Comparison of Landsat TM-derived and ground-based albedos of Haut Glacier d'Arolla, Switzerland

• Published in: International journal of remote sensing Vol. 20; no. 17; pp. 3293 - 3310
• Main Authors: Knap, W. H., Brock, B. W., Oerlemans, J., Willis, I. C.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 01.01.1999; Taylor and Francis
• Subjects: Applied geophysics; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Internal geophysics; Snow. Ice. Glaciers; Switzerland; Central Europe; Switzerland; Valais Switzerland; glaciers; Thematic Mapper; Europe; Space remote sensing; ablation; anisotropy; Landsat; surveys; satellite measurements; ice; snow; atmospheric correction; calibration; albedo
• ISSN: 0143-1161; 1366-5901
• DOI: 10.1080/014311699211345

Measurements of the surface albedo of Haut Glacier d'Arolla (Switzerland) derived from Landsat Thematic Mapper data (alpha TM ) are compared with ground-based albedo measurements (alpha g ). The analysis is based on (a) 137 aground-based measurements made at 67 sites during three extensive glacier surveys in the 1993 ablation season, and (b) data acquired during three corresponding cloud-free Landsat overpasses on 29 May, 1 and 17 August. For the first overpass large differences in the snow albedo are found (average:alpha TM 0.73, alpha g 0.55), which are attributed to snowfall and metamorphism of snow between the times of the satellite overpass and the ground measurements. For the second overpass there is much better agreement between the two snow albedos (average: alpha TM 0.56, alpha g 0.51). For the second and third overpass there is good agreement between alpha TM and alpha g of glacier ice (average:alpha TM 0.17, alphag 0.19). However, the scatter in alpha TM alpha g is large which is very probably related to the high spatial variability of the ice albedo over distances of only a few metres and the smallscale coverage (in terms of ground area) of the ground measurements compared to the TM pixel size. In addition, there is a tendency for alpha TM to overestimate low values of alpha g and to underestimate high values. This is explained by a possible bias in the ground-based measurements towards selecting either relatively clean or relatively dirty ice surfaces. Several errors associated with uncertainties in the method of albedo retrieval are discussed. It is suggested that the assumption of an isotropically reflecting surface is a main source of error in the satellite-derived albedo.