Narrowband-to-broadband albedo conversion for glacier ice and snow based on aircraft and near-surface measurements

摘要

This article presents albedo measurements of snow and glacier ice at Vatnajokull (Iceland) and the Kangerlussuaq transect (Greenlandr Radiative fluxes were measured in the broadband and in four narrowbands, namely, Thematic Mapper (TM) Bands 2 and 4, and Advanced Very High Resolution Radiometer (AVHRR) Bands 1 and 2. The incoming fluxes were measured near the ground and the outgoing fluxes from a helicopter. Extracts of the data collected over snow, ice, supraglacial moraines, supraglacial lakes, and tundra are discussed. Using the data sets from Iceland and Greenland, and data sets with entirely ground-based albedo measurements from the Morteratschgletscher (Switzerland) and Scharffenbergbotuen (Antarctica), new equations for narrowband-to-broadband (NTB) conversion were developed. They have a residual standard deviation of 0.011 for TM and 0.008 for AVHRR and can be applied without having to classify the surface. The helicopter data are also used to develop criteria for distingnishing different types of surfaces, which are needed for the application of Bidirectional Reflectance Distribution Functions (BRDFs). Snow can be distingnished from ice by defining a threshold for a single narrowband albedo. The ratio of the albedos in TM4 and TM2, and to a lesser extent, the ratio of the albedos in AVHRR2 and AVHRR1, may serve as a proxy for the surface characteristics of glacier ice in terms of concentrations of water; debris, and dust.