Update Geo Reference Operator

This operator updates the Geo reference of the source product. The geocoding generated from the latitude and logitude tie point grids of the source product is generally not accurate. This is because topography was not taking into consideration when latitude and longitude tie point grids were generated. This operator generates a new geocoding for a given source product using DEM, orbit state vectors of the source image, and mathematical modeling of SAR imaging geometry.

Interpolation Methods Supported

The operator supports the following interpolation methods:

Nearest-Neighbour interpolation
Bilinear interpolation
Cubic Convolution interpolation
Bicubic interpolation
Bisinc interpolation

DEM Supported

Right now only the DEMs with geographic coordinates (Pא, Pא, Ph) referred to global geodetic ellipsoid reference WGS84 in meters are properly supported.

By default the following DEMs are available:

ACE
GETASSE30
SRTM 3Sec GeoTiff
ASTER GDEM

Since the height information in ACE and SRTM is referred to geoid EGM96, not WGS84 ellipsoid, correction has been applied to obtain height relative to the WGS84 ellipsoid.

User can also use external DEM file which, as specified above, must be WGS84 (Pא , Pא, Ph) DEM in meters.

Parameters Used

The following parameters are used by the operator:

Source Band: All bands (real or virtual) of the source product. User can select one or more bands for target product. If no bands are selected, then by default all bands are selected. The selected bands together with lat_band and lon_band are output.
Digital Elevation Model: DEM types. Choose from the automatically tiled DEMs or specify using a single external DEM file by selecting "External DEM".
DEM Resampling Method: Interpolation method for obtaining elevation values from the original DEM file.
External DEM: User specified external DEM file. Currently only WGS84-latlong DEM in meters is accepted as geographic system.
DEM No Data Value: Place holder for no data cell in DEM.
Re-grid method: Checkbox indicating selection of one of the two methods for defining lat/lon grid. By default, this checkbox is unselected and source geocoding is used as the starting point in computing the new geocoding. If this checkbox is selected, then a lat/lon grid that covers the imaged area is used in computing the new geocoding.