OS23E-01
Impact of Backscattering Spectra and Fluorescence on NIR Retrieval Algorithms for Coastal Waters
With the increasing recognition of the need for using the NIR bands for Chl retrieval in coastal waters, the necessity to properly model the water leaving signal in that spectral region is important. In particular, there is a need to account not only for the spectral modulation of the elastic backscatter by the Chl absorption spectra, as it is normally done, but to also take into account the spectral signature of the backscatter itself, whether from mineral or organic particulates, include the contribution of Chl fluorescence and to assess how all these factors affect retrieval algorithms. While approximations for these spectral signatures and magnitudes and sophisticated instruments for their measurement have existed for some time, detailed and accurate information about the interconnection between absorption, scattering spectra and fluorescence contributions to them and comparisons of theory and experimental observations, including field measurements is rarely available. This is especially true for coastal waters, where simultaneous scattering contributions from several particulate components (phytoplankton, detritus and minerals) significantly complicate the issue. To analyze these effects, we have performed numerical simulations using an extensive database of water components appropriate to Case II waters and compared the results of these simulations with the results of field measurement campaigns in the Chesapeake Bay, Long Island and Georgia waters, where hyper-spectral measurements of absorption and extinction were obtained using a WET Labs ACS instrument in conjunction with the bb9 instrument for direct measurement of backscatter, as well as for fluorescence measurement of Chl concentration. The simulations used synthetic datasets created using the HYDROLIGHT radiative transfer code, and where IOP's were connected to parameterized microphysical models in accordance with procedures used to generate the IOCCG dataset, improved by higher (1 nm) spectral resolution and a wider range of parameters typical for coastal waters. Simulations were compared with our recent field measurements. The relevant WET Labs absorption and attenuation data were used as inputs into HYDROLIGHT radiative transfer simulations to obtain the backscattering spectral distributions, using least squares optimization, as a function of Chl and total suspended solids. HYDROLIGHT simulations of elastic reflectance using attenuation/extinction spectra, measured in the field, followed by subtraction from measured field reflectance, permitted retrieval of the fluorescence contribution to the latter, for comparisons with the data set simulations. Generally, the combination of results shows that it is possible to find appropriate bands in the NIR for efficient Chl retrieval. However, the results showed small fluorescence contributions to surface reflectance for mineral concentrations greater than 5 mg/l, because of strong attenuation in the excitation zone and enhanced elastic reflectance making fluorescence detection unrealistic. For lower mineral concentrations, we also find that some combinations of NIR observation bands permit reasonably good FLH retrievals in conditions where specific absorption spectral variation is not very high.
OS23E-02
Statistical Modelling of New Zealands Southland Front From Space
The Southland Front is a localised section of the global southern Subtropical Front that runs along the southeast coast of South Island, New Zealand. It is the boundary between warmer subtropical water in the north and colder subantarctic water from the south. It is associated with strong physical and nutrient gradients which lead to enhanced biological productivity. In this paper we discuss a new method to determine the position and gradient (i.e.strength) of a thermal ocean front. A weighted local likelihood estimation technique in which estimates of frontal parameters (position and strength) are based upon weighted contributions from surrounding points is described. We use this new technique to study the characteristics of the Southland Front and the variation in its properties over the period 1985-2005 from AVHRR imagery. We find the mean path of the Southland Front to be bounded by the 500m isobath and observe a gradual increase in meandering intensity northwards along its path. Its mean width increases from 17 to 30 km and its thermal gradient decreases from 0.22 to 0.13 ° C.km-1 as it flows northwards from Otago Peninsula towards the Chatham Rise. These trends are maintained throughout the seasons, with the exception of winter, where a constant width and gradient of 20 km and 0.17 ° C.km-1 respectively are observed along the length of the front. Spectral analysis of the 21 year time series reveals evidence for possible links with the El Nino Southern Oscillation.
OS23E-03
Long-Term and Event-Based Evaluation of QuikSCAT and COAMPS Model Vector Wind Products with Ocean Buoy Data for the Gulf of Mexico
Wind measurements obtained in 2005 and 2006 from the QuikSCAT/SeaWinds satellite and the COAMPS Central America Regional Model are compared to buoy data operated by the National Data Buoy Center (NDBC) at both the nearshore and offshore locations in the northern Gulf of Mexico. Comparisons between buoy wind data and the QuikSCAT Level 3 and Level 2B standard products at 25 and 12.5 km2 spatial resolution respectively were made using a minimum distance of 0.1° and a maximum time difference of 20 min between the two data sets. Preliminary analysis indicates the two datasets to be reasonably well correlated. Data from the COAMPS regional model at spatial resolution of 0.2°, will also be similarly evaluated. The time period being considered includes the energetic season of 2005 during which Hurricanes Katrina and Rita occurred, providing an evaluation of model and satellite data performance during extreme events. The limitations of QuikSCAT wind data for light (<3m/s) and very strong winds (>20m/s) will be assessed for the study region. Rain contamination can also affect data adversely, however, for the time period considered in this study, the effect of rain does not show a noticeable change in correlation between the datasets. This study will provide a comprehensive evaluation of the most commonly used wind measurement methods and their reliability for coastal regions.
OS23E-04
Overview of the heritage Calibration/Validation system for NOAA/NESDIS operational global Sea Surface Temperature products from AVHRR
Operational polar-orbiting NOAA satellites provide repetitive daily global coverage of the Earth. NESDIS has pioneered global production of Sea Surface Temperature (SST) from the Advanced Very High Resolution Radiometers (AVHRR) flown onboard NOAA satellites in the early 1980s and operational production has continued ever since. An important element of the global SST production is a continuous match-up of satellite data with in-situ SSTs. Early in satellite lifetime, the match-up data are used to train the regression-based Multi Channel and Non Linear SST (MCSST/NLSST) algorithms, i.e., derive coefficients of SST equations. This stage is referred to as calibration. Later in the satellite missions, the match-up data are used to continuously evaluate SST product performance. This stage is referred to as validation. Currently, it includes calculating a global bias and root-mean-squared deviation (RMSD) between the satellite and in-situ SSTs, on a monthly basis. The primary objective of this paper is to describe the heritage NESDIS AVHRR SST Cal/Val system, and document the latest AVHRR SST validation results from NOAA 16, 17, and 18 satellites from 2003 until present. Typically, global monthly bias is within ±0.1K and RMSD ~ 0.55K. The second objective is to check the robustness and seasonal stability of the derived MC/NLSST coefficients and RMSD, and in particular, estimate their sensitivity to the removal of outliers. Currently, outliers are identified by comparison of both in situ and satellite SSTs with the Bauer-Robinson 1985 SST climatology. We conclude the presentation with identifying potential improvements to the heritage AVHRR SST Cal/Val system.
OS23E-05
CDOM Ocean Color Algorithm for a River-Dominated Coastal Environment: An Assessment
Colored dissolved organic matter (CDOM) absorption at 412 nm and the ratios of reflectances Rrs(412)/Rrs(510), Rrs443)/Rrs(510), and Rrs(510)/Rrs(555) were found to be highly correlated for coastal waters influenced by the Mississippi River. A preliminary assessment of these relationships indicate the Rrs(510)/Rrs(555) band ratio provides the best estimates of CDOM absorption from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite imagery. Using an extensive field data set of CDOM absorption collected during four hydrographic cruises of the eastern Texas-Louisiana Shelf in March, May, July, and August of 2005, we further assess the performance of these algorithms in a highly dynamic coastal environment influenced by discharge from the combined Mississippi-Atchafalaya River system. Linear relationships between CDOM absorption and salinity during the various cruises indicated strong hydrographic controls on CDOM distribution with potential for using satellite ocean color data for estimating salinity patterns in coastal waters influenced by large rivers. As the fresh nutrient-rich river water controls the timing and placement of organic flux to the benthos, an improved CDOM algorithm for this system may have important implications for the prediction of the seasonal hypoxia in the region.
OS23E-06
AMSU-A Measurements of Brightness Temperatures Over Amazon Rainforest
Angular distributions of brightness temperatures over the Amazon rainforest observed by the Advanced Microwave Sounding Unit-A (AMSU-A) window channels are studied and simulated with a radiative transfer model. The model is based on a combination of the atmospheric radiative transfer model and a vegetation canopy model which treats the rainforest as a uniform layer with an effective canopy temperature. Since emission from the ground surface is heavily attenuated by the rainforest canopy, only radiations from the rainforest canopy and the atmospheric medium contribute to the measurements. The measured angular distribution of brightness temperatures at the four window channels 1-3 and 15 (with frequencies centered at 23.8, 31.4, 50.3, and 89 GHz, respectively) has a relatively small angular dependence that is attributed to the atmospheric path length. Diurnal variation of the brightness temperatures observed by NOAA-KLM AMSU-A over Amazon Rain Forest is also investigated and modeled with Fourier Series. It shows that a second order of Fourier series can reproduce the observed pattern of diurnal variation of the brightness temperatures. The stable pattern and small variation of angular distributions can be potentially useful for post-launch calibration of new microwave radiometers. The AMSU-A is the first satellite borne instrument that has provided a large range of angular measurements of brightness temperatures over the Amazon rainforests and other global scenes. The establishment of a land calibration target is an important addition to the few tools available for calibration and validation of space-borne microwave instruments. Sample results will be presented and discussed.
OS23E-07
Improved Beach Zone Segmentation From Airborne Lidar Measurements Using Intensity Measures
In an effort to monitor beach zone stability along the St. Augustine Beach region of Florida, high-resolution airborne laser swath mapping (ALSM) data are routinely acquired by the University of Florida's Geosensing and Engineering Mapping (GEM) Center. ALSM, often referred to as Light Detection and Ranging (LiDAR), systems enable sub-meter sampling of the near-shore coastal topography and the subsequent creation of digital elevation images with rms errors of less than 10cm over minimally-vegetated surfaces, such as beaches. Currently, there are seven collection dates spanning August 2003 to February 2007. This high spatial resolution coupled with the multiple acquisitions through time provided several results: two separate beach nourishment efforts were captured in the data allowing sediment spreading rate to be modeled and volume loss quantified, shoreline change rates were estimated for temporal scales ranging from a few months to over two years at various spatial frequencies from < 5m to > 300m, storm and seasonal wave climate induced shoreline response were modeled, and novel approaches to morphological feature extraction and identification of localized erosional hot- spots were developed. All previous analyses are based on range measurements; however, the ALSM system also records the intensity (peak voltage from the APD) for each return. Intensity has traditionally been under utilized as a feature for image classification because it does not represent true terrain radiance. We show that in areas with minimal topographic relief, such as beaches, intensity measures have great potential for improved beach zone segmentation. Segmentation of the beach zone is important for several factors including identification of the wet-dry line for traditional shoreline comparison and change-detection, and removal of water points to allow analysis of beach-only zones. Several intensity-based features are extracted from ALSM training data collected along the St. Augustine beach and partitioned into three classes, wet beach, dry beach, and water to detect the water line. Class-conditional probability density functions are estimated for each feature to assess which are most informative and their separability is ranked. Results indicate significant class separation using centroidal features, such as mean and median, suggesting robust segmentation of the beach using intensity measures is possible. The method presented provides a novel geometric feature extraction and a systematic feature selection procedure for high-resolution ALSM intensity data.
OS23E-08
Laser-based fluorometer for real-time plankton mapping by an autonomous underwater vehicle
We are constructing a laser-based chlorophyll fluorometer that will be integrated into a REMUS AUV platform. This poster will report on our construction progress and on the expected oceanographic data, based on bench testing with sea-water trials. The eventual REMUS deployment has forced many design constraints onto this work, in particular on power consumption and overall instrument volume. We feel as if we have reached an optimal and feasible design. The instrument itself consists of a 440 nm laser, which matches the blue absorption line of Chlorophyll-a (CHL-a), the primary green pigment in phytoplankton. The laser is pulsed at between 1 and 10 kHz with 50 ns-long pulses. We expect the laser to stimulate CHL-a fluorescence up to 5 meters from the vehicle in coastal waters. Stimulated fluorescence in the beam volume is imaged using a streak camera, which yields both spatial and temporal evolution of the fluorescence in a single shot. Hence, the instrument will enable real-time rapid spatial mapping of phytoplankton communities. Our experimental goal is to map plankton communities real-time for a few meters from the vehicle in a single shot. Our choice of the laser (small, battery operated), has 50 nanosecond flashes, spaced at 1 millisecond. Such pump light has thrown this work into a fluorometry regime unseen in previous in-situ work. With such short pump light flashes, we do not observe variable fluorescence in live sea-water, and the laser pulse is too long to resolve in situ fluorescent lifetimes. After a single actinic light pulse however, we are able to extract a flash saturation curve, yielding F0 (minimal fluorescence) and Fsat (saturating fluorescence) with each shot of the laser. From this we are able to compute the phytoplankton photochemistry cross section, presumably of the PSII reaction center, nearly continuously along the vertical water traversed by the laser beam.
OS23E-09
Title Satellite measurements reveal lower oceanic wind power input
Surface winds working on the oceanic general circulation are traditional regarded, along with tides, as the largest mechanical energy source driving the mixing of density that maintains the thermohaline circulation, and therefore regulating climate change. The wind power input to on the oceanic general circulation is estimated based on state-of-the-art satellite measurements of wind stress by the QuikSCAT radar scatterometer and surface ocean currents by multiple altimeter satellites and a gravity satellite. It suggests that previous estimates of the wind power input are too large by close to 50%. These measurements challenge the traditional view of the role of the winds in regulating the thermohaline circulation and climate, suggesting either a remarkably larger amount of energy input from other sources, or the need for revised estimates of the density mixing rate.
OS23E-10
NOAA CoastWatch: Applications of Remote Sensing
NOAA CoastWatch is an operational program that evolved from a harmful algal bloom (red tide) incidence in the East Coast of the US in 1987. It began as a weekly program of sea surface temperature (SST) analysis from the Advanced Very High Resolution Radiometer (AVHRR) and the surface wind field and advection forecasts. Through the leadership of the senior author, CoastWatch continues to develop and expand in areas and parameters of coverage. Processing of remote sensing data and additional meteorological and oceanographic parameters is being done at the CoastWatch office at the NOAA Science Center in Camp Springs, Maryland. The data are available to the different CoastWatch nodes in the US. Users of the information then connect to the node responsible for their local area. We have applied up to date processing algorithms, conducted calibration/validation of the data, and provided processing tools to node centers and other users. We will be presenting the products and services that the program provides. Similar programs are being hosted in other areas of the world in collaboration with NOAA CoastWatch.
OS23E-11
Optical Characterization of Runoff in the Chesapeake Bay
As part of an ongoing effort to optically characterize the Chesapeake Bay in an effort to develop regional remote sensing ocean color algorithms, the Marine Optical Characterization Experiment (MOCE) team sampled the middle portion of the Chesapeake Bay in an effort to document and characterize a high-sediment, fresh water plume cascading down the Bay following record breaking rainfall totals in the Chesapeake Bay Watershed during the summer of 2006. These plumes can have potentially devastating effects on the Chesapeake Bay's fragile ecosystem by increasing nutrient loads, depositing sediments, and decreasing salinity and light levels. Sampling took place from July 5th through July 7th spanning the front of the advancing feature. Measurements of total suspended matter, chlorophyll a, chromophoric dissolved organic material absorption, and hyperspectral optics were collected. The optical measurements included above water surface irradiance (Es), in-water downwelling irradiance (Ed) and in-water upwelling radiance (Lu). From the optical measurements we can derive water clarity (K490), normalized water-leaving radiance, and remote sensing reflectance. These parameters will better enable the detection and tracking of these types of events in the future utilizing remote sensing techniques.
OS23E-12
Red tide optical index: in situ optics and remote sensing models
Harmful Algal Blooms (HABs) are recurring events in the coastal ocean, and local economies that depend on beach and coastal use are often adversely affected by these events. Inherent optical properties (absorption and backscattering) of the HAB dinoflagellate Lingulodinium polyedrum were measured in order to develop specific index that would enable easier detection of this HAB organism in the field. It has been noticed that red to blue and red to green ratio of absorption in this species is much lower then other measured species. A red tide ratio was tested in the field during a red tide episode in the San Pedro Channel, using a Wetlabs acS flow-through system. The red tide index gave a distinguishable signal in areas where L.polyedrum was present. Remote sensing reflectance was calculated from field and laboratory IOP measurements, using reverse Quasi-Analythical Alghoritm and Hydrolight to evaluate if the red tide index can be detected in the remote sensing ocean color measurements.
OS23E-13
Nearshore Processes, Currents and Directional Wave Spectra Monitoring Using Coherent and Non-coherent Imaging Radars
Two new radar systems have been developed for real-time measurement of near-shore processes, and results
are presented for measurements of ocean wave spectra, near-shore sand bar structure, and ocean currents. The
first is a non-coherent radar based on a modified version of the Sitex radar family, with a data acquisition system
designed around an ISR digital receiver card. The card operates in a PC computer with inputs from a Sitex radar
modified for extraction of analogue signals for digitization. Using a 9' antenna and 25 kW transmit power system,
data were collected during 2007 at the U.S. Army Corps of Engineers Field Research Facility (FRF), Duck, NC
during winter and spring of 2007. The directional wave spectrum measurements made are based on using a
sequence of 64 to 640 antenna rotations to form a snapshot series of radar images of propagating waves. A
square window is extracted from each image, typically 64 x 64 pixels at 3-m resolution. Then ten sets of 64
windows are submitted to a three-dimensional Fast Fourier Transform process to generate radar image spectra
in the frequency-wavenumber space. The relation between the radar image spectral intensity and wave spectral
intensity derived from the FRF pressure gauge array was used for a test set of data, in order to establish a
modulation transfer function (MTF) for each frequency component. For 640 rotations, 10 of such spectra are
averaged for improved statistics. The wave spectrum so generated was compared for extended data sets beyond
those used to establish the MTF, and those results are presented here. Some differences between the radar and
pressure sensor data that are observed are found to be due to the influence of the wind field, as the radar echo
image weakens for light winds. A model is developed to account for such an effect to improve the radar estimate
of the directional wave spectrum. The radar ocean wave imagery is severely influenced only by extremely heavy
rain-fall rates, so that acceptable quality were assured for most weather conditions on a diurnal basis using a
modest tower height.
A new coherent microwave radar has recently been developed by ISR and preliminary testing was conducted in
the spring of 2007. The radar is based on the Quadrapus four-channel transceiver card, mixed up to microwave
frequencies for pulse transmission and back down to base-band for reception. We use frequency-modulated
pulse compression methods to obtain 3-m spatial resolution. A standard marine radar pedestal is used to house
the microwave components, and rotating radar PPI images similar to marine radar images are obtained. Many of
the methods used for the marine radar system have been transferred to the coherent imaging radar. New
processing methods applied to the coherent data allow summing of radial velocity images to map mean currents
in the near shore zone, such as rip currents. A pair of such radars operating with a few hundred meter separation
can be used to map vector currents continuously in the near shore zone and in harbors on a timely basis. Results
of preliminary testing of the system will be presented.
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