GENERAL DESCRIPTION Elevations are given in meters Magnitudes are given in meters/year Orientation relative to Grid North Polar stereographic Projection WGS 84 ellipsoid For more information on RAMP please visit our website www-bprc.mps.ohio-state.edu/rsl A velocity product consists of this README file, a parameter file, five data files, and the source code for two programs to access the data: README velocity_overview.par velocity_overview.dat velocity_overview.conf velocity_overview.ind velocity_overview.dem velocity_overview.img m_data2raster.c read_vmd.c The following is a description of each. 1) velocity_overview.par The parameter file contains the names of the data files, image dimensions, upper left corner map coordinates and pixel spacing. 2) velocity_overview.dat This data file is a binary file containing 8 different elements for each velocity point. Each element is a 32 bit float raster file. Each point internally is defined by the following structure: FIELD NAME DESCRIPTION magnitude flow speed in m/yr elevation; Elevation of point in meters slope_x; East component of terrain slope slope_y; West component of terrain slope Vx; East component of ice velocity Vy; North component of ice velocity Vz; Vertical component of ice velocity speed_error; Speed Error dir_error; Directional Error long int offset; Offset to entry in conflation file Each data element can be extracted from the *.dat file using the m_data2raster.c code provided (see below). 3) velocity_overview.conf The Conflation file contains for each point, information on all source data contributing to that point. The conflation index can be extracted using read_vmd.c code (see below). The offset field gives the number of bytes to the start of each conflation block for each point. a. 1 byte-method contains the method that the velocity measurement was made. The methods are: Mode 1: Offsets only - Azimuth offset. The refined baseline and a DEM is used to remove the DEM deduced azimuth and slant range components from the original offsetmap. The velocity vector is assumed to lie on the top surface plane. Any slope of the place where the tie point is will affect the direction of the velocity vector. A DEM will be needed to calculate the local slope. An option will be given to the operator so that the velocity vectors will be only horizontal. The Accuracy is about 4 ~ 10 m/y for fine beam and 7 ~ 16 m/y for standard beams for this mode. Mode 2: Azimuth offset - Range phase. In addition to the offsetmap the phase image of the interferogram is also used for the velocity estimation. A smililar procedure as that used in mode 1 will be used to remove the DEM deduced phase components from the original interferogram by using the refined baseline and a DEM. The Accuracy of this mode is about 2 ~ 4 m/y both fine beam and standard beams. Mode 3: Azimuth - Azimuth offset only. The ascending and descending interferograms of the same site are used. This mode uses azimuth offset only to calculate the velocities. Accuracy is about 2 ~ 4 m/y depending on the crossing angle of the ascending and descending orbits. Mode 4: Range - Unwrapped phase only. The ascending and descending interferograms of the same site are used. This mode used the unwrapped phase only for the velocity map calculation. Accuracy is about 0.1 ~ 0.4 m/y depending on the crossing angle of the ascending and descending orbits. b. 32 bit float - Speed error c. unsigned short - Index refers to the entry in the index table described below. 4) velocity_overview.ind The datatake index file contains the information on the datatake pair from which the velocities were derived. The datatake index can be extracted using read_vmd.c code (see below). After extraction, the following information will be given for each datatake: Datatake Index Number, Beam ID, reference orbit number, reference date, secondary orbit number, secondary date, baseline, doppler overlap, number of Velocity control points. ie) 6: S6 25576 20000928 25233 20000904 -182.048248 461.418304 16 This is followed by a list of VCP's, each containing map East, map North, elevation, speed, direction and source. 5) velocity_overview.dem This contains a 400meter 16-bit binary coregistered DEM covering the area of interest. 6) velocity_overview.img This contains a 400meter 16-bit binary coregistered power image (SAR orthorectified mosaic) covering the area of interest. 7) The software consists of the following: The codes are written in 'c' and can be compiled on UNIX/IRIX/LINUX platforms as follows cc -o read_vmd.c cc -o m_data2raster.c -lm m_data2raster - Extracts any of the velocity elements from the velocity_overview.dat into a floating point raster. usage: m_data2raster -in velocity_overview.par -out -field_name Field names are as follows: -elevation -slope_x -slope_y -magnitude -Vx -Vy -Vz -speed_error -dir_error [-swab_in] -If using a Linux or windows box. [-swab_out] -Can be used if on a big endian box and generating a file for use on a little endian box. [-h] -print usage read_vmd.c - For any point given in the raster will print out all information concerning that point (extacts data contained in the velocity_overview.conf and velocity_overview.ind usage: read_vmd velocity_overview.par - Options : -line : line position (row) -pixel : pixel position (column) -x : easting coordinate (polar stereographic map coordinate) -y : northing coordinate (polar stereographic map coordinate)