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

Bibliographic data

Multivolume work

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:: [TP-2 SPECTRAL SIGNATURES]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: EFFECTS OF SPECTRAL SHIFTS ON SENSOR RESPONSE. P. M. Teillet

Document type:: Multivolume work

Structure type:: Chapter

EFFECTS OF SPECTRAL SHIFTS ON SENSOR RESPONSE 59 P.M. Teillet Canada Centre for Remote Sensing 1547 Merivale Road, Nepean, Ontario, Canada K2G 4V3 ABSTRACT The effect of spectral filter shifts on sensor outputs are presented for the case of the Thematic Mapper (TM) imaging vegetation and the Moderate Resolution Imaging Spectrometer-Nadir (MODIS-N) imaging vegetation and water. Errors in excess of 5% per 5 nm spectral shift are noted for TM bands 1 and 2, and the error decreases with increasing wavelength for the TM bands in general. Most MODIS-N bands in the solar reflective spectrum can be affected by the spectral shift problem, with the largest errors (several hundred percent) occurring for the 10-nm water vapour band centred at 0.935 micrometers. INTRODUCTION Spectral bandpasses made by interference filters are susceptible to changes in response charac teristics with time and due to changes in environ mental conditions. It is not uncommon for the entire bandpass to shift toward shorter wave lengths and/or for the long-wavelength side of the bandpass to shift toward shorter wavelengths. Suits et al. (1988) have developed an analytical approach to examine the effect of spectral response shifts on the outputs of several sensors. They comment that the linear assumption implicit in their approach may not be appropriate for non linear conditions such as those considered here. Markham and Barker (1985) have noted a 9-nm shift in the long wavelength cut-off of the band-3 filters in the fourth Landsat Multispectral Scanner System (MSS) after storage at normal pressure, temperature and humidity over an 18- month period. The cut-on at shorter wavelength was unchanged because it was mainly defined by a stable absorption filter. The cut-off was provided by an interference filter, thus the half- width and therefore the total transmittance of the filter changed (Slater, 1989, personal communica tion). The same effect has been observed in the case of the SPOT-1 HRV filters. Here the effect was most noticeable as expected for the narrow filters. For example, Dinguirard et al. (1988) report a 27% transmittance change in multispectral band 2 with a change from air to vacuum conditions. The broad panchromatic band on the other hand exhibited only a 3% change in trans mittance . A shift of a narrow filter can produce a sig nificant change in measured radiance even when the filter transmittance remains constant. This is because of the presence of Fraunhofer absorption lines in the solar output. It can be shown that a 10-nm filter with a rectangular profile centered at 480 nm, when shifted through 5 nm, can cause an 8% change in the recorded signal (Slater, 1989, personal communication). For this reason, the system must be radiometrically calibrated in flight using solar radiation and/or a sensitive wavelength calibration must be employed. It is also desirable to use interference filters that have been manufactured using ion bombardment to reduce the porosity and therefore increase the stability in refractive index of the dielectric layers (Slater, 1989, personal communication). As the spectral bands on satellite sensors become narrower and selected for specific scientific measurements, it becomes more important to assess the impact of any changes in the response charac teristics of the bands if interference filters are used. The flexibility and speed of the 5S atmospheric code (Tanre et al., 1986) lend themselves well to some initial studies of this problem. In particular, the code's principal mode of operation is to produce band-integrated results. It also allows the user to input spectral response profiles on a 5-nm grid. Therefore, it is a relatively simple matter to run different cases to determine the error incurred if, unknown to the user, a spectral band has shifted. In this study, the effect of partial (long-wavelength side only) and full spectral band shifts on radiances output from a radiative transfer code were examined for reflective bands from two sensor systems: (i) the Landsat Thematic Mapper (TM) and (ii) the planned Moderate Resolution Imaging Spectrometer-Nadir (MODIS-N), should interference filters be used to construct its spectral bandpasses. In both cases, it was found that spectral shifts introduce significant changes in sensor response for many of the bands. Landsat Thematic Mapper Bands The effect of partial (long-wavelength side only) and full spectral band shifts on outputs from the 5S program were examined for the case of the reflective TM bands. The input conditions are listed in Table 1 and assume, in particular, a vegetated surface. For each of the six reflective TM bands, forward runs of the 5S code were made for no spectral shift, for partial spectral shifts of 5, 10, and 15 nanometers (Figure 1), and for full spectral shifts of 5, 10, and 15 nanometers (Figure 2) toward shorter wavelengths. (A forward run of the code computes apparent reflectance at the sensor given the surface reflectance.) The apparent reflectances at satellite altitude output from these 5S runs were then used as input values for reverse runs (Teillet, 1989) with no spectral band shifts of any kind. The predicted surface reflectance differs substantially from the original surface reflectance in many cases (Figures 3, 4, and 5). The greatest differences occur in TM band 1, with a 25 percent error for a full shift of 15 nm and 12 percent for a partial shift of 15 nm. For the TM bands in general, the error decreases with increasing wavelength. MODIS-N Bands MOD IS is an instrument that will be part of the

Access restriction

Copyright

fullscreen: Proceedings of the Symposium on Global and Environmental Monitoring (Part 1)

Multivolume work

Volume

Chapter

Chapter

Table of contents

Cite and reuse

Volume

Chapter

Image

Image fragment

Citation links

Citation recommendation