Landsat TM derived and in situ summer reflectance of glaciers in Svalbard

Abstract

Winther, J-G. 1993: Landsat TM derived and in situ summer reflectance of glaciers in Svalbard. Polar Research 12(1), 37-55.The paper presents satellite-derived and in situ reflectance from the Austre Br~ggerbreen and Midre LovCnbreen glaciers located 78"50", 1 l"50'E in the Svalbard archipelago. The satellite data are Landsat-5 TM images recorded on 7 August 1987 and 31 August 1988. In situ measurements of shortwave and spectral reflectance of snow, glacier ice and moraine were carried out in August 1991 and in June 1992. In 1987, Austre Br~ggerbreen had a positive net mass balance of +0.22 m of water equivalent while the net mass balance in 1988 was negative (-0.52 m). This is reflected in the atmospherically corrected satellitederived albedo which shows that the reflective characteristics of the ablation and accumulation zones are more uniform and better separated in 1987 than in 1988. Besides the long-term year to year variations of surface albedo, the glaciers show a considerable short-term as well as spatial variability in reflectance. For example, the satellite-derived TM Band 4 albedo was found to vary between 0.19 and 0.65 at Midre Lovtnbreen on 31 August 1988. In silu measurements show a drop in daily mean albedo from 0.88 to 0.13 during 4 days at a fixed location on Austre Br~ggerbreen in August 1991 (300 m.a.s.1.). Furthermore, spectral measurements of snow albedo in June 1992 clearly demonstrate that the near-infra-red albedo decreases when the snow metamorphoses, i.e. when the characteristic grain size increases. The effect of cloud cover on the snow albedo is also discussed. The integrated albedo (37CL900 nm) increased from 0.812 to 0.869 (7%) when the weather condition changed from clear sky to 100% overcast within 2 hours on 9 June 1992. The bidirectional reflectance of snow is measured by taking spectral scans for viewing angles 0" (nadir), 15". 30". 45" and 60" for viewing directions facing the sun and at azimuths 90" and 180" away from the sun. The increase in albedo relative to the nadir albedo is found to be 8, 15, 19 and 26% for viewing angles 15". 30". 45" and 60". respectively. The largest anisotropy is seen for metamorphosed snow in measurements facing the sun. Consequently, it may be necessary to correct for the specular properties of snow if satellite-derived surface reflectance is going to be considered in terms of absolute values. Hydrotechnical Laboratory, N-7034 Trondheim, Norway. Jan-Gunnar Winther, SINTEF Norwegian

Narrowband to broadband conversion of Landsat TM glacier albedos

“…This problem and other aspects of surface-albedo retrieval from TM data are discussed by e.g. Winther (1993) and Knap et al (1998 ).…”

Remote sensing of alpine glaciers in visible and infrared wavelengths: a survey of advances and prospects

“…In the same year, Hall et al (1987) proposed Landsat TM band ratio (band 4/band 5) for enhancing snow and ice features owing to large difference in spectral response of these features in the respective bands. In subsequent years, more of such research followed, but as a significant contribution, Winther (1993) used Landsat TM and in situ summer reflectance of glaciers in Svalbard for determining spatio-temporal variations of glacier summer albedo and estimating anisotropic snow reflectance. The study demonstrated and discussed in detail the large range of surface albedo present on glacier, particularly at the end of mass balance year (late August), and thus paved the way for more studies to follow.…”

“…Year-round melting occurs in the ablation zone of a glacier, subsequently exposing the ice, whilst the accumulation area mainly consists of wet snow, percolation and dry snow facies (Winther 1993). As already discussed, different facies represent surfaces with different reflectance characteristics, thus playing a crucial part in the earthatmosphere energy balance (Warren & Wiscombe 1985).…”

Using SAR satellite data time-series for regional glacier mapping

“…Generally, TSLs are visually more apparent on optical images than on SAR backscatter images, but it may still be challenging to derive the TSL when superimposed ice is present (e.g. Winther, 1993;Kundu and Chakraborty, 2015).…”