1. David Antoine, European prospects
for a geostationary ocean color sensor: the
“ocean color advanced permanent imager” (OCAPI)
David Antoine,
on behalf of the OCAPI science team
Laboratoire d’Océanographie de Villefranche (LOV),
CNRS, Villefranche sur mer, France

2. From where OCAPI comes from …? (1/2)
A first proposal was submitted to ESA in 2002 (“BIOGEOSAT”). Included a sensor on a geostationary platform plus a constellation of 3 micro-satellites…. (“Earth explorer call”)
A number of studies were carried out to assess the feasibility and interest of ocean color observations from the geostationary orbit.
We also conducted a study for the KORDI (GOCI preparation), in order to quantify the atmospheric signal measured by an ocean color sensor in the GEO configuration, and to analyze the geometry of the problem.
In the meantime, several technical studies were carried out at CNES, ASTRIUM, and other companies in order to progressively discern and design the possible characteristics of such missions.
A proposal was submitted to CNES in 2008  Selected as a high priority at the occasion of the 2009 quadrennial CNES “scientific prospective seminar”. Called “OCAPI”, which means Ocean Color Advanced Permanent Imager

3. From where OCAPI comes from …? (2/2)
Proposal submitted to ESA (8th “Earth Explorer” opportunity mission) in June 2010
Was not selected (budget and launcher), yet received an excellent scientific evaluation and a specific recommendation: “It is recommended that the OCAPI mission is further addressed in another programmatic framework”
Phase 0.2 studies have been carried out at CNES to further define the concept (by Astrium and Thales). A phase A study might start in 2014
Based on the ESAC recommendation, another proposal was submitted to ESA in summer 2011, called HOCI “Hosted Ocean Color Imager”. The logic was to embark a OCI-like instrument on a commercial telecommunication platform (the EDRS-C satellite). This proposal is unsuccessful for the moment. We watch out for other such opportunities to embark a mission on platform of opportunity
Science studies are ongoing, for instance on the diurnal cycle of optical properties

4. Science focus of the OCAPI mission
Encompasses open ocean and the coastal environment.
Includes:
The diurnal cycle of ocean optical properties, and its relation to physics and biogeochemistry
Biological-physical coupling at (sub)meso scale
Data assimilation into coupled biological-physical models
Improved marine biogeochemistry and ecosystem models
Dynamics of coastal environments and ecosystems
Sediment transport
Aerosol transport
Land – ocean interactions
Operational services in the coastal zones

5. Coastal only versus “global” ?
Remember the « Coastal Zone Color Scanner » (CZCS)
From Acker et al. L&O bulletin, 2013:
“Dick Barber noted that the first images from the CZCS demolished the commonly held misperception of alongshore continuity–“jets” and “squirts” and variability in current meandering indicated that the ocean was a much more complex place than point sampling had led many to believe.”
The step we’ll make with the advent of geostationary observations will likely be as important as the one we did after the CZCS launch
That’s why we think we should not only observe coastal areas

6. OCAPI: overarching objectives
1. Within a range of conditions of observation (solar & view angles, clouds, …), the diel dynamics of the ocean will be accessible. The 1st objective in this case is to study the ocean ecosystem functioning at the diurnal scale. The diurnal cycle of photosynthesis / respiration .. generates a diel cycle in the particulate pool, hence of the optical properties and of the recorded signal
2. In the above conditions and also when a little less observations will be available over a day, the 2nd group of objectives is related to observation & understanding of rapidly evolving phenomena (river outflows, aerosol plumes, phytoplankton blooms, (sub)meso-scale features ..). These phenomena are not necessarily linked to the biological functioning, and rather under the influence of physical forcings
3. When the conditions of observation do not allow the diel changes to be sampled, there is still the capability to dramatically improve coverage, with at least one observation of good quality per day in many areas. This is of tremendous importance for all operational uses, from data assimilation into coupled biological-physical 3D models to services in coastal zones

7. Diurnal cycle of optical properties
Can go from Dcp to DPOC.
After integration over the productive zone, one gets either NCP or NPP
From Gernez, Antoine and Huot, 2011, L&O, 56, 17-36

8. Average diurnal variability at BOUSSOLE

9. Sediment transport in coastal zones :
An example using SEVIRI on MSG
from: K. Ruddick & G. Neukermans, MUUM

10. COVERAGE
Mean(left) and max (right) number of daily available observations, for two LEOs complemented by OCAPI in March, June and December (top to bottom).
The observation area is here constrained by the MSG observation area (from which realistic cloud coverage was taken)

11. Coupled physical-biological models
Data assimilation in
Coupled physical-biological models
Current limitations:
Spatial resolution, data frequency for assimilation, inadaptation of assimilation schemes for incorporation of biogeochemistry
Needed evolutions:
○ Improving ocean-atmosphere coupling (air-sea interface)
○ Extension to the coastal domain
○ Adaptation of assimilation schemes to incorporate biogeochemistry
Satellite
Nemo-Lobster
R&D: NATL4 + LOBSTER
Demo: ORCA025 + PISCES
Source: P. Brasseur CNRS-LEGI, Grenoble

12. Operational services in the coastal zones
Such services exist as demonstration studies.
Truly operational services are rare, however, because the availability of LEO observations is insufficient
 Very high potential of the GEO observations
HABs
Front detection
Images courtesy, ACRI-st
The quality / reliability of these services is, again, much dependent on the significant improvements we’ll be able to bring to ocean color interpretation in optically-complex waters

13. Context Constrained by the ESA EE-8 call (2009-2010):
Ceiling cost was ~100 M€ industrial cost for the space segment and mission specific ground segment (i.e. excluding launcher, operations, generic ground segment, level 2 processor and ESA internal costs) at 2009 economic conditions.
We had to cover all mission objectives with 1 instrument only
That’s why we don’t have, for instance, SWIR bands (would mean a second instrument) although we recognize their usefulness
CNES alone cannot afford such a mission. International cooperation is mandatory (ongoing…)

14. Products & associated requirements (1/2)
Product types S: “standard” I: “intermediate” R:”research”

15. Products & associated requirements (2/2)

16. Band set SNRs are for a 250m resolution
Grey cells indicate continuity /
compatibility with MERIS and OLCI
Last column is priority for the mission

17. Other requirements (1/2)

18. Other requirements (2/2)

19. OCAPI: preliminary mission elements
Observation of all ocean areas (open + coastal) on the Earth disk at a ~1h temporal resolution from a geostationary orbit (slightly inclined geosynchronous have been evaluated also)
Step & stare concept
250m SSP
18 bands from 395 to 1020 nm (OLCI compatibility)
High SNR required for ocean colour 1-km resolution)
On-board calibration devices (solar diffusers)
Other characteristics typical of what’s required for ocean colour (see IOCCG#13)

20. Orbit

21. International context
One mission has been launched in 2010: COMS-1 / GOCI from KARI/KORDI
NASA includes GEO observations as one of its priorities, in the “Advanced plan for NASA’s Ocean Biology and Biogeochemistry Research, NASA, 2007”, and has the GeoCAPE mission proposal under investigation
ESA : Geo OCULUS (R&D stage). Very high resolution for risk assessment.
ISRO also considers the GEO orbit for future Earth observations missions (GEO-HR mission for risk monitoring / assessment)
CNES is investigating the OCAPI mission proposal
IOCCG has set up a working group on ocean color observations from the GEO orbit. This group has prepared an IOCCG monograph (report), to be published by mid 2012.
The EC Implementation Group of the Marine Core Service : “GMES should allow for research and technological developments. In particular, the possibility of embarking new instruments with the potential to meet GMES needs should be considered. Wide Swath altimetry and geostationary ocean color are the two most important new technology development that will benefit the GMES MCS in the long run.”

22. Soon available

23. Areas where we need more work
Atmospheric corrections (open ocean and coastal zones)
Generic difficulties of atmospheric correction of ocean color observation, plus some specific aspects (e.g., backscattering geometry)
Diurnal cycles of IOPs and AOPs
Radiative transfer for low solar elevations and grazing observation angles
Calibration / validation (including vicarious calibration)
Cloud “masks”
Exploitation of the temporal / spatial coherency of the oceanic structures under observation by a GEO ocean color sensor …

24. Ongoing studies
Diurnal IOPs  AOPs  satellite signal  inversion (based on in field measurements at BOUSSOLE) (D. Antoine, LOV)
As above, but under the form of a “scene generator” (A. Roman, ISITV, Toulon)
Exploitation of GOCI data for analyzing sediment transport in coastal areas (D. Doxaran, LOV)
Assimilation of high frequency data into coupled BGC models (P. Brasseur, LGGE, Grenoble)
Exploiting high-res (spatial & temporal) numerical simulations of phytoplankton distribution (M. Lévy, LOCEAN, Paris)
Diurnal variability of fluorescence (M. Babin, Takuvik, Canada)
MTF study starting from HICO data
Extension of mission goals (aerosols, clouds, land vegetation)
Cal/val studies

25. (
Thank you
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