Abstract. Long-term measurements by the AERONET program of spectral aerosol optical depth, precipitable water, and derived Angstrom exponent were analyzed and compiled into an aerosol optical properties climatology. Quality assured monthly means are presented and described for 9 primary sites and 21 additional multiyear sites with distinct aerosol regimes representing tropical biomass burning, boreal forests, midlatitude humid climates, midlatitude dry climates, oceanic sites, desert sites, and background sites. Seasonal trends for each of these nine sites are discussed and climatic averages presented. IntroductionMan is altering the aerosol environment through land cover change, combustion of fossil fuels, and the introduction of particulate and gas species to the atmosphere. Each perturbation has some impact on the local aerosol environment. How much aerosol man is contributing to the atmosphere is not •øUniversity of New Mexico, Albuquerque, New Mexico.•qnstituto de Pesquisas Espaciais, Sao Jose dos Campos, San Paolo, Brazil.•2National Oceanic and Atmospheric Administration, Silver Spring, Maryland.•3Scripps Institute of Oceanography, La Jolla, California.•4Department of Applied Science, Brookhaven National Laboratory, Upton, New York.•SNow at Naval Research Laboratory, Washington, D.C.•6Ben Gurion University of the Negev, Sede Boker, Israel.•7CARTEL, Universit6 de Sherbrooke, Sherbrooke, Quebec, Canada.•sSAIC-GSC, Beltsville, Maryland, and NASA GSFC, Greenbelt, The simplest, and, in principle, the most accurate and easy to maintain monitoring systems are ground based. Aerosol optical depth is the single most comprehensive variable to remotely assess the aerosol burden in the atmosphere from groundbased instruments. This variable is used in local investigations to characterize aerosols, assess atmospheric pollution, and make atmospheric corrections to satellite remotely sensed data. It is for these reasons that a record of aerosol optical depth spanning most of the twentieth century has been measured from Sun photometers. The vast majority are site specific, short-term investigations with little relevance for seasonal, annual, or long-term trend analysis, however a few multiyear spatial studies have contributed to our knowledge and experience (Table 1). The following section reviews these investigations, past and present, which significantly addressed long-term measurements over widely distributed locations or provided a significant contribution that allowed development of a network for long-term photometric aerosol observations. The earliest systematic results come from the Smithsonian Institution solar observatories. Roosen e! al. [1973] computed extinction coefficients from 13 widely separated sites during the first half of the twentieth century using spectrobolometer observations by the Astrophysical Observatory of the Smithsonian Institution. They concluded the aerosol burden did not 12,067
A semianalytical radiance model is developed which predicts the upwelled spectral radiance at the sea surface as a function of the phytoplankton pigment concentration for Morel Case 1 waters. The model is in good agreement with experimental measurements carried out in waters which were not included in the data base used to derive it. It suggests that the observed variability in the radiance is due to variations in the backscattering of plankton and the associated detrital material. The model is extended to include other material in the water, such as dissolved organic material, referred to as yellow substances, and detached coccoliths from coccolithophorids, e.g., Emiliana huxleyi. Potential applications include an improved bio‐optical algorithm for the retrieval of pigment concentrations from satellite imagery in the presence of interference from detached coccoliths and an improved atmospheric correction for satellite imagery. The model also serves to identify and to interpret deviations from Case 1 waters.
The processing algorithms used for relating the apparent color of the ocean observed with the Coastal-Zone Color Scanner on Nimbus-7 to the concentration of phytoplankton pigments (principally the pigment responsible for photosynthesis, chlorophyll a) are developed and discussed in detail. These algorithms are applied to the shelf and slope waters of the Middle Atlantic Bight and also to Sargasso Sea waters. In all, four images are examined, and the resulting pigment concentrations are compared to continuous measurements made along ship tracks. The results suggest that over the 0.08-1.5-mg/m3 range the error in the retrieved pigment concentration is of the order of 30-40% for a variety of atmospheric turbidities. In three direct comparisons between ship-measured and satellite-retrieved values of the water-leaving radiance the atmospheric correction algorithm retrieved the water-leaving radiance with an average error of approximately 10%. This atmospheric correction algorithm does not require any surface measurements for its application.
The Moderate Resolution Imaging Spectroradiometer (MODIS) will add a significant new capability for investigating the 70% of the earth's surface that is covered by oceans, in addition to contributing to the continuation of a decadal scale time series necessary for climate change assessment in the oceans. Sensor capabilities of particular importance for improving the accuracy of ocean products include high SNR and high stability for narrower spectral bands, improved onboard radiometric calibration and stability monitoring, and improved science data product algorithms. Spectral bands for resolving solar-stimulated chlorophyll fluorescence and a split window in the 4-m region for SST will result in important new global ocean science products for biology and physics. MODIS will return full global data at 1-km resolution. The complete suite of Levels 2 and 3 ocean products is reviewed, and many areas where MODIS data are expected to make significant, new contributions to the enhanced understanding of the oceans' role in understanding climate change are discussed. In providing a highly complementary and consistent set of observations of terrestrial, atmospheric, and ocean observations, MODIS data will provide important new information on the interactions between earth's major components. I. INTRODUCTION U SE OF satellite image data to investigate oceanic processes has become an essential component of oceanographic research and monitoring. Data from the Coastal Zone Color Scanner (CZCS) provided the first demonstration of the ability to observe the abundance and distribution of phyto-Manuscript
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