Michael Crowley Masters Thesis - May, 1993
Monitoring the Gulf Stream:
An Application of Remote Sensing and Geographic Information Systems
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Abstract
A new method of portraying the ocean surface has been applied to the Gulf Stream Meander and Ring Region. The GRASS Geographic Information System (GIS) was used to create accurate weekly surface maps of the Gulf Stream's north wall and ring locations using a combined remote sensing and in situ database assembled for this project. The database includes AVHRR imagery calibrated for sea surface temperature, Geosat altimeter measurements of sea surface height, and expendable bathythermograph (XBT) measurements of subsurface temperatures. The weekly surface maps created during data rich periods are ultimately used to test and improve dynamical ocean forecast models. The use of a GIS to overlay and interpret the multiple platform database aids in creating more accurate maps than in previous studies of the same time period by NOAA and Harvard University. The development of a new AVHRR compositing technique further increases accuracy by eliminating the feature smearing experienced with the more common warmest pixel composite technique.
The GIS is also used to statistically compare the Gulf Stream locations obtained with the three data sets. The AVHRR-derived surface north wall is 13.2 +/- 14.8 kilometers north of the Geosat-derived maximum velocity axis. The XBT -derived subsurface north wall is 8.9 +/- 11.2 kilometers to the north of the Geosat maximum velocity axis. Average offsets and RMS values between the axis and north wall increase as one moves from meander trough, to a flat Stream, and on to a meander crest. This demonstrates that the Gulf Stream width increases with increasing anticyclonic curvature, confirming the expected effects of centripetal acceleration on the flow.