91 
the CCRS InSAR) and n is a positive integer. In the case of water which has a large 
dielectric constant, this is the main scattering mechanism and thus all of the geophysical 
parameters which affect the capillary waves also affect the scattering properties of the 
ocean at radar wavelengths. The precise relationship between the radar cross section 
(RCS) of the ocean and the relevant geophysical parameters is difficult to define, however, 
and different models have been suggested [i.e. Alpers et al., 1981; Hasselmann et al., 
1985; Moore, 1985]. 
Along track InSAR provides a more direct way of observing the properties of the ocean 
than conventional SAR imagery. The phase difference between the radar images received 
by two antennas separated along the flight path of the aircraft is used to directly measure 
the velocity of each target pixel in the radial direction (approximately parallel to the radar 
boresight). This type of measurement is independent of the target’s RCS, removing one 
layer of complexity from the problem. It is still necessary to relate the radial velocity to the 
desired geophysical parameters, but this is, in principle, a much simpler procedure. During 
the past few years several groups have used the along track interferometry technique to 
study ocean waves [Marom et al., 1991; Schuchman et al., 1992; Goldstein et al., 1994], 
ocean currents [Goldstein et al., 1987, Shemer et al., 1993; Ainsworth et al., 1994] and 
ship wakes [Orwig et al., 1992; Thompson et al., 1993]. 
Between May 31 and June 3, 1994, the CCRS along track InSAR carried out a series of 
flights over the Minas Channel in the Bay of Fundy. The tides in this area are among the 
most dynamic in the world and produce currents with extreme spatial and temporal 
variability. There are also several interesting underwater features in this area, such as the 
Scots Bay and Margaretsville dune fields. Conventional SAR imagery has previously been 
used to detect dune fields using the modulations in Bragg scattering caused by the 
changing depth affecting the velocity of currents passing over the dunes [van der Kooij et 
al., 1995]. This is useful, because it is extremely important to keep track of bottom 
topography and especially the location of potential shipping hazards such as shoals or 
dune fields. Currently this information is usually gathered through ship based surveys. In 
the Bay of Fundy mission the goal was to determine whether along track InSAR could be 
used to enhance the detection and mapping of these types of subsurface features and also 
to investigate the ability of the InSAR to produce detailed maps of the currents in this 
dynamic environment. The Canadian Hydrographic Services vessel, NSC Frederick G. 
Creed, was engaged in a dune survey during this time period. This allowed the sonar data 
from this survey to be used to validate the conclusions drawn from the InSAR data. After 
this initial experiment, a more difficult area was chosen for the following year. On June 24, 
1995 the InSAR imaged the Letete Passage area at the entrance to Passamaquoddy Bay to 
determine if currents could also be mapped in the more difficult imaging environment of a 
series of narrow channels through multiple islands. 
In Section 2 of this paper, the equipment used in both the airborne and ship based parts of 
the experiment is described. In Section 3, the results obtained by the airborne InSAR in 
both the 1994 and 1995 missions are reported and analyzed in terms of mapping surface 
currents. Section 4 considers the measurements which were related to detecting