Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data shows promise for the estimation of foliar biochemical concentrations at the scale of the canopy. There are, however, several problems associated with the use of AVIRIS data in this way and these are detailed in recent Plant Biochemical Workshop Report. The research reported was concentrated upon three of these problems: field sampling of forest canopies, wet laboratory assay of foliar chemicals, and the visualization of AVIRIS data

Curran, Paul J.

Smith, Geoffrey M.

English

NASA Technical Reports Server

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N94-1668 
EXPLORING THE REMOTE SENSING OF FOI IAR BIOCHEMICAL
CONCENTRATIONS WiTH AVIRIS DATA
Geoffrey M. Smith and Paul J. Curran.
Department of Geography, University College of Swansea,
University of Wales, Singleton Park, Swansea SA2 8PP, UK.
1. INTRODUCTION
AVIRIS data shows promise for the estimation of foliar biochemical
concentrations at the scale of the canopy (Committee on Earth Science 1989,
Wessman et aL 1988, Curran 1989). There are, however, several problems
associated with the use of AVIAIS data in this way and these are detailed in a
recent Plant Biochemical Workshop Report (Peterson 1991). The research
reported here has concentrated upon three of these problems: field sampling of
forest canopies, wet laboratory assay of foliar chemicals and the visualisation of
AVIRIS data.
2. STUDY SITES
Two study sites were used in this research. The first is north east of
Gainesville, Florida, , is NSF funded and is maintained by the University of
Florida (UF). This site is covered by a slash pine (Pinus elliottil) plantation and
contains 8 fertilised and 8 control plots, each 50m x 50m in size. These were
overflown by AVIRIS in March and September 1990, with multiple overpasses
on each date (Curran et al. 1991). The second study site is around Llyn Brianne
in Wales, UK. The upland site is covered by a Sitka spruce (Picea sitchensis)
plantation with small areas of other plantation species (japanese larch, Larix
kaempferi; Iodgepole pine, Pinus contorta var. latifolia) and contains 51, 50m x
50m plots. These were overflown twice by AVIRIS in July 1991 as part of the
NASA MAC Europe (Curran and Plummer 1992).
3. PROBLEMS
3.1. Field sampling of forest canopies
The five main stages were: choosing the study site, choosing the study
plots, locating the plots, collecting forest mensuration data and finally sampling
the foliage. These will be discussed in turn.
The two study sites have a history of environmental research. The site in
Florida has a homogeneous canopy on a flat site and the site in Wales has a
heterogeneous canopy on a rugged site.
The Florida study site contained established plots. At the Welsh study
site the establishment of plots was made difficult by windthrow and drains. In
addition, flat areas were seasonally waterlogged and suffered from large
variations in tree growth over small distances. Collecting ground data in such
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areas would mean sampling virtually every tree within the plot. Therefore, the
range of plots chosen to represent relative levels of tree vigour were all on
drained, slightly sloping land where neighbouring trees were similar. Sitka
spruce plantations afford limited access to their interior and so a network of
access paths had to be cut, by the removal of lower branches.
The Global Positioning System (GPS) was to be used to locate the plots.
Unfortunately, hand-held systems when used within the forest could not pick up
the signals from the GPS transmitters. Any future use of GPS for plot location
within forest stands would require an external aerial that could be placed above
the canopy. Classical surveying techniques were therefore used to locate the
plots on both study sites.
UF collected forest mensuration data for each plot at the Florida study
site (Gholz et aL 1991). During NASA MAC Europe, a wide range of forest
mensuration data (diameter at breast height, leaf area index, tree height) were
collected for each plot at the Welsh study site.
The open canopy and lack of low level branches at the Florida study site
meant the canopy could be sampled by shooting small branches from the
canopy which then fell to the ground. The Sitka spruce at the Welsh study site
had a very dense canopy and retains its dead branches on lower whorls
preventing sample branches from reaching the ground. Two methods were used
to sample this canopy. At some points within the plots the lower dead branches
from the tree were cleared until the live canopy was reached. A ladder and
pruning pole were then used to remove the selected live branches from the
canopy. At other points within the plots a tree was felled. Once the tree was
horizontal hand pruners could be used to remove the required parts of the
canopy. In total 539 foliage samples were collected, 384 for the study site in
Florida and 155 from the study site in Wales.
3.2. Wet laboratory analysis of foliar chemicals
The sampled foliage was bagged by age class and frozen for return to
the University College of Swansea (UCS). The samples were then analyzed
using standard wet laboratory techniques for chlorophyll, moisture, lignin,
cellulose, nitrogen and carbon, with replication. So far the chlorophyll and
moisture analyses have been completed and these show statistically significant
differences between the fertilised and control plots at the Florida site and the
relative level of tree vigour at the Welsh site.
3.3. Visualisation of AVIRIS data
The Department of Geography at UCS was oriented towards the analysis
of broad band remote sensing data and so initial analysis of the AVIRIS data
cube was slow and relatively unproductive. This early processing was divided
into two sections: spatial analysis and spectral analysis. The original data cube
remained on a VAX 8820 and the required data were displayed spatially on a
GEMS image processing system, running GEMSTONE software and spectrally
on a 386PC, running in-house software. This separation of the data made it
hard to link images and spectra together. Effective processing was achieved
using SUN SPARC stations running PV-Wave software which is designed for
the visualisation of multi-dimensional data sets. A set of routines is being
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developed in the PV-Wave Command Language to perform the necessary
processing associated with AVIRIS data.
4. FUTURE RESEARCH
The work described above continues in an effort to better understand the
relationships between foliar biochemical concentrations and remotely sensed
spectra. The NASA MAC Europe involved other sensors. Broad band
multispectral scanners provide estimates of the foliar biomass and the AIRSAR
provides estimates of the amount of wood within forest stands. These data sets
will be integrated and applied to ecosystem simulation models to derive
estimates of net primary productivity at a regional scale.
5. CONCLUSIONS
The remote sensing of foliar biochemical concentrations is an important
contribution to the development of ecosystem models on regional to global
scales. Field campaigns are vital if it is to be demonstrated that the AVI RIS can
provide such information. This paper has emphasised the complexity of such
campaigns, in particular the need for meticulous site preparation and a large
number of foliar samples, backed up by the facilities necessary for wet
laboratory assay and the visualisation of AVIRIS data.
6. REFERENCES
Committee on Earth Sciences, 1989, Our Changing Planet: The FY1990
Research Plan (The U.S. Global Research Program). U.S. Department of
Interior, Reston, Va.
Curran, P.J., 1989, The remote sensing of foliar chemistry. Remote Sensing of
Environment, 29, 271-278.
Curran, P.J., Dungan, J.L. and Smith, G.M., 1991, Increasing the signal-to-noise
ratio of AVlRIS imagery through repeated sampling. Proceedings of the Third
Airborne Visible Infrared Imaging Spectrometer (AVIRIS) Workshop. R.O.
Green. (Ed). JPL Publication 91-28, California Institute of Technology,
Pasadena, Ca, 164-167.
Curran, P.J., and Plummer, S., 1992, Remote sensing of forest productivity.
NERC News, 20, 22-23.
Gholz, H.L., Vogel, S.A., Cropper, W.P.Jr., McKelvey, K., Ewel, K.C., Teskey,
R.O. and Curran, P.J., 1991, Dynamics of canopy structure and light
interception in Pinus elliottii stands, North Florida. Ecological Monographs, 61,
33o51.
Peterson, D.L., 1991, Report on the Workshop Remote Sensing of Plant
Biochemical Content: Theoretical and Empirical Studies. NASA White Paper.
NASA Ames Research Center, Ca.
Wessman, C.A., Abet, J.D., Peterson, D.L. and Melillo, J.M., 1988, Remote
sensing of canopy chemistry and nitrogen cycling in temperate forest
ecosystems. Nature, 335, 154-156.
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