90 
Measuring Surface Currents and Subsurface 
Phenomena with the CCRS Along Track InSAR 
John W. M. Campbell, A. Laurence Gray and Karim E. Mattar 1 
Canada Centre For Remote Sensing, 588 Booth St., Ottawa, Ontario, Canada 
Tel: (613) 998-9060, Fax: (613) 993-5022, Email: jcampbel@ccrs.emr.ca 
John Hughes Clarke 
Ocean Mapping Group, Dept. Geodesy and Geomatics Engineering 
Univ. of New Brunswick, P.O. Box 4400, Fredericton, NB, Canada 
Tel: (506) 453-4568, Fax: (506) 453-4943, Email: jhc@atlantic.cs.unb.ca 
1 - Employee of Intera Information Technologies, Ottawa, under contract to CCRS 
ABSTRACT 
The Canada Centre for Remote Sensing owns and operates a C/X-band airborne synthetic 
aperture radar (SAR) with both polarimetrie and interferometric capabilities. In 1993, this 
SAR was modified to operate in an along track interferometric mode at C-Band 
(A = 5.656cm) in HH polarization using a microstrip antenna mounted on the right side of 
the aircraft. This antenna is divided into two sub-antennas with phase centres separated by 
approximately 0.46 meters along the aircraft. In June, 1994 the interferometric SAR 
(InSAR) was flown in a series of missions over the Bay of Fundy in conjunction with a 
dune survey experiment undertaken by the Canadian Hydrographic Services vessel, NSC 
Frederick G. Creed. A second experiment without the NSC Creed was undertaken in June, 
1995. These missions were used to test the ability of the InSAR to measure ocean surface 
velocities and use them to produce surface current vector maps and to detect subsurface 
features such as shoals or sand dunes. Measurements from the Simrad EM 1000 multibeam 
sonar on board the ‘Creed” were used to verify the measurements made by the airborne 
InSAR in the June, 1994 experiment. The results indicate that airborne along track InSAR 
is capable, under the right conditions, of detecting changes in bottom topography and of 
providing a high resolution snapshot of the surface currents in a large area at a specific 
time. 
1. INTRODUCTION 
Conventional SAR imagery has been used to study the ocean for many years. Short 
wavelength (centimeter scale) capillary waves on the surface of the water are affected by 
many geophysical parameters, such as the wind stress, the local currents, and larger scale 
gravity waves. Bragg scattering occurs between the microwaves transmitted from a SAR 
and any surface which has modulations of the appropriate wavelength, A = nA / (2 sin 0), 
where 0 is the radar incidence angle, A is the radar wavelength (5.656 cm in the case of