Data Management Plan

This feature class contains internal wave packets extracted from SAR imagery that were binned in 30x30 second latitude/longitude polygon grid cells. Statistics were calculated for each polygon grid cell---in particular, internal wave packet frequency, total internal wave packet area, average internal wave packet area, minimum internal wave packet area, maximum internal wave packet area, the variance of internal wave packet areas and the standard deviation of internal wave packet areas. These statistics were calculated so as to better understand the frequency, size and location of internal wave packets in Massachusetts Bay.

Process Steps:

• 2006-02-01 00:00:00 - BACKGROUND:Synthetic Aperture Radar (SAR) can detect internal waves by emitting pulses of X-band (3cm), C-band (6cm) and L-band (24 cm) microwave energy, producing a two-dimensional radar backscatter map of the roughness of the ocean surface (Jackson and Apel, 2004 p.21, 41). In SAR imagery, internal waves appear as packets or groups of waves characterized by :1) Alternating bands of bright and dark bands. The bright band is associated with the convergence zone, as determined by the orbital particle motion within the internal wave. 2) Curvilinear wave crests bent by refraction 3) Decreasing wave crest lengths from front to back of each packet 4) Decreasing wavelengths from front to back of each packet, indicating propagation direction and that nonlinear wave dispersion is in effect. 5) Decreasing wave amplitudes from front to back of each packet 6) Propagation parallel to significant isobaths Less often, internal waves may also be seen composed of only dark bands with no associated bright bands. This varying appearance is due to sensitivity to wind speed and wind direction, as well as to the orientation of the wave groups to the radar platform (Jackson and Apel, 2004 p.47). METHODS: In this study, the following methodology was used to identify and delineate internal wave packets in ESRI ArcGIS (ArcView) 9.1. First of all, a search extent was defined in order to narrow the geographic area in which to look for the internal waves. This area roughly covered from 42 deg 44 min 19 sec N to 41 deg 30 min 2 sec N and from 71 deg 8 min 3 sec W to 69 deg 36 min 30 sec W.. Each of the 66 SAR images (which were taken between May 14, 1997 and August 29, 2003) were examined for internal waves, using the internal wave packet characteristics listed above as an identification guide. A ESRI polygon shapefile was created with columns recording the SAR image tile name, its year, date and time, as well as the internal wave packet area, packet propagation direction and moon phase during which it occurred. All internal wave packets were digitized at a 1:350,000 scale and saved in this shapefile, along with the necessary attribute information. The internal wave packet data were analyzed using a non-parametric Kruskal-Wallis test for significant differences in the median with a Dunn's post hoc test.

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