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3 June 2013 Analyzing radiometric requirements for diurnal observations of coastal/oceanic waters from geostationary orbits
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Over the decades, ocean color imaging sensors placed in Low Earth Orbits (LEO) have enabled nearly daily measurements of ocean water properties. Such observations, however, are restricted by cloud/atmospheric conditions. More importantly, such systems could not provide sufficient number of measurements to study the diurnal dynamics of coastal/oceanic ecosystems. One way to surmount such limitations is to leverage geo-stationary orbits to significantly improve temporal observations over such dynamical coastal/oceanic environments. In this study, it is desired to examine whether 50% changes in chlorophyll-a concentration (< 1.5 ug⁄l) on a semi-diurnal basis are above the noise level. To do so, the top-of-atmosphere radiance (Lt) is modeled for the planned GEO-CAPE mission intended for monitoring coastal ecosystem and river plumes. The input to the simulations includes diurnal remote sensing reflectances (Rrs), which are propagated through a moderately clear atmospheric conditions using a radiative transfer code. The simulations are carried out for two footprints to investigate two extremely different sun-sensor geometries. From these simulations, the temporal change in spectral reflectances between the hours relative to an average noise is examined. Based on the preliminary results, it was found that while the signal change is, on average, 13x the average noise for near-nadir footprints, the change in signal, on average, is only 1.5x the average noise level for near-edge footprints at top of the atmosphere. Such a contrast suggests difficulties in retrieving diurnal variability for locations near the edge of the field of regard (FOR).
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Nima Pahlevan, Zhongping Lee, Chuanmin Hu, and John R. Schott "Analyzing radiometric requirements for diurnal observations of coastal/oceanic waters from geostationary orbits", Proc. SPIE 8724, Ocean Sensing and Monitoring V, 87240K (3 June 2013);

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