The NASA VIIRS Ocean Science Team (VOST) has the task of evaluating Suomi NPP VIIRS ocean color data
for the continuity of the NASA ocean color climate data records. The generation of science quality ocean color
data products requires an instrument calibration that is stable over time. Since the VIIRS NIR Degradation
Anomaly directly impacts the bands used for atmospheric correction of the ocean color data (Bands M6 and
M7), the VOST has adapted the VIIRS on-orbit calibration approach to meet the ocean science requirements.
The solar diffuser calibration time series and the solar diffuser stability monitor time series have been used to
derive changes in the instrument response and diffuser reflectance over time for bands M1–M11. The lunar
calibration observations have been used, in cooperation with the USGS ROLO Program, to derive changes in
the instrument response over time for these same bands. In addition, the solar diffuser data have been used to
develop detector-dependent striping and mirror side-dependent banding corrections for the ocean color data. An
ocean surface reflectance model has been used to perform a preliminary vicarious calibration of the VIIRS ocean
color data products. These on-orbit calibration techniques have allowed the VOST to produce an optimum timedependent
radiometric calibration that is currently being used by the NASA Ocean PEATE for its VIIRS ocean
color data quality evaluations. This paper provides an assessment of the current VIIRS radiometric calibration
for the ocean color data products and discusses the path forward for improving the quality of the calibration.
Following the launch of the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polarorbiting
Partnership (NPP) spacecraft, the NASA NPP VIIRS Ocean Science Team (VOST) began an evaluation of
ocean color data products to determine whether they could continue the existing NASA ocean color climate data record
(CDR). The VOST developed an independent evaluation product based on NASA algorithms with a reprocessing
capability. Here we present a preliminary assessment of both the operational ocean color data products and the NASA
evaluation data products regarding their applicability to NASA science objectives.
For several years, the NASA/Goddard Space Flight Center (GSFC) NPP VIIRS Ocean Science Team (VOST) provided
substantial scientific input to the NPP project regarding the use of Visible Infrared Imaging Radiometer Suite (VIIRS) to
create science quality ocean color data products. This work has culminated into an assessment of the NPP project and
the VIIRS instrument's capability to produce science quality Ocean Color data products. The VOST concluded that
many characteristics were similar to earlier instruments, including SeaWiFS or MODIS Aqua. Though instrument
performance and calibration risks do exist, it was concluded that programmatic and algorithm issues dominate concerns.
The VIIRS Ocean Science Team (VOST) has been developing an Ocean Data Simulator to create realistic
VIIRS SDR datasets based on MODIS water-leaving radiances. The simulator is helping to assess instrument
performance and scientific processing algorithms. Several changes were made in the last two years
to complete the simulator and broaden its usefulness. The simulator is now fully functional and includes
all sensor characteristics measured during prelaunch testing, including electronic and optical crosstalk influences,
polarization sensitivity, and relative spectral response. Also included is the simulation of cloud and
land radiances to make more realistic data sets and to understand their important influence on nearby ocean
color data. The atmospheric tables used in the processing, including aerosol and Rayleigh reflectance coefficients,
have been modeled using VIIRS relative spectral responses. The capabilities of the simulator were
expanded to work in an unaggregated sample mode and to produce scans with additional samples beyond the
standard scan. These features improve the capability to realistically add artifacts which act upon individual
instrument samples prior to aggregation and which may originate from beyond the actual scan boundaries.
The simulator was expanded to simulate all 16 M-bands and the EDR processing was improved to use these
bands to make an SST product. The simulator is being used to generate global VIIRS data from and in
parallel with the MODIS Aqua data stream. Studies have been conducted using the simulator to investigate
the impact of instrument artifacts. This paper discusses the simulator improvements and results from the
artifact impact studies.
One of the roles of the VIIRS Ocean Science Team (VOST) is to assess the performance of the instrument and scientific processing software that generates ocean color parameters such as normalized water-leaving radiances and chlorophyll. A VIIRS data simulator is being developed to help aid in this work. The simulator will create a sufficient set of simulated Sensor Data Records (SDR) so that the ocean component of the VIIRS processing system can be tested. It will also have the ability to study the impact of instrument artifacts on the derived parameter quality. The simulator will use existing resources available to generate the geolocation information and to transform calibrated radiances to geophysical parameters and visa-versa. In addition, the simulator will be able to introduce land features, cloud fields, and expected VIIRS instrument artifacts. The design of the simulator and its progress will be presented.
SeaWiFS was launched onboard the OrbView-2 satellite on 1 August 1997. On 4 September 1997, the day of first light for the instrument, SeaWiFS global images were processed automatically using the instrument’s prelaunch calibration and distributed on the World Wide Web. With the first reprocessing of SeaWiFS data in January 1998, the radiometric calibration coefficients for the SeaWiFS visible bands were linked to the water-leaving radiances measured by the Marine Optical Buoy (MOBY). In addition, the calibration coefficient for the 765 nm SeaWiFS infrared band was adjusted to give values consistent with those for an atmosphere with the maritime type of aerosol found in the vicinity of the MOBY buoy. Since the infrared bands were designed to allow the inference of aerosol type for the SeaWiFS atmospheric correction algorithm, this vicarious calibration forces their agreement with the conditions for a known aerosol type. With the second reprocessing in August 1998, temporal changes in the radiometric sensitivities of the SeaWiFS near infrared bands were corrected using lunar and solar measurements. The third SeaWiFS reprocessing in May 2000 introduced small time dependent calibration corrections to some visible bands. Future SeaWiFS reprocessings are scheduled to occur on an annual to biennial basis. With the third reprocessing, the emphasis of the instrument calibration program has shifted to the assessment of the surface truth comparisons used by SeaWiFS, principally those with MOBY.