Nicolas Reul, Joe Tenerelli IFREMER

Vincent Kerbaol, Fabrice Collard BOOST Technologies, Brest, France

Catherine Bouzinac

ESANiels Skou

TUD Many Other Folks at ESA, TUD, HUT,

IEEC…

COSMOS-OS campaignAnalysis Status

COSMOS-OS campaignAnalysis Status

SMOS SAG meeting, Villafranca, 2-3/11 2006

CoSMOS-OS ObjectivesCoSMOS-OS Objectives

– Support validation of the SMOS Level 2 prototype processor critical sub models:

Roughness impact corrections Galactic and sun glint corrections SSS Inversion methodology using NWP products

– Investigate physical sources for observed wiggles in the previously measured Tb azimuthal signals (LOSAC, JPL, ..):

Hypothesis for the wiggles: rough sea surface scattering of galactic reflections, signature of spatial heterogeneities in surface roughness (internal wave

signatures, mesoscale activity due to wave interaction with current or bathymetry, slicks,..)

Campaign Site: North Sea

O.5 KO.3 K O.5 K

Relatively Homogeneous site

Optimal Experiment AreaFree of fixed structures, near oil rig with MIROS wave radar, Ferry Box line

Baseline Flight Plans

• Focus on circle flights, performed over an area between Ekofisk and SleipnerA, which exhibits maximally uniform geophysical conditions. Good for galactic and sunglint impact studies. Also, Ekofisk and SleipnerA provides good wave and meteorological information

• Make use of the numerous straight-line flight legs from Stavenger to circle flight site to tentatively retrieve the SSS front from averaging procedure

• Sun glint flights: several flights dedicated to sunglint during morning

• All Flight times were aligned with ENVISAT overpasses.

Equipment and Auxilliary Data

HUT Skyvan Specs

• Typical airspeed range 170 - 290 km/h (92 - 160 knots).

• Maximum/Cruising speed278 km/h (150 knots).

• Max. range: 1200 km, (980 km + 45 min reserve).

• Flight max. duration: 4 hours (3h 15 min + 45 min reserve).

• Maximum altitude 3000 m standard, 6000 m with oxygen (5500 m recommended)

• Max. take off weight 5670 kg.

• Payload: 1800 kg (700 kg with full tank).

• Max. payload on rear cargo ramp 180 kg.

• Max. payload in rear cargo area 450 kg.

• Navigation unit for measurement flights: DGPS, 2 m accuracy, independent recording.

• GPS/INS Output rate 10hzAccuracy: 1 mrad (attitude), 1.5 mrad (heading).

Aircraft Equipment Layout

EMIRAD-2 (Niels Skou)

1.5 km

Radiometer Footprint at Flight altitude (~3km)

Aft-looking 0° antennaAft-looking 40° antenna

Auxilliary Data & Sources

• IR radiometer on aircraft: provided by a non – imaging IR sensor used by the Finnish Institute of Marine Research (FIMR) for airborne sea surface temperature observations. The sensor was installed in the nose radome of the aircraft.=>SST

• SleipnerA: MIROS wave radar. (scanning radar providing information on directional distribution of spectrum)+météorological station: wind, waves

• Ekofisk: WaMoS radar, vertical radar, waverider buoy. wind, waves

• FerryBox System: low-cost opportunity observations on commercial ships. Norwegian Institute for Water Research=> SSS, SST

• ENVISAT/ASAR data – flights coordinates with overpasses: o, wind, waves, currents

• GPS reflectometry system (PARIS) on aircraft. o, wind, mss

• Met data from Norwegian Meteorological Institute (Hirlam, rain radar ) wind, rain

• Hycom model daily data (SSS, SST & currents at 5x5 km)

• Medspiration analysis (SST)

• MERIS & MODIS (Ocean color)

• Solar Fluxes at 1.4GHz (NODC)

SSS Data

Circle & sunglint flights

IR radiometer data still under analysis

Circle & sunglint flights

SST Data

Sea surface roughness and wind vector field.A western wind from 5 to 7 m/s (10 to 15 knots) is observed on the circle flight with higher winds coming from the west. The wind is rather calm (less than 4 m/s) between the circle flight area and the coast except within 10 miles from the coast where the wind is locally reaching 5 to 6 m/s. A strong North-Western swell of 310m wavelength is present in the circle flight area. Some signature of oceanic fronts are visible on the sea surface roughness map. From these modulations, the intersection of the main salinity front and the direct route from Stavanger to the circle flight area center is estimated to be about 58deg 17' N 4deg 19' E

ASAR Data

+ données Hirlam

GNSSR Data :mean square slopes of sea surface

Rain Radar from Metno: 1mes every 1/4 hour

Ocean Color MODIS/MERISHycom currents 4km res

Analysis Methods

Calculation of observation geometry for each 3dB antenna lobe along track

Colocalisation with auxilliary data: (a priori sur la SSS)

Application of forward models at surface levels: Dielectric constant Emissivity of order 0 (flat sea) Delta of emissivity due to roughness:SPM, Kirchhoff, SSA, 2-scale, LCA, RCA Delta of emissivity due to foam

Transport surface-> antenna Atmospheric attenuation Celestial contributions : galactic & solar radiation scattering Polarization mixing in antenna plane Weigthing by antenna gain patterns

Comparison and Inversion/Minimization Tbmes-TbmodelScientific Analysis

Sunglint Flights

Measured Sunglint signaturesFrom aft looking 40° antenna 10 K

LOSAC:

Residual azimuthal oscillations after galactic correction (specular reflection) of order Tb 1 K -uncorrelated with wind direction but correlated with wind speed. Typical persistence scale of order 1-15 km. Doesn’t disappear with increasing aircraft altitude from (1 to 4 km).

Research on physical mechanisms

responsible for azimuthal

“wiggles” (LOSAC, JPL, ..):

Development of the L2 galactic glint forward model

Galactic glint formulation:

Additional azimuthal harmonics 0 compared to the direct rough surface emissivity

Phase & amplitude of second azimuthal harmonics of the galactic glint

spsskyss

swssgg

sp dTutT

)(cos4

)secexp(=),,,,,,( 10

).(2sin)(2sin),,,(

)(2cos)(2cos),,,(

),,,(=),,,,,(

010

2

010

2

100

10

rwsisosop

rwsisosop

sosopwssoop

u

u

uu

,tan=cossincossinsinsinsinsin

tan=),,,( 11

x

y

ooss

oossssoosi

dd

),,0,,(=),,(0soosisoosi

Mathematical FormulationTractable representation of the galactic glint contribution:

with Upper Hemisphere orientation angle [deg]

'w Relative angle between the direction towards which the 10 meter

wind is blowing and the scattering direction towards the radiometer [deg]

•Not necessarily a pure second harmonic:

can reach 0.5 K azimuthal variation amplitude

Impact of Wind Direction

• Two issues arise:– Amplitude of wind second

harmonic– Phase of wind second

harmonic

• In the emission problem, models typically imply reflectivity amplitudes on the order of .5 K with a cos(2*wd) phase of 0 deg for H-pol and 180 deg for V-pol (i.e., a 90 deg phase shift wrt wind direction).

Wind Direction Harmonic Amplitudes

At nadir and 3 m/s, amplitude of scattered signal harmonics peaks at around .25 K.

A little less at 40 deg incidence angle and 7 m/s.

But the Phase is varying All over the Place

Here the phase is the same for both H and V pol!

Wind direction harmonic phase for H-pol at nadir for 7 m/s wind speed.

V-polH-pol

From theoretical point of view,Galactic glint is a very likely source for observed azimuthal wiggles, but with expected wiggles amplitudes slightly lower than those observed during LOSAC

To be validated from on going CoSMOS data analysis