Water Stratification Raster Images for the Gulf of Maine

This geodatabase contains seasonal water stratification raster images for the Gulf of Maine. They were created by interpolating water density (sigma t) values at 0 meters and 50 meters binned by season, and subtracting the water density surface at 0 meters from the water density surface at 50 m. This subtraction (as denoted by the raster value) indicates the differences in water density throughout the Gulf of Maine during the year. The more positive or negative the raster value, the larger the difference between the water density raster at 0 m and the water density raster at 50 m and thus, the more stratified the water. Similarly, the closer the raster value is to 0, the smaller the difference between the water density raster at 0 m and the water density raster at 50 m and thus, the less stratified the water. We tried this density difference calculation with 0 and 10 meters as well as 0 and 30 meters. We chose to use 50 meters as the lower water density depth because water less than 10 meters may have been subject to wind and convective mixing, and water less than 30 meters may have been influenced by internal waves. Water at 50 meters, however, illustrated the greatest difference in stratification strength (buoyancy frequency squared) between layers in the water column (Brown and Irish, 1993). The naming convention of the raster includes the year (or years) included in the the interpolation, the season, and the depth (in meters). So for example, the name: ws_1997_2004_Fall would indicate that this water stratification raster was created by subtracting water density rasters that were interpolated using data from 1997-2004 for the fall. The seasons were defined using the same months as the remote sensing data--namely, fall = September, October, November; winter = December, January, February; Spring = March, April, May and Summer = June, July, August.

This data was created in order to support a biogeographic assessment of the Stellwagen Bank National Marine Sanctuary.

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Brown, W.S. and J.D. Irish. 1993. The annual variation of water mass structure in the Gulf of Maine: 1986-1987. Journal of Marine Research. 51:53-107.

These data were prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views and opinions expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Although all data have been used by NOAA, no warranty, expressed or implied, is made by NOAA as to the accuracy of the data and/or related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by NOAA in the use of these data or related materials.NOAA makes no warranty regarding these data, expressed or implied, nor does the fact of distribution constitute such a warranty. NOAA can not assume liability for and damages caused by any errors or omissions in these data, nor as a result of the failure of these data to function on a particular system.

Please contact the Stellwagen Banks NMS Research Coordinator for additional information on data access (david.wiley@noaa.gov);

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None. Acknowledgement of the National Oceanic and Atmospheric Administration, National Ocean Service, National Centers for Coastal Ocean Science, Center for Coastal Monitoring and Assessment, Biogeography Program would be appreciated in products derived from these data.

Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 2; ESRI ArcCatalog 9.1.0.722

The spatial distribution of water density measurements varied between seasonal and yearly bins.

The accuracy of these water stratification rasters was not assessed. The accuracy of the water density layers on which these water stratification rasters were based, however, were validated. Specifically, 25% of the water density measurements were set aside before the interpolation. After the interpolation, the corresponding validation points were intersected with the interpolated rasters to calculate a simple difference between the observed (validation points) and the predicted (interpolated surface) measurement. These validation points and values are located in the Water_Stratification_Points geodatabase, Validation_Points feature data set.