Proceedings of the Symposium on Global and Environmental Monitoring: Proceedings of the Symposium on Global and Environmental Monitoring

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Persistent identifier:: 856665355

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts ; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856665355

Language:: English

Document type:: Multivolume work

Volume

Persistent identifier:: 856669164

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Scope:: XIV, 912 Seiten

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856669164

Illustration:: Illustrationen, Diagramme, Karten

Signature of the source:: ZS 312(28,7,1)

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: International Society for Photogrammetry and Remote Sensing, Commission of Photographic and Remote Sensing Data

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [THP-1 HIGH SPECTRAL RESOLUTION MEASUREMENT]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: SPECTRAL VARIABILITY EFFECTS ON THE ATMOSPHERIC CORRECTION OF IMAGING SPECTROMETER DATA FOR SURFACE REFLECTANCE RETRIEVAL. P. M. Teillet and J. R. Irons

Document type:: Multivolume work

Structure type:: Chapter

579 SPECTRAL VARIABILITY EFFECTS ON THE ATMOSPHERIC CORRECTION OF IMAGING SPECTROMETER DATA FOR SURFACE REFLECTANCE RETRIEVAL P.M. Teillet Canada Centre for Remote Sensing 1547 Merivale Road, Nepean, Ontario, Canada K2G 4V3 and J.R. Irons Biophysical Sciences Branch NASA Goddard Space Flight Center, Greenbelt, Maryland, USA 20771 ABSTRACT Based on apparent radiances (nadir-looking) from the airborne Advanced Solid-State Array Spectro- radiometer (ASAS) and measured optical depth values, a surface reflectance spectrum was computed by an atmospheric code run (i) monochro- matically at band center wavelengths, (ii) for rectangular bandpasses, and (iii) for spectral response profiles. A comparison of the results from these different cases indicates that anomalous results for surface reflectance can be obtained in the vicinity of absorption features in the monochromatic case and that bandpass computa tions yield better results. Even with bandpass calculations, if there is no information available on gaseous absorption at the time of image acquisition and standard values are used in the atmospheric correction of high spectral resolution data, it is shown that the retrieved surface reflectances can depart significantly from normal values in spectral regions affected by absorption. INTRODUCTION In remote sensing, an atmospheric radiative transfer code is used to determine surface reflectances given image data acquired by satellite or aircraft sensors. The more accurate models of radiative transfer through the atmosphere are complex and can require a lot of computer processing time. Thus, in remote sensing studies, such models are often run monochromati- cally to represent a spectral band in order to save time. With the relatively narrow bands of imaging spectrometers, such an approach should work well throughout most of the relevant spectral domain. However, the narrowness of the imaging spectrometer bands also implies greater sensitivity to atmospheric absorption features, which can be very spectrally selective. The effects of these factors on atmospheric correction of imaging spectrometer data were examined using data from the airborne Advanced Solid-state Array Spectroradiometer (ASAS), used by the NASA Goddard Space Flight Center for multiple direction reflectance observations (Irons et al., 1989). The sensor primarily consists of a charge injection device with a 512 by 29 silicon photodetector array. A diffraction grating is used to distribute the spectral information onto the 29-array dimension, from which 29 channels are obtained in the 465-871 nm range. For a flight altitude of 5000 feet, the nadir pixel size is 4.5 m across track. The data acquisition strategy is to change the pointing direction of the sensor from 45 degrees fore to 45 degrees aft while flying over a specific target location. In this way, seven images are acquired at 15 degree increments in view angle for a given target area. Thus, ASAS is a particularly useful instrument for studying bidirectional reflectance distribution functions of natural surfaces. ASAS data were acquired by NASA over Konza prairie grass in 1987 as part of the First ISLSCP Field Experiment (FIFE), where ISLSCP stands for the International Satellite Land Surface Climatology Project. Radiometric calibration coefficients were used to convert the data recorded during the flight to physical radiance units. An individual radiance spectrum was extracted from a nadir image acquired over vegetation. In the present atmospheric correction study, attention was focused on 9 channels encompassing the spectral range from about 0.670 to 0.805 micrometers, with each individual channel having a bandwidth of 0.015 micrometers. This portion of the reflectance spectrum of vegetation includes the chlorophyll minimum in the visible and the rise up to the infrared plateau region. The feasibility of retrieving surface reflectances from the measured radiances has been investigated with the help of the 5S atmospheric code (Tanre et al., 1986; Teillet, 1989). ANALYSIS AND RESULTS Monochromatic Case Based on the input conditions listed in Table 1 and the ASAS apparent radiances, surface reflectances were computed by 5S monochromatically at the band center wavelengths listed in Table 2. However, computations in the 5S code are tied to a wavelength grid with 0.005 micrometer spacing. Thus, if the specified wavelength is 0.678 micro meters, for example, the code will actually generate results for a wavelength of 0.680 micro meters, the nearest grid wavelength. Results from this approach are listed in Table 2 under the heading "5S LAMBDA GRID". Rectangular Bandpass Case Each individual ASAS band is not monochromatic but rather has a bandwidth of 0.015 micrometers. A rectangular bandpass was adopted and used in a second series of 5S runs to approximate the spectral response profile of each ASAS channel. The results are presented in Table 2 under the heading "5S BAND (RECT)". Profile Bandpass Case It can be argued that a rectangular bandpass of 0.015 micrometers is not very representative of

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