Merlin P. Lawson

Benthic Habitat Mapping in Tropical Marine Environments Using QuickBird Multispectral Data

The objective of this research focused on the utility of QuickBird multispectral data for identifying and classifying tropical-marine benthic habitats after applying atmospheric and water-column corrections for an area around Roatan Island, Honduras. Atmospheric (Rayleigh and aerosol path radiance) and water column corrections (water depth and water column attenuation) were applied to the imagery, making it an effective method for mapping benthic habitats. Water depth for each pixel was calculated based on a linear model by regressing transformed radiance over known homogenous benthos against measured depths. Water column correction was achieved by deriving absorption and backscattering coefficients for each band of the image using a 50 � 50 window of clear water pixels. Corrections for water path radiance and water column attenuation of the bottom reflected radiance were made for the entire scene, allowing the bottom albedo to be determined for shallow coastal areas. An image of the bottom (i.e., an albedo image), minus the water column, was produced. Albedos were ≤8 percent for seagrass benthos, approximately 8 to 18 percent for coral areas, and ≥18 percent for sand dominated areas. An unsupervised classification algorithm was applied to the bottom albedo image, generating a classified map of benthic habitats. Accuracy assessment based on 383 reference points revealed an overall accuracy of 81 percent, with an overall Kappa value of 0.774.

High-resolution ocean color remote sensing of benthic habitats: a case study at the Roatan island, Honduras

Natural resource managers clamor for detailed reef habitat maps for monitoring smaller scale disturbances in reef communities. Coastal ocean color remote sensing techniques permit benthic habitats to be explored with higher resolution than ever before. The objective of this research was to develop an accurate benthic habitat map for an area off the northwest coast of Roatan Island, Honduras, using high-resolution multispectral IKONOS data. Atmospheric (Rayleigh and aerosol path radiance) and water column corrections (water depth and water column attenuation) were applied to the imagery, making it a robust method for mapping benthic habitats. Water depth for each pixel was calculated based on a site-specific polynomial model. A mechanistic radiative transfer approach was developed that removed the confound effect of the water column (absorption and scattering) from the imagery to retrieve an estimate of the bottom reflectance (albedo). Albedos were /spl les/ 12% for seagrass benthos, 12% to 24% for coral areas, and /spl ges/ 24% for sand-dominated areas. The retrieved bottom albedos were then used to classify the benthos, generating a detailed map of benthic habitats, followed by accuracy assessment.

Twentieth century changes in winter climatic regions

The configuration of the northern hemispheric general atmospheric circulation system shifted from a zonal to a meridional pattern in the early 1950s. Winter climatic regions in the conterminous United States are developed for a ten year period dominated by zonal flow and a second decade of meridional flow using a combination of principal components factor analysis and a Euclidean distance clustering algorithm. The results demonstrate that regional patterns in the surface climatic data substantially changed as the circulation system shifted its basic configuration. The regional structures of the eastern United States and the Great Plains appeared to be particularly sensitive to the change in the upperlevel flow pattern.

Bathymetric Mapping Using IKONOS Multispectral Data

The objective of this research was to develop an accurate bathymetric map for an area around Roatan Island, Honduras using high-resolution multispectral IKONOS data based on a variation of a linear regression model. Linear regression models estimate water depths by regressing brightness values over known benthos (albeit non-homogeneous) and known depths. However, we contend that if mixed bottom types are used, the regression coefficients deteriorate because the variability in brightness values from a heterogeneous bottom has a deleterious effect on the correlation coefficient. By selecting uniform bottom types, this variability can be reduced and a strong correlation between depth and brightness value can be established, thus improving the accuracy of estimated depths. Three uniform bottom types (seagrass, coral, and sand) were selected, and the transformed brightness values derived from principal components analysis for each bottom type were regressed against known depths. The most statistically significant coefficient (r 2 = 0.909 for seagrass benthos) was then used in the depth estimation algorithm and a bathymetric map was derived. A comparative evaluation between estimated and actual depths was performed and the bathymetric map was found to be within a standard error of 0.648 m. Consequently, our results suggest that accurate depth estimates can be derived by using transformed input brightness values over homogeneous bottom types from IKONOS multispectral imagery.

Proximal Sensing of Coral Features: Spectral Characterization of Siderastrea siderea

Remote sensing has been suggested as a potential tool for monitoring coral-reef ecosystems. However, before remote sensing can be viewed as a practical monitoring and diagnostic tool for entire coral communities, there is a need to understand the spectral responses from individual coral species. Toward that end, it seems important to not only establish the range of natural variability in spectral reflectance but also to develop procedures to enhance understanding of the spectra. This paper describes our data collection approach as well as a procedure for examining the spectral features associated with one species of coral (Siderastrea siderea). The paper also examines the spectral variability in reflectance within samples of the same species and suggests a procedure for highlighting the spectral positions of absorbers/pigments, thus yielding useful information about pigment composition in one coral species.

Seasonal temperature forecasts as products of antecedent linear and spatial temperature arrays

Abstract Our objective is to evaluate the potential for extracting the maximum information contained in antecedent temperature patterns that operationally could be used in formulating winter seasonal forecasts in the United States. In particular, examination of the predictability of winter temperatures given autumn temperatures is made using derived contingency tables, discriminant equations of antecedent principal components, and canonical correlation analysis. Contingency tables were constructed based on tercile classifications of a seventy-five year dependent record (1895–1969). Testing of an independent data period (1970–78) using these tables produced winter forecasts with no appreciable skill in the aggregate (−0.04). Discriminant analysis deprived linear combinations of the five principal components of the antecedent seasonal (autumn) temperatures to distinguish between specific terciles of the predictand season (winter). Despite encouraging results for the dependent period, forecast skill for the ...

Compensating for Irradiance Fluxes When Measuring the Spectral Reflectance of Corals In Situ

This study employed an ensemble of instruments to monitor irradiance fluxes during measurement of the spectral reflectance of one coral in situ at Roatan Island, Honduras. The underwater light field (400-700 nm) was considerably more variable under sunny or partially cloudy sky conditions than the above-water light field. Measurements under overcast conditions had low variability both above and at the coral target. Correlations between simultaneously collected above water and underwater downwelling fluxes had R 2 values of 0.02%, 63.0%, and 96.3% under sunny, variable, and overcast sky conditions, respectively. Simultaneous measurements of both upwelling radiance and downwelling irradiance using a dual-fiber hyperspectral sensor significantly reduced the variance in the spectral reflectance of a coral target, regardless of sky conditions, especially as compared with a single-fiber configuration.

Analysis of the climatic signal in the South Dome, Greenland ice core

The purpose of this research was to investigate the statistical relationship between an oxygen isotope chronology from southern Greenland and climatic variables recorded at a coastal village. The response of the oxygen isotope time series to monthly temperature and precipitation data was calculated using a combination of principal components factor analysis and multiple regression analysis. Orthogonal eigenvectors extracted from 35 yr of climatic data reliably explained 59% of the temporal variance in mean annual oxygen isotope values. The response functions demonstrate an apparent seasonal reversal in the relationship between oxygen isotope values and temperature, with the response varying between a positive (direct) relationship in winter, spring, and autumn, and a negative (indirect) relationship in summer. The results, and their implications, are shown to be useful in the historical climatic reconstruction of the South Greenland region.