May 2006
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20 Reads
Studies of intertidal organisms have contributed significantly to the understanding of complex biological responses to climate change. The intense thermal stresses characteristic of rocky coastal settings facilitate rapid population shifts, causing these habitats to be especially susceptible to deviations in weather patterns. Traditional in situ measurements are confined to specific areas and often span short time periods. This study proposes the use of satellite remote sensing techniques to expand these highly important climate studies into regional-scale monitoring over longer periods of time. To test this application, study sites were chosen along the Pacific coast of the U.S. within the rocky intertidal zones of California, Oregon, and Washington. Data from in situ sensors are used as ground references, and are the result of an on-going 10-year study of Mytilus californianus conducted at the Univ. of South Carolina. Satellite imagery includes a compilation of ASTER and MODIS land surface temperature (LST) data sets, with resolutions of 90 m and 1 km, respectively. Satellite data are also compared to outputs from a thermal engineering model adapted from the NOAA Land-Surface Model. Upon acquisition of the LST images, corresponding logger data and model outputs were selected by date and time, such that all three measurements are essentially coeval. Subsets of images were created to isolate areas coinciding with logger locations. DOQQs (1 m resolution) were used to categorize individual pixels as land, ocean, coast or a combination. These pixel values were then directly compared to in situ measurements and model results to determine which sensor (ASTER or MODIS) better reflects the conditions experienced by the intertidal mussels. Surprisingly, initial comparisons show that MODIS temperatures are more similar to in situ observations despite having a lower resolution than ASTER. Futhermore, individual logger readings within a given pixel can vary by as much as 10°C. These apparently incongruous results may actually point to a limitation in the nature of the in situ testing. Since each logger records conditions specific to one very small point on the shore, it does not adequately portray temperatures experienced within that general region of the coast. Therefore the satellites may in fact better characterize the general thermal conditions along the coastal boundary. This observation is being further investigated, along with better methods of locating loggers within satellite images.