Hydrology

Here we provide global grids of loading derived from the NASA Global Land Data Assimilation System (GLDAS). Data sets here are updated as often as GLDAS data are updated.

The 3-dimensional displacements have been derived using the method originally outlined in van Dam and Wahr [1987]:

van Dam, T. and J. Wahr, 
Displacements of the Earth's surface due to atmospheric loading: 
Effects on Gravity and Baseline Measurements, 
J. Geophys. Res., 92, 1281-1286, 1987.

The data are first organized by reference frame. Within each reference frame directory the data are organized by year, then by month. Each individual file contains the global (2.5 deg. X 2.5 deg) 3-dimensional surface displacement (in mm) for the epoch corresponding to the file name.

Each file can be read using the following algorithm (or something equivalent) where dvt is surface displacement to the north, dvl is surface displacement to the east, and du is surface displacement in the radial direction:

     do ihr=1,4
        read(iunit,1001) chyr,cdoy,chhr(ihr),ref
1001    format(a4,1x,a3,1x,a2,1x,a2)
        do ilon=1,144
           rlon=(ilon-1)*2.5
           do ilat=1,73
              rlat=90.-(ilat-1)*2.5
              read(unit,1002) vt(ilon,ilat),vl(ilon,ilat),du(ilon,ilat) 
1002          format(3(f10.4,2x))
           end do
        end do
     end do

You may use the program gldas_tseries.f to extract the data for a single latitude and longitude. The program will need to be adapted to your particular needs. However, before altering the program, please compile on your system and confirm that you obtain the results similar to those in stjo.cws. Details are inserted as comments in the fortran file.

Anyone using this data set is requested to use the following citation:

van Dam, T., 2010, Updated October 2010. 
GLDAS Derived monthly, global surface displacements at 2.5 x 2.5 degree spacing. 
Data set accessed YYYY-MM-DD at http://geophy.uni.lu/hydrology

For questions regarding this data set, please contact T. van Dam, tonie.vandamuni.lu