Calibration of SeaWiFS I Direct techniques

Abstract

We present an overview of the calibration of the Sea-viewing Wide Field-of View Sensor (SeaWiFS) from its performance verification at the manufacturer's facility to the completion of its third year of on-orbit measurements. These calibration procedures have three principal parts: a prelaunch radiometric calibration that is traceable to the National Institute of Standards and Technology; the Transfer-to-Orbit Experiment, a set of measurements that determine changes in the instrument's calibration from its manufacture to the start of on-orbit operations; and measurements of the sun and the moon to determine radiometric changes on orbit. To our knowledge, SeaWiFS is the only instrument that uses routine lunar measurements to determine changes in its radiometric sensitivity. On the basis of these methods, the overall uncertainty in the SeaWiFS top-of-the-atmosphere radiances is estimated to be 4-5%. We also show the results of comparison campaigns with aircraft- and ground-based measurements, plus the results of an experiment, called the Southern Ocean Band 8 Gain Study. These results are used to check the calibration of the SeaWiFS bands. To date, they have not been used to change the instrument's prelaunch calibration coefficients. In addition to these procedures, SeaWiFS is a vicariously calibrated instrument for ocean-color measurements. In the vicarious calibration of the SeaWiFS visible bands, the calibration coefficients are modified to force agreement with surface truth measurements from the Marine Optical Buoy, which is moored off the Hawaiian Island of Lanai. This vicarious calibration is described in a companion paper.

PARASOL in-flight calibration and performance

“…Regarding theoretical error budgets for each method [4,18,21,23,31], effective behaviors of results (bias and root mean square error), spectral shapes of the targets leading to potential errors into the model, and finally the temporal sampling, the calibration over white convective clouds was preferred as the best compromise. In addition, this reference is physically very close to the white moon diffuser that provided essential results for SeaWiFs [29]. Fig.…”

“…In all cases, difficulties are encountered: aging of the lamp or diffuser themselves may occur requiring a complementary on-board monitoring through diffuser duplication for example [27,28]. Complementarily, the moon is used as a natural and external diffuser to monitor SeaWiFS long-term trends using acquisitions for specific lunar phases [29]. Alternative methods using natural targets from the Earth-atmosphere system were developed: over desert sites [23,24], viewing sunglint [18] or over Antarctica [30].…”

Seasonal and interannual variability of ocean color and composition of phytoplankton communities in the North Atlantic, equatorial Pacific and South Pacific

“…This global dataset is not affected by cruise or method biases, unlike the in situ data sets. Furthermore, careful calibration of this instrument (Barnes et al, 2001;Eplee et al, 2001) may make it possible to detect possible long-term evolution of chlorophyll a concentration with time, a point of interest in the context of climate change.…”

Applying spaceborne reflectivity measurements for calculation of the solar ultraviolet radiation at ground level

“…Daily sums of UV irradiance using ISCCP data indicate a similarly good performance with respect to the standard deviations . Herman et al (2009) made a long-term analysis of the Lambertian Equivalent Reflection (LER) data set on a global scale, also including data from the Sea-viewing Wide Field-of-view Sensor (Barnes et al, 2001). Diurnal variations were investigated showing that generally abovesea LER peaks in the morning, in contrast to LER over land, which peaks in the afternoon (Labow et al, 2011).…”