Speckle tracking velocity maps of the Sorsdal and East Ranvik Glaciers

The orbits are sun-synchronized and repeat (to within a few hundred meters) every 167 orbits. So the repeat pattern gives rise to 167 tracks , and mm = nnnnn mod 167 File Format The directory for each track contains the following files: mosaicOffsets.meta: metadata for the image acquisitions mosaicOffsets.vx, mosaicOffsets.vy: velocity components in gridded format mosaicOffsets.ex, mosaicOffsets.ey: optional files providing pixel-by-pixel error estimates for the corresponding .vx and .vy files mosaicOffsets.??.geodat: location information for grid The metadata for each track take the sample form: Central Julian Date (CE) for Pair = 2457443.621 First Image Date (MM:DD:YYYY) = Feb:13:2016 Second Image Date (MM:DD:YYYY) = Mar:06:2016 Nominal Time for Pair (HH:MM:SS) = 14:53:56 Sensor = TSX/TDX Product Center Latitude = -68.95923 Product Center Longitude = 78.21724 Production Date/Time = Sep-18-2017-14:01:46 where the nominal time is the algebraic mean of the acquisition times of the image pair used.

The Production Date/Time refers to the time at which the speckle-tracking processing was completed. The specific numerical entries in the meta data obviously differ from the example above for different tracks. Antarctic Polar Stereographic coordinates are used, with a standard latitude of 71 South.

The location information provided by the *.geodat files takes the following sample form: # 2 ; ; Image size (pixels) nx ny ; 1080 720 ; ; Pixel size (m) deltaX deltaY ; 125.000000 125.000000 ; ; Origin, lower left corner (km) Xo Yo ; 2195.000000 427.000000 The numerical values for image size, pixel size and lower left corner of the grid will in general differ from those given above; the pixel size, pixel number and location (in polar stereographic coordinates) of the lower left-hand corner allow the entire grid to be reconstructed without needing to save each pixel location redundantly.

The vx and vy components of velocity are contained in the files mosaicOffsets.vx and mosaicOffsets.vy. The x- and y- directions are those specified by the Polar Stereographic grid. All data files are in 4-byte IEEE floating point format with the same byteordering used by non-Intel Macintosh computers and most linux workstations (note that this is not the standard PC byteorder).

No data (NaN) values are marked as -2.0e9; these should be replaced by a platform-specific not-a-number signifier before displaying the data. Joughin, I.: Ice-sheet velocity mapping: A combined interferometric and speckle-tracking approach, Ann Glaciol, 34, 195–201, 2002.