------------------------------------------------------------------------------- Earth2014 1 arcmin global topography and relief models - readme-file V1.1 ------------------------------------------------------------------------------- Contact: Christian Hirt Western Australian Centre for Geodesy Curtin University Perth c.hirt(use the at here)curtin.edu.au & c.hirt(use the at here)tum.de Last edited 2015-04-20 List of changes - All shape grids in folders /data_1min/shape_grids and /data_5min/shape_grids updated (2015-04-20) and type of latitude for shape grids clarified (Sect. 4.2). 1. SUMMARY ---------- Earth2014 is a suite of 1 arc-min resolution grids of Earth's relief in different representations (topography, bedrock, ice) composed of recent data sets. The model suite provides 1.) elevation grids, 2.) Earth shape grids, and 3.) ultra-high degree spherical harmonic coefficients to degree 10,800. Earth2014 is the successor of Curtin's Earth2012 models. Citation: --------- Hirt, C. and M. Rexer (2015), Earth2014: 1 arc-min shape, topography, bedrock and ice-sheet models - available as gridded data and degree-10,800 spherical harmonics, International Journal of Applied Earth Observation and Geoinformation 39, 103-112, doi:10. 10.1016/j.jag.2015.03.001. Permanent link to the Earth2014 data sets and paper --------------------------------------------------- http://ddfe.curtin.edu.au/models/Earth2014/ http://ddfe.curtin.edu.au/models/Earth2014/hirt_rexer2015_Earth2014.pdf 2. INPUT DATA ------------- The Earth2014 model suite is based on - Bedmap2 (Fretwell et al. 2013) bedrock and ice data over Antarctica, - GBT v3 Greenland bedrock topography data over Greenland (Bamber et al. 2013), - SRTM30_PLUS v9 (Becker et al. 2009) bathymetry over the oceans and major inland lakes, and over land in high northern latitudes (except for Greenland), - SRTM V4.1 Topography (Jarvis et al. 2008) over continents/islands. 3. PROCESSING PROCEDURES ------------------------ are described in detail in Hirt and Rexer (2015). A pdf is available via http://ddfe.curtin.edu.au/models/Earth2014/hirt_rexer2015_Earth2014.pdf 4. EARTH2014 PRODUCTS AND DIRECTORIES ------------------------------------- We provide gridded data of the topography (Section 4.1), of shape models (4.2), of mask files (4.3) and spherical harmonic coefficients (SHCs) of the topography layers (4.4). There are two levels of resolution available, 1-arcmin (original data) and 5 arc-min (as derived products). The data is organised in directories as follows. /data_1arcmin .. directory for 1-arcmin and degree 10,800 products |--> /topo_grids .. topography, bedrock w.r.t MSL |--> /shape_grids .. topography, bedrock w.r.t geocenter |--> /masks .. mask files |--> /shcs_to10800 .. SHCs to degree 10,800 as binary files |--> /GMT .. gridded data in GMT (Generic Mapping Tools) format /data_5arcmin .. directory for 5-arcmin and degree 2,160 products |--> /topo_grids .. obtained as 5x5 box mean values from the 1-arcmin grids |--> /shape_grids .. obtained as 5x5 box mean values from the 1-arcmin grids |--> /shcs_to2160 .. obtained from 10,800 files by truncating after degree 2160 |--> /GMT .. gridded data in GMT format /software .. directory containing Matlab scripts for data access 4.1 Topography/relief layers To satisfy multiple applications of global relief data, Earth2014 provides readily usable grids of (1) the physical surface SUR, (2) bedrock BED (Earth`s relief without water and ice masses), (3) topography, bedrock and ice TBI (Earth without water masses), (4) rock-equivalent topography RET (ice and water masses condensed to layers of rock) as mass representation, and (5) ice sheet thicknesses. Table 1 details the five available layers, and Table 2 the filenames, filesize and formats. The Earth2014 grids listed in Table 2 are provided in terms of geodetic latitudes (on the GRS80 ellipsoid) and use the mean sea level (MSL) in approximation as height datum. The RET-layer (also denoted RET2014) models ice, water and rock masses based on a uniform mass-density of 2670 kg/m3. Table 1 - Earth2014 layers and their representation --------------------------------------------------------------------------- Layer Representation Dry land Major lakes Oceans Major ice sheets --------------------------------------------------------------------------- SUR Earth's surface Topography Surface 0 Surface BED Earth's bedrock Topography Bedrock Bedrock Bedrock TBI Topo, bedrock, ice Topography Bedrock Bedrock Surface RET Rock-equivalent topo Topography RET RET RET ICE Major ice sheets 0 0 0 Ice thickness -------------------------------------------------------------------------- Table 2 - filenames of the topography models --------------------------------------------------------------------------- Layer Filename Filesize Format (binary) --------------------------------------------------------------------------- SUR Earth2014.SUR2014.1min.geod.bin 455MB Int16, "ieee-be" BED Earth2014.BED2014.1min.geod.bin 455MB Int16, "ieee-be" TBI Earth2014.TBI2014.1min.geod.bin 455MB Int16, "ieee-be" RET Earth2014.RET2014.1min.geod.bin 455MB Int16, "ieee-be" ICE Earth2014.ICE2014.1min.geod.bin 455MB Int16, "ieee-be" -------------------------------------------------------------------------- 4.2 Shape layers For geophysical applications and geo-visualisation, shape models were derived for selected Earth2014 topography models. While the relief models (4.1) provide elevations of the topography or bedrock with respect to the mean sea level, shape models represent the geometry of the planet via the planetary radius, i.e., distances between the geocenter and the surface points. These were obtained as sum of ellipsoidal radii of the GRS80 ellipsoid, EGM96 geoid undulations, and the elevations from the models in Table 1. Table 3 details the four available shape models. Note that a constant value of 6,371,000 m has been subtracted from all shape models to make it 'storable' as int16. Like the topography grids, all shape grids are equally spaced in geodetic latitude. We have updated the shape grids in April 2015 to fix a minor error in the computation of the ellipsoidal radii. Table 3 - filenames of the shape models --------------------------------------------------------------------------- Layer Filename --------------------------------------------------------------------------- SUR Earth2014Shape_minus_6371000m.SUR2014.1min.geod.bin BED Earth2014Shape_minus_6371000m.BED2014.1min.geod.bin TBI Earth2014Shape_minus_6371000m.TBI2014.1min.geod.bin RET Earth2014Shape_minus_6371000m.RET2014.1min.geod.bin -------------------------------------------------------------------------- 4.3 Mask grid files for land types and input data sources To distinguish between various land types, a land type mask is provided: MSK2014_landtypes.1min.geod.bin (455MB size in Int16, "ieee-be" format). It flags land types as follows: 0 - land topography above mean sea level (MSL), 1 - land topography below MSL, 2 - ocean bathymetry, 3 - inland lake, bedrock above MSL, 4 - inland lake, bedrock below MSL, 5 - ice cover, bedrock above MSL, 6 - ice cover, bedrock below MSL, 7 - ice shelf, 8 - ice covered lake (Vostok). To distinguish between the different data sources used in the Earth2014 products, the file MSK2014_inputdatasets.1min.geod.bin flags the input data sets as follows: 0 - SRTM30_PLUS inland bathymetry, 1 - SRTM30_PLUS ocean bathymetry, 2 - SRTM30_PLUS land topography (high Northern latitudes), 3 - SRTM V4.1 land topography, 4 - GBT Greenland patch (ice, topo, bedrock & bathymetry), 5 = Bedmap2 Antarctica patch (ice, topo bedrock & bathymetry). 4.4 Spherical harmonic coefficients (SHCs) For use of Earth2014 in spectral modelling, sets of fully-normalized (4pi) SHCs complete to degree and order 10,800 were derived from the 1 arc-min grids listed in Table 2 through harmonic analysis. Table 4 reports the filenames of the SHC data sets. Table 4 - filenames of the spherical harmonic coefficients. --------------------------------------------------------------------------- Layer Filename Filesize Format (binary) --------------------------------------------------------------------------- SUR Earth2014.SUR2014.degree10800.bshc 933MB double precision BED Earth2014.BED2014.degree10800.bshc 933MB double precision TBI Earth2014.TBI2014.degree10800.bshc 933MB double precision RET Earth2014.RET2014.degree10800.bshc 933MB double precision ICE Earth2014.ICE2014.degree10800.bshc 933MB double precision -------------------------------------------------------------------------- 5. DATA ACCESS AND FILE FORMATS ------------------------------- 5.1 Gridded data (1-arc min) All gridded data (Table 2 and 3) with extension ".bin" is stored in "int16" and "ieee-be" format. Each grid file contains 10,800 x 21,600 = 233,280,000 records at 1 arc-min resolution, and is 455 MB in size. The elevation data is stored in cell-centred format (thus the poles, and integer meridians are excluded). The coordinates of the cell centres of the grid extends from -90+1/120 deg to +90-1/120 deg in latitude direction, and from -180+1/120 deg to +180-1/120 deg in longitude direction. Records proceed along parallels from West to East, then rows from South to North. The first record is the South-West corner (-89.9917 deg latitude, -179.9917 deg longitude), and the last record is the North-East corner (89.9917 deg latitude, 179.9917 deg latitude). Important note: To work with the shape model grids, users have to add a constant value of 6,371,000 m to the data contained in the files listed in Table 3. 5.2 Spherical harmonic coefficients (SHCs) SHCs are stored in Curtin University's binary SHC (bshc)-format in "double precision". The bshc-format holds the data as follows: n_min n_max C-coefficients ascending in degree, followed by the order, S-coefficients ascending in degree, followed by the order, our files thus contain: 0 10800 C(0,0), C(1,0), C(1,1), C(2,0), C(2,1), ... C(10800,10799), C(10800,10800), S(0,0), S(1,0), S(1,1), S(2,0), S(2,1), ... S(10800,10799), S(10800,10800). Each file listed in Table 4 contains 58,325,400 C- and 58,325,400 S-Coefficients, and is 933 MB in size. 5.3 Derived data (5 arc-min resolution) Folder /data_5arcmin contains grid data at a lower resolution of 5 arc-min. The grids were derived from applying 5x5 boxmeans. The storage is the same as in case of the 1 arc-min grids. The 5 arc-min grids contain 2,160x4,320 data points, are 18 MB in size and extend from -90+5/120 deg to +90-5/120 deg in latitude direction, and from -180+5/120 deg to +180-5/120 deg in longitude direction. The SHCs available in folder /data_5arcmin/SHCs_to2160 are simple truncations of the degree-10,800 files to degree 2,160. 5.4 Matlab scripts (I/O) In folder /software there are Matlab scripts provide that demonstrate how to read the previously described file formats (5.1, 5.2, 5.3). access_Earth2014_grids1min.m .. work with 1 arcmin grids, shapes & masks access_Earth2014_shcs10800.m .. work with degree-10800 SHC filkes access_Earth2014_grids5min.m .. work with 5 arcmin grids & shapes access_Earth2014_shcs2160.m .. work with degree-2160 SHC files read_SHCs_bshc2tri.m .. reading routines for bshc-files 5.5 Gridded data in GMT format ------------------------------ For convenience of use, all gridded Earth2014 data is also provided in GMT (Generic Mapping Tools) grid-format (Wessel et al. 2013), both at 1 arcmin and 5 arcmin resolution in folders /data_1arcmin/GMT and /data_5arcmin/GMT. REFERENCES ---------- Bamber, J.L., J. A. Griggs, R. T. W. L. Hurkmans, J. A. Dowdeswell, S. P. Gogineni, I. Howat, J. Mouginot, J. Paden, S. Palmer, E. Rignot, and D. Steinhage (2013), A new bed elevation dataset for Greenland. The Cryosphere, 7, 499-510, doi:10.5194/tc-7-499-2013. Becker, J.J., D.T. Sandwell, W.H.F. Smith, J. Braud, B. Binder, J. Depner, D. Fabre, J. Factor, S. Ingalls, S-H. Kim, R. Ladner, K. Marks, S. Nelson, A. Pharaoh, R. Trimmer, J. Von Rosenberg, G. Wallace and P. Weatherall (2009), Global Bathymetry and Elevation Data at 30 Arc Seconds Resolution: SRTM30_PLUS. Marine Geodesy 32(4): 355-371. Fretwell, P., H.D. Pritchard, D.G. Vaughan, J.L. Bamber, et al. (2013), Bedmap2: improved ice bed, surface and thickness datasets for Antarctica, The Cryosphere, 7, 375-393, doi:10.5194/tc-7-375-2013, 2013. Hirt, C. and M. Rexer (2015), Earth2014: 1 arc-min shape, topography, bedrock and ice-sheet models - available as gridded data and degree-10,800 spherical harmonics, International Journal of Applied Earth Observation and Geoinformation 39, 103-112, doi:10. 10.1016/j.jag.2015.03.001 Jarvis, A., H.I. Reuter, A. Nelson, and E. Guevara (2008), Hole-filled SRTM for the globe Version 4, Available from the CGIAR-SXI SRTM 90m database. Available at: http://srtm.csi.cgiar.org. Wessel, P., W. H. F. Smith, R. Scharroo, J. F. Luis, and F. Wobbe (2013) Generic Mapping Tools: Improved version released, EOS Trans. AGU, 94, 409-410. DISCLAIMER ---------- Neither Curtin University nor any of its staff accept any liability in connection with the use of data and models provided here. Neither Curtin University nor any of its staff make any warranty of fitness, completeness, usefulness and accuracy of the data and models for any intented or unintended purpose.