INTEGRATED AIRBORNE IFSAR MAPPING SYSTEM 
Ming Wei and Tim Coyne 
Intermap Technologies Corp., 1200, 555-4th Avenue S.W., Calgary, Alberta, Canada T2P 3E7 - 
mwei@intermap.ca and tcoyne@intermap.com 
Commission I, WG 1/2 
KEYWORDS: Synthetic Aperture Radar (SAR), Interferometry, IFSAR, DEM, GPS/INS, Airborne gravity system, Geoid 
ABSTRACT: 
A Digital Elevation Model (DEM) is fundamental information for the geo-spatial data infrastructure framework. Many applications 
require three-dimensional (3-D) geo-spatial data with high spatial resolution and accuracy. One leading technology of the nationwide 
3-D mapping is airborne interferometric SAR mapping system due to its all-weather acquisition capability. Compared to other 
airborne mapping systems, the other advantage of the IFSAR mapping system is the efficiency. Flying at an altitude of 10 km, the 
Intermap IFSAR system can map an area of 10000 to 20000 km2 per flight. The airborne IFSAR system consists of synthetic 
aperture radar sensor with two radar antennas and the GPS/INS components. The radar pulse signals are collected from two radar 
antennas and compressed by digital match filtering to extract the interferometric phase information. The GPS/INS system can 
provide highly accurate position and orientation information. Combining the SAR interferometric information and the GPS/INS 
navigation results the ortho-rectified radar image with 3-D information can be obtained. Based on the GPS/INS components of the 
IFSAR system a new airborne gravity and geoid mapping system is developed by Intermap. The regional geoid undulation can be 
determined by the airborne gravity system and the ellipsoid height is transformed to the orthometric height directly from the 
integrated IFSAR system. Thus the integrated IFSAR system can simultaneously provide both sea level referenced DEM data and 
gravity field information. This opens the application of IFSAR DEM mapping in the rural and mountain areas where accurate gravity 
data and geoid are not available. 
1. INTRODUCTION 
Airborne Interferometric Synthetic Aperture Radar (IFSAR or 
INSAR) technology attracts much attention in the geospatial 
community over the last decade. Advantages associated with 
airborne IFSAR mapping include flexibility of system 
deployment, near weather-independent operation, cloud 
penetrating capability, versatile map products, and quick turn 
around time. Leaders in the geospatial community are gradually 
realizing that airborne IFSAR is emerging as a complementary 
or competitive cost-effective 3-D mapping technology which 
mainly provides digital surface models (DSM), digital terrain 
models (DTM), and orthorectified radar imagery (ORI). 
The new development of Intermap IFSAR system focuses on 
the two major issues: enhance the system efficiency and 
improve the mapping accuracy. This can be achieved by 
improving the data acquisition process, the IFSAR processing 
algorithm including GPS/INS integration algorithm and the 
calibration method. 
For the 3-D mapping applications, accuracy is one of the most 
important performance indicators of the IFSAR system. In this 
paper, a detailed error model of 3-D SAR image and DEM is 
presented for an analytic assessment. The comparison of the 
IFSAR DEM to external DEM data demonstrates that the 
accuracy of 0.5 - 1.0 m of DEM can be achieved by the 
Intermap IFSAR mapping system. 
The DEM height based on the GPS solution is normally referred 
to the ellipsoid. To obtain the orthometric height the accurate 
geoid undulation is required. Based on the GPS and IMU 
components of the IFSAR system, Intermap has developed an 
airborne inertial gravity system to extract the gravity 
disturbance information from highly accurate IMU 
measurements. Using the gravity information the precise local 
or regional geoid over the flight area can be determined. By 
using a global geoid model, such as EGM96, the accurate 
absolute geoid with adequate resolution is determined and the 
ellipsoid height is transformed to the orthometric height. The 
mapping products of the Intermap IFSAR system can be 
directly referenced to the geoid without the external geoid 
information. In the paper, the algorithm of determination of the 
local or regional geoid from the integrated GPS/INS data is 
presented. The evaluation results show that an accuracy of 2-3 
mGal for the airborne gravity measurement and 5-10 cm for the 
geoid, determined by Intermap IFSAR airborne gravity and 
geoid mapping system, can be achieved. 
The objective of this paper is to present the integrated airborne 
IFSAR mapping system, developed by Intermap, for both DEM 
and geoid mapping applications. An overview of the IFSAR 
mapping process including the principle of the geo-coding for 
3-D mapping is given in the paper. Also, the concept of 
integrated airborne IFSAR mapping system will be introduced. 
The roll of GPS/INS as georeferencing for the 3-D mapping, the 
principle of airborne geoid mapping based on GPS/INS are also 
included in the paper. The characteristics and the accuracy of 
the integrated mapping system are discussed in detail. The 
critical issues in mapping rural and mountain areas with limited 
ground supports are included. The results from some test 
examples demonstrate the capability of the integrated IFSAR 
mapping system. 
2. AIRBORNE IFSAR TECHNOLOGY 
2.1 Principle of SAR Interferometry 
3-D mapping using IFSAR system is typically based on the 
principle of interferometry of two SAR images. The radar pulse