Modelling the radiation budget of alpine snowfields with remotely sensed data: model formulation and validation

Abstract

A model for estimating the radiation balance of alpine snowfields is presented. Shortwave and longwave downward flux densities are computed for sloping surfaces using a modified version of the two-stream radiative transfer scheme of Zdunkowski and others (1982). Surface albedo and thermal exitance values are estimated using Landsat-5 Thematic Mapper (TM) imagery and digital terrain data. The LOWTRAN7 radiative transfer code is utilized in order to remove atmospheric effects in satellite imagery as well as calculating solar irradiance within TM spectral bands, for the determination of the near-nadir reflectance of snow. Under a Lambertian assumption, near-nadir reflectance measurements obtained from a few TM bands are used to calculate the total hemispherical reflectance (albedo) of snow. The net all-wave radiation of snowfields is then simulated for the complete day on the same date as that of the Landsat overflight. The model is tested using Landsat TM data acquired in late June 1984, and results compared with field measurements acquired on Niwot Ridge, Colorado, U.S.A. Preliminary results are very encouraging but problems remain in the estimation of surface albedo from near-nadir satellite reflectance measurements of TM. These problems are discussed and recommendations for future model improvements are given.

Validation of AVHRR- and MODIS-derived albedos of snow and ice surfaces by means of helicopter measurements

“…Obviously, validation of the satellite-derived albedos is required. Studies to validate Thematic Mapper (TM)-and Advanced Very High Resolution Radiometer (AVHRR)derived albedos have been conducted by Hall and others (1989), Duguay (1993), De Abreu and others (1994), Knap and Oerlemans (1996), Stroeve andothers (1997, 2001), Knap and others (1999) and Reijmer and others (1999).…”

GIS Applications to Glaciology: Construction of the Mount Rainier Glacier Database

“…Concerning other glacier surface characteristics, Lindsay and Rothrock (1993) map the spatial distribution of Arctic sea ice surface temperature and albedo from A VHRR data. Studies of ice surface radiation and albedo have been carried out by Hall et al (1987) and Duguay (1993). Aerial photography and satellite remote sensing data also may provide for the recognition of glacial features, such as frozen lakes on the glacier surface (Winther 1993).…”