The summary data presented here is but a small fraction of the survey data collected on the Juneau Icefield. The purpose of this data is to provide a quick overview of the temporal velocity and surface elevation changes across the Juneau Icefield. The data are organized as a series of tables, each presenting the velocity and surface elevation data for a specific movement profile versus the year in which the data were collected. All movement profiles detailed here are standard profiles on the Juneau Icefield. These were primarily established with the aid of real-time GPS. Unlike glacier movement studies in Antarctica, Greenland, and other areas with minimal snowfall, the profiles on the Juneau Icefield must be re-established every summer. This is due to the extreme amount of winter accumulation which would completely bury the movement stakes if they were left in place from year to year. Re-establishment of the profiles every summer is accomplished with the aid of real-time GPS, allowing for the placement of the stakes to within 10-20 centimeters of their previous-year positions (as listed in the JIRP Movement Profile Stake-out Coordinate tables). This level of placement accuracy ensures the validity of year-to-year evaluations of velocity and surface elevations.

All data presented here were obtained with rapid static and real-time differential GPS methods, using Leica System 300 and Leica System 530 GPS receivers. These are survey grade, L1/L2 receivers capable of centimeter-level accuracy. Data were post-processed with Leica RT-SKI software. Initial point coordinate solutions are based on the International Terrestrial Reference Frame of 1993 (ITRF93), with the primary Juneau Icefield control points (N1, Scott) linked to International GPS Service for Geodynamics (IGS) stations in Fairbanks, Alaska; Alberthead, British Columbia; Penticton, British Columbia; and Yellowknife, Northwest Territories. The initial ITRF93 coordinates were projected into a Transverse Mercator projection centered on the Juneau Icefield. The parameters of the JIRP coordinate system are shown in Table 1. All surface elevations are with respect to the WGS84 ellipsoid. Additional details concerning the connection of the Juneau Icefield to ITRF93 are discussed by Lang (1995). All final point positions have an absolute accuracy of approximately 1-2 centimeters horizontally and approximately 5 centimeters vertically.

Table 1:   Parameters of the JIRP coordinate system.

You will notice that the summary tables do not present survey data collected prior to 1993. This is because GPS was not employed on the Juneau Icefield until 1992. During that year, all profiles were established without the aid of surveying-in the flags. It was not until 1993 that a systematic method of profile establishment was used. This method relied on the use of theodolites and EDMs to survey-in the flags of Profile 4 (1993 and 1994). Real-time GPS was employed for the first time in 1995 and has been used extensively since then in the annual establishment of the profiles. In order to ensure that only consistent profile locations are analyzed in the summary tables, only those profiles which have been surveyed-in with either theodolite/EDM or GPS are presented. Thus velocity and elevation data prior to 1993 are not shown.

Lang, M. (1995)  Geodetic Activities of the 1995 Juneau Icefield Research Program Field Season. Foundation for Glacier and Environmental Research, Juneau Icefield Research Program. Open File Survey Report.

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