Franz, Bryan: NASA Goddard Space Flight Center (Project Lead)
Project Funding:
2014 - 2017
NRA: 2013 NASA: Suomi National Polar-orbiting Partnership (NPP) Science Team and Science Investigator-led Processing Systems for Earth System Data Records From Suomi NPP
Funded by NASA
Abstract:
This proposal will seek to develop, validate, and maintain a time-series of ocean color products from NPP/VIIRS that is consistent with the current NASA global time-series established with SeaWiFS and MODIS. The product suite will include water-leaving remote sensing reflectance (Rrs) at each VIIRS visible spectral band, chlorophyll concentration (Chl), marine diffuse attenuation at 490nm (Kd490), the inherent optical properties (IOPs) of total and component absorption and scattering. The proposing team are all members of the NASA Ocean Biology Processing Group (OBPG), which is currently responsible for maintaining the quality and consistency of the SeaWiFS and MODIS ocean color products and developing many of the algorithms employed.
Rrs is the fundamental product derived from ocean color sensors, from which most bio- optical or bio-geochemical products are derived. Development and maintenance of a consistent Rrs product at the highest possible quality is thus paramount to continuation of meaningful ocean color science into the VIIRS era. The retrieval of Rrs from spaceborne sensors, however, is highly sensitive to instrument calibration and the retrieval algorithms. The establishment of Rrs time-series of sufficient quality for ocean color science has historically required significant efforts to quantify and correct for sensor degradation issues that change radiometric performance over time, across scan, and between detectors and mirror sides. The OBPG has augmented the calibration of MODIS using vicarious techniques to achieve a level of accuracy and stability that far exceeds what can be achieved through the on-board (solar, lunar) calibration alone, and we propose to extend this level of effort to VIIRS. We also seek to maintain the Rrs algorithm for VIIRS consistent with the algorithm currently employed for MODIS. This algorithm has many components, collectively referred to as atmospheric correction, that account for the radiative transfer of light from the sun through the atmosphere, into the euphotic zone of the upper ocean and back to the sensor. A consistent atmospheric correction algorithm for VIIRS has already been developed by the OBPG, and extensive radiative transfer simulations have been performed to produce the atmospheric models specific to the VIIRS bandpasses. Here we propose to maintain VIIRS compatibility as NASA's multi-sensor atmospheric correction algorithm evolves and advances.
The standard MODIS Chl and Kd490 algorithms are empirical band ratio algorithms derived by relating field measurements of spectral Rrs to field measurements of Chl and Kd490 using the NASA bio-Optical Marine Algorithm Dataset (NOMAD) in situ archive. These MODIS algorithms and the NOMAD dataset are currently maintained by the OBPG. We propose to establish these same empirical algorithms for VIIRS, accounting for the VIIRS-specific band centers and updating as necessary to maintain currency with NOMAD and consistency with MODIS and SeaWiFS. Similarly, the

current MODIS IOP and other derived-product algorithms require only minor refinements for applicability to VIIRS band centers. We will establish the full suite of VIIRS ocean color algorithms consistent with those currently employed for MODIS standard ocean color products, and maintain those algorithms to incorporate any advancements developed by the MODIS science team, the OBPG, or the broader research community.
More details may be found in the following project profile(s):
