ASTER와 AVIRIS 원격탐사법을 이용한 Yellowstone National Park 내의
hot spring과 이와 관련된 광상에 대한 분석
Melanie J. Hellman*, Michael S. Ramsey
Department of Geology and Planetary Science, University of Pittsburgh,
Pittsburgh, PA 15260-3332, USA
Accepted 5 December 2003
VNIR (visible/near infrared)에서부터 TIR (thermal infrared)까지의 파장을 이용한 ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer)와 AVIRIS (Airborne Visible/IR Image Spectrometer) 자료를 이용하여 Yellowstone 국립공원의 Lower, Midway, 그리고 Upper Geyser 분지의 hot spring 광상의 성격을 규정하였다. 이들 분지에 대한 현장 관찰로부터 원격탐사 결과와 비교되는 결정적인 ground-truth를 인지할 수 있었다. 크기, 광상의 형태, thermal activity 등의 다양성에 기초하여 14개의 연구지역을 선정하였으며, 이들 지역에 대하여 land cover analysis, 사진, GPS 자료수집, 방사능 검사, VNIR 분광분석 등에 대한 자세한 탐사를 실시하였다. hot spring 광상, geyser 광상, 토양에 대한 시료 또한 수집하였다. ASTER 자료에 대한 분석을 통해 열적 이상대(thermal anomaly)에 대한 인지를 포함한 광역적인 hot spring들과 이들과 관련된 광상들에 대한 성격을 규정하였다. AVIRIS 고해상도 SWIR 분광분석법으로 열수변질광물을 인지해낼 수 있었다. image analysis를 통해 열에 의한 변질의 범위, 변질광물의 위치와 양 그리고, 간헐천의 양태(active, near-extinct, extinct) 등의 관점에서 이들 분지들의 차이점이 인지되었다. 우리는 VNIR-SWIR-TIR 스펙트럼의 변화를 조합하여 각 지역의 활동 정도(activity level) - 이는 ASTER의 영역에 포함되는 TIR에 의해 인지되는 상승온도(elevated temperature)의 존재와 같다. - 를 결정할 수 있었다. 이 연구의 결과들은 지구와 화성의 활동을 멈춘 열수광상들에 대한 탐사에 적용될 수 있다.
Fig. ASTER VNIR reflectance spectra, with band 3=(0.76~0.86㎛), band 2=(0.63~0.69 ㎛), and band 1=(0.52~0.60 ㎛). (A) Sunset Lake (site 9) is an active spring in the Upper Geyser Basin. (B) Fountain Flats (site 7) is an extinct spring in the Lower Geyser Basin. The spectra are vegetation dominated, however they do not resemble pure vegetation. Spectral mixing with the soil background is likely because of the higher reflectance in the 0.52~0.69 ㎛ region. |
Fig. SWIR reflectance spectra from White Dome (site 13) in the Lower Geyser Basin (an active spring). (A) AVIRIS spectra (1.65~2.51 ㎛) showing the absorption feature of siliceous sinter at 2.25 mm. (B) AVIRIS spectra of silica sinter as observed by Kruse (1999) (note, only relative reflectivity was displayed on the y-axis of the original figure). The spectrum is similar in shape to the spectra in (A), and especially similar to the spectra in Fig. 7A. (C) ASTER reflectance spectra (1.65~ 2.40 ㎛) showing that the siliceous sinter cannot be easily identified due to the broader spectral band passes. The spectra most resemble a mix of dry and green vegetation, but significant spectral mixing occurs. |
Analysis of hot springs and associated deposits in Yellowstone National Park
using ASTER and AVIRIS remote sensing
Melanie J. Hellman*, Michael S. Ramsey
Department of Geology and Planetary Science, University of Pittsburgh,
Pittsburgh, PA 15260-3332, USA
Accepted 5 December 2003
Abstract
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the irborne Visible/IR Image Spectrometer (AVIRIS) data were used to characterize hot spring deposits in the Lower, Midway, and Upper Geyser Basins ofYellowstone National Park from the visible/near infrared (VNIR) to thermal infrared (TIR) wavelengths. Field observations of these basins provided the critical ground-truth for comparison with the remote sensing results. Fourteen study sites were selected based on diversity in size, deposit type, and thermal activity. Field work included detailed site
surveys such as land cover analysis, photography, Global Positioning System (GPS) data collection, radiometric analysis, and VNIR spectroscopy. Samples of hot spring deposits, geyser deposits, and soil were also collected. Analysis of ASTER data provided broad scale characteristics of the hot springs and their deposits, including the identification of thermal anomalies. AVIRIS high spectral resolution short-wave infrared (SWIR) spectroscopy provided the ability to detect hydrothermally altered minerals as well as a calibration for the multispectral SWIR ASTER data. From the image analysis, differences in these basins were identified including the extent of thermal alteration, the location and abundance of alteration minerals, and a comparison of active, nearextinct, and extinct geysers. We determined the activity level of each region using a combination of the VNIR-SWIR-TIR spectral differences as well as the presence of elevated temperatures, detected by the TIR subsystem of ASTER. The results of this study are applicable to the exploration of extinct mineralized hydrothermal deposits on both Earth and Mars.
D 2004 Elsevier B.V. All rights reserved.
Keywords : remote sensing; instruments and techniques; geothermal systems; Mars