Paul E. Lyon

Satellite retrieval of inherent optical properties by linear matrix inversion of oceanic radiance models: An analysis of model and radiance measurement errors

The linear summability of inherent optical properties (IOPs) is exploited to provide matrix equations for retrieval of phytoplankton absorption, dissolved organic matter, and constituent backscatter. Spectral models for the phytoplankton pigment absorption coefficient, chromophoric dissolved organic matter (CDOM) absorption coefficient, and total constituent backscatter (TCB) coefficient are first used to calculate 5 × 105 water-leaving spectral radiances for a wide range of normally distributed IOP values at 410, 490, and 555 nm. Then, the spectral radiances are inverted to simultaneously provide phytoplankton pigment absorption coefficient, CDOM absorption coefficient, and total constituent backscatter coefficient on a pixel-by-pixel basis to demonstrate that (1) matrix inversion is very rapid and well conditioned, (2) the IOPs are exactly determined when the water-leaving radiances and IOP spectral models are error free, (3) for equal radiance errors sequentially occurring in one of three sensor bands, phytoplankton pigment retrieval errors are generally higher than CDOM and TCB coefficient errors, (4) retrieval errors for all the IOPs are strongly dependent on phytoplankton pigment spectral model Gaussian width errors, (5) phytoplankton pigment absorption and CDOM absorption retrieval errors are more sensitive to CDOM spectral slope errors than the TCB coefficient retrievals, and (6) TCB wavelength-ratio-exponent errors produce less impact on the phytoplankton absorption coefficient retrieval than upon the CDOM absorption or the TCB coefficient retrievals.

Inherent optical properties imagery of the western North Atlantic Ocean: Horizontal spatial variability of the upper mixed layer

Until now, no satellite methods were available for the study of inherent optical properties (IOPs) over wide areas of the worlds oceans. Herein the coefficients of phytoplankton absorption, chromophoric dissolved organic matter (CDOM)-detritus absorption, and total backscattering have been retrieved from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) 412, 490, and 555 nm reflectances by linear matrix inversion of an oceanic radiance model. The retrieved phytoplankton absorption coefficient from an October 6, 1997, image of the Middle Atlantic Bight (MAB) reveals (1) characteristic patchiness over the shelf, slope, Gulf Stream, and Sargasso Sea, (2) a warm-core ring being encircled by a spiral streamer of phytoplankton-containing cooler shelf water, and (3) phytoplankton prominence at South Atlantic Bight capes and remarkable minima between the capes. The retrieved CDOM-detritus absorption coefficient image readily shows (1) the characteristic offshore 20× decline from ∼0.4 to 0.02−1, (2) a sharp drop at the Gulf Stream NW boundary, (3) striations of CDOM-detritus within the Gulf Stream, and (4) that during the fall, non-bloom season, the dominant absorbing constituent over the MAB continental shelf is not phytoplankton but CDOM-detritus. The retrieved total backscattering coefficient image shows a patchy depression over the middle to outer shelf (compared to the Gulf Stream and inner shelf). A feature common to all three inherent optical property images is the northeasterly extrusion of phytoplankton, CDOM-detritus, and other constituents from Cape Hatteras coastal/shelf water along a streamer adjacent to the Gulf Stream. No similar evidence of shelf water export was observed over the Diamond Shoals area south of Cape Hatteras where previous researchers have reported episodic offshore advection of shelf water. A second mechanism for carbon export can be seen in the New York Bight where a tongue of outflow from the Hudson River can be seen to cross the shelf and interact with the northern wall of a warm-core ring. A concurrent 150 m altitude airborne underflight with a calibrated ocean-viewing 256-channel spectroradiometer provided supplementary atmospheric correction to the SeaWiFS remote sensing reflectances and validation of the resulting SeaWiFS IOP retrievals. Simultaneous airborne lidar fluorescence was used to confirm further the SeaWiFS CDOM-detritus and phytoplankton absorption coefficient IOP retrievals. The results strongly suggest that if satisfactory atmospheric correction can eventually be achieved without airborne underflights, then the SeaWiFS data will readily allow global-scale IOP variability studies.

Interaction of Hurricane Katrina With Optically Complex Water in the Gulf of Mexico: Interpretation Using Satellite-Derived Inherent Optical Properties and Chlorophyll Concentration

When Hurricane Katrina passed over southern Florida, Florida Bay and the West Florida Shelf, and into the Gulf of Mexico, empirically derived chl a increases were observed in the Tortugas Gyre circulation feature, and in adjacent waters. Analysis of the empirically derived chl a increase within the gyre has been primarily attributed to initiation of a phytoplankton bloom promoted by nutrients upwelled by Katrinas winds. Detailed analysis of inherent optical properties derived from remotely sensed radiances, however, indicated the interaction of Katrina with shallow coastal and shelf waters likely entrained waters with higher concentrations of chromophoric dissolved organic matter (CDOM) into the gyre circulation, augmenting the chl a signal. Storm-induced upwelling would also transport optically active CDOM to the surface. Increases in empirically derived chl a in the Florida coastal waters influenced by Katrinas winds were therefore partly due to increased absorption by CDOM. This analysis indicates that elevated empirically derived chl a in hurricane-influenced waters should not be unambiguously attributed to increased phytoplankton productivity, particularly in an optically complex coastal environment.

An automated de-striping algorithm for Ocean Colour Monitor imagery

Ocean Colour Monitor, OCM, is a push broom sensor design with 3740 detectors across scan for each of its eight channels. Along track striping caused by poorly characterised detector to detector calibration results in derived ocean colour products that are hardly usable. Because OCM is turned on only for purchased orbits, the coefficients needed to correct each cross scan detector are not constant for all orbits. An algorithm has been developed to remove the effects of striping which is based on the information contained in each image. The algorithm performance depends only on the quantity of contiguous pixels over the water for each detector. Along scan detectors that have sufficient water pixels within the image to derive statistically significant correction coefficients are corrected with a fixed vector of scale factors. This paper outlines the automated de‐striping algorithm (ADM), shows the results of ADM, quantifies the improvement to the images achieved and describes the limitations of the method.

Chlorophyll biomass in the global oceans: satellite retrieval using inherent optical properties

In the upper layer of the global ocean, 2082 in situ chlorophyll biomass values (Chl) are retrieved by concurrent satellite-derived inherent optical properties (IOP). It is found that (1) the phytoplankton absorption coefficient IOP alone does not provide satisfactory (Chl) retrieval; (2) the chromophoric dissolved organic matter (CDOM) absorption coefficient IOP must also be used to obtain satisfactory retrieval through (Chl) alpha a ph + pa CDOM where p is a constant and a ph and aCDOM are, respectively, the phytoplankton and CDOM absorption coefficients; (3) the IOP-based (Chl) retrieval performance is comparable to standard satellite reflectance ratio retrievals (that have CDOM absorption intrinsically embedded within them); (4) inclusion of the total backscattering coefficient IOP does not contribute significantly to (Chl) retrieval; and (5) the new IOP-based algorithm may provide the possibility for future research to establish the actual role of extracellular CDOM from all sources in the intracellular production of chlorophyll biomass.

Development of finer spatial resolution optical properties from MODIS

Typical MODIS ocean color products are at 1 kilometer (km) spatial resolution, although two 250 meter (m) and five 500 m bands are also available on the sensor. We couple these higher resolution bands with the 1km bands to produce pseudo-250m resolution MODIS bio-optical properties. Finer resolution bio-optical products from space significantly improve our capability for monitoring coastal ocean and estuarine processes. Additionally, increased resolution is required for validation of ocean color products in coastal regions due to the shorter spatial scales of coastal processes and greater variability compared to open-ocean regions. Using the 250m bands coupled with the 1km and 500m bands (which are bi-linearly interpolated to 250m resolution), we estimate remote sensing reflectances (Rrs) at 250m resolution following atmospheric correction. The aerosol correction makes use of the 1km near infrared (NIR) bands at 748 nanometers (nm) and 869 nm to determine aerosol type and concentration. The water leaving radiances in the NIR bands are modeled from retrieved water leaving radiances in the visible bands using the short wave infrared (SWIR) channels at 1240 nm and 2130 nm. The increased resolution spectral Rrs channels are input into bio-optical algorithms (Quasi-Analytical Algorithm (QAA), Water Mass Classification, OC2, etc.) that have traditionally used the 1 km reflectances resulting in finer resolution products. Finer resolution bio-optical properties are demonstrated in bays, estuaries, and coastal regions providing new capabilities for MODIS applications in coastal areas. The finer resolution products of total absorption (at), phytoplankton absorption (aph), Color-Dissolved Organic Matter (CDOM) absorption (ag) and backscattering (bb) are compared with the 1km products and in situ observations. We demonstrate that finer resolution is required for validation of coastal products in order to improve match ups of in situ data with the high spatial variability of satellite properties in coastal regions.

Night vision goggle stimulation using LCoS and DLP projection technology, which is better?

High fidelity night-vision training has become important for many of the simulation systems being procured today. The end-users of these simulation-training systems prefer using their actual night-vision goggle (NVG) headsets. This requires that the visual display system stimulate the NVGs in a realistic way. Historically NVG stimulation was done with cathode-ray tube (CRT) projectors. However, this technology became obsolete and in recent years training simulators do NVG stimulation with laser, LCoS and DLP projectors. The LCoS and DLP projection technologies have emerged as the preferred approach for the stimulation of NVGs. Both LCoS and DLP technologies have advantages and disadvantages for stimulating NVGs. LCoS projectors can have more than 5-10 times the contrast capability of DLP projectors. The larger the difference between the projected black level and the brightest object in a scene, the better the NVG stimulation effects can be. This is an advantage of LCoS technology, especially when the proper NVG wavelengths are used. Single-chip DLP projectors, even though they have much reduced contrast compared to LCoS projectors, can use LED illuminators in a sequential red-green-blue fashion to create a projected image. It is straightforward to add an extra infrared (NVG wavelength) LED into this sequential chain of LED illumination. The content of this NVG channel can be independent of the visible scene, which allows effects to be added that can compensate for the lack of contrast inherent in a DLP device. This paper will expand on the differences between LCoS and DLP projectors for stimulating NVGs and summarize the benefits of both in night-vision simulation training systems.

Automated Validation of Satellite Derived Coastal Optical Products

Automated validation methods and a suite of tools have been developed in a Quality Control Center to analyze the stability and uncertainty of satellite ocean products. The automatic procedures analyze match-ups of near real time coastal bio-optical observations from Marthas Vineyard Coastal Observatory (MVCO) with satellite-derived ocean color products from MODIS Aqua and Terra, SeaWIFS, Ocean Color Monitor, and MERIS. These tools will be used to compare MVCO in situ data sets (absorption, backscattering, and attenuation coefficients), co-located SeaPRISM-derived water leaving radiances, and the Aerosol Robotic Network (AeroNet) derived aerosol properties with daily satellite bio-optical products and atmospheric correction parameters (aerosol model types, epsilon, angstrom coefficient), to track the long term stability of the bio-optical products and aerosol patterns. The automated procedures will be used to compare the in situ and satellite-derived values, assess seasonal trends, estimate uncertainty of coastal products, and determine the influence and uncertainty of the atmospheric correction procedures. Additionally we will examine the increased resolution of 250m, 500m, and 1 km satellite data from multiple satellite borne sensors to examine the spatial variability and how this variability affects assessing the product uncertainty of coastal match-ups of both bio-optical algorithms and atmospheric correction methods. This report describes the status of the QCC tool development and potential applications of the QCC tool suite.