Digital Topographic Data from Topsar Radar Interferometry: 
' Fernandina Volcano Galapagos Islands 
Peter J. Mouginis-Mark, 
University of Hawaii, U.S.A. 
ABSTRACT 
In May 1993, the TOPSAR airborne Interferometric radar collected a digital topographic 
data set for Volcan Fernandina, Galapagos Islands. These data have a spatial resolution of 
10 meters, and a vertical accuracy of about 2 meters. In addition to the topographic 
measurements simultaneous quad-pol L-band (24 cm) and P-band (70-cm) SAR data were 
collected. Almost the entire island (about 550 square kilometers) was mapped during a 
series of over flights by the radar, which is flown on the NASA/JPL DC-8. To help 
interpret these TOPSAR data, we have assembled a data base that includes Landsat 
Thematic Mapper, panchromatic SPOT, and JERS-1 OPS and SAR images. Furthermore, 
the island represents one of our Space Shuttle Radar (SIR-C/X-SAR) "Super-Sites", which 
will be imaged during flights planned for April and August 1994. 
The resultant topographic map is a unique set for Volcan Fernandina, which has previously 
never been completely mapped topographically due to cloud cover. The TOPSAR data 
serve as both a test case for the validation of the radar interferometric measurements, and 
for the analysis of this infrequently visited basaltic shield volcano. For example, the 
production of shaded relief and slope maps from TOPSAR data, and their comparison with 
the SPOT and TM images, has proven to be the most useful analysis method to date. 
While lava flows can be mapped from the optical data, shaded relief maps that simulated 
diverse lighting geometries aid the identification of cinder cones and show that there are no 
prominent rift zones on the volcano that indicate structural control on the distribution of 
intrusions. Maximum slopes exceed 30-degrees on the upper flanks of the valcano, and 
pose major problems for current models for the internal structure of the volcano's summit 
area. 
This paper will review the utility of TOPSAR data for volcano logical studies, and will 
include an analysis of the "error maps" which describe the quality of the phase correlation 
generated by the radar on a pixel-by-pixel basis. TOPSAR data were also collected for the 
adjacent Isabela Island (about 4,500 square kilometers), and an up-date for the on-going 
analysis of these data will also be presented. 
16 
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