Nasa Scatterometer (NSCAT)

Launched on August 16, 1996 Launched on August 16, 1996 abord the Advanced Earth abord the Advanced Earth Observing Satellite (ADEOS)Observing Satellite (ADEOS)

Near-polar Sun-synchronous Near-polar Sun-synchronous orbitorbit

Height of 800kmHeight of 800km Inclination of 98.6Inclination of 98.6°° Period of 101 minutesPeriod of 101 minutes 41 day repeat cycle41 day repeat cycle Study runs from October Study runs from October

1996-June 1997 while NSCAT 1996-June 1997 while NSCAT was operationalwas operational

Defense Meteorological Satellite Defense Meteorological Satellite ProgramProgram

Designs, builds, launches, and maintains satellites that Designs, builds, launches, and maintains satellites that monitor meteorological and oceanographic environmentsmonitor meteorological and oceanographic environments

Each satellite has a near-polar Sun-synchronous orbitEach satellite has a near-polar Sun-synchronous orbit Height of 830kmHeight of 830km Period of 101 minutesPeriod of 101 minutes Study focuses on Special Sensor Microwave Imagers Study focuses on Special Sensor Microwave Imagers

(SSM/I) aboard the F10-F14 satellites (SSM/I) aboard the F10-F14 satellites

Real time observations and Real time observations and calculations to compare satellite calculations to compare satellite

estimates toestimates to Buoy NetworksBuoy Networks

Observe wind speed and direction, air and sea surface Observe wind speed and direction, air and sea surface temperatures, and on some, relative humiditytemperatures, and on some, relative humidity

Data collected from three networksData 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)

ShipsShips Comprehensive Ocean-Atmosphere Data Set (COADS)Comprehensive Ocean-Atmosphere Data Set (COADS) COADS based on quality-controlled marine surface observations COADS based on quality-controlled marine surface observations

from shipsfrom ships Also from moored environmental buoys and near-surface Also from moored environmental buoys and near-surface

measurements from oceanographic profilesmeasurements from oceanographic profiles

Observations/Calculations, continuedObservations/Calculations, continued

Atmospheric analysesAtmospheric analyses European Centre for Medium-Range Weather Forecasts European Centre for Medium-Range Weather Forecasts

(ECMWF)(ECMWF) Analyses of 10-m wind vectors and surface latent heat fluxesAnalyses of 10-m wind vectors and surface latent heat fluxes Calculates sea surface values using the SST analysis released daily Calculates sea surface values using the SST analysis released daily

by NOAA/NCEPby NOAA/NCEP National Centers for Environmental Prediction-National Center National Centers for Environmental Prediction-National Center

for Atmospheric Research (NCEP-NCAR)for Atmospheric Research (NCEP-NCAR) Used 4 times daily surface wind speed fields and daily averaged Used 4 times daily surface wind speed fields and daily averaged

latent heat fluxes calculated and given on the NOAA Climate latent heat fluxes calculated and given on the NOAA Climate Diagnostic Center Web siteDiagnostic Center Web site

Weekly averages of the ECMWF and NCEP-NCAR wind Weekly averages of the ECMWF and NCEP-NCAR wind speeds and latent heat flux fields compiled for comparison with speeds and latent heat flux fields compiled for comparison with satellite estimatessatellite estimates

Collecting Satellite Estimates (Wind Speeds)Collecting Satellite Estimates (Wind Speeds)

ERS-2 ScatterometerERS-2 Scatterometer Measured backscatter from sea surface of a 5.3-GHz elecromagnetic Measured backscatter from sea surface of a 5.3-GHz elecromagnetic

signal emitted at different incidence anglessignal emitted at different incidence angles 10-m wind speeds derived over one swath 500km wide using ERS-2 10-m wind speeds derived over one swath 500km wide using ERS-2

backscatter coefficients based on the The Center for Satellite backscatter coefficients based on the The Center for Satellite

Exploitation and Research (CERSAT) wind algorithmExploitation and Research (CERSAT) wind algorithm NSCAT ScatterometerNSCAT Scatterometer

Measured backscatter using a 14.1-GHz signalMeasured backscatter using a 14.1-GHz signal Wind speed values taken over two swaths 600km wide from the Jet Wind speed values taken over two swaths 600km wide from the Jet

Propulsion Laboratory (JPL)Propulsion Laboratory (JPL) SSM/I radiometers on the DMSP F10-F14 SatellitesSSM/I radiometers on the DMSP F10-F14 Satellites

Measured surface brightness temperatures at frequencies of 19, 22, 37, Measured surface brightness temperatures at frequencies of 19, 22, 37, and 85 GHz respectivelyand 85 GHz respectively

Wind speeds taken over swaths of 1394km width using a modified Wind speeds taken over swaths of 1394km width using a modified algorithm that includes a water vapor content correctionalgorithm that includes a water vapor content correction

All satellite wind fields merged into a single weekly gridded wind All satellite wind fields merged into a single weekly gridded wind fieldfield

Collecting Satellite Estimations (Latent Heat Collecting Satellite Estimations (Latent Heat Flux)Flux)

Uses the following equation:Uses the following equation:

QQE E = - = - ll ρρ CCE E ((ŪŪaa – Ū – Ūss)(q)(qaa – q – qss))

QQE E = latent heat flux= latent heat flux

l l = latent heat of evaporation= latent heat of evaporation ρρ = air density = air density CCE E = bulk transfer coefficient for water vapor (Dalton = bulk transfer coefficient for water vapor (Dalton

Number)Number) ŪŪa a = surface wind speed at height of 10m= surface wind speed at height of 10m

ŪŪs s = ocean surface speed (set to 0)= ocean surface speed (set to 0)

qqa a = near-surface air specific humidity= near-surface air specific humidity

qqs s = air specific humidity= air specific humidity

Latent Heat Flux, continuedLatent Heat Flux, continued

Errors can occur in wind speed, exchange coefficient, Errors can occur in wind speed, exchange coefficient, SST, and specific air humidity due to instrumental SST, and specific air humidity due to instrumental errors, boundary layer models, sampling schemes, and errors, boundary layer models, sampling schemes, and aliasing problemsaliasing problems

Assumptions made for calculation:Assumptions made for calculation:1.1. SST at a grid point is constant over a daySST at a grid point is constant over a day

2.2. Surface pressure is constant at 1013.25hPaSurface pressure is constant at 1013.25hPa

3.3. Air temperature at 10m is 1.25K less than at sea surfaceAir temperature at 10m is 1.25K less than at sea surface

As with wind speeds, estimations are collected into As with wind speeds, estimations are collected into weekly averages for comparisons with other weekly averages for comparisons with other observations and calculationsobservations and calculations

Comparisons/ResultsComparisons/Results

Results, continuedResults, continued

Results show a generally good agreement between Results show a generally good agreement between satellite estimates, buoy and ship data, and atmospheric satellite estimates, buoy and ship data, and atmospheric analysesanalyses

Differences in satellite estimates and ECMWF and Differences in satellite estimates and ECMWF and NCEP-NCAR calculations suggest satellites may be NCEP-NCAR calculations suggest satellites may be becoming more accurate than atmospheric analysesbecoming more accurate than atmospheric analyses

One error not corrected estimating specific air humidity One error not corrected estimating specific air humidity to neutral stratificationto neutral stratification Value of error not expected to be large since winds are neutral Value of error not expected to be large since winds are neutral

and most of the ocean is in near-neutral stratification during the and most of the ocean is in near-neutral stratification during the averaging periodaveraging period

Suggestions for Future WorkSuggestions for Future Work

The source of the error between satellite estimations and The source of the error between satellite estimations and the ODAS network needs further researchthe ODAS network needs further research

Include the stratification correction for specific air Include the stratification correction for specific air humidity to further test satellite accuracieshumidity to further test satellite accuracies

Including stress, divergence, and curl from the wind field Including stress, divergence, and curl from the wind field into the estimations of the flux fieldsinto the estimations of the flux fields Satellites to be used include QuikSCAT and ADEOS-2Satellites to be used include QuikSCAT and ADEOS-2

Questions/Comments?Questions/Comments?

[email protected]@eden.rutgers.edu