LOADING PREDICTION FILES README

The loading prediction files are available for most stations in the NGL database.  
Each file has a header line plus additional rows for each epoch for which a 
loading displacement estimte is provided for that station, up until the time of 
the last loading model update.  
These files are typically updated every few months.

Available files include the following:
NTAL - Non-tidal atmospheric loading
NTOL - Non-tidal ocean loading
GRACE Mascon - Loading estimated from Gravity Recovery and Climate Experiment (GRACE) mascon data.
CMCF - File that translates between CM and CF reference frame, in east, north, up for the station.

The header line has format:
station  latitude longitude type notes_on_source_and_latency

The subsequent rows have a six-column format:
  1. station  (SSSS)
  2. JPL_date (YYMMMDD)
  3. decimal_year (yyyy.yyyy)
  4. east displacement (m)
  5. north displacement (m)
  6. up displacement (m)


The predictions are from ESMGFZ Product Repository (https://rz-vm480.gfz.de, 
Dill and Dobslaw, JGR, 2013; Dill, 2008). Their hydrological model is from from 
24-hourly terrestrial water storage global hydrological model LSDM forced by ECMWF 
operational atmospheric data produced by IERS Associated Product Centre Deutsches 
GeoForschungsZentrum (GFZ) Potsdam. LSDM masses are given on a regular 0.5x0.5 degrees.
http://rz-vm115.gfz-potsdam.de:8080/repository/entry/show?entryid=dadb0121-32f0-4eaa-a3ec-b5f37860e4d1
We get the NTAL, NTOL, measurements at each GPS station by fitting a spline to GFZ's 
lat, lon grids using their program "extractlatlon_bicubintp".

The "CM:CF Translation" file supplies for the specific station the geocenter motion in 
east, north, up coordinates.  This translates between the CM and CF versions of the 
loading prediction files.  NGL time series are in CM (IGS20).  To place the time 
series in CF you should subtract the values in the CM:CF file. These are based on 
the Altamimi et al. 2023 J. Geodesy, Table 3 geocenter motion.