Stereo Processor is an integrated software package specially
intended for generation of the ground relief digital elevation models (DEM)
via processing of the pairs of images acquired by spaceborne SAR's.
Stereo processor provides for users an extraction of terrain height information from stereo pairs of SAR satellite
imagery. It allows to generate an accurate digital elevation models (DEMs) of imaged ground surface.
The inputs of Stereo Processor are RADARSAT imagery distributed as georeferenced imagery of SGF or SGX data types.
All input data should be in CEOS format. Sophisticated radar sensor modeling ensures the precise DEM generation
results. The needed parameters for processing are derived by importer automatically from the CEOS headers.
It is done simultaneously with loading of SAR imagery into internal environment.
Co-registration of the stereo pair of images could be done by two ways: through the tie ground point and using
platform ephemeris data. Stereo processor correlates stereo pairs of SAR imagery automatically to extract radar
parallaxes needed for height extraction. User may define and customize correlator in order to meet the local
ground features. But the correlator can work without user's participation.
The resulted DEM pixel spacing is user's definable. An output DEM accuracy could be achieved up to several metes
that mostly depend of input data spatial resolution.
The output of processor is DEM in geographic projection on WGS-84 ellipsoid.
Review of processing flow
Approaches to stereo images coregistration
Coregistration step is needed for proper overlapping of two stereo images as
the preparation for the followed joint processing. Coregistration includes turning
of one of stereo pair image relatively to other and coregistration of images
along the SAR platform path (azimuth) axes.
Below two coregistration approaches are regarded which are both realized in
current version of Stereo Processor software:
coregistration with use of
two pair of tie points
coregistration via surveys
The coregistration approach with use of two pair of tie points may
be described as following. The user set two tie points on each image of stereo
pair. This operation is conducted interactively, i.e. both images are opened
into separate viewers, and user did this operation through GCP tool. Each tie
point on one image corresponds to tie point on other one. The aim of the turning
of slave image relatively of master one is their overlapping in such way that
the azimuth file coordinates of same ground elements became corresponded on
both images with some constant value. After that this constant value could be
transformed to zero one via shift of turned slave image along the azimuth exes.
All these successive operations allow reduce the matching procedure to one-dimensional
case. The one-dimensional matching is more preferred than two-dimensional one
because of much less computational cost and time of processing. However, in
principal it could be achieved only if all imaged ground surface elements are
located on the same elevation level. For the ground surface, which shows some
expressed relief, that is a common case, the precise overlapping for all surface
elements could not be achieved. This fact leads to necessity of two-dimensional
Coregistration on an ephemeris. As for the previous approach, the
two tie points should be set on each scene of stereo pair. The main difference
of second coregistration approach from first consists of those features, that
the turning angle are calculated upon the some reference surface independently
of tie points location and the elevation of reference surface may be controlled
by user. For resolving of this task we will use an ephemeris of each surveys,
which could be derived from auxiliary date accompanying processed scenes. These
allow us to realize the procedure of the chose of reference surface in such
way that minimizes the coregistration errors induced by different elevations
of the imaged relief.
This is a 3-D presentation of Canadian west coast site.
Picture is being composed through draping of Radarsat SAR image (standard
mode) over a relief digital matrix generated via Radarsat SAR stereo pair