October 29, 2014

This is an update of V22 that includes an additional year of CryoSat-2 data.  Everything else is the same.

November 3, 2013

This directory now contains the final version of the V22 gravity grid.  There are two
changes with respect to the September 30, beta version.  

1) The low-pass filter that is applied to the gravity depends on depth as follows.

#  depth    filter    filename
#   0        13km      grav0.img
#   1        14        grav1.img
#   2        15        grav2.img
#   3        16        grav3.img
#   4        17        grav4.img
#   5        18        grav5.img
#   6        20        grav6.img

2) A slope correction was applied to the altimeter profiles to account for the 
offset of the footprint away from NADIR due to a high geoid slope.

September 30, 2013 David T. Sandwell

Note these are beta versions of V22 as presented in the IAG meeting in Potsdam.

Global gravity grids.  The V21 gravity models as published in:
http://topex.ucsd.edu/sandwell/publications/142.pdf
http://topex.ucsd.edu/sandwell/publications/144.pdf

grav_16km_V22b.img - 16 km low-pass filter, spherical mercator projection for use in GMT (img2grd)
           
grav_16_cart.float4 - 16 km low-pass filter, geographic co-orginates for Nikos

These are the characteristics of the netcdf files.  After this the headers were removed to make
flat binary files.

grav_16_cart.grd: Title: 
grav_16_cart.grd: Command: grdsample -R0/360/-80/80 -I0.0166667 -fg grav_16_cart.grd -Ggrav_16_cart.grd
grav_16_cart.grd: Remark: 
grav_16_cart.grd: Pixel node registration used
grav_16_cart.grd: Grid file format: cf (# 10) GMT netCDF format (float) (deprecated)                  
grav_16_cart.grd: x_min: -360 x_max: 0 x_inc: 0.0166667 name: longitude [degrees_east] nx: 21600
grav_16_cart.grd: y_min: -80 y_max: 80 y_inc: 0.0166667 name: latitude [degrees_north] ny: 9600
grav_16_cart.grd: z_min: -367.236 z_max: 942.516 name: z
grav_16_cart.grd: scale_factor: 1 add_offset: 0
grav_16_cart.grd: median: -1.8857 scale: 21.4016