Satellite Remote Sensing of Ocean Fronts and Eddies off Mid-Norway

The oil industry requires more knowledge about currents and eddies for the deepwater exploration west of Mid-Norway. The study is part of the Metocean Project of the Norwegian Deep Water Programme coordinated by Norske Shell. More than 60 Synthetic Aperture Radar (SAR) scenes from the ERS-2 satellite, each covering 100 by 100 km, were investigated for low wind conditions allowing observation of current patterns and fronts. Location, scale and rotation of eddies was determined from the SAR images. The eddy circulation from SAR images was compared with in situ current measurements from arrays of moorings, showing a general agreement between the two techniques. In addition, altimeter data from ERS and TOPEX/Poseidon satellites, obtained during the period from 1992 to 1998, were analyzed in order to estimate geostrophic currents in the study area. Sea level anomaly data from altimeter can be used to calculate seasonal eddy kinetic energy and 10-day averaged geostrophic velocity anomalies presented as gridded data on maps. Geostrophic velocity anomalies from an altimeter track located near current meter moorings were correlated with current measurements over a three year period. The highest correlation of 0.65 was found between current at 300 m depth and altimeter points located about 30 km from the mooring. Preliminary comparisons between the SAR and altimeter results indicate that there is qualitative agreement between interpolated velocity vectors from altimeter and instantaneous current pattern observed in SAR imagery. The time and spatial scales of the two methods are different, however, which makes it difficult to perform accurate comparisons. The study showed that satellite SAR and altimeter data can play an important role to obtain synoptic information about current regimes over larger areas, which is complementary to standard buoy measurements at fixed locations and model simulations.NERSC Technical Report no. 179. Funded by Norska Shell AS, Order no. NDP.1999.0