Gamma ISP: Reference Manual

Generate SLC/MLI iamge parameter file for UAVSAR SLC and MLC data

NAME

par_UAVSAR_SLC - Generate ISP image parameter file from UAVSAR annotation file (ann) for SLC and MLC data products

SYNOPSIS
par_UAVSAR_SLC <ann> <SLC/MLI_par> <image_type> <image_format>

<ann>	(input) UAVSAR annotation file (*ann.txt)
<SLC_par>	(output) ISP SLC parameter file (example: yyyymmdd.slc.par)
<image_type>	image type flag 0: SLC (slc) in slant range coordinates 1: MLC (mlc) in slant range coordinates HHHH, VVVV, HVHV* are FLOAT format HHHV, HHVV, HVVV* are FCOMPLEX format
<image_format>	image data format flag 0: FCOMPLEX (pairs of 4-byte float (re,im)) 2: FLOAT (4-bytes/value)

EXAMPLES

par_UAVSAR_SLC cscade_06701_09075_001_090928_L090_CX_01.ann.txt cscade_06701_09075_001_090928_L090_CX_01.mlc.par 1 2

Reads the annotation file cscade_06701_09075_001_090928_L090_CX_01.ann.txt and generates the cscade_06701_09075_001_090928_L090_CX_01.mlc.par file. This parameter file should be used with MLC products that are FLOAT format.

DESCRIPTION

UAVSAR is a reconfigurable L-Band airborne radar built and operated by JPL http://uavsar.jpl.nasa.gov/. It can operate in both full polarimetric and repeat track interferometric modes.   Data can be obtained using the on-line search capability and can be downloaded freely. There are also sample data products available, see http://uavsar.jpl.nasa.gov/data.html.

Each data set consists of an text format annotation file consisting of keyword value pairs. The data products that comprise the data set are listed at the start of the annotation file. An example of this listing including the file extensing and description of the individual product files is shown here:
; Parameter file for cscade_06701_09075_001_090928_L090_CX_01 ; search for parameters/value rather than placement in file ; slc = single look complex slant range image ; mlc = multi look cross product slant range image ; dat = compressed stokes matrix of multi-looked data ; grd = ground range projected (equiangular) and multi-looked data ; hgt = dem that grd were projected ; slc_mag and slc_phase are derived from the same 8 bytes per pixel of the slc input file ; mlc_mag and mlc_phase are derived from the same 8 bytes per pixel of the complex mlc input files ; grd_mag and grd_phase ground range projected (equiangular) complex cross-products image ; Peg position is the nadir position of aircraft at the middle of the datatake ; Projection of image is relative to the flightline (S - along track position, C - cross track position) ; S0, C0 is offset to upper left coordinate of SLC in meters ; to display MLC amplitude and phase in mdx: ; mdx -h cscade_06701_09075_001_090928_L090_CX_01.ann cscade_06701_09075_001_090928_L090HHVV_CX_01.mlc -set mlc_mag cscade_06701_09075_001_090928_L090HHVV_CX_01.mlc -set mlc_phase ; general location of data (non-unique) Site Description = Cascades volcanoes ; URL of JPL website for precision data URL     = http://uavsar.jpl.nasa.gov/kml/2009/cscade_06701_09075_001_090928_L090_CX_01.htm ; list of precision data files slcHH   = cscade_06701_09075_001_090928_L090HH_CX_01.slc                      ; File Size 12739557600 bytes     slcHV   = cscade_06701_09075_001_090928_L090HV_CX_01.slc                      ; File Size 12739557600 bytes slcVH   = cscade_06701_09075_001_090928_L090VH_CX_01.slc                      ; File Size 12739557600 bytes slcVV   = cscade_06701_09075_001_090928_L090VV_CX_01.slc                      ; File Size 12739557600 bytes mlcHHHH = cscade_06701_09075_001_090928_L090HHHH_CX_01.mlc                    ; File Size 176932800   bytes mlcHVHV = cscade_06701_09075_001_090928_L090HVHV_CX_01.mlc                    ; File Size 176932800   bytes mlcVVVV = cscade_06701_09075_001_090928_L090VVVV_CX_01.mlc                    ; File Size 176932800   bytes mlcHHHV = cscade_06701_09075_001_090928_L090HHHV_CX_01.mlc                    ; File Size 353865600   bytes mlcHHVV = cscade_06701_09075_001_090928_L090HHVV_CX_01.mlc                    ; File Size 353865600   bytes mlcHVVV = cscade_06701_09075_001_090928_L090HVVV_CX_01.mlc                    ; File Size 353865600   bytes dat     = cscade_06701_09075_001_090928_L090_CX_01.dat                        ; File Size 442431000   bytes grdHHHH = cscade_06701_09075_001_090928_L090HHHH_CX_01.grd                    ; File Size 834474168   bytes grdHVHV = cscade_06701_09075_001_090928_L090HVHV_CX_01.grd                    ; File Size 834474168   bytes grdVVVV = cscade_06701_09075_001_090928_L090VVVV_CX_01.grd                    ; File Size 834474168   bytes grdHHHV = cscade_06701_09075_001_090928_L090HHHV_CX_01.grd                    ; File Size 1668948336 bytes grdHHVV = cscade_06701_09075_001_090928_L090HHVV_CX_01.grd                    ; File Size 1668948336 bytes grdHVVV = cscade_06701_09075_001_090928_L090HVVV_CX_01.grd                    ; File Size 1668948336 bytes hgt     = cscade_06701_09075_001_090928_L090_CX_01.hgt                        ; File Size 834474168   bytes kmz     = cscade_06701_09075_001_090928_L090_CX_01.kmz                        ; File Size 202830277   bytes

The data files themselves are without headers and in little-endian byte order. To use these files with the Gamma software, they must be converted to big-endian byte order using the program swap_bytes. A script has been written that automates that process by taking a list of files and swapping the bytes and placing the swapped files in a specified directory swap_bytes_all.

The different types of data files supported by the Gamma software are:

SLC:   Single-look complex data, 8 bytes per value (FCOMLEX), 4-bytes float real (FLOAT), 4-bytes float imaginary (FLOAT), SLCHH, SLCHV, SLCVH, SLCVV

MLC: Multi-look complex data. Three of these files are 4-byte/value float: mlcHHHH, mlcVVVV, mlcHVHV and three are complex valued: mlcHHHV, mlcHHVV, and mlcHVVV. These products are calibrated and multi-looked, typically with 3 range-looks and 12 azimuth looks and are sufficient for full polarimetric analysis.

GRD: These products are float or FCOMPLEX and have been resampled to geographic coordinates in latitude and longitude. Use the program par_UAVSAR_geo to create the Gamma DEM parameter file to describe these products. The terrain geocoding uses a DEM for the geocoding. This DEM is also provided in the data set as an HGT product. See documentation on par_UAVSAR_geo in the DIFF package.

Note that the GRD products can be either FLOAT or FCOMPLEX data format and require byte-swapping just like the MLC or SLC products.

Because the UAVSAR is an aircraft that does not move at constant velocity or on a perfectly smooth track, motion compensation is applied to the data, and a new reference track is created. This reference track is at a constant altitude and is part of a spherical orbit with a reference heading relative to North. This geometry is given the name SCH coordinate system. The coordinate system is locally defined by a reference point called the peg point, and a heading angle relative to north that follows the heading of the radar platform at the peg point. The peg point is chosed near the center of the track. The projection coordinates are:

S:   Along track distance in meters along the track relative to the peg point
C: cross-track coordinate in meters
H: altitude above the peg point

SCH is based on an approximating sphere to the ellipsoid at the peg point. The radius of this sphere is the ellipsoid radius of curvature in the along-track direction. The h unit vector is defined as the vector perpendicular to the ellipsoid at the peg point. It is also perpendicular to the approximating sphere. The prime meridian is the intersection of the plane perpendicular to the h vector containing the sphere center. The s unit vector is perpendicular to h and is parallel to the heading vector. The equator of the sphere is the great circle passing though peg point along the direction of the heading vector. The heading angle is defined as the clockwise rototation angle relative to north of the track. The c vector is defined as h x s completing the SCH coordinate system definition.

The state vectors in the ISP parameter are generated using the SCH geometry track information and then converted to geocentric XYZ in the WGS84 datum.
A constant velocity for the aircraft of 227 m/s is then used to create an artificial constant velocity SAR system flying along S at the reference altitude provided in the annotation file.

Note, because the UAVSAR track can have any direction, the SCH coordinate system and SCH map projection are preferred. Geocoding with other map projections will generally have large regions with 0.0 when SAR data are mapped. Furthermore, the DIFF/GEO program gc_map produces accurate layover-and shadow maps only when the projection is parallel to the map coordinate axies. Since SCH is defined parallel to the track, this condition is fulfilled. To use SCH as the projection, resample initial DEM to SCH coordinates using DEM_trans. An example image of the sample data scene of Mount Shasta Volcano in California is shown below. The track covers is about 90 km long and is parallel to the bottom of the page

Mt Shasta UAVSAR MLI image