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3. SURFACE CURRENT MEASUREMENTS 
One important reason for testing the InSAR in the Bay of Fundy was that this area has 
extremely fast flowing dynamically changing currents. In order to obtain a full vector plot 
of these currents in a given area, it is necessary to combine the interferogram velocity 
information from two different flight lines flown close together in time over this area with 
nearly perpendicular aircraft track angles. The necessity of reorienting the aircraft on a 
new track and initializing the InSAR for data from a new flight line, means that the 
minimum time between tracks is approximately twenty minutes. Only currents which 
remain constant over this time period can be properly measured. An example of the results 
obtained with this technique near Cape Split during a flood tide is shown in Figure 1. This 
image represents a 10.5 km by 10.5 km square, with the colour of each pixel representing 
the magnitude of the velocity vector at that pixel. The colour map stretches from black (0 
m/s) through red, orange, yellow and finally white (5 m/s). The arrows show the current 
vectors for averaged areas of 250 m by 250 m centred at the base of each arrow. The 
shear current around the tip of Cape Split as the tide flows into the Minas Basin is clearly 
seen in the figure, as is the division of water flow between that which passes Cape Split 
and that which hits Cape Split directly and then eddies back into Scots Bay (SE of the area 
shown in the figure). The phase calibration of this image appears to be quite accurate, 
since all of Cape Split and the small portion of the New Brunswick shore visible in the NE 
of the image appear very dark. This image represents a ‘snapshot’ of the currents over a 
wide area during a twenty minute period in the tidal cycle. The pattern of currents is 
consistent with existing models for this area during a flood tide. 
Figure 2 shows a close-up view of a 1600 m by 1600 m area NW of Cape split. In this 
image the velocity vectors were generated from 40 m by 40 m averaged areas. A distinct 
funnel effect can be seen as much of the current is directed towards a channel of faster 
flowing water (yellow and orange pixels surrounded by red) moving NE. This indicates 
that the area contains some unusual bottom topographic feature. A bottom trench or some 
underwater obstruction with a hole in it where the funnel passes through are both plausible 
explanations. This is interesting, because sonar maps of the area do indicate a trench 
leading NE from the Scots Bay dune field which is to the SW of this image and a 
corresponding depth anomaly also appears to the NE of this image. No sonar map is 
available for this area because the rapid currents and eddies combined with the proximity 
to Cape Split make navigation too hazardous for survey vessels to approach. The presence 
of the funnel in the surface currents does suggest, however, that the trench continues 
through this area. Even more detailed close-up views are possible, since the current vector 
data is produced by the InSAR on a 5 m by 5 m Universal Transverse Mercator (UTM) 
grid. 
Figure 3 shows a current vector map superimposed on a radar magnitude image (rather 
than a color coded velocity image as in Figures 1 and 2) which was obtained under the 
much more difficult conditions imposed during the imaging of the area near Letete 
Passage at the entrance to Passamaquoddy Bay. Here the bright islands in the image can 
saturate the radar and make it difficult to observe the water. This 5 km by 5 km scene also