Earth Observing System (EOS). A description of 
the planned instrument may be found in the MODIS 
Instrument Panel Report (1986) and Salomonson et 
al. (1989). For the nadir version of the sensor, 
MODIS-N, there will be 36 spectral bands at a 
variety of spectral and spatial resolutions and 
ranging from the blue to the thermal infrared. 
Because they are relatively narrow, the 19 solar 
reflective bands (Table 2) were studied to 
illustrate the potential effects of spectral band 
shifts should interference filters be used to 
construct these MODIS-N bandpasses. 
Forward runs of the 5S atmospheric code were made 
for no spectral shifts, for partial spectral 
shifts of 5, 10, and (in some cases) 15 ran, and 
for full spectral shifts of 5, 10, and (in some 
cases) 15 nm toward shorter wavelengths. The 
input conditions were the same as those used for 
the TM bands in the previous section, except that 
a water surface reflectance case was also used in 
addition to the vegetation one. The apparent 
reflectances at satellite altitude for shifted 
cases were compared to the apparent reflectance at 
satellite altitude obtained from the no-shift 
cases. 
In the absence of any specific design information, 
spectral response profiles were synthesized for 
the MODIS-N bands under consideration. The same 
shape was used for all bands, but scaled in the 
wavelength dimension according to the bandwidth. 
For example, the relative response profile for the 
30 nm band at 0.905 micrometers is listed in Table 
3, and Figures 6 and 7 illustrate the profiles for 
the unshifted and shifted bandpasses. Because the 
5S code is based on a 5-nm grid, the response 
values are specified every 5 nm. 
The complete results are presented in Tables 4-7 
and the 10-nm full-shift cases in particular are 
shown in Figures 8 and 9. Substantial differences 
arise between the shifted and unshifted results 
for many of the bandpasses. The key results are 
as follows. 
CONCLUDING REMARKS 
The effect of partial (long-wavelength side only) 
and full spectral band shifts on radiances output 
from a radiative transfer code were examined for 
the reflective TM bands over vegetation and for 
the reflective MODIS-N bands over vegetation and 
over water. In the case of TM, the greatest 
errors due to spectral band shifts occurred in the 
shorter wavelength bands. For example, in TM band 
1, a 25% error occurs for a full shift of 15 nm 
and a 12% error results from a partial shift of 15 
nm. Most MODIS-N bands in the solar reflective 
spectrum can be affected by spectral filter 
shifts, with errors of several hundred percent 
possible in some cases. Full spectral band shifts 
almost always give rise to larger errors than do 
partial shifts. The main factors responsible for 
the effects of spectral shifts on sensor output 
vary from band to band and can include surface 
reflectance, gas absorption, solar irradiance, and 
molecular scattering. 
ACKNOWLEDGEMENTS 
The author wishes to thank P.N. Slater for 
valuable discussions, as well as G. Fedosejevs and 
A. Kalil for assistance in the preparation of the 
manuscript. 
REFERENCES 
Dinguirard, M., Begni, G., and Leroy, M. (1988), 
SPOT-1 results after 2 years of flight, 
Proceedings, SPIE, 924:89-95. 
Markham, B.L., and Barker, J.L. (1985), Spectral 
characteristics of the Landsat-4 MSS sensors, 
Landsat-4 Science Characterization Early Results, 
1:1-23-1-56, NASA Conf. Pub. 2355. 
MODIS Instrument Panel Report (1986), Earth 
Observing System, Volume lib, National Aeronautics 
and Space Administration, Code NIT-4, Washington, 
D.C., 20546-0001. 
(i) The largest errors due to spectral shifts 
arise in a water vapour absorption region 
in the MODIS-N bands at 0.905, 0.936, and 
0.940 micrometers, regardless of whether 
the background surface is water or vegeta 
tion. Even a 5-nm shift of the 10-nm band 
at 0.936 micrometers can alter the apparent 
reflectance at the sensor by 100% (cf. 
Tables 4 and 6). 
(ii) In all but a few instances, partial 
spectral band shifts give rise to smaller 
errors than full shifts. One exception is 
the 50-nm band at 0.659 micrometers when 
observing vegetation, which has a 
relatively narrow chlorophyll absorption 
dip in that spectral region (cf. Tables 4 
and 5). 
Salomonson, V.V., Barnes, W.L., Mayroon, P.W., 
Montgomery, H.E. and Ostrow, H. (1989), MODIS: 
Advanced Facility Instrument for Studies of the 
Earth as a System, IEEE Transactions on Geoscience 
and Remote Sensing, 27:145-153. 
Suits, G.H., Malila, W.A., and Weller, T.M. 
(1988), The prospects for detecting spectral 
shifts due to satellite sensor aging, Remote 
Sensing of Environment, 26:17-29. 
Tanré, D., Deroo, C., Duhaut, P., Herman, M., 
Morcrette, J.J., Perbos, J., and Deschamps, P.Y. 
(1986), Simulation of the satellite signal in the 
solar spectrum, Laboratoire d'Optique 
Atmosphérique, Université des Sciences et 
Techniques de Lille, 59655 Villeneuve d'Ascq 
Cédex, France, 343 pages. 
(iii) Outputs from the 5S code runs were examined 
to determine the principal spectral 
variable causing the differences resulting 
from spectral shifts (cf. Tables 4-7). In 
about half the MODIS-N bands, surface 
reflectance is the main factor whereas, in 
other bands, the principal causative 
variable can be gas absorption or solar 
irradiance or, in the case of the band at 
0.470 micrometers imaging water, molecular 
scattering. 
Teillet, P.M. (1989), Surface Reflectance 
Retrieval Using Atmospheric Correction Algorithms, 
Proceedings of the 1989 International Geoscience 
and Remote Sensing Symposium (IGARSS'89) and the 
Twelfth Canadian Symposium on Remote Sensing, 
Vancouver, B.C., pp. 864-867. 
60