Sea Surface Current Estimates Off Central California as Derived from Enhanced AVHRR Infrared Images
Sea Surface Current Estimates Off Central California as Derived from Enhanced AVHRR Infrared Images

Author: Chung-Ming Fang

Publisher:

Published: 1987

Total Pages: 51

ISBN-13:

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A technique is presented which uses an interactive computer program to estimate sea surface current velocities from the displacement of sea surface temperature (SST) patterns apparent in enhanced sequential infrared images obtained from the NOAA-6 Advanced Very High Resolution Radiometer. This technique was applied to the surface currents of the California Current System using IR image data from 27 and 28 April 1981. This technique, which uses enhanced pseudocolor gradient imagery, produced more current vectors than an earlier technique develop by O'Hara (1987) which used unenhanced gray scale imagery. The resultant surface vectors agree well in direction but underestimate velocities obtained from Doppler Acoustic Log (DAL) measurements taken during the same period. The two methods produced closest agreement of current velocities of less than 40 cm/sec and with satellite-derived velocities obtained with sequential 12 hour images rather than sequential 24 hour images. Satellite-derived velocities in the rapid flow area (larger than 40 cm/sec) showed poor correspondence to DAL-measured velocities. The strong current shear in these areas may distort the surface SST patterns making identification of features between two images more difficult. The satellite derived surface velocities are assumed to be representative of the velocities of the upper mixed layer, which is usually 10 to 30 m deep in the study region.

An Investigation of Surface Current Patterns Related to Upwelling in Monterey Bay, Using High Frequency Radar
An Investigation of Surface Current Patterns Related to Upwelling in Monterey Bay, Using High Frequency Radar

Author: Andres Enriquez

Publisher:

Published: 2004-06-01

Total Pages: 101

ISBN-13: 9781423518105

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High Frequency (HF) radar backscatter instruments are under development and testing in the marine science and defense science communities for their abilities to remotely sense surface parameters in the coastal ocean over large areas. In the Navy context, the systems provide real-time mapping of ocean surface currents and waves critical to characterization and forecasting of the battlespace environment. In this study, HF radar, aircraft and satellite information were used to investigate and describe surface current in Monterey Bay, California, for a period of ten months, from June 1, 2003 to March 31, 2004. A network of five CODAR-type HF radar instruments measured hourly surface currents over the bay. The measurements were averaged over one-hour intervals and total surface velocities were mapped on a grid in the Monterey Bay. Major upwelling events were observed during the period of June 14 to June 27, July 4 to July 19, August 8 to August 18 and other upwelling events were observed until late October. These periods of upwelling favorable winds are common during summer with durations of 10 to 20 days. Cyclonic circulation cells are developed on shore during upwelling conditions and an anticyclonic circulation in the middle of the bay is observed when the wind shifts to the southwest producing a strong flow out of the bay close to the coastline off Point Pi os. Downwelling conditions are much less common than upwelling, with occurrences during winter and early fall storms with events lasting between two to five days. When the wind blows to the northeast with an intensity of 4 m/s or more for more than 12 hours, a well developed anticyclonic gyre forms in the middle of the bay. This is associated with a strong current, 35 to 40 cm/s, which flushes out in the southern part of the bay close to the coast off Point Pi os. This flow reverses when the winds veer to the southwest and enter into the Bay with less intensity.