MISSION

 

Introduction

Current ocean color satellites such as MODIS and the planned NPOESS VIIRS system are optimally designed for open ocean imagery, calibrated for low radiances and producing coarse spatial and spectral resolution. The coastal ocean, in contrast, is one of the most difficult places to accurately retrieve ocean color and benthic ecosystem reflectanceal. Radiance signal magnitude is highly variable, ranging from very dark values in clear, deep water to very bright values at water's edge. Signals are also highly variable in space and time, due to many dynamic processes. Aerosol plumes from continental sources complicate the task of atmospheric correction. The spatial (~1 km) and temporal (~daily) coverage from the satellite instruments normally used for the open ocean is of marginal use in coastal waters. Water-leaving radiance in the blue, critical for discriminating pigments from colored dissolved material, exhibit low signals, which often become negative using standard reprocessing methods for MODIS and SeaWiFS. Additionally, the lack of mid-range spectral bands on most existing sensors makes it difficult or impossible to detect events such as "red tides," one of the main targets for coastal remote sensing. There is a clear need for high temporal, spatial, and spectral resolution data to meet these challenges; for the foreseeable future, this will require airborne instrumentation.

The science goal of this project is to develop and fly a portable airborne sensor suite for NASA science missions addressing the challenges of an optically complex coastal ocean zone in support of research areas such as water quality, ocean productivity and biogeochemistry, coastal landscape alteration, coastal and estuarine ecosystem productivity, atmospheric correction, and regional climate variability.

More specifically, this project will enable measurements of several properties of biological interest in the coastal ocean, especially apparent optical properties (AOPs). These properties are key to characterizing estuaries, river plumes, kelp beds, coral reefs, and phytoplankton including harmful algal blooms.

One field validation experiment is planned for this one-year project. It will consist of flying the HIS instrument, together with the AATS-14 and microradiometers at various altitudes over instrumented surface (see diagr. The AATS-14 will provide a simultaneous empirical characterization of the atmospheric column (AOD and water vapor), which will be used to refine the radiative transfer component of the validation experiments. The in-water microradiometer system (Biospherical Instruments C-OPS) that includes an underwater housing will be deployed from a ship during aircraft overflight and will determine apparent optical properties (AOP) in the shallow water sites. The C-OPS consists of two radiometers: one measuring in-water upwelling radiance, and the other either downward irradiance or upward irradiance. Both radiometers are equipped with 19 wavebands and are mounted on a free-fall frame. The frame can be optimized for either slow descent rates for work in very shallow coastal waters sites, or faster descent rates for observations in the open ocean. The radiometers are a replicate of the aircraft microradiometers and will provide data sets for valid comparison.

We anticipate that the instrument suite would also eventually participate in the vicarious calibration experiments routinely conducted by other NASA airborne instrument teams, such as AVIRIS and MAS, on a piggy-back basis on other platforms.

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