Follow this link to skip to the main content

Interferometric (InSAR) Pair Data Format


UAVSAR data format for repeat-pass interferometry products

The format of the following files are described:

  • SLC files (.slc): calibrated single look complex files for each flight track (track 1, T1; and track 2, T2), floating point format, little endian, 8 bytes per pixel, corresponding to the same element of the scattering matrix. These files are available by request, but are not normally included in the data distribution.
  • AMP files (.amp1 and .amp2): calibrated multi-looked amplitude products, one file per repeat track, floating point format 4 bytes per pixel, little endian.
  • INT files (.int): interferogram product, one file per pair of repeat tracks, complex floating point format 8 bytes per pixel, little endian.
  • UNW files (.unw): unwrapped interferometric phase product, one file per pair of repeat tracks, floating point format 4 bytes per pixel, little endian.
  • COR files (.cor): interferometric correlation product, one file per pair of repeat tracks, floating point format 4 bytes per pixel, little endian.
  • GRD files (.grd): interferometric products projected to the ground in simple geographic coordinates (latitude, longitude). There is a fixed number of looks for each pixel. Floating point or complex floating point, little endian, 8 or 4 bytes per pixel.
  • HGT file: the DEM that the imagery was projected to, in the same geographic coordinates as the ground projected files. Floating point (4 bytes per pixel), little endian, ground elevation in meters.
  • KML and KMZ files (.kml or .kmz): these files allow you to view a representation of their corresponding file type in Google Earth or similar software.
  • PNG files (.png): these are representations of the corresponding products in standard PNG Format.
  • ANN file (.ann): a text annotation file with metadata. Example

File Naming Convention

Each filename consists of the following components, separated by underscores:

  • Six character abbreviation for the desired target site (image may contain other sites)
  • For track 1 and 2, three digits indicating the aircraft heading followed by a incremented alphanumeric counter. (this is set during flight planning). This 5 character ID is the same for both tracks.
  • For track 1, five digits in which the first two digits are the last two digits of the year, and the next three digits are the flight number by UAVSAR counted sequentially from the first flight of the year.
  • For track 1, three digits indicating which flight line of the flight this acquisition was from, counted sequentially from the beginning of the flight and starting from zero.
  • For track 2, five digits in which the first two digits are the last two digits of the year, and the next three digits are the flight number by UAVSAR counted sequentially from the first flight of the year.
  • For track 2, three digits indicating which flight line of the flight this acquisition was from, counted sequentially from the beginning of the flight and starting from zero.
  • Four digists followed by the letter d. The four digits indicate the number of days between track 1 acquisition and track 2 acquisition.
  • A three character ID.This is typically equal to s01.
  • Between 6 and 8 characters, a single character indicating the frequency band, followed by the steering angle (three digits) followed by the polarization. The polarization may be between 2 characters (first character is the transmit polarization, and second character is the receive polarization) and 4 characters (if the file represents a cross product).
  • Two digits indicating the processing version number.
  • If this is SLC data, the track number is indicated as T1 or T2.
  • Three or four digit file extension indicating the data type. If the data is geocoded (grd), a kml file (kml), a kmz file (kmz), or a png file, that is indicated as an additional final three characters of the file name. For example:

    SanAnd_26501_09083-010_10028-000_0174d_s01_L090HH_01.amp1.grd

    where SanAnd is the site name, 265 degrees is the heading of UAVSAR in flight, with a counter of 01; track 1 was obtained on the 83rd flight by UAVSAR in 2009, this data take was the eleventh data take during the flight; for track 2, the data was obtained on the 28th flight of 2010, and was the first data take during the flight; there were 174 days between track 1 and track 2, the arbitrary ID is set to s01, the frequency band was L-band, pointing at perpendicular to the flight heading (90 degrees), this file contains the HH data, this is the first interation of processing, the data type is AMP for track 1, and is orthorectified.

Formation of Interferometric Products:

Prior to creating interferometric products, the SLC images from both tracks are co-registered to each other using GPS data and the data itself to estimate and compensate for the variable motion between the tracks.

The single look complex (SLC) data for each track is summed in range and azimuth by the number of looks specified in the annotation file ("Number of Looks in Range" and "Number of Looks in Azimuthz") (typically 3 looks in range and 12 looks in azimuth), divided by the product of the number of looks in range and azimuth, and output as the amp1 and amp2 files.

The interferogram in the .int file is formed by multiplying the single look complex image from track 1 times the complex conjugate of the single look complex image from track 2. The resulting complex values are then summed in range and azimuth according to the desired number of looks in the range and azimuth direction, with each pixel then divided by the product of the the number of azimuth looks and the number of range looks.

The correlation file .cor is formed by dividing the interferogram values (the .int file) by the product of the multilooked amplitude values for track 1 and track 2 (the .amp1 and .amp2 files).

The unwrapped interferometric phase file UNW (the .unw file) is obtained by applying the Goldstein/Werner method on the interferogram: Goldstein, R. M. and Werner, C. L., 1998. Radar interferogram filtering for geophysical applications. Geophysical Research Letters, 25(21):4035-4038.

Data format description

  • SLC data:

    The SLC is a pure binary file (complex floating-point, 8 bytes per pixel) with no header bytes. The number of lines and samples are entered in the annotation file as *not currently in annotation file* and *not currently in annotation file* respectively. There is a separate file for each polarization channel (HH, HV, VH, and VV). The pixel spacing in meters is given in the annotation file by *not currently in annotation file* and *not currently in annotation file* for the azimuth and range directions, respectively. The projection of the data is in the natural slant range projection. The geographic coordinates of the data are defined by the " Peg position and heading ", and by the cross track and along track offset of the upper left pixel (given by Slant Range Data at Near Range, and Slant Range Data Starting Azimuth in the annotation file). The byte order is little endian. The units of the data are linear radar amplitude (rather than db units).

    These files are available by request, but are not normally included in the data distribution.

    The four complex SLC files correspond to the measurement of the scattering matrix:

    Shh
    Shv
    Svh
    Svv

  • AMP data:

    The AMP files for track 1 and track 2 are pure binary files with no header bytes. They are floating point, 4 byte per pixel. These products are derived from the average (usually 3 pixels in range, and 12 pixels in azimuth, given precisely by " Number of Looks in Range" and "Number of Looks in Azimuth " in the annotation file) of the SLC values from the two tracks. They are in linear amplitude, not power units.

    The number of lines and samples are entered in the annotation file as " Slant Range Data Azimuth Lines" and " Slant Range Data Range Samples" respectively. The pixel spacing in meters is given in the annotation file by " Slant Range Data Azimuth Spacing" and " Slant Range Data Range Spacing" for the azimuth and range directions, respectively. The projection of the data is in the natural slant range projection. The geographic coordinates of the data are defined by the "Peg position and heading", and by the cross track and along track offset of the upper left pixel (given by Slant Range Data at Near Range, and Slant Range Data Starting Azimuth in the annotation file). The byte order is little endian. The units of the data are linear radar amplitude (rather than db units). For the interferogram products, no cross talk correction is applied.

  • INT data:

    There is one .int file per pair of tracks. This file is a pure binary file with no header bytes. It is complex floating point format, 8 bytes per pixel. The byte order is little endian.

  • UNW data:

    There is one .unw file per pair of tracks. This file is a pure binary file with no header bytes. It is floating point format, 4 bytes per pixel. The byte order is little endian.

  • COR data:

    There is one .cor file per pair of tracks. This file is a pure binary file with no header bytes. It is floating point format, 4 bytes per pixel. The byte order is little endian.

  • GRD data:

    The grd files consists of the same values as described above, except they are orthorectified to the DEM used in processing (the HGT file). They have the same number of bytes per pixel as before, but now the number of lines and samples are now indicated in the annotation file as " Ground Range Data Latitude Lines" and " Ground Range Data Latitude Samples" . The pixel spacing is now in degrees, and is given by " Ground Range Data Latitude Spacing" and " Ground Range Data Longitude Spacing" in the annotation file. The upper left coordinate of the file is given by " Ground Range Data Starting Latitude" and " Ground Range Data Starting Longitude" in the annotation file.

    UAVSAR projects slant range images to ground range using the backward projection method. An equiangular grid is found with latitude and longitude boundaries that cover the entire slant range image. For each point on the ground range grid, the corresponding indices are calculated on the multilooked slant range image. The data value closest to the coordinates pointed by the calculated slant range indices is assigned to the point on the ground range grid.

    These files are co-registered to the HGT file.

  • HGT data:

    The height file is a pure binary floating point file, 4 bytes per pixel, where the number of lines and samples may be found in the annotation file and are given by Ground Range Data Latitude Lines and Ground Range Data Latitude Samples respectively. This height file contains the values of elevation used to project the slant range data to the Earth's surface. The value of the ground elevation is given in meters. The datum is given by "DEM Datum" in the annotation file. The source of the DEM is given by "DEM source" in the annotation file. The data is in an equiangular coordinate system in which each line and pixel increments in latitude and longitude by Ground Range Data Latitude Spacing and Ground Range Data Longitude Spacing degrees from the upper left corner coordinate given by Ground Range Data Starting Latitude and Ground Range Data Starting Longitude

    Because there are few areas for which a DEM exists that is comparable in resolution to the UAVSAR imagery, the DEM that the UAVSAR data is projected to is interpolated to the pixel spacing of the UAVSAR data. In some cases, the known DEM is much worse resolution than that of UAVSAR, and therefore errors in projection may occur.

    This file is co-registered to the GRD files.

  • Annotation file:

    The annotation file (.ann) is a keyword/value ASCII file in which the value on the right of the equals sign corresponds to the keyword on the left of the equals sign. The number of keywords may change with time, so the line number should not be assumed to be constant for any given keyword. In addition, the spacing between keywords and values may change. The units are given in parenthesis between the keyword and equal sign, and may change from annotation file to annotation file and within each annotation file. Comments are indicated by semicolons (;), and may occur at the beginning of a line, or at the middle of a line (everything after the semicolon on that line is a comment). The length of each text line is variable, and ends with a carriage return. There may be lines with just a carriage return or spaces and a carriage return.

Calibration of the data:

Please see the calibration page for documentation on calibration of the data.