Ryan Weatherbee

Coastal sea surface temperature variability from Landsat infrared data

Abstract A time series of 23 Landsat Thematic Mapper (TM) band 6 thermal infrared images over the period 1986–1996 is used to quantify variability of sea surface temperature (SST) along the central coast of Maine, a morphologically complex region of bays, estuaries, and islands. An iterative regression scheme using coregistered, temporally coincident, daily composites of Advanced Very High Resolution Radiometer (AVHRR) Pathfinder SST data is used to scale the TM digital numbers in each scene to SST, approximating an atmospheric correction. This approach provides temporally concurrent match-ups, even for Landsat scenes more than 10 years old and over 1000 data points to most regressions. Analysis of the TM scenes by year–day delivers temporal resolution sufficient for insight into overall seasonal pattern and allows identification of recurring seasonal features within the study area. The dominant seasonal patterns is a cross-shelf SST gradient of coldest water nearshore in winter which reverses sign in summer and disappears in spring and fall. Differences in summer SST are evident between four adjacent bays, attributable to differences in residual circulation, freshwater input, and flushing. Recurrent frontal zones evident in summer are identified and compare well to available but noncoincident in situ hydrographic data.

Comparisons of chlorophyll variability between the four major global eastern boundary currents

The first two years of SeaWiFS (Sea viewing Wide Field of view Sensor) data (1997–1999) are used to document the variability of large-scale surface chlorophyll patterns within the coastal region along the full latitudinal extent of each of the four major global eastern boundary currents; the California, Humboldt, Benguela and Canary Currents. Seasonal chlorophyll patterns are compared to coincident seasonal cycles of Ekman transport calculated from satellite scatterometer data. In all four regions, maximum chlorophyll concentrations are generally temporally and latitudinally coincident with the seasonal maximum in upwelling (offshore Ekman transport) over most of their latitudinal range, but exceptions are documented. Interannual differences are evident in each region, most notably in the two Pacific regions where the 1997–1998 chlorophyll seasonality was affected by El Niño conditions. Significant differences between previously published chlorophyll seasonality deduced from the relatively sparse coverage of the Coastal Zone Color Scanner (CZCS) and the more complete coverage of SeaWiFS in both Southern Hemisphere regions are evident.

Oyster Aquaculture Site Selection Using Landsat 8-Derived Sea Surface Temperature, Turbidity, and Chlorophyll a

Remote sensing data is useful for selection of aquaculture sites because it can provide water-quality products mapped over large regions at low cost to users. However, the spatial resolution of most ocean color satellites is too coarse to provide usable data within many estuaries. The Landsat 8 satellite, launched February 11, 2013, has both the spatial resolution and the necessary signal to noise ratio to provide temperature, as well as ocean color derived products along complex coastlines. The state of Maine (USA) has an abundance of estuarine indentations (~3,500 miles of tidal shoreline within 220 miles of coast), and an expanding aquaculture industry, which makes it a prime case-study for using Landsat 8 data to provide products suitable for aquaculture site selection. We collected the Landsat 8 scenes over coastal Maine, flagged clouds, atmospherically corrected the top-of-the-atmosphere radiances, and derived time varying fields (repeat time of Landsat 8 is 16 days) of temperature (100 m resolution), turbidity (30 m resolution), and chlorophyll a (30 m resolution). We validated the remote-sensing-based products at several in situ locations along the Maine coast where monitoring buoys and programs are in place. Initial analysis of the validated fields revealed promising new areas for oyster aquaculture. The approach used is applicable to other coastal regions and the data collected to date show potential for other applications in marine coastal environments, including water quality monitoring and ecosystem management.