Wayne E. Esaias

Ocean color: Availability of the global data set

The National Aeronautics and Space Administration/ Goddard Space Flight Centers Nimbus Project Office, in collaboration with the NASA/GSFC Space Data and Computing Division, the NASA/GSFC Laboratory for Oceans and the University of Miami/Rosenstiel School of Marine and Atmospheric Science, have undertaken to process all data acquired by the Coastal Zone Color Scanner (CZCS) to Earth-gridded geophysical values and to provide ready access to data products [Esaias et al., 1986]. An end-to-end data system utilizing recent advances in data base management and both digital and analog optical disc storage technologies has been developed to handle the processing, analysis, quality control, archiving and distribution of this data set. A more complete description of this system, which has been fully operational for the past 2 years, is in preparation. The entire Level-1 data set (see Tables 1, 2) has been copied from magnetic tape to digital optical disc, and all data from the first 32 months (50% of the total scenes acquired, and covering the period November 1978 through June 1981) have been processed to Levels 2 and 3 and are now available for distribution. The remainder of the data set should be completed and released by fall 1989.

Annual cycles of phytoplankton chlorophyll concentrations in the global ocean: A satellite view

Conceptual and mathematical models show that annual cycles of phytoplankton biomass are different within different regions of the ocean. The purpose of this manuscript is to use coastal zone color scanner chlorophyll imagery (CZCS-Ch1) to determine annual cycles in phytoplankton chlorophyll (biomass) averaged over very large areas of the global ocean. A possible result is that large-scale averaging of CZCS-Ch1 will yield no interpretable signals because of spatial variability in annual cycles at scales much smaller than our averaging scale. Alternatively, if our analyses show regular and persistent global patterns, then our results will jprovide a basin-scale overview of phytoplankton biomass seasonally for comparison with model results or with other large-scale oceanographic measurements. Our results show that monthly mean CZCS-Ch1 imagery (and using in situ concentrations for winter at latitudes poleward of 40 deg) resolves important differences in annual phytoplankton chlorophyll cycles for different ocean basins and latitude belts. As predicted by simple models of plankton dynamics, our results show: (1) global subtropical waters have circa 2X higher CZCS-Ch1 concentrations in winter than in summer and (2) subpolar waters in the northern hemisphere (NH) have mean monthly CZCS-Ch1 concentrations during May and June that are manyfold higher than in winter, particularly in the North Atlantic. Our results also show: (1) Northern Indian Ocean is the major subtropical anomaly, (2) subpolar waters in the SH do not show differences between spring maxima and winter minima as large as those in the subpolar NH and (3) larger ocean area in the SH is compensated by higher mean annual CZCS-Ch1 concentrations in the NH, so that annual hemispherical integrals (mean annual concentrations multiplied by ocean areas) are very similar. The simple patterns we report imply that mean annual cycles in phytoplankton biomass averaged over very large areas of the global ocean are largely explainable by very simple mathematical models such as those presented several decades ago by Cushing, Riley, Steele, and others.

The remote sensing of ocean primary productivity: Use of a new data compilation to test satellite algorithms

We tested global pigment and primary productivity algorithms based on a new data compilation of over 12,000 stations occupied mostly in the northern hemisphere, from the late 1950s to 1988. The results showed high variability of the fraction of total pigment contributed by chlorophyll a (ρ), which is required for subsequent predictions of primary productivity. Two models, which predict pigment concentration normalized to attenuation length or euphotic depth, were checked against 2,800 vertical profiles of pigments (chlorophyll a, phaeopigment and total pigment). Phaeopigments consistently showed maxima at about one optical depth below the chlorophyll maxima. We also checked the global Coastal Zone Color Scanner (CZCS; daily 20km resolution) archive for data coincident with the sea truth data. A regression of satellite-derived pigment versus ship-derived pigment had a coefficient of determination (r2) of 0.40 (n=731 stations). The satellite underestimated the true pigment concentration in mesotrophic and oligotrophic waters ( 1 mg pigment m-3). The error in the satellite estimate showed no trends with time between 1978 and 1985. In general the variability of the satellite retrievals increased with pigment concentration. Several productivity algorithms were tested which utilize information on the photoadaptive parameters, biomass and optical parameters for predicting integral production. The most reliable algorithm which explained 67% of the variance in integral production for 1676 stations suggested that future success in deriving primary productivity from remotely sensed data will rely on accurate retrievals of “living” biomass from satellite data, as well as the prediction of at least one photoadaptive parameter such as maximum photosynthesis.

Surface-ocean color and deep-ocean carbon flux: how close a connection?

Abstract Seven years of simultaneous, quasi-continuous data collected by the Nimbus-7 Coastal Zone Color Scanner and by a deep-ocean sediment trap in the Sargasso Sea allow the derivation of empirical relationships between remotely sensed ocean color and the sinking of particulate carbon into the deep sea. In agreement with earlier observations, the results indicate a 1.5-month lag between surface-ocean events observed by the satellite and arrival of a record of those events, carried by sinking particles, at a depth of 3200 m. In addition, the results suggest that the sea-surface area most influential on particle-flux characteristics recorded by the sediment trap in the Sargasso Sea lies to the northeast of the traps mooring site. The results point towards possible ways of quantifying the role of marine biota in the regulation of atmospheric carbon dioxide through use of satellite observations.

An overview of the SeaWiFS Project

It is apparent to the oceanographic community that due to the dynamic nature of the worlds oceans and climate and the importance of the oceans role in global change, a follow-on sensor to the Coastal Zone Color Scanner (CZCS) should be flown [Ocean Color Science Working Group, 1982; Joint EOSAT/NASA SeaWiFS Working Group, 1987]. Acquisition of ocean-color data from space in the early 1990s is a high-priority goal that has been recognized in National Academy of Sciences reports. NASAs Office of Space Science and Applications (OSSA) and Goddard Space Flight Center (GSFC) have designated the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) Project to develop and operate an ocean-color research data system.

Multiplafform sampling (ship, aircraft, and satellite) of a Gulf Stream warm core ring.

The purpose of this paper is to demonstrate the ability to meet the need to measure distributions of physical and biological properties of the ocean over large areas synoptically and over long time periods by means of remote sensing utilizing contemporaneous buoy, ship, aircraft, and satellite (i.e., multiplatform) sampling strategies. A mapping of sea surface temperature and chlorophyll fields in a Gulf Stream warm core ring using the multiplatform approach is described. Sampling capabilities of each sensing system are discussed as background for the data collected by means of these three dissimilar methods. Commensurate space/time sample sets from each sensing system are compared, and their relative accuracies in space and time are determined. The three-dimensional composite maps derived from the data set provide a synoptic perspective unobtainable from single platforms alone.

Coverage opportunities for global ocean color in a multimission era

The international community, recognizing the importance of global ocean color observations in the global carbon cycle, has proposed or flown six global ocean color missions over the next decade: the Ocean Color and Temperature Sensor (OCTS), Sea-viewing Wide Field-of-view Sensor (SeaWiFs), Moderate Resolution Imaging Spectrometer-AM (MODIS-AM), Medium Resolution Imaging Spectrometer (MERIS), Global Imager (GLI), and MODIS-PM. Each of these missions contains the spectral band complement considered necessary to derive oceanic pigment concentrations (i.e., phytoplankton abundance). This paper assesses whether assembling and merging data from these missions can improve ocean coverage, since clouds and Sun glint prevent any single satellite from observing more than about 15% of the ocean surface in a single day, and whether new information about diel cycles of phytoplankton abundance is possible. Extensive numerical analysis, given the orbit and sensor characteristics of each mission, showed that merging data form three satellites can produce better ocean coverage in less time. Data from three satellites can improve coverage by 58% for a single day, including the obscuring effects of clouds and sun glint. Thus, observation of approximately 25% of the ocean can be provided, instead of only about 15-16% from a single satellite. After four days, approximately 62% of the ocean surface was observed, an increase from 43% observed by a single satellite. The addition of more satellites produced diminishing returns. Since the proposed missions have different orbits, the view the same location of the ocean at different times of day. This leads to the possibility of using data from the set of six missions to help understand diel phytoplankton dynamics.

Validation of Terra-MODIS phytoplankton chlorophyll fluorescence line height. I. Initial airborne lidar results.

The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra spacecraft contains spectral bands that allow retrieval of solar-induced phytoplankton chlorophyll fluorescence emission radiance. Concurrent airborne laser-induced (and water-Raman normalized) phytoplankton chlorophyll fluorescence data is used to successfully validate the MODIS chlorophyll fluorescence line height (FLH) retrievals within Gulf Stream, continental slope, shelf, and coastal waters of the Middle Atlantic Bight portion of the western North Atlantic Ocean for 11 March 2002. Over the entire approximately 480-km flight line a correlation coefficient of r2 = 0.85 results from regression of the airborne laser data against the MODIS FLH. It is also shown that the MODIS FLH product is not influenced by blue-absorbing chromophoric dissolved organic matter absorption. These regional results strongly suggest that the FLH methodology is equally valid within similar oceanic provinces of global oceans.

Satellite detection of phytoplankton export from the mid-Atlantic bight during the 1979 spring bloom

Abstract Analysis of CZCS imagery confirms shipboard and in situ moored fluorometer observations of resuspension of near-bottom chlorophyll within surface waters (1–10 m) by northwesterly wind events in the mid-Atlantic Bight. As much as 8–16 μg Chl l −1 are found during these wind events from March to May, with a seasonal increase of algal biomass until onset of stratification of the water column. Rapid sinking or downwelling apparently occurs after subsequent wind events, however, such that the predominant surface chlorophyll patterns is ≈0.5–1.5 μg l −1 over the continental shelf during most of the spring bloom. Perhaps half of the chlorophyll increase observed by satellite during a wind resuspension event represents in situ production during that 4–5 day interval, with the remainder attributed to accumulation of algal biomass previously produced and temporarily stored within near-bottom water. Present calculations suggest that at least 10% of the primary production of the spring bloom may be exported as ungrazed phytoplankton carbon from mid-Atlantic shelf waters to those of the continental slope.

Development of a consistent multi-sensor global ocean colour time series

The advent of a new generation of space-borne ocean colour sensors brings the prospect of global ocean measurements for decades into the future. These measurements will provide the basis for characterizing variability in the structure of the oceans phytoplanktonic communities and the response of those communities to climatic change. In addition, the measurements will allow development of the scientific basis necessary to manage the sustainable resources of marine ecosystems. These studies will require a merged, long-term, multi-satellite ocean colour time series extending beyond the operational lifetimes of individual instruments. The Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Project has been tasked to develop the tools required to create this time series. Among these tools are a comprehensive in situ (field collected) bio-optical dataset for validating ocean optics algorithms and associated models of oceanic properties; a programme to evaluate different atmospheric correction techniques; a programme to link the calibrations of individual satellite instruments; a programme to develop consistent calibration and validation datasets for satellite instruments; and a set of alternate methods to combine ocean colour measurements from different sources into a single time series. We report on the progress of this development work by the SIMBIOS Project.