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Ramage, J.M., 2001

Satellite remote sensing of daily, seasonal, and annual changes on southeast Alaska glaciers, 1986-1998

Bibliographic Reference

Ramage, J.M., 2001, Satellite remote sensing of daily, seasonal, and annual changes on southeast Alaska glaciers, 1986-1998: Ithaca, New York, Cornell University, Ph.D. dissertation, 283 p., illust.

Abstract

Satellite observations from visible and near infrared, synthetic aperture radar (SAR), and passive microwave data were used to monitor glacier changes on daily to decadal scales in southeast Alaska between 1986 and 1998. Late summer Landsat Thematic Mapper (TM) images showed a snowline rise from 1986 to 1995 on outlet glaciers of the Juneau Icefield. SAR data were used to monitor seasonal changes of Juneau Icefield snow pack properties using four radar glacier zones: the frozen snow zone (F), initial melt zone (M), second melt zone (M2), and bare ice zone. Field observations constrained the interpretations of the M and M2 zones. The SAR transition from the M to M2 zone was shown to be the result of the wet glacier surface's becoming rough on the scale of the radar wavelength (5.6 cm) due to surface ablation. Passive microwave Defense Meteorological Satellite Program Special Sensor Microwave Imager (SSM/I) data have better temporal coverage with twice daily global observations. The difference between twice daily brightness temperature (T b ) observations increased abruptly by more than 10°K when the surface started to melt, due to the effect of liquid water on Tb . The SSM/I record from 1988-1998 showed a tendency toward earlier melt onset and a longer ablation season in the later part of the period. These results applied widely in southeast Alaska; eleven regions within southeast Alaska and the average for southeast Alaska showed this trend. Monthly temperature anomalies show that both spring and summer monthly temperatures increased from 1985 to 1998. The patterns of higher snow lines, earlier snow melt, somewhat later freeze up, and longer duration of the ablation season are due in part to decreasing (though variable) winter accumulation and increasing average monthly summer temperatures. The period of record is too short to attribute these observations to global warming, but they are consistent with that possibility. In this northeast Pacific region it is also possible that the trends are due to shorter term climate variations such as El Nino or the Pacific decadal oscillation.

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