The Sea surface KInematics Multiscale () proposal for ESA EE9 the team : https://www.facebook.com/4ee9 http://tinyurl.com/onrg http://www.umr-lops.fr/projets/projets-actifs/
14 years of Doppler oceanography: When science and technology come together You may not know, but... Drifter data Doppler oceanography works, Even from space! Envisat SAR data Image courtesy of A. Mouche & N. Reul 21 June 2017, LEFE-GMMC, Brest, slide 2
Outline of this presentation : Towards a new satellite mission 1- Context of ESA Earth Explorers How? 2- The concept for measuring surface velocity (currents & ice drift) & ocean wave spectra 21 June 2017, LEFE-GMMC, Brest, slide 3
Outline of this presentation : Towards a new satellite mission 1- Context of ESA Earth Explorers How? 2- The concept for measuring surface velocity (currents & ice drift) & ocean wave spectra 3- Why a new mission Why? 4- Challenges and opportunities in marginal ice zones & the future Arctic Performance 5- Expected resolution & accuracy in different current / wind / wave regimes Summary 6- Questions and anwers : find the proposal on ResearchGate 21 June 2017, LEFE-GMMC, Brest, slide 4
1. ESA, Earth Explorers and you ESA has been dedicated to observing Earth from space ever since 1977. ESA's Living Planet Programme : - operational : Copernicus Sentinel missions - science and research element : Earth Explorer (EE) missions. EEs are research missions designed to address key scientific challenges identified by the science community while demonstrating breakthrough technology in observing techniques. Involving the science community : - definition of new missions - peer-reviewed selection - data required by the user = science community. There has been 8 EEs selected so far : EE1 : GOCE 2009-2013. EE2 : SMOS 2009-... EE3 : Cryosat 2010-... EE4 : Swarm 2013- EE5 : ADM-Aeolus 2017 EE6 : EarthCARE 2018 EE7 : Biomass EE8 : FLEX EE9 :?? 12 proposals submitted last week 21 June 2017, LEFE-GMMC, Brest, slide 5
2. What is? It is a combination of Ka-band radar altimeter, + disco ball, and speed gun + = - «altimeter on steroids» : best ever flown (Ka-band, 32 Khz PRF, 200 MHz bandwidth, SAR unfocused) very low noise for sea level, wave height, ice freeboard - «disco ball» : a rotating plate with 8 horn feeds : one nadir beam (classic altimeter) 7 other beams at 6 and 12 incidence - «speed gun» : Doppler analysis surface currents, ice drift & wave orbital velocities. 21 June 2017, LEFE-GMMC, Brest, slide 6
2. What is? and how it works Example of horn positions with 8 beams : And resulting beam patterns : T_turn = 17.7 s 60 azimuths / beam (6 resolution) 21 June 2017, LEFE-GMMC, Brest, slide 7
3. Why a new satellite? Primary objective : total surface current - transport of heat, salt, biota, microplastics - western boundary currents - equatorial currents - marginal ice zones From Collard et al. (SEASAR 2008) but accurate currents require 21 June 2017, LEFE-GMMC, Brest, slide 8
3. Why a new satellite? Primary objective : total surface current - transport of heat, salt, biota, microplastics - western boundary currents - equatorial currents - marginal ice zones but accurate currents require Secondary objective : directional ocean wave spectra - wave-current interactions - air-sea fluxes : wind stress & wind work - coastal hazards - marginal ice zones - sources of microseisms 21 June 2017, LEFE-GMMC, Brest, slide 9
3. Why we need waves to measure currents will resolve much shorter waves (<20 m) than Sentinels (~ 150 m) or CFOSAT (70 m) fraction of resolved wave energy Measuring shorter waves surface Stokes drift Uss UWB bias for currents (not in ice): Uss UWB = G Uss 21 June 2017, LEFE-GMMC, Brest, slide 10
4. Marginal ice zones & the future Arctic Polar applications : The Arctic is becoming a giant marginal ice zone wave & drift data needed by 2025 to observe this regime shift...large areas of the Arctic Ocean previously covered by pack ice to the wind and surface waves leads to Arctic pack ice cover evolving into the Marginal Ice Zone. The emerging state of the Arctic Ocean features more fragmented thinner sea ice, stronger winds, ocean currents and waves.. (Aksenov et al., Marine Policy 2017) 21 June 2017, LEFE-GMMC, Brest, slide 11
4. Marginal ice zones & the future Arctic Polar applications : The Arctic is becoming a giant marginal ice zone (Aksenov et al., Marine Policy 2017): wave & drift data needed by 2025 to observe this regime shift...large areas of the Arctic Ocean previously covered by pack ice to the wind and surface waves leads to Arctic pack ice cover evolving into the Marginal Ice Zone. The emerging state of the Arctic Ocean features more fragmented thinner sea ice, stronger winds, ocean currents and waves.. Excellent revisit : example of 1-day coverage 21 June 2017, LEFE-GMMC, Brest, slide 12
4. Marginal ice zones & the future Arctic Polar applications : - ice drift in marginal ice zone : Today's sensors fail at ice edge, - waves, - currents - freeboard thickness? 21 June 2017, LEFE-GMMC, Brest, slide 13
5. Expected resolution & accuracy 21 June 2017, LEFE-GMMC, Brest, slide 14
5. Expected resolution & accuracy OSSE using TOPAZ ensembles SLA is expected to have a larger impacts than today's altimeters (but less than SST) 21 June 2017, LEFE-GMMC, Brest, slide 15
7. Conclusions - adds new variable for Earth monitoring : total surface velocity focus : strong currents & marginal ice zones - leap forward for waves : new applications from nearshore to solid Earth monitoring. - possibly other uses (warm rain, river flow ) Questions, Comments? https://www.facebook.com/4ee9 http://tinyurl.com/onrg http://www.umr-lops.fr/projets/projets-actifs/ 21 June 2017, LEFE-GMMC, Brest, slide 16 1.5 km
Bonus slides : B3. Measuring waves in ice No SAR only range bunching should work at 6 incidence (caustic for 10 % slope) For this type of waves (Hs ~ 2 m, L ~ 160 m) significant slope ~ 8 %. Sutherland & Gascard (GRL 2016) 21 June 2017, LEFE-GMMC, Brest, slide 17
Bonus slides : B1. The wave bias The current is obtained from the Line-of-Sight (LOS) velocity Level 1 : ULOS = UNG+sin i UGD Level 2 : UR = UGD - UWB The wave bias is UWB = G Uss, with Uss the surface Stokes drift (wave effect) G is a function of : - incidence angle - radar frequency - sea state (via mss_shape see Nouguier et al. 2016, Hence Mostly wind and Hs ). For : - 6, mss_shape = 0.035 : G ~ 53-12, mss_shape = 0.035 : G ~ 55 For wind speed ~ 7 m/s, Uss ~ 8 cm / s, G x Uss ~ 4 m/s 21 June 2017, LEFE-GMMC, Brest, slide 18
Bonus slides : B1. The wave bias The wave bias is UWB = G Uss, G=-1.*dsig0./sig0./dθi /(2.*tan(θi)) 21 June 2017, LEFE-GMMC, Brest, slide 19
Bonus slides : B1. The wave bias 21 June 2017, LEFE-GMMC, Brest, slide 20
Bonus slides : B2. mss_shape Roughly we need to get UWB = G Uss, within 4 % to get an error under 20 cm/s (in the wind direction, for 4 to 7 m/s) 21 June 2017, LEFE-GMMC, Brest, slide 21