5.B.i.d. Greenland

Data coverage for Greenland was available from Zwally (and others)/NSIDC/JPL and DCW, with very limited NIMA coverage. A review by J.-P. Muller of University College London determined that the JPL version compared much more favorably with available point elevation control (Muller and Mandanayake, 1998a; Muller and others, 1998b). NGDC’s assessment of the DEMs suggested that the Zwally (and others)/NSIDC/JPL DEM was best in the interior and northerly coastal areas characterized by permanent ice. DCW (or DTED where available) was preferred in southerly coastal areas.

NGDC scientists inspected Zwally (and others)/NSIDC/JPL, DCW, and DTED DEMs, to determine which sources were preferable for which areas. Using inspection, a two-degree wide zone for linear blending was created. The two DEMs were used equally in the middle of the zone. Weighting was adjusted 4 percent every 5 minutes throughout the zone.

In very limited areas, the DCW coverage extends oceanward from the mosaicked DTED and Zwally (and others)/NSIDC/JPL data. This is because of different interpretations of coastlines between the three candidate DEMs in this area. Such differences in interpretation of coastline are common. They are especially common in polar areas where the edge seasonal or "permanent" ice may be accepted as coastline in some data sets when it overlaps coasts onto the ocean, whereas other data sets discount such ice features and attempt to determine the "dry land" coastline below such ice. In such areas, the DCW data were patched into GLOBE Version 1.0.

In other limited areas, the Zwally (and others)/NSIDC/JPL DEM extended oceanward of the limits of DCW or DTED coverage. In these cases, the coastal mask used in GTOPO30 data was honored by GLOBE, so any Zwally (and others)/NSIDC/JPL DEM coverage coincident with this ocean mask was not used in GLOBE.

Note that several alternative candidate data sets are available for Greenland. These are still under evaluation, with further development being pursued. This may (or may not) result in improved coverage for Greenland in a future version of GLOBE.