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Geodetic Data for Juneau Icefield Glaciers: Orthophotos, Digital Elevation Models, and Glacier Boundaries

October 24, 2019

Since the 1940s, the Juneau Icefield Research Program (JIRP) has been measuring surface mass balance on the Juneau Icefield. This is the longest ongoing program of its kind in North America. The program nominally occurs between late June and late August, traversing between Juneau, Alaska and Atlin, British Columbia. JIRP has examined the surface mass balance of the Juneau Icefield since 1946, with principal efforts focused on Lemon Creek Glacier and Taku Glacier. Glaciological, geodetic, and meteorological data have been collected by JIRP to characterize the interaction between the climate and glaciers of the Juneau Icefield. Direct field measurements of point glaciological data are combined with weather and geodetic data to estimate the seasonal and annual mass balance at each glacier in both a conventional and reference surface format (Cogley and others, 2011). The basic analysis framework (O'Neel, 2019, McNeil and others, 2019) is the same at each glacier to enable cross-comparison between output time series. For Taku and Lemon Creek glaciers, temperature lapse rates are optimized using on-icefield weather data. This changes the degree day factor in the melt model, giving small post-geodetic calibration differences on the order of 2-3 cm. Details are described in McNeil (2019). Vocabulary used follows Cogley and others (2011) Glossary of Glacier Mass Balance.
This portion of the data release includes geodetic data used in mass balance analyses. The USGS uses geodetic data to quantify glacier area, glacier hypsometry, and the change in glacier volume and mass (e.g., Cogley and others 2011; Zemp and others 2013; van Beusekom and others, 2010; O'Neel and others 2014). Here we describe these basin-scale data, how they are produced, and the format in which they are preserved and disseminated.
Gridded products comprise the first class of data and include orthorectified images and Digital Elevation Models (DEMs). Prior to the early 2000s, these grids were derived from aerial stereo photography or historic topographic maps. More recently, high-resolution space-borne imagery facilitated DEM and ortho-image production using approaches described herein.
The second class of data are vector geospatial files of glacier margins. These are interpreted products, produced via manual digitization of the boundary between rock and ice identified from ortho-rectified images, or the boundary between neighboring glaciers identified from ice divide velocity maps. Additional data for Lemon Creek Glacier, part of the Juneau Icefield, is available in a separate data release of USGS Benchmark Glacier geodetic data at https://doi.org/10.5066/P9R8BP3K. The data is documented but is not included here in order to avoid duplication.