Ian Barton (ian.barton@ml.csiro.au), Commonwealth Scientific and Industrial Research Organization (CSIRO), Australia
The nfrared and Visible Optical Sensors (IVOS) sub-group of the Committee on Earth Observations Satellites (CEOS) Working Group on Calibration and Validation (WGCV) held a special meeting in Lanham, MD May 1, 1995, on international activities related to ocean color sensors. The meeting was aimed at exchanging information on future ocean color sensors and developing closer collaboration in the calibration/validation (cal/val) activities of the various national space agencies and institutes.
The IVOS chairman, Ian Barton, welcomed the representatives from the international ocean color community and gave a brief description of CEOS, its structure and charter, and how the ocean color community could benefit from participation in CEOS activities. Several invited experts from different agencies then described the cal/val activities of their national programs.
A general overview of ocean color physics was presented by Howard Gordon of the University of Miami. Correcting ocean color radiances for the effect of the atmosphere was described as one of the major sources of error. The techniques used for the Coastal Zone Color Scanner (CZCS) were outlined and these were extended to SeaWiFS and MODIS, where there are more bands available and a better correction is possible. A range of aerosol models was used in the correction procedures, and simulations had been carried out for different sun angles, view angles, and aerosol loadings.
Chuck McClain (Goddard Space Flight Center) presented details of NASA's plans for SeaWiFS calibration. An update on the status of SeaWiFS and the Seastar spacecraft was given: the hardware integration of SeaWiFs is now complete and the launch manifest showed a launch as early as September, but February 1996 was a more-likely launch date. (NOTE: Since the Pegasus XL failure in June 1995, the SeaWiFS launch remains uncertain.) Data from SeaWiFS should be available about 6 weeks after launch. The cal/val program would concentrate on algorithm development, calibration verification, and derived-products validation. The calibration/verification would rely on the Marine Optical Buoy (MOBY) to be deployed off Hawaii and the use of high-altitude lakes. On-board calibration would use the sun and the moon as standard sources.
A report on a recent ocean color meeting held in Miami was presented by Wayne Esaias, NASA Goddard. He reported that there was a decision not to fly an ocean color sensor on Landsat-7. The Miami meeting had been more of a fact-finding meeting where the need for a 3-day, international cal/val meeting coupled with MODIS and SeaWiFS plans was stated. Some form of international infrastructure was required that would coordinate at-sea activities for the different ocean color missions. (NOTE: This now seems to be under way‹see later discussion on international collaboration.)
The Japanese National Space Development Agency's (NASDA) plans for Ocean Color and Temperature Scanner (OCTS) calibration were outlined by Masanobu Shimada of NASDA. A delay of six months was now expected in the ADEOS launch date (launch date is now August 1996). The ADEOS platform was described and details of the cal/val goals for both the thermal and visible channels of the OCTS instrument were presented. The main post-launch validation would be undertaken using an optical buoy moored on Yamato Bank in the Japan Sea. Currently, a network of sites is logging the aerosol distribution around the Japanese islands. Mutsu Bay, in the north of Japan, is also being used as a validation site for the thermal channels. Several instrumented buoys have been deployed in this large, partly land-locked, bay. OCTS also has an on-board calibration capability using an internal lamp and the sun as alternative sources.
Giuseppe Zibordi of the European Joint Research Center at Ispra, Italy, presented European plans for ocean color validation. Current activities center on two major campaigns, but a proposal to the European Commission's Marine Science and Technology (MAST) Program is seeking funding to operate a total of four European sites. The first program described was CoASTS (Coastal Atmosphere and Sea Time Series Project), which involves the deployment of an optical buoy in the northern Adriatic Sea near Venice. The data collected would be used to develop atmospheric corrections and bio-optical algorithms for ocean color data from OCTS, SeaWiFS, and Polarization and Directionality of Reflectances (POLDER). The second campaign was PlyMBody (the Plymouth Marine Optical Buoy), which would be moored off the south coast of England. This program would include weekly collection of in situ water samples. The MAST proposal (with the acronym of PICASSO) included these two sites plus two more‹one in the Nordic Sea and the second in the North Sea.
Lasse Petterssen (Nansen Environmental Research Centre, Norway) and Gerald Moore (Plymouth Marine Labs, UK) also presented some further details of PICASSO plans in the Nordic Sea and southern UK waters respectively.
Robert Frouin of NASA Headquarters presented details of a proposal for the formation of an international ocean color working group. The proposal suggested that the international working group would present their recommendations to CEOS. In particular, the CEOS WGCV would review techniques and standards for calibration of the ocean color sensors and validation of the geophysical parameters. The proposal also suggested that a special CEOS standing subgroup on ocean color could be established to deal with ocean color issues. This subgroup would report to the two working groups of CEOS (WG on Data [WGD], and WGCV).
These proposals were discussed at length, and it was felt that the endorsement of cal/val procedures was outside the charter of CEOS WGCV. Also the formation of a specific subgroup on ocean color would not be necessary as the current working groups of CEOS encompass the interests of the ocean color community. Data management and data exchange issues were discussed briefly, and it was decided that these matters should be brought to the attention of the CEOS WGD.
The funding of cal/val campaigns was briefly discussed, but it was agreed that while each agency should go ahead and fund its own campaigns, they should also be aware of the great mutual benefits to be gained from close collaboration in international activities.
In summary, the outcomes of the ocean color meeting were: