Sca$erometer and Salinity missions: Status and Needs

Transcription

1 Sca$erometer and Salinity missions: Status and Needs Subra Bulusu Satellite Oceanography Laboratory School of the Earth, Ocean and Environment University of South Carolina, Columbia, USA US CLIVAR POS Panel Meeting: July 18-20, 2016

2 Sca$erometer Status and Needs Acknowledgements: Mark Bourassa, FSU Paul Chang, NOAA Ernesto Rodriguez, JPL

3 ScaDerometer Basics Radar scaderometers are the only instruments that measure wind speed and direcgon over the ocean Only way to directly esgmate key climate drivers, such as wind convergence, wind stress and wind stress curl which drive Ekman circulagon and pumping The physical measurement is most sensigve to wind stress, which is converted to winds assuming neutral stability condigons

4 Scatterometer Constellation Evolution ISS RapidScat Winds CalibraGon Winds + CalibraGon 2014-current Winds 2003 ISRO OSCAT on OceanSat current ISRO ScatSat Winds (?)

5 Climate Data Record Now Exists Comparision of gloab wind speed averages between QuikSCAT, ASCAT, and TMI. A consistent global climate data record is now available stargng from Wentz, F. (2015), A 17-Yr Climate Record of Environmental Parameters Derived from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager, Journal of Climate, 28(17), , doi: /jcli-d

6 Sampling Requirements -InternaGonal ConstellaGon PerspecGve - Constellation requirement for an optimum (minimum) scatterometer constellation At least 3 scatterometers in orbits designed to roughly meet WMO requirements (observations available every 6 hours) One instrument in a non-sun-synchronous orbit for sampling the diurnal cycle, better mid-latitude sampling and provide inter-calibration Intercalibrated observations to specified standard These requirements do not address the need to understand diurnal and semidurnal variability not cycles more complicated Substantial impact on coupling between clouds and the surface Surface and upper ocean

7 Global Coverage in 1 day Ascat Alone 7

8 Global Coverage in 1 day RapidScat and Ascat 8

9 OSVW ConstellaGon Status and Health ASCAT (METOP-A&B) and RapidScat Open and near real-time data access ASCAT available through EPS-SG(SCA) ~2023 RapidScat at least until September 2017 SCA (ASCAT Follow-On, EPS-SG) ~2022/23 ScatSat late July 2016 (not yet official)(inject into ~9:45 am local crossing time and drift to 8:30 am) Open and near real-time data access OSCAT follow-on (OceanSat-3) ~2018 Committee on Earth Observation Satellites

10 CEOS Ocean Vector Surface Winds Virtual ConstellaJon (OSVW-VC) Current status and outlook NRT data access Launch /06 METOP-A Europe C-band 06/99 QSCAT USA Oceansat-2 India METOP-B Europe 03/04 METOP-C Europe Post EPS Europe Oceansat-3A India Oceansat-3 India SCATSAT India Ku-band HY-2A China RapidSCAT USA HY-2B China CFOSAT China/France Meteor-M N3 Russia Meteor-MP 3 Russia No NRT data access commi$ed Combined C- and Ku-band FY-3E China FY-3G China GCOM-W2 Japan/India/USA? Advanced Scat series India Design Life Extended Life Design Life Extended Life Proposed OperaGng Approved Source: WMO OSCAR database and direct interacjons with agencies

11 DESCENDING NODE CROSSING TIME Ocean Vector Surface Winds ConstellaJon Local Jme coverage assessment (ground track) - NRT data access Launc h :30 GCOM W2/ Design Life Extended Life Design Life Extended Life Proposed Operating No NRT data access commi$ed WMO observajon cycle requirement: 6 h Approved Source: WMO OSCAR database and direct interacjons with agencies 06:00 HY-2 A/B/C 06:00 FY-3E/G 08:30 SCATSAT 06:00 SCATT O.S. 07:00 CFOSAT 09:30 EPS (ASCAT) 09:30 EPS-SG (SCA) 12:00 OceanSAT 2/3 12:00 Meteor M/MP Committee on Earth Observation Satellites

12 What Improvements are Needed? Finer spatial resolution to calculate spatial derivatives (including curl and divergence) Divergences calculated on the scale (e.g., diameter) of one or two grid cells are quite noisy compared to those calculated on the scale of 3 or more grid cells. Spatial derivatives are very important for coupling with clouds (divergence of winds) Ocean currents near the surface, in the Ekman layer, and in the deep ocean (curl of stress) Frontogenesis (gradient of winds) Ocean upwelling and primary productivity We need to observe winds roughly every 5km to address these interests About 2.5 times finer than the existing measurements

13 Diurnal and Semidurnal Variability Diurnal and Semidurnal Variability have quite substantial signals as seen by RapidSCAT on the ISS not cycles more complicated Substantial impact on coupling between clouds and the surface Surface and upper ocean We need an intercalibrated constellation (or a wide swath scatterometer in mid-earth orbit, with a huge antenna to get the resolution) Differences between C-band and Ku-band are becoming smaller and are likely to be very small except for very isolated conditions in the next few years Therefore the real gap is in sampling throughout the day, and in particular for high resolution data

14 Tehuantepec: COAPS Climatology C. M. Risien and D. Chelton, A global climatology of surface wind and wind stress fields from 8 years of quikscat scatterometer data, Journal of Physical Oceanography,

15 Zonally Averaged Wind Differences Between RapidScat and ASCAT 15

16 New Concept: Simultaneous Wind and Surface Currents Surface currents are poorest observed ocean surface variable Surface currents play important roles in coupling the atmosphere and the ocean, and are different from geostrophic currents in critical ways Key outstanding questions How are winds and surface currents coupled? How great is the equatorial upwelling, and what is the wind-induced variability? How do winds and currents move fresh water Arctic and Nordic Seas? Applications: Debris transport, nutrient transport and primary productivity, iceberg transport and primary productivity, ice motion, seasonal to interseasonal forecasting, ocean forecasting and more

17 WaCM Measurement Concept Winds and Current Mission 800 km 700 km Ka-band rotagng pencil beam Doppler scaderometer Ku-band rotagng beam scaderometer Winds measured from Ka/Ku σ 0 measurements at mulgple azimuth angles - Heritage: QuikSCAT, RapidScat, OSCAT Surface currents from Doppler measurements at mulgple azimuth angles - Heritage: SAR Doppler, Along-track interferometry Temporal coverage achieved by 1600 km swath JPL/Caltech Proprietary - Not for Public Release or RedistribuGon 17

18 Improved Temporal Sampling of Surface Currents Courtesy D. Chelton, OSU Doppler scaderometer wide swath capabiliges allow near daily 2D observagons of surface currents. Simultaneous wind vectors are collected as well. SWOT (2021) will measure 2D geostrophic currents with a 22 day cycle.

19 Currents Spaceborne DemonstraGon Radial direction Agulhas main stream Mesoscale eddy Surface velocity measurements along the line of sight direcgon have been demonstrated mulgple Gmes from spaceborne SARs. Example from Aghulas current observed by ASAR at 10km resolugon. Nadir algmeters can observe one dimensional geostrophic currents. By combining mulgple algmeters, 2D geostrophic currents can be esgmated at ~200km resolugon. JPL/Caltech Proprietary - Not for Public Release or RedistribuGon Comparison of Doppler currents with algmeter radial velocity esgmates along the SAR line of sight. Both capture an eddy, but only the high spagal Doppler resolugon captures the narrow Agulhas main stream current. 19

20 Sea Surface Salinity from Space: Status and Needs Acknowledgements: Tony Lee, JPL

21 Three satellite missions that pioneered salinity remote sensing Soil Moisture & Ocean Salinity (SMOS) Mission by European Space Agency L-band radiometer Aquarius/SAC-D Mission by NASA & CONAE L-band radiometer + radar June 2011-June 2015 Nov present NASA s Soil Moisture AcJve-Passive (SMAP), January 2015-present L-band radiometer + radar (radar stopped funcjoning July 2015)

22 Aquarius SSS (V4.0) 09/ /2015 Aquarius SSS (V4.0) 09/ /2015 Complementary to the Argo array by providing finer spagotemporal sampling and global coverage (incl. ArcGc Ocean, coastal ocean, & marginal seas).

23 Status of Aquarius Mission, its SSS products, and the ongoing SMAP SSS retrievals Aler the lost of the mission due to a power failure of the spacecral, the Aquarius project is in Phase-F (closeout phase). Version 4.0 SSS released in late 2015 (the evaluagon of its quality is presented next). Version 5.0 is scheduled to be released by June 2017, aiming to reduce Gme-mean and seasonal biases at high lagtudes). Aquarius Phase-F will end December SMAP SSS Beta version released in early Version 2 release soon (evaluagon of SMAP SSS Beta version is also presented here).

24 SMAP s soil moisture and SSS highly synergisjc for water cycle research

25 SMAP spajal resolujon a significant advantage (Aquarius ~ 150 km, SMAP 40 km, similar to SMOS) (a) ARGO May 2015 (b) HYCOM May 2015 From JPL (c) Aquarius TB -only May 2015 From JPL (d) SMAP TB -only May 2015

26 Comparison of SMAP SSS with in-situ data in the Bay of Bengal Courtesy of of Sree Lekha and Debasis Sengupta, Indian Inst of Sci.

27 Summary of SMAP SSS evaluajon Beta version of SMAP SSS has very encouraging quality. For monthly and 1, global RMS (STD) of SMAP(beta)-Argo SSS is 0.26 (0.20) psu, comparing to Aquarius(V4)-Argo SSS of 0.21 (0.16) psu. SMAP SSS quality was affected by the loss of the radar in July The higher resolugon SMAP SSS may also cause larger deviagons from the smoother Argo OI maps because of smaller-scale variability not resolved by Aquarius & Argo. Imminent public release of SMAP SSS V2, significant improvement expected.

28 Future Need: Community white paper in response to US NRC Decadal Survey for Earth Science and ApplicaJons from Space Call for InformaJon #2 Lee et al. (2016): Linkages of salinity with ocean circulajon, water cycle, and climate variability Emphasized importance of sustaining and enhancing satellite SSS to study ocean circulagon and linkages to climate variability and water cycle. Advocated for the use of Aquarius and SMAP heritage (combined AcGve-Passive design of L-band radiometry and scaderometry) with an addigon of P-band radiometry to improve high-lagtude SSS and first-year sea ice thickness measurements (up to 1.5 m, not well measured by radars such as those on ICESat). SynergisGc technology for measurements of soil moisture, land-surface flux, and vegetagon (2-3 other decadal survey white papers proposing similar technology).

29 Large changes of SSS in the ArcJc Ocean means that even L-band SSS data are sjll valuable for studying ocean-cryosphere interacjon, but the combined L-P band will further enhance the capability SpaGal distribugon of 20-m salinity based on in-situ measurements in the ArcGc Ocean during m salinity difference between 2012/13 and 1970s climatology