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The spectra of GRACE (2013-14)

Hughes and Williams 2010 (PDF) treated sea level spectra as light spectra. I and my co-authors applied their methodology to GRACE, revealing the first “full color” GRACE maps and comparing them to the Noah/GLDAS water storage model.

Update: Here are new images (68 MB) and output data (421 MB).

  • Newer GRACE spectra (“SS76y” on bottom row) are less colorful than the preliminary GRACE data used in the 2013 AGU poster (“SS23x” on top row). This indicates more wide spectrum power is present in the new GRACE spectra, which makes them look more similar to GLDAS spectra. Also, a new triple colorscale (modeled after the colorscales in Hughes and Williams 2010 figure 1) shows the spectra of light curves with three different widths; wider light curves make the colorscale more faded and “pastel”. The triple colorscale is unfinished; still need to decide how to automatically and objectively normalize three different colorscales- right now the colorscale on the left (with the most narrow light curve) is too dark.
  • This experiment tests another way to detect tides: map the acceleration spectrum (without inverting for surface mass) immediately around a tidal frequency (O1 here) onto the visible light spectrum. The resulting map of O1 has a spatial pattern that roughly corresponds to that of the O1 tidal acceleration map obtained by using least squares to find the best-fit O1 acceleration amplitudes.
  • GRACE spectra based on the older “SS23x” GRACE solutions (top row) are compared to GRACE spectra based on CSR Tellus, JPL Tellus and GAIA’s prototype monthly GRACE maps.

In the Hughes and Williams 2010 appendix, matrices 4 and 5 should be swapped, as well as the two parts of equation 7.

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