Satellite observations of maritime glacier terminus positions at Kenai Fjords National Park

This geodatabase contains outlines of glacier terminus positions for 19 maritime glaciers in KEFJ digitized using available spring and autumn Landsat images between 1984 and 2021. For each glacier, we created the following static features, stored within a corresponding feature class within this ESRI File Geodatabase:
- a point marking the glacier location centroid, with a unique ID number for each glacier;
- a centerline (RGI Consortium, 2014) that extends to the maximum observed length of the glacier (not the entire glacier length);
- a reference box, with one side drawn perpendicular to glacier flow and down-glacier of any tributary glaciers 
  connecting to the main trunk, two additional lines extending laterally along the glacier edges past the terminus, and 
  open-ended in the down-flow direction; 
- a reference line (or “gate”) with which to intersect each digitized glacier outline, equivalent to the back end of the 
  reference box but extended beyond the full width of the glacier. 

We used spring and autumn Landsat images to digitize seasonal ice margins. We limited our image search to spring (May and June) and autumn (mid-August through mid-October) to approximately capture the seasonal maximum and minimum extents of the glaciers. Additionally, because repeat mapping of glacier features requires high geometric precision, we included only images with Landsat's Tier 1 (T1) and Level-1 Precision and Terrain (L1TP) classifications, which meet Landsat's highest geometric precision standards. While this selection ensures high geometric precision within a given Landsat scene coordinate, we observed that the geometric precision between overlapping scene coordinates was inconsistent. Therefore, we limited our image search to scene coordinate 069/018 (under the Worldwide Reference System-2 (WRS-2) path/row notation), which fully covers the glaciers of interest in this study. The WRS-2 was first used with Landsat-4, launched in 1982. Prior to Landsat-4, the Landsat series used the WRS-1 system. The WRS-1 scene coordinate 074/018 covers our glaciers of interest; however, we found no images at this coordinate that satisfied the T1 and L1TP criteria. Therefore, the earliest potential year from which we could acquire images was 1982.

With these constraints in mind, we searched the Landsat Public Data on Google Cloud Platform for all Landsat product identification numbers that met these requirements and downloaded all resulting images. All images were re-projected into the NAD83(2011) / Alaska Albers coordinate reference system (EPSG:6393), the standard system used by the NPS Alaska region, including KEFJ. The red, green, and blue bands were combined to create a true-color composite for each image. Finally, for Landsat-7 and Landsat-8, the color composite image was pan-sharpened using the panchromatic band. This process yielded over 200 true-color image candidates at 15m to 30m resolution.

Tags: ecological-framework-geology-and-soils-geomorphology-coastal-oceanographic-features-and-process, ecological-framework-geology-and-soils-geomorphology-glacial-features-and-processes, nps-gov-subject-site-alaska, nps-gov-subject-site-alaska-nature-and-science, nps-gov-subject-site-glaciers
Organization: Department of the Interior