5
the range-Doppler SAR processor and the parameter file. Appendix C provides the theory
for InSAR processing on a spherical Earth with no approximations. Appendix D
describes the algorithm that we use for ALOS-1 ScanSAR interferometry. Appendix E
describes the geometric image alignment algorithms developed for the TOPS-mode data
from Sentinel-1. Appendix F provides data on the geolocation accuracy of SAR imagery.
Appendix G provides instructions for installation and testing the GMTSAR package.
1.1 Objectives and limitations of GMTSAR
Creating synthetic aperture radar (SAR) images and interferograms (InSAR) from
satellite radar measurements requires specialized front-end computer codes for focusing
imagery and computing interferometric phase. However, much of the back-end
processing and display can be accomplished with existing generic codes. We have
developed a SAR/InSAR processing system that starts with raw (or SLC) SAR data in
radar coordinates, along with precise orbital information, and computes interferometric
products in geographic coordinates. Our design goals are to have a modular and portable
system based on a minimum set of new software. The system relies on precise orbital
information, as discussed below, and a consistent geometric model to achieve proper
focus and image alignment. The SAR processor code was originally derived from the
Stanford/JPL FORTRAN and re-written in the C programming language ensuring
compilation on many platforms using the standard gcc compiler. The remainder of the
front-end code has been developed and refined over the past decade as part of the
SIOSAR and ALOS_preprocess packages.
For the back-end processing we use the Generic Mapping Tools (GMT), which is an
open source collection of programs designed for manipulating and displaying geographic
data sets [Wessel and Smith, 1998; Wessel et al., 2013]. It is widely used among the
geophysical community, well documented, and continuously updated. GMT includes
efficient and robust programs for regridding, filtering, and trend removal, which makes it
highly useful for some aspects of InSAR processing. GMT uses the NETCDF file
format that allows the exchange of files among computers having different architectures.
The combined front- and back-end processing is done using the c-shell scripting
language which is available on all UNIX platforms. We encourage the development of
new modules and InSAR processing recipes from the broader InSAR community. The
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