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Monthly oceanographic data from remote
sensing
for marine analysis in the Gulf of Alaska and Bering Sea
Abstract
We prepared long term monthly time series at
a spatial resolution of 9 km x 9 km resolution to support several
research projects on marine habitat use and fisheries economics.
Data included chlorophyll-a concentrations, sea surface temperature,
sea level anomaly, and wind speed. The Geographic Information
System-compatible raster (gridded) data sets were created from
available on-line sources, and required considerable processing
to create a North Pacific perspective, and to ensure that the
data sets were correctly aligned. Given the work invested in
data preparation, we have prepared the data collection for distribution,
along with Federal Geographic Data Committee (FGDC) compatible
metadata files. The data are provided in binary float (.flt)
format making them compatible with most spatial data programs.
The collection is available on request from the authors.
Introduction
An on-going area of research at
the Marine Mammal Research
Unit (MMRU) is the at-sea distribution
of marine mammals and their prey. Habitat studies of widely distributed
marine species require data sets at similar extents. Data from
remote sensing are one of the few sources of the comprehensive
data sets necessary for such analyses.
Many of these data sets are now
available via on-line servers, allowing anyone with a computer
and internet access to obtain the various data sets. The data can
be obtained for different study areas, at different temporal resolutions,
and occasionally at different spatial resolutions. While the data
are available at various levels of processing, often from the raw
satellite data through to the end product (i.e., temperature),
it is typically the final products that are relevant to marine
analyses.
However the work to make the data
compatible for analysis in typical Geographic Information System
(GIS) tools begins after the data of interest are obtained. Different
variables are often provided in different digital formats, and
the spatial extents of global coverages typically range from -180
to +180 degrees longitude, adding an extra step to the data preparation
for North Pacific analyses.
As part of our studies, the MMRU
has obtained and prepared average monthly values for chlorophyll-a
concentrations ([Chla]), sea surface temperature (SST), sea level
anomaly (SLA), and surface wind speed (SW) for all months from
1992 to 2005, though not all data are available for all months,
because of the availability of the different sensors. The longest
time series available are for SST and SLA, while the shortest is
for [Chla]. Spatial resolution is also variable, with [Chla] being
obtained at our target resolution, SST obtained at a higher resolution
(4 km), and SLA and SW obtained at a coarser (0.25 degrees) resolution.
The data in the series have been
rectified to the same study area boundaries, with matching raster
grids and resolutions, and consistent spatial extents and projections.
Methods and Results
Study area description …
The steps described for each of
the parameters below were automated using VB programs using the
IDRISI Application Programmer Interface to apply spatial opertions
to the images … download scripts … ???
The following sections describe
in general terms how each data set was derived. More technical
details are contained in the associated metadata files.
Chlorophyll Concentration
Figure 1: Example of chlorophyll-a concentrations for the Bering Sea / Gulf
of Alaska study area.
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Sea surface
temperature
Figure 2: Example of Sea Surface Temperature for the Bering
Sea / Gulf of Alaska study area, for July 2005.
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FOR DETAILS
Figure 3: Example of sea surface temperature
slopes for the Bering Sea / Gulf of Alaska study area for July,
2007.
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FOR DETAILS
Sea level anomaly
Figure 4: Example of sea level anomaly for the Bering Sea
/ Gulf of Alaska study area for July 2005.
Surface wind speed
Figure 5: Example of surface wind speed for the Bering Sea
/ Gulf of Alaska study area for July, 2005.
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FOR DETAILS
Bathymetry
Figure 6: Bathymetry for the Bering Sea / Gulf of Alaska
study area.
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FOR DETAILS
Conclusions
This collection of monthly, physical oceanographic data is suitable
for a range of oceanographic analyses at the temporal scale of
months and seasons. The spatial scale of 9x9 km2 is a suitable
scale for the monthly data, and could be aggregated if seasonal
or long-term temporal averages were desired. Thus, these data
can support analyses in the North Pacific and Bering Sea across
a range of temporal and spatial scales. We hope this collection
will be of use to marine scientists interested in species distributions,
habitat description, marine classification, and protected area
designation.
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Chlorophyll Concentration
