SRTM15+V2.5.5 - March 20, 2023

This version includes 240 small polygon edits provided by Pauline Weatherall to serve as the base for GEBCO_2023

SRTM15+V2.5 - January 6, 2023

This is a slightly revised version with 279 new cruises from the British Ocean Data Center. Most of these are multibeam data.

SRTM15+V2.5 - August 10, 2022

The gravity predicted depths are based on the V32 global gravity at 1 minute resolution.
This version 32 includes an additional 12 months of Altika, Cryosat LRM, Cryosat SAR and Sentinel-3A/B.
Waveform retracking was performed on the following altimeter data Jason-1/2, Envisat, Altika, and Cryosat-LRM.
This was done to reduce the wavelength of the SWH smoothing filter from 45 km to 30 km.  In addition, we solved
for the optimal sea state bias for all the altimeters to reduce the SWH noise in the > 30 km wavelength band.
Finally, we implemented a mask to remove all data within 3 km of any land.  This helps to reduce land-contaminated
waveforms.  A precise land mask has been applied to all products to further reduce land/ocean edge effects.

This version also includes 106 multibeam cruises recently released by NCEI.  Many of these were in the Antarctic region and required considerable editing.

SRTM15+V2.4 - March 7, 2022

The gravity predicted depths are based on the V31 global gravity at 1 minute resolution.
This V2.4 has significant edits from Pauline Weatherall. 
Sarah Maher has added the IBCAO V4 grid for the Arctic for latitudes > 80. 
In addition, the data around Hawaii were replaced with the Hawaii multibeam synthesis
and a Doldrums grid in the Equatorial Atlantic was added.
That was followed by more than 600 small edits.

SRTM15_V2.4.nc: Title: Produced by grdmath
SRTM15_V2.4.nc: Command: grdmath SRTM15+V2.1_land_masked.nc debug/polished.unmasked.grd AND = SRTM15_V2.4.nc
SRTM15_V2.4.nc: Remark: 
SRTM15_V2.4.nc: Pixel node registration used [Geographic grid]
SRTM15_V2.4.nc: Grid file format: nf = GMT netCDF format (32-bit float), CF-1.7
SRTM15_V2.4.nc: x_min: -180 x_max: 180 x_inc: 0.00416666666667 (15 sec) name: longitude n_columns: 86400
SRTM15_V2.4.nc: y_min: -90 y_max: 90 y_inc: 0.00416666666667 (15 sec) name: latitude n_rows: 43200
SRTM15_V2.4.nc: v_min: -11058 v_max: 8627 name: z
SRTM15_V2.4.nc: scale_factor: 1 add_offset: 0
SRTM15_V2.4.nc: format: netCDF-4 chunk_size: 128,129 shuffle: on deflation_level: 3

SID_V2.4.nc: Title: z
SID_V2.4.nc: Command: xyz2grd -di0 -R/geosat2/srtm15_V2/1_BATHY_PROCESSING/data/topo//debug/wet.grd -G/geosat2/srtm15_V2/1_BATHY_PROCESSING/data/topo//sid.grd=ni
SID_V2.4.nc: Remark: 
SID_V2.4.nc: Pixel node registration used [Cartesian grid]
SID_V2.4.nc: Grid file format: ni = GMT netCDF format (32-bit integer), CF-1.7
SID_V2.4.nc: x_min: -180 x_max: 180 x_inc: 0.00416666666667 name: x n_columns: 86400
SID_V2.4.nc: y_min: -90 y_max: 90 y_inc: 0.00416666666667 name: y n_rows: 43200
SID_V2.4.nc: v_min: 0 v_max: 65506 name: z
SID_V2.4.nc: scale_factor: 1 add_offset: 0
SID_V2.4.nc: format: netCDF-4 chunk_size: 128,129 shuffle: on deflation_level: 3
SID_V2.4.nc: Default CPT: 


V2.4 will form the base layer or GEBCO_2022.

SRTM15+V2.3 - June 29, 2021

This V2.3 is a major update of V2.2. Hugh harper and David Sandwell downloaded about 1400 new multibeam cruises from the NEIC site.  These were processed with MB_system to remove outer beams and flatten the rails of the innermost beams.  About 156 of the cruises were very bad or duplicated areas already well charted.  905 of the cruises were kept and went through 5 rounds of editing to remove outliers. 

In addition, we downloaded 9 composite grids of unique data mainly in the Indian ocean.
aden.cm		antilles.cm	fiji.cm		guiana.cm	iotj.cm		kerguelen.cm	reunion.cm	saint_paul.cm	swir.cm
SRTM15+V2.2 - April 1, 2021

This V2.2 is an update of V2.1. Note that V2.2 was made special for the GEBCO 2021 grid.  It is the same as V2.1 except that
there were about 1000 small edits to clean up the issues with outer beams, etc.  These were done by Pauline Weatheral , David Sandwell and
Brook Toxer. In addition two land tiles were replaced. This grid was never distributed to the public.

SRTM15+V2.1 - February 10, 2020

See file SRTM15V2.1_change_log.pdf for a more complete discussion of changes.
This V2.1 is an update to V2.0.  The main improvements are a fix to a northward shift in all the
AGSO gridded data.  In addition NaN's in the coastal and land areas have been eliminated and
there has been more extensive data editing.

SRTM15+V2.1.nc: Title: Produced by grdmath
SRTM15+V2.1.nc: Command: grdmath SRTM15+V2.1_land_masked.nc debug/polished.unmasked.grd AND = SRTM15_V2.1.nc
SRTM15+V2.1.nc: Remark: 
SRTM15+V2.1.nc: Pixel node registration used [Geographic grid]
SRTM15+V2.1.nc: Grid file format: nf = GMT netCDF format (32-bit float), COARDS, CF-1.5
SRTM15+V2.1.nc: x_min: -180 x_max: 180 x_inc: 0.00416666666667 name: longitude [degrees_east] n_columns: 86400
SRTM15+V2.1.nc: y_min: -90 y_max: 90 y_inc: 0.00416666666667 name: latitude [degrees_north] n_rows: 43200
SRTM15+V2.1.nc: z_min: -10997.7089844 z_max: 8627 name: z
SRTM15+V2.1.nc: scale_factor: 1 add_offset: 0
SRTM15+V2.1.nc: format: netCDF-4 chunk_size: 128,129 shuffle: on deflation_level: 3

SID_GRID_SRTM15+V2.1.nc: Title: 
SID_GRID_SRTM15+V2.1.nc: Command: xyz2grd -di0 -R/geosat2/srtm15_gmt5/data/topo//debug/wet.grd -G/geosat2/srtm15_gmt5/data/topo//sid.grd=ni
SID_GRID_SRTM15+V2.1.nc: Remark: 
SID_GRID_SRTM15+V2.1.nc: Pixel node registration used [Geographic grid]
SID_GRID_SRTM15+V2.1.nc: Grid file format: ni = GMT netCDF format (32-bit integer), COARDS, CF-1.5
SID_GRID_SRTM15+V2.1.nc: x_min: -180 x_max: 180 x_inc: 0.00416666666667 name: longitude [degrees_east] n_columns: 86400
SID_GRID_SRTM15+V2.1.nc: y_min: -90 y_max: 90 y_inc: 0.00416666666667 name: latitude [degrees_north] n_rows: 43200
SID_GRID_SRTM15+V2.1.nc: z_min: 0 z_max: 65506 name: z
SID_GRID_SRTM15+V2.1.nc: scale_factor: 1 add_offset: 0
SID_GRID_SRTM15+V2.1.nc: format: netCDF-4 chunk_size: 128,129 shuffle: on deflation_level: 3

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SRTM15+V2.0 - March 29, 2019
Details on the improvements in V2 are described in our publication.
http://topex.ucsd.edu/sandwell/publications/180_Tozer_SRTM15+.pdf

Note the V2 grid is in pixel registration while the V1 grid was in gridline registration.

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SRTM15_PLUS: DATA FUSION OF SRTM LAND TOPOGRAPHY WITH MEASURED AND ESTIMATED SEAFLOOR TOPOGRAPHY

SRTM15_PLUS V1 - November 14, 2014
David T. Sandwell dsandwell@ucsd.edu
Joseph J. Becker <joseph.becker.ctr@nrlssc.navy.mil>
Chris Olson <cjolson@ucsd.edu>
Amber Jackson <amberleajackson@gmail.com>

The SRTM15_PLUS is available in netcdf format

topo15.grd netcdf format to use in GMT
topo15.grd: Remark: Derived from the full resolution shorelinen
topo15.grd: Gridline node registration used
topo15.grd: Grid file format: nf (# 18) GMT netCDF format (float)  (COARDS-compliant) [DEFAULT] 
topo15.grd: x_min: -180 x_max: 180 x_inc: 0.00416666666667 name: longitude [degrees_east] nx: 86401
topo15.grd: y_min: -90 y_max: 90 y_inc: 0.00416666666667 name: latitude [degrees_north] ny: 43201
topo15.grd: z_min: -10927.5117188 z_max: 8726 name: z
topo15.grd: scale_factor: 1 add_offset: 0

_________________________________________________________________________________________
November 13, 2014
Version 1 of SRTM15 is based on V11 of the SRTM30_PLUS grid. The main improvements will be described
in a publication and this README will be updates.  Basically the land data is completely new
based on a combination of SRTM, ASTER, and CryoSat-2 ice sheet topography.
The ocean data are the same as SRTM30_PLUS but required more extensive editing to remove the bad 
points mostly along edges of the swath data.  
_________________________________________________________________________________________
May 22, 2014
Version 10. has the identical format as previous versions. Enhancements from V9.0
1) 685 new multibeam cruises were added from the NGDC multibeam archive.
2) 104 tiles of multibeam grids were added from the AGSO.
3) New multibeam grids from GEOMAR from the Southeast Pacific and Cape Verde
4) additional editing of all these data
_________________________________________________________________________________________
December, 2013
Version 9.0 has the identical format as previous versions. Enhancements from V8.0
1) The predicted depth is based on the new V22 gravity model which includes all new data from Cryosat-2, Jason-1, and Envisat resulting in about a factor of 2 improvement in gravity accuracy.  In addition both the gravity and the predicted depth have a filter wavelength that is about 2 km shorter than previous versions (i.e., 14 km wavelength instead of 16 km).
2) There has been a lot of editing of bad soundings especially on the continental margins where the deep holes
were eliminated.
3) About 446 new JAMSTEC multibeam cruises were added. These data were sampled at 15 arcseconds to prepare for
an SRTM15.
_________________________________________________________________________________________
December 2012
Version 8.0 has the identical format as previous versions.  Enhancements from V7.0
Arctic bathymetry north of 70 N is based on IBCAO V3.0 http://www.ngdc.noaa.gov/mgg/bathymetry/arctic/.
Predicted depth based on new global Gravity V20.1.  This included 2 years of altimetry data
from CryoSat, 1.5 years from Envisat, and 120 days from Jason-1.
A new A-coefficient for the downward continuation parameter was used based
on a coherence analysis performed by Karen Marks.
_________________________________________________________________________________________
December 2011
Version 7.0 has the identical format as previous versions.  Enhancements from V6.0
include the addition of all US multibeam data stored at NGDC as of April 2011.
Edited multibeam data from Ewing and Palmer cruises was provided by the Marine Geoscience
Data System. http://www.marine-geo.org/index.php
In addition a 500-m grid of Great Barrier Reef bathymetry from Rob Beaman
http://e-atlas.org.au/content/gbr-jcu-bathymetry-gbr100
One other change as the latitude cutoff for the IBCAO Arctic grid was lowered ftom 80 N to
70 N.  This eliminates some of the "orange peel areas of predicted depth between 70 and 80.
_________________________________________________________________________________________
November 2009
Version 6.0 has the identical format as previous versions.
This version includes a significant number of new depth
soundings.  This version is based on an more accurate prediction
between gravity anomaly and depth.  In addition is contains many 
more depth soundings than all previous versions and has extensive 
editing to remove blunders.
_________________________________________________________________________________________
September 2009
Version 5.0 has the identical format as previous versions.
This version includes a significant number of new depth
soundings.
A more complete description of the new data and processing
was prepared for publication in early 2008.  This
is a collaborative effort between NGA, NOAA, NAVO and SIO.
The predicted depths are based on the V16.1 gravity anomaly
model in an adjacent directory.  
_________________________________________________________________________________________
May 2008
Version 4.0 has the identical format as previous versions.
This version includes a significant number of new depth
soundings, especially for depths between 0 and -300 m.
A more complete description of the new data and processing
will be prepared for publication in early 2008.  This
is a collaborative effort between NGA, NOAA, NAVO and SIO.
The predicted depths are based on the V16.1 gravity anomaly
model in an adjacent directory.  

This version has gone through 6 iterations of
identifying bad tracks, editing the offending profiles and constructing
a new grid.   If you find anomalies (there are several remaining)
please send an e-mail with the problem location and we will
address it.
_________________________________________________________________________________________
December 2007
Version 3.0 has the identical format as V1.0.  On land areas (except Anartctica)
the land data ov Version 3.0 are identical to Version 2.0 which are identical to
Version 2 of the SRTM30 land data.

1) Ocean data 
The ocean data are based on V9.1 of our global predicted depth.
This 1-minute grid includes a significant number of new depth 
soundings, especially for depths between 0 and -300 m.
A more complete description of the new data and processing
will be prepared for publication in early 2008.  This
is a collaborative effort between NGA, NOAA, NAVO and SIO.
The predicted depths are based on the V16.1 gravity anomaly
model in an adjacent directory.  Please send comments to
dsandwell@ucsd.edu.

2) Antarctica
The land adat on Antarctica are from 
Digital Elevation Models of the Antarctic and Greenland Ice Sheets Using Data From ICESat
John P. DiMarzio12, Anita C. Brenner23, Helen A. Fricker4, Jack L. Saba23, Bob E. Schutz5, Christopher A. Shuman2, H. Jay Zwally2
2007 Jan 5
DESCRIPTION OF THE DIGITAL ELEVATION MODELS
The ICESat/GLAS Antarctic and Greenland Digital Elevation Models (DEMs) are polar-stereographic projection of the ICESat/GLAS elevation data in raster format. The elevation grids were used to compute the slope and slope azimuth grids.

_________________________________________________________________________________________
July 2006
Version 2.0 has the identical format as V1.0.  There are two main improvements:

1) The land data come from version 2 of the SRTM30 processing.  Here is the
information on SRTM V2 provided by Tom Farr of JPL on October 10, 2005.

"NASA has released version 2 of the Shuttle Radar Topography Mission digital topographic 
data (also known as the "finished" version). Version 2 is the result of a substantial 
editing effort by the National Geospatial Intelligence Agency and exhibits well-defined 
water bodies and coastlines and the absence of spikes and wells (single pixel errors), 
although some areas of missing data ('voids') are still present. The Version 2 directory 
also contains the vector coastline mask derived by NGA during the editing, called the 
SRTM Water Body Data (SWBD), in ESRI Shapefile format.

The data may be obtained by anonymous ftp to:  e0srp01u.ecs.nasa.gov and moving to the 
directory srtm where both version 1 and version 2 directories may be found. Please read 
the appropriate documentation, also found in the directories."

2) We have added several new bathymetry grids derived from large multibeam
surveys.  The new data include a large IFREMER survey of the Southwest Indian Ridge 
provided by Mathilde Cannat, a compilation of the Lau Basin provided by Brian Taylor of
SOEST, and a large survey of the Foundation Seamounts provided bu Marcia Maia at IFREMER.

_________________________________________________________________________________________
SRTM30_PLUS V1.0 November 11, 2004
INTRODUCTION
This data consists of 33 files of global topography in the same format as the SRTM30 products 
distributed by the USGS EROS data center. The grid resolution is 30 seconds which is roughly 
one kilometer.Land data are based on the 1-km averages of tropography derived from the 
USGS SRTM30 gridded DEM data product created with data from the NASA Shuttle Radar Topography 
Mission. GTOPO30 data are used for high latitudes where SRTM data are not available. Ocean data 
are based on the Smith and Sandwell global 2-minute grid between latitudes +/- 72 degrees. 
Higher resolution grids have been added from the LDEO Ridge Multibeam Synthesis Project and the 
NGDC Coastal Multibeam Data. Arctic bathymetry is from the International Bathymetric Chart of 
the Oceans (IBCAO) [Jakobsson et al., 2003]. All data are derived from public domain sources 
and these data are also in the public domain.The pixel-registered data are stored in 33 files 
with names corresponding to the upper left corner of the array shown below.

The USGS SRTM30 data and documentation is available at
ftp://edcsgs9.cr.usgs.gov/pub/data/srtm/SRTM30

The US continental coastal multibeam data is available at 
www.ngdc.noaa.gov/mgg/coastal/coastal.html
Data from Puerto Rico and Hawaii is -NOT- presently included.

The ocean ridge multibeam data is available at 
www.ocean-ridge.ldeo.columbia.edu/general/html/home.html

The artic ocean bathymetry is from 
http://www.ngdc.noaa.gov/mgg/bathymetry/arctic/arctic.html

The Antarctica data (starting at 72S) is not very 
interesting; the terrestrial data is from GTOPO30,
and the limited bathymetry is from JEBCO.

_________________________________________________________________________________________
DATA FORMATS
Data are provided as binary integers in exactly the same format
as SRTM30.  The files must be uncompressed with gzip and are 16-bit
big endian byte order.  

These files can be used directly by ER_Mapper software using the header files 
stored in the subdirectory ermapper_headers.

These files can be converted to Generic Mapping Tools (grd-netcdf) format
using the scripts in the subdirectory grd.
_________________________________________________________________________________________
