An operational software program is now available for deriving 'scaled surface reflectances' from spectral data collected by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). The program simulates both the atmospheric scattering and absorption effects. Brief descriptions of the algorithm, inputs, outputs, the limitations of the software, and procedures for obtaining the software are given

Gao, Bo-Cai

Goetz, Alexander F. H.

Heidebrecht, Kathleen

English

NASA Technical Reports Server

SOFTWARE FOR THE DERIVATION OF SCALED SURFACE
REFLECTANCES FROM AVIRIS DATA
Bo-Cai Gao l, Kathleen Heidebrecht 1, and Alexander F. H. Goetz 1'2
1Center for the Study of Earth from Space/CIRES
2Department of Geological Sciences
Campus Box 449, University of Colorado
Boulder, Colorado 80309-0449, U.S.A.
1. INTRODUCTION
An operational software program is now available for deriving "scaled surface
reflectances" from specual data collected by the Airborne Visible/Infrared Imaging
Spectrometer (AVIRIS) (Vane, 1987). The program simulates both the atmospheric
scattering and absorption effects. Brief descriptions of the algorithm, inputs, outputs, the
limitations of the software, and procedures for obtaining the software are given.
2. FUNCTIONAL OVERVIEW
The program derives scaled surface reflectances using an approximate
atmospheric radiative transfer model. Horizontal surfaces having Lambertian reflectances
are assumed. The scaled surface reflectance_s can be converted to the real surface
reflectances if the slopes and aspects of the surfaces are known. For simplicity, the scaled
surface reflectances are referred to as "surface reflectances" in this document.
The atmospheric scattering effects are modeled using the Simulation of the
Satellite Signal in the Solar Spectrum (5S) code (Tanre et al. 1986). The transmittances
of seven gases are calculated based on an assumed atmospheric model, the solar and
observational geomelries, and using the Malkmus (1967) narrow band spectral model.
Water vapor values are derived from AVIRIS data in the 0.94 lain and 1.14 lam regions
using a 3-channel ratioing technique and a look-up table procedure. The derived water
vapor values are used in the process of removing atmospheric gaseous absorption effects
from AVIRIS data. Fig. la shows an AVIRIS spectrum over a vegetated area. Fig. lb
shows the corresponding derived surface reflectance spectrum.
3. INPUT DATA
The program requires an input file containing information on the AVIRIS scene
including geometric parameters, spectral parameters, atmospheric parameters, and
input/output parameters. Table 1 shows a sample input t-de. The input values are based
on information provided with the AVIRIS data and knowledge of the aerosol condition
when the data were collected. The program can be executed without the need of any field
measurements as inputs. However, a measurement of the aerosol optical depth when the
AVIRIS data were collected will improve the accuracy of the derived surface reflectances.
The input data are described further below:
1. Geometric Parameters
• Date and Time: the date and time in GMT that the AVIRIS data was measured.
• Latitude and Longitude: the latitude and longitude of the center position of the
AVIRIS scene.
2. Spectral Parameters
• Wavelength File: the name of the AVIRIS wavelength file.
n 94-167oo
101
https://ntrs.nasa.gov/search.jsp?R=19940012227 2020-06-16T20:21:39+00:00Z
3000:
0.4 0.6 0.8 [.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
WAVELENGTH (urn)
(a)
0.8_
Co)
0.8'-
. ii i
0,4 0,6 0.8 l.O Z.2 1.4 1.6 18 2.0 2.2 2.4
WAVELENGTH (urn)
Figure 1. (a): An AVIRIS spectrum over a vegetated area, and (b) the corresponding
derived surface reflectance spectrum.
Table 1. An example input file.
Input Comment
07 23 1990 20 58 32
37 30 08
N
117 13 17
W
/unp/aviris.wav
10.
1
0.8630 1.0550 3 3 0.9398 7
1.0550 1.2470 3 3 1.1414 7
2
1111111
0.34
1 100
1.5
/tmp/aviris.cub
0
/tmp/aviris_atm.cub
10.
/tmp/aviris.vap
/tmp/aviris.lib
date and time
latitude
hemisphere of the earth (N or S)
longitude
hemisphere of the earth (E or W)
wavelength t'lle
spectral resolution of AVIRIS data
channel ratio parameters (if "0", defaults used)
atmospheric model number
gas selectors
total column ozone amount (atm-cm)
aerosol model and visibility
average elevation of the surface scene
input AVIRIS data
input AVIRIS dimensions
output image file
output data resolution
output water vapor t-de
output spectral library t-de
• Spectral Resolution: the AVIRIS spectral resolution in nanomc|crs.
• Channel Ratio Parameters: the center positions and widths of window channels and
absorption channels for the 0.94-1am and the 1.14-1am water vapor bands.
3. Atmospheric Parameters
• Atmospheric Model: a model atmosphere close to the measurement condition,
• Gas Selectors: indicators for determining which of the seven gases that have
absorption features in the 0.4-2.5 lain will be included in atmospheric gaseous
transmission calculations. The seven gases are water vapor, carbon dioxide.
ozone, nitrous oxide, carbon monoxide, methane, and oxygen.
• Total Ozone: the vertical column amount of ozone (in units of atm-cm) that is
contained in the atmosphere (typically 0.34 atm-cm).
• Aerosol Model and Visibility or Optical Depth at 0.55 Ixm: a model of the aerosol
conditions and the visibility or the optical depth at 0.55 _ when the AVIRIS
measurements were made.
t02
• Average Elevation: the average elevation (in units of kin) of the scene.
4. Input/Output Parameters
• Input AVIRIS Image: the path and f'de name of the input AVIRIS data.
• Input AVIRIS Image Dimensions: the dimensions of the input AVIRIS image
including the header size in bytes, the number samples, the number of lines, the
number of channels, and the storage order.
• Output Image File: the path and file name of the output surface reflectance data.
• Output Spectral Resolution: the desired resolution of the output spectra in
nanometers. If the output specual resolution is coarser than the input spectral
resolution, then the output spectra will be smoothed using a gaussian function.
• Output Water Vapor File: the path and f'de name of output water vapor image file.
• Output Spectral Library File: the path and file name of output spectral library file.
4. OUTPUT DATA
1. Surface Reflectance Image
a surface reflectance image that has the same size as the input AVIRIS image.
2. Water Vapor Image
a single spatial image containing the column water vapor amount at each pixel.
3. Transmittance Lookup Table
a file containing atmospheric transmittance spectra and band ratios for each of the 60
column water vapor values.
5. LIMITATIONS
The elevations within an image are not allowed to vary. As a result, the program
is mostly applicable to images with surface elevation variations less than about 1 km.
The atmospheric adjacency effect and the topographic adjacency effect ate not modeled.
When using our program for surface reflectance retrievals, the band positions between
observed and calculated spectra must be matched to 0.5 nm or better.
6. SOFTWARE AVAILABILITY
The source code and user documentation is prodded free of charge or royalties.
However, CSES retains the title and copyright to the software and documentation.
Recipients of this software are required to execute a memorandum of understanding
(MOU) provided by CSES that specifies in detail all of the associated conditions. Send
requests for an MOU to:
e-mail: sips@cses.colorado.edu
voice: (303) 492-1866
fax: (303) 492-5070
7. ACKNOWLEDGEMENTS
This work was partially supported by the NASA Goddard Space Flight Center under
contract NAS5-30552.
8. REFERENCES
Malkmus, W., Random Lorentz band model with exponential-tailed S line intensity
distribution function, J. Opt. Soc. Am., 57, 323-329, 1967.
Tanre, D., C. Deroo, P. Duhaut, M. Herman, and J. J. Morcrette, J. Perbos, and P. Y.
Deschamps, Simulation of the Satellite Signal in the Solar Spectrum (5S), User's
Guide 0d.S.T. de Lille, 59655 Villeneuve d'aseq, France: l.aboratoire d'Optique
Atmospherique), 1986.
Vane, G. (Ed.), Airborne visible/infrared imaging spectrometer (AVIRIS), JPL Publ. 87-
38, Jet Propul. Lab., Pasadena, Calif., 1987.
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Software for the derivation of scaled surface reflectances from AVIRIS data

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