On The Atmospheric Correction for a Hyperion Scene
Tian-Yuan Shih
Department of Civil Engineering
National Chiao-Tung University
Hsin-Chu, Taiwan
Fax: 886-3-5716257
E-mail: tyshih@mail.nctu.edu.tw
ABSTRACT
The atmospheric correction is performed with a scene of Hyperion over the Taiwan area
acquired from the USGS. This study compares the radiance and the corrected reflectance
spectra. The software FLAASH was used in this experiment. The cloud mask and water
content image generated are compared with an optical image. Different MODTRAN resolution
settings and the spectral polishing effect are also studied with the spectra.
INTRODUCTION
Hyperion sensor is a hyperspectral imager on-board of EO-1 satellite. There are 220
spectral bands ranging from 400 – 2500 nm. The spatial resolution is 30 meter per pixel and
swath width is 7.7 km. Each scene covers either 42 km, or 185 km. The product is distributed
by USGS, and the level one product, which is only radiometrically corrected, is available. The
EO-1 satellite was launched on November 21, 2001 as part of a one-year technology
validation/demonstration mission. After the original EO-1 mission was successfully completed
in November 2001, the remote sensing research and scientific communities expressed high
interest in continued acquisition of image data from EO-1. Based on this user interest, an
agreement was reached between NASA and the USGS to allow continuation of the EO-1
Program as an Extended Mission (Pearlman, et al., 2003; USGS, 2004a).
The EO-1 spacecraft follows Landsat-7 by approximately one minute, the descending
equatorial time of 10A.M. It is capable of cross-track pointing to allow potential imaging within
one full adjacent WRS path in each direction from the current flight path. The orbit altitude is
the same as the Landsat, which is approximately 705 km. The Hyperspectral imaging has wide
ranging applications in mining, geology, forestry, agriculture, and environmental management.
Detailed classification of land assets through the Hyperion will enable more accurate remote
mineral exploration, better predictions of crop yield, and assessments, and better containment
mapping (USGS, 2004b).
The apparent reflectance should be derived because the data released from USGS is the
level one, radiometrically corrected only, for spectral analysis based applications. This process
is named atmospheric correction. There are currently several packages commercially available
for this function, such as ACORN (ImSpec, 2004), ATCOR (Leica, 2004), and FLAASH. This
study uses FLAASH in ENVI (RSI, 2001). This software is a MODTRAN based package.
With several defined atmosphere models and aerosol models, the user interface is simplified.
The process of this experiment is documented in this paper and the resulting spectra is also
compared with those original ones. Compared with ACORN, FLAASH is less sophisticated and
has lesser input requirement. For example, FLAASH does not require the spectral center
wavelength and the FWHM (Full Width Half Maximum) value. Therefore, the center
wavelength shifting of each bands in Hyperion image, will not be dealt with using FLAASH.
There is no offset setting in FLAASH either, which may be important when the offset value
does exist, such as the MASTER image.
