NASA Goddard Space Flight Center   Geodesy and Geophysics Laboratory

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Tips of using the International Mass Loading Service

• What loading?

  The International Mass Loading Service provides displacements due to four loadings (in decreasing their magnitude): 1) ocean tidal loading atmospheric pressure loading; 2) atmospheric pressure loading; 3) land water storage loading; 4) non-tidal ocean loading. You need to apply all of them.

• Whether the loading time series contain harmonic variations?

  The time series contain harmonic variations with periods more than 1.5 days, namely annual and semi-annual consitiuents, but they do not contain harmonic variations with periods shorter than 1.5 days.

• Whether I need to apply harmonic loading variations at diurnal and sub-diurnal band?

  Depends on the problem you want to solve. These loading variations are real, and their omission in data reduction will cause systematic errors. So, in general, both loading time series and loading harmonic variatinos should be applied

• How to get the loading from my stations?

  There are three ways:

  1. If your station is in the list of stations with pre-computed loadings or is located within 2000 m of a station with the pre-computed loading, you can just download the files with loading displacements for your statinon.
  2. You can compute loading dislacements at the mass loading server using the ondemand form.
  3. You can download the coefficients of B-spline expansion of the displacement field from the massloading server and then compute the time series by interpolation.

• How to automatize downloading pre-computed loadings?

  First, fill the form with downloading pre-computed loading. Set the output type "wget control file". Submit it. Then examine the long URL in your browser. Copy this line. Then find the start and stop dates. Replace the start and stop dates and execute this url as an argument of wget. You need embrace the URL with apostrophes. Command wget will get you the list of wget commands. Execute this list. Then write a simple program (or script) in whichever language your prefer that combines these two steps.

• There are more than one models for loadings. Which to use?

  All models are good. Models that failed validation are not put in the International Mass Loading Service. Read the papers with model description, ask your colleagues, toss a coin. Reanalysis MERRA2 models start at 1980.01.01, run through present ans has latency 15–50 days. They are supposed to be the most stable models, in a sense that no changes in the processing chain is made. Semi-operational GEOSFPIT models start at 2000.01.01, run through and have latency 6–15 hours. They are considered less stable than MERRA2.

  The models that I use in routine data analysis: ATM_GEOSFPIT, LWS_GEOSFPIT, TOC_FES2014B, EQUIL01, NTO_OMCT. For epochs before 2000.01.01 when GEOSFPIT is unavailable, I use ATM_MERRA2 and LWS_MERRA2. I use harmonic variations at diurnal and sub-diurnal bands for all these loadings, except for the non-tidal loading. I use for data reduction only the S₁ contribution to harmonics variations of non-tidal loading model OMCT05 (i.e. the variation with the period exactly one day: 86400 s).

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Last update: 2025.03.05_20:28:25