As a calibrated imaging spectrometer flying at a 20 km altitude, AVIRIS may contribute to the Landsat and the Advanced Land Remote Sensing System efforts. These contributions come in the areas of: (1) on-orbit calibration, (2) specification of new spectral bands, (3) validation of algorithms, and (4) investigation of an imaging spectrometer of the Advanced Land Remote Sensing System

Green, Robert O.

Simmonds, John J.

English

NASA Technical Reports Server

N95- 23866
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A Role for AVIRIS in the Landsat and Advanced Land Remote Sensing System Program
Robert O. Green and John J. Simmonds
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109
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ABSTRACT
As a calibrated imaging spectrometer flying at a 20 km altitude, AVIR1S may contribute to the Landsat and
the Advanced Land Remote Sensing System efforts. These contributions come in the areas of: 1) on-orbit
calibration, 2) specification of new spectral bands, 3) validation of algorithms and 4) investigation of an
imaging spectrometer fl)r the Advanced Land Remote Sensing System.
1.0 INTRODUCTION
AVIRIS is a NASA-sponsored Earth-looking imaging spectrometer that measures the total upwelling
radiance from 400 to 2500 nm through 224 imaging channels. A plot showing the 224 channels of AVIRIS
and the six bands of the Landsat Thematic Mapper is shown in Figure I. For AV1RIS, typically up to 10
images of 11 by up to 100 km at 20 m spatial resolution are acquired on a single flight. AVIRIS data are
rigorously calibrated in the laboratory (Chrien et al., 1990) and validated inflight with respect to their
spectral and radiometric characteristics. These characteristics are summarized in Table 1.
Currently Landsat has 6 bands in the 400 to 2500 nm spectral region. There is an increasing requirement
that Landsat data be well calibrated to fulfill the measurement and monitoring roles of the Landsat data.
Under the Advanced Land Remote Sensing System (ALRSS) there are options to add to the spectral
coverage of sensors beyond Landsat 7. In this paper we describe potential contributions by AV1RIS in the
areas of calibration and measurement augmentation to Landsat and ALRSS program.
2.0 RADIOMETRIC AND SPECTRAL CALIBRATION
Valid radiometric calibration is essential for many of the current and proposed algorithms and monitoring
activities of Landsat. Because AVIRIS is a calibrated imaging spectrometer operating at 20 km altitude,
underflights of Landsat by AVIRIS may be used to validate and/or establish the on orbit spectral and
radiometric characteristics.
Spectral calibration algorithms are being developed to use concurrently acquired AVIRIS and Landsat-type
data. These algorithms use a concurrently acquired AVIRIS and spaceborne sensor data to solve directly for
the spectral band shapes. Concurrently acquired data over spectrally varying surface and atmospheric targets
are required. From these data, a least squared error fitting algorithm is used to calculate the spectral band
shape of the spaceborne sensor.
The radiometric calibration of Landsat may be established through underflight of Landsat by AVIRIS.
Because AVIRIS is calibrated inflight (Green et al., 1993a) and AVIRIS measures data at a 20 km altitude, a
Landsat calibration may occur in a nonclear sky or even cloudy conditions. This is a significant operational
advantage over ground based calibrations.
AVIRIS is currently being used in this mode to calibrate the Optical Sensor (OPS) on board the Japanese
Environmental Satellite JERS-I (Green et al., 1993b). A plot showing the accurate convolution of the
AVIRIS channels to the JERS-10PS bands is given in Figure 2. In Figure 3 the upwelling OPS radiance
derived from AVIRIS is given. In the Landsat program, AVIRIS could be used in this mode beginning with
Landsat 6.
3.0 SPECIFICATION OF FUTURE ALRSS BANDS
Analysis of AVIRIS data sets may be used to specify future bands for measuring and monitoring the Earth's
surface as well as collecting information for the atmospheric correction of ALRSS data. Based on research
with AVIRIS data there is evidence that additional spectral bands would improve measurements of: soils
and rocks; manmade objects; vegetation; snow and ice; as well as coastal and inland waters.
In addition, based on analysis of AVIRIS data sets, ALRSS bands might be specified to measure: water
vapor, aerosols, surface pressure, cirrus clouds, etc. for atmospheric correction (Green et al., 1993c: Goetz et
al., 1993).
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https://ntrs.nasa.gov/search.jsp?R=19950017446 2020-06-16T08:30:35+00:00Z
AVIRISdatamaybeusedto investigateheoptimalspatialresolutionof ALRSSbands.For example,
bands devoted to atmospheric characterization may not require the same high spatial resolution required for
the measurement of surface features.
4.0 TESTING AND VALIDATION OF ALGORITHMS
Once a set of bands have been designated fl)r the ALRSS sensor, AVIRIS data may be acquired and
spectrally convolved to the exact band shapes. These simulated ALRSS images may bc used to test
proposed algorithms for the surface and atmosphere under a range of conditions. With this preparation,
validated algorithms will be in place in advance of the spaceborne sensor launch.
5.0 AN IMAGING SPECTROMETER ON BOARD THE ALRSS
AVIRIS data are currently used fl)r investigations spanning the disciplines of: terrestrial ecology: geology
and soils oceanography and linmology: hydrology: atmospheric gas and aerosol investigations: snow
hydrology: general spectral signature detection and evaluation: calibration: and algorithm development. It
has been proposed to support these investigations and applications globally that an imaging spectrometer be
included on an ALRSS. AVIRIS data may be used to evaluate requirements anti tradeoffs between the
spectral and spatial coverage fl_r such a sensor on the ALRSS.
6.0 CONCLUSION
AVIRIS currently measures data for NASA investigators from the 20 km altitude of the ER-2 aircraft
platform. Work is ongoing to maintain and improve the performance characteristics of the AVIRIS sensor.
The current spectral, radiometric, geometric and calibration characteristics of AVIRIS allow it to fulfill an
important role in the calibration of Landsat sensors. In addition, AVIRIS may be used to specify new bands
and new capabilities on the ALRSS.
7.0 ACKNOWLEDGMENTS
This research was carried out at the Jet Propulsion Laboratory, Califi)rnia Institute of Technology, under
contract with the National Aeronautics and Space Administration.
8.0 REFERENCES
Chrien, T. G., R. O. Green, and M. Eastwood, "'Laboratory spectral and radiometric calibration of the
Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)", SPIE Vol. 1298, Imaging spectroscopy of the
terrestrial environment, 1990.
Goetz, A. H. F., "Effects of Water Vapor and Cirrus Clouds on TM-Derived Apparent Reflectance Based on
AVIRIS Experience", Workshop on Atmospheric Correction of Landsat Imagery, 29 June to 1 July,
Torrance, CA, 1993.
Green, Robert O. and Bo-Cai Gao, "Inflight Calibration of AVIRIS in 1992 and 1993", Proc. Fourth JPL
Airborne Geoscience Workshop, JPL Pub. 93-26, Jet Propulsion Laboratory, Pasadena, CA, 1993a.
Green, Robert O., James E. Conel, Jeannette van den Bosch, Masanobu Shimada and Masao Nakai, "On-
orbit Calibration of the Japanese Earth Resources Satellite-I Optical Sensor Using the Airborne Visible-
Infrared Imaging Spectrometer", IGARSS'93, Tokyo Japan, Optical Sensor and Calibration, in press, 1993b.
Green, Robert O. and James E. Conel, "Atmospheric Correction of Data collected by Airborne Visible-
Infrared Imaging Spectrometer (AVIRIS) and Application to the Advanced Land Remote Sensing Systems",
Workshop on Atmospheric Correction of Landsat Imagery, 29 June to 1 July, Torrance, CA, 1993c.
86
9.0 TABLE
Table 1. AVIRIS Data Characteristics
SPECTRAL
Wavelength range
Sampling
Spectral response (fwhm)
Calibration
RADIOMETRIC
Radiometric range
Sampling
Absolute calibration
lntraflight calibration
Precision/noise
GEOMETRIC
Field of view (FOV)
Instantaneous FOV
Calibration
Flight line length
400 to 2500 nm
< 10nm
10 nm nominal
<= 1 nm
0 to maximum lambertian
-1 dn noise rms
<=7%
<=2%
exceeding NEdL/SNR requirement
30 degrees
1.0 mrad
<= 0.2 mrad
Up to ten 100 km flight lines
10.0 FIGURES
0.9
0.8
0.7
E 0.6
c
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;= 0.4
0.3
0.2
AVIRIS 224 Spectral Channels
Atmospheric Transmission
0 I _/ 6 Landsat Bands as Gaus:
400 600 800 1000 1200 1400 1600
Wavelength (nm)
1800 2000 2200 2400
Figure 1. 224 AV1RIS channel plotted with the 6 visible to short wavelength infrared bands of the Landsat
Thematic Mapper modeled as gaussian functions. A terrestrial transmission spectrum is shown as well.
87
0.9 ] <_
_ 0.8 :
0
0.7
0.6
0.5
0.4 i i
0.3
z
0.2
0.1 ._
0 - _
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Wavelength(nm)
Figure 2. Weighted convolution filters mapping AVIRIS spectral channels to JERS-l OPS bands.
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400
Figure 3.
spectrum.
/
.... AVIRIS Radiance 100km
\ _)"---- JERS-10PS Convolved Radiance
600 800 1000 1200 1400 1600 1800 2000 2200 2400
Wavelenglh (nm)
Measured upwelling radiance convolved to the JERS-I OPS bands and AVIRIS radiance
88


A role for AVIRIS in the Landsat and Advanced Land Remote Sensing Systems program

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