Subsurface optical layers distributed at two different depths were investigated in Monterrey Bay, East Sound, and the Black Sea based on spatial statistics of remote sensing reflectance (Rrs). The main objective of this study was to evaluate the use of Rrs(443)/Rrs(490) (hereafter R1) skewness (ψ) as an indicator of vertical optical structure in different marine regions. Measurements of inherent optical properties were obtained using a remotely operated towed vehicle and R1 was theoretically derived from optical profiles. Although the broad range of trophic status and water stratification, a common statistical pattern consisting of lower ψR1-a deeper optical layer was found in all study cases. This variation was attributed to optical changes above the opticline and related to horizontal variability of particulates and spectral variations with depth. We recommend more comparisons in stratified coastal waters with different phytoplankton communities before the use of ψR1 can be generalized as a noninvasive optical proxy for screening depth changes on subsurface optical layers.
Optical properties derived from ocean color imagery represent vertically-integrated values from roughly the first
attenuation length in the water column, thereby providing no information on the vertical structure. Robotic, in situ
gliders, on the other hand, are not as synoptic, but provide the vertical structure. By linking measurements from these
two platforms we can obtain a more complete environmental picture. We merged optical measurements derived from
gliders with ocean color satellite imagery to reconstruct vertical structure of particle size spectra (PSD) in Antarctic shelf
waters during January 2007. Satellite-derived PSD was estimated from reflectance ratios using the spectral slope of
particulate backscattering (γbbp). Average surface values (0-20 m depth) of γbbp were spatially coherent (1 to 50 km
resolution) between space and in-water remote sensing estimates. This agreement was confirmed with shipboard vertical
profiles of spectral backscattering (HydroScat-6). It is suggested the complimentary use of glider-satellite optical
relationships, ancillary data (e.g., wind speed) and ecological interpretation of spatial changes on particle dynamics (e.g.,
phytoplankton growth) to model underwater light fields based on cloud-free ocean color imagery.
Characterization of 3-D underwater light fields from above the sea surface requires passive and active remote sensing
measurements. In this work, we suggest the use of passive ocean color sensors and lidar (Light Detection and Ranging)
to examine the vertical structure of optical properties in marine waters of the Northern Part of the Gulf of Alaska
(NGOA). We collected simultaneous airborne remote sensing reflectance (Rrs) in the spectral range 443-780 nm
(MicroSAS, Satlantic) and lidar-derived volume backscattering (β) profiles (0-20 m depth, wavelength = 532 nm) during
August 17 2002 in shelf waters situated south of Kodiak Island off Alaska (57.48°-58.04° N, 152.91°-151.67° W). We
evaluated the spectral response of Rrs to perturbations on vertical distribution of β by comparing the spatial variability
between aggregated (250 m horizontal resolution x 1 m vertical resolution) Rrs spectral ratios and different lidar statistics
per bin (Maximum β per bin, mean β per bin, βm, standard deviation of β per bin, βstd, integrated β per bin, βint) or
group of bins (lidar volume extinction coefficient of β between 0 and 5 m depth). Sub-surface changes of βm, βint, and
βstd were mainly correlated with Rrs (490)/Rrs (555) variability along the flight-track (Semi-partial correlation
coefficients = 0.12 to 0.21). Our results evidenced linkages between above and below-sea surface optical properties that
can be used to derive water optical constituents as a function of depth based on combined passive-active data.
Variability of particulate beam attenuation coefficient at 532 nm (cp (532)) and microbial planktonic community
(heterotrophic bacteria and phytoplankton) was analyzed in coastal waters of Southern California. The goal of this study
was to explore heterotrophic bacteria (HB) response (cell abundance, BA, and carbon production, BCP) with respect to
different particle characteristics (concentration, size distribution, and composition) related with cp(532). We observed a
fairly complex pattern of HB response and particle dynamics during seven experiments throughout the summer and
winter, which reflected variations in cp(532). The first experiment showed relatively high values of cp(532), in
conjunction with high chlorophyll a concentration (chl) of about 5.4 mg m-3. For experiments 2 and 3, a sharp decrease
of chl was accompanied by an increased role of detrital particles (non-living matter) as evidenced by increased detrital
absorption (ad). The highest values of particle-attached (>1 μm) and free living (<1 μm) BA and BCP were observed in
experiment 3. These changes in particle assemblage including HB maintained cp(532) at relatively high level,
comparable to that observed when phytoplankton dominated. A significant decrease of cp(532) was observed in
experiment 4 and 5, which coincided with relatively low BA, BCP, and ad values. In experiment 7, cp(532) magnitude
was comparable to the first experiment and was accompanied by high chl, BA and SPM (suspended particulate matter).
Greatest changes in cp(532) coincided with greatest variations in BA, even though our estimates of the direct contribution
of heterotrophic bacteria to cp(532) for all experiments remained quite low (<10%).
There are 361 ports of interest to the US Coast Guard regarding homeland security issues. Speed and accuracy of inspections there for “foreign objects” is critical to maintaining the flow of commerce through these ports. A fusion of acoustic and optical imaging technologies has been implemented to rapidly locate anomalies acoustically and inspect them optically. Results of field tests are presented. Effective deployment of AUV- or ROV-mounted optical sensors to inspect ship hulls and port facilities will depend on accurate, real-time prediction of the sub-surface optical environment and upon accurate sensor models parameterized for the time and place of inspection. For bi-static laser-line scanner sensors such as the Real-time Ocean Bottom Optical Topographer (ROBOT), ambient light decreases the range to the inspection object (e.g. hull) for which laser-line contrast is adequate for ranging and imaging in 3-D. Reduced range implies narrower swaths and longer inspection times. A 2-D and 3-D hybrid marine optical model (HyMOM) of the environment beneath ships or adjacent to sea walls and pilings has been developed, applied and validated in eutrophic and mesotrophic settings, and a Monte Carlo sensor model of ROBOT has been developed. Both are discussed and combined to evaluate sensor performance in different environments. To provide the inherent optical properties needed to run such models, data from the Autonomous Marine Optical System (AMOS) were collected and transmitted back to the laboratory. Examples of AMOS results and model outputs are presented.