Barrett N. Rock

Detection of changes in leaf water content using near- and middle-infrared reflectances

Abstract Detection of plant water stress by remote sensing has been proposed using indices of Near-Infrared (NIR, 0.7–1.3 μm) and Middle-Infrared (MIR, 1.3–2.5 μm) wavelengths. The first objective of this study was to test the ability of the Leaf Water Content Index (LWCI) to determine leaf Relative Water content (RWC) of different species with different leaf morphologies. The second objective was to determine how the Moisture Stress Index (MSI; MIR / NIR) varies with RWC and the Equivalent Water Thickness (EWT). Reflectance factors at 0.82 μm and 1.6 μm were measured on leaves of Quercus agrifolia (sclerophyllous leaves), Liquidambar styraciflua (hardwood deciduous tree leaves), Picea rubens and Picea pungens (conifer needles), and Glycine max (herbaceous dicot leaves) as they dried on a laboratory bench. RWC and EWT were measured concurrently with the reflectance measurements. The results showed that LWCI was equal to RWC for the species tested. However, the results of a sensitivity analysis indicated the reflectances at 1.6 μm for two different RWC must be known for accurate prediction of unknown RWC; thus the LWCI is impractical for field applications. MSI was linearly correlated to RWCwith each species having a different regression equation and to log10 EWT with data of all species falling on the same regression line. Because EWT is correlated with leaf area index, MSI should also be correlated with leaf area index. Assuming that the linear regression equation of MSI to EWT can be applied to canopies, then the minimum significant change of RWC that can be detected is 52%. For most plants, the natural variation in RWC from water stress is only about 20%, so that we conclude that indices derived from NIR and MIR reflectances cannot be used to remotely-sense water stress.

Red edge spectral measurements from sugar maple leaves

Abstract Many sugar maple stands in the northeastern United States experienced extensive insect damage during the 1988 growing season. Chlorophyll data and high spectral resolution spectrometer laboratory reflectance data were acquired for multiple collections of single detached sugar maple leaves variously affected by the insect over the 1988 growing season. Reflectance data indicated consistent and diagnostic differences in the red edge portion (680-750 nm) of the spectrum among the various samples and populations of leaves. These included differences in the red edge inflection point (REIP), a ratio of reflectance at 740-720 nm (RE3/RE2), and a ratio of first derivative values at 715-705 nm (D715/D705), All three red edge parameters were highly correlated with variation in total chlorophyll content. Other spectral measures, including the Normalized Difference Vegetation Index (NDVI) and the Simple Vegetation Index Ratio (VI), also varied among populations and over the growing season, but did not correla...

Comparison of in situ and airborne spectral measurements of the blue shift associated with forest decline

Abstract During August 1985, extensive field activities were conducted at spruce/fir (Picea and Abies) sites in Vermont and Baden-Wurttemberg (FRG) currently undergoing rapid forest decline suspected of being due to various forms of air pollution. High-spectral resolution in situ reflectance curves and photosynthetic pigment determinations were acquired for common branch samples from specimens of spruce typical of both high- and low-damage sites. Similar spectral responses (reflectance data) were exhibited for specimens collected from high-damage sites in both the United States and FRG. Both current year and older foliage from high-damage sites in both countries showed an approximately 5 nm shift away from the normal inflection point of the red edge reflectance feature toward shorter wavelengths (a blue shift). This blue shift was associated with an observed reduction in chlorophyll b and a relative decrease in chlorophylls for needles collected from the high-damage sites, as compared with those from low-damage sites. An airborne high-resolution imaging spectrometer (the Fluorescence Line Imager or FLI) was flown over the Vermont study sites in August 1985 and has detected a blue shift of the chlorophyll absorption maximum at the high-damage site. Red edge parameters (wavelength position of the chlorophyll absorption maximum, red radiance, and NIR radiance) detected by the FLI have been used to image and map areas of damage in a highly accurate manner. Since data presented here suggest that the blue shift is a previsual symptom of damage, the ability to remotely detect such subtle spectral symptoms may serve as an early indicator of certain types of forest damage, and thus could be of considerable value in monitoring forest condition and state of health.

Spectral reflectance measurements of boreal wetland and forest mosses

High-spectral resolution reflectance data were acquired in the laboratory for several species of boreal forest and peatland mosses. Feather mosses and lichens (forests), brown mosses (rich fens), and Sphagnum species (bogs and poor fens) were collected from sites in the northern study area (NSA) of the Boreal Ecosystem-Atmosphere Study (BOREAS) near Thompson, Manitoba, and from three peatlands in southeastern New Hampshire. Because mosses are indirect indicators of soil moisture, trace gas flux, and carbon accumulation, these data may enable hyperspectral remote sensing systems, such as the airborne visible and infrared imaging spectrometer and the compact airborne spectrographic imager (AVIRIS) (CASI), as well as future systems such as Lewis and the first New Millennium Project, to infer differences in hydrology and carbon cycling in boreal ecosystems at small spatial scales (< 1–900 m2). Mosses exhibit distinctly different spectral characteristics from vascular plants in the visible, near-infrared (NIR) and short-wave infrared (SWIR) regions. In the visible portion of the spectrum, mosses exhibit typical absorption in the blue and red regions but differ from vascular plants in having a “green” peak reflective of the color (red, brown, or green) of the individual species. The moss reflectance in the NIR spectral region is typically less reflective than the same region in vascular plants and is characterized by strong water absorption features located at approximately 1.00 and 1.20 μm, resulting in pronounced reflectance peaks at approximately 0.85, 1.10, and 1.30 μm (identified as NIR 1, 2, and 3, respectively). The variations in the relative brightness of the three NIR peaks in each of the three groups of mosses (Sphagnum, feather, and brown mosses) are diagnostic and may be indicative of different cellular characteristics. The slope of the NIR plateau as determined by the NIR 3/1 ratio, as well as the shape of the NIR 1 peak and relative dominance of NIR 2, separate the three groups. In addition, the NIR 1 peak in Sphagnum species is marked by a minor absorption feature at 0.85 μm, which is absent in all brown mosses and feather mosses, as well as in vascular plants. Because this absorption feature results in a narrow NIR 1 peak, and the red absorption is also narrow in Sphagnum, the standard normalized difference vegetation index/simple vegetation index ratio (NDVI/VI) methods do not work well in characterizing biomass or greenness. The overall reflectance of mosses in the SWIR region (1.50–2.50 μm) is lower than that of vascular plants because of the higher water content of the moss tissue. In lichens, reflectance in this region is higher than either mosses or vascular plants, due likely to tissue dryness. The lichens included in this study are most dissimilar from mosses and vascular plants in the visible portion of the spectrum.

Detection of initial damage in Norway spruce canopies using hyperspectral airborne data

Current broadband sensors are not capable of separating the initial stages of forest damage. The current investigation evaluates the potential of hyperspectral data for detecting the initial stages of forest damage at the canopy level in the Norway spruce (Picea abies (L.) Karst) forests of Czech Republic. Hyperspectral canopy reflectance imagery and foliar samples were acquired contemporaneously for 23 study sites in August 1998. The sites were selected along an air pollution gradient to represent the full range of damage conditions in even-aged spruce forests. The changes in canopy and foliar reflectance, chemistry and pigments associated with forest damage were established. The potential of a large number of spectral indices to identify initial forest damage was determined. Canopy hyperspectral data were able to separate healthy from initially damaged canopies, and therefore provided an improved capability for assessment of forest physiology as compared to broadband systems. The 673-724 nm region exhibited maximum sensitivity to initial damage. The nine spectral indices having the highest potential as indicators of the initial damage included: three simple band ratios, two derivative indices, two modelled red-edge parameters and two normalized bands. The sensitivity of these indices to damage was explained primarily by their relationship to foliar structural chemical compounds, which differed significantly by damage class.

Use of thematic mapper data for the detection of forest damage caused by the pear thrips

Abstract This study evaluates the potential of measuring, mapping, and monitoring hardwood damage caused by pear thrips in southern Vermont and northwestern Massachusetts using Landsat Thematic Mapper (TM) data. Images displayed using the TM 1.65/0.83 μ (TM5/4) band ratio, the 1.65 μ band, and the 0.66 μ band (TM Band 3), in the order of red, green, and blue, were found to clearly distinguish between high and low damage areas. Imagery employing a TM 0.83 μ band difference data set (which was produced by subtracting coregistered 1988 from 1984 0.83 μ band data) in the red plane, in conjunction with 1988 1.65 μ and 0.66 μ bands in the green and blue planes, respectively, was also found to clearly distinguish between high and low damage areas. The 0.83 μ band difference data set was used to estimate the amount of damage in the region. of approximately 0.83 million acres (0.33 million ha) of deciduous forest in the study area, 39.4% was classified as medium damage, and 9.7% was classified as high damage.

ASPEN BARK PHOTOSYNTHESIS AND ITS SIGNIFICANCE TO REMOTE SENSING AND CARBON BUDGET ESTIMATES IN THE BOREAL ECOSYSTEM

Aspen bark was investigated for photosynthetic function, pigment content, and spectral characteristics during the 1993–1994 Boreal Ecosystem-Atmosphere Study (BOREAS) summer field campaigns in the boreal zone of Saskatchewan, Canada. Parameters related to photosynthetic function were similar for bark and leaves: chlorophyll (Chl) concentration; fluorescence responses; and spectral reflectance. Similar increases along a vertical gradient from base to tree top were observed for incident photosynthetically active radiation (PAR), photosynthetic pigment content, photosynthetic capacity, and spectral reflectance variables. Since transmittance of aspen bark periderm was 20–30% in the blue, and 50–60% in the red Chl absorption bands, the PAR available to the photosynthetic cortical layer in the natural, canopy environment (<1000 μmol m−2 s−1) was sufficient to support positive net assimilation (<8–10 νmol CO2 m−2 s−1) under ideal conditions (e.g., light, temperature, saturating CO2), a rate approximately 30–50% that of leaves. However, the respiring tissues comprising the greater fraction of bark tissue bias the balance of CO2 exchange in favour of respiration for the whole bark. Therefore, net photosynthesis under ambient conditions on the whole bark was, in general, negative. The total bark surface area was estimated to contain 17–40% of the whole tree Chl. The contribution of the bark surface area fraction of the full canopy (leaves plus bark) increased with age (<60 years), with a similar trend expected for bark in total tree (and stand) photosynthesis. A spectral reflectance variable, the red edge inflection point (REIP), was related to total bark Chl content (r2=0.74). A better predictive relationship (r2=0.82) for total bark Chl was observed using a spectral index calculated from the reflectance ratio of two narrow wavebands (R3/R2: R2 and R3 are between 0.715–0.726 μm and 0.734–0.747 μm, respectively), which may have greater utility in landscape remote sensing. The bark spectra for Chlcontaining bark should improve understanding of carbon balance in aspen forests, based on landscape-level radiative transfer simulations.

High-spectral resolution field and laboratory optical reflectance measurements of red spruce and eastern hemlock needles and branches☆

Abstract Branch samples were collected from canopies of red spruce ( Picea rubens ) and eastern hemlock ( Tsuga canadensis ) on 11 and 12 September 1989 and 5 and 6 September 1990, and spectrally characterized by needle age class (first- and second-year). Needles from the branch samples were analyzed for complete optical properties (0.4–1.0 μm), pigment content (total chlorophylls), and anatomical (cellular) condition. Spectral differences between spruce and hemlock first- and second-year needles include differences in green peak reflectance features, red edge parameters, and amplitude features of the NIR plateau. Second-year needles of both species exhibit increased absorptance in the NIR when compared with first-year needles. Chlorophyll concentrations, as determined using both quantitative and empirical techniques [ratio analysis of reflectance spectra (RARS)] were greater in second-year needles in both species and highest overall in second-year hemlock needles. Substantial anatomical differences are seen between needles of the two species, as well as between age classes of the same species. Relative differences among total area occupied by cells, intercellular void space, and total needle volume likely contribute to the differences in the NIR response patterns observed. The reflectance spectra (0.4–2.5 μm) measured for single age-class branch segments of both species are similar in shape to reflectance spectra measured at the needle level. However, differences in the magnitude of reflectance are seen when branch and needle data are compared.

Spectral characteristics of lignin and soluble phenolics in the near infrared- a comparative study

Prediction of canopy chemical compounds including lignin based on reflectance or absorbance in the near infrared has been demonstrated using hyperspectral data. Little attention has been paid to the fact that many types of plant phenolics have chemical structures similar to lignin and may have similar spectral responses in the near infrared. To address this problem we have analysed near infrared spectral signatures of dry powder standards of lignin and tannin, dissolved lignin, tannin and other soluble phenolics, lignin and soluble phenolics extracted from Norway spruce needles, as well as wooden blocks containing varying amounts of tannin. Our results provide solid evidence that the spectral signatures of lignin and tannin are very similar and that spectral features and wavelengths used previously for lignin determination are in fact likely to be due to tannin and lignin reflectance features. This similarity may greatly affect near infrared assessments of canopy lignin concentrations and impact analyses for which these predictions are used. Additionally, certain near infrared reflectance properties associated with increasing levels of foliar damage may be due to increased levels of tannins in affected mesophyll cells. We have also identified the existence of a threshold lignin concentration below which spectrometry cannot precisely detect lignin.

Student Scientist Partnerships and Data Quality.

The Student Scientist Partnership introduces students to hands-on, minds-on science and provides them an opportunity to participate in a program that is real and important, and also introduces the student to the rigor of science through the focus on data quality. The student has the opportunity to experience and learn the Scientific Method, not just memorize it, to stimulate creative thinking, inquiry based learning, and many other key components of the educational objectives. The scientist should provide skill appropriate scientific inquiry tools that the student uses to help them improve the quality of their data and to understand the science concept being addressed. By making the measurements suggested, and establishing the quality of their data, the student begins the journey of understanding scientific research. The scientist not only uses the student-generated data in their on-going research activities, but also provides higher level information products back to the student. Ultimately, it must be clearly remembered that there are two important but quite different objectives for both the student and the scientist. For the student, the primary objective is the generation of the knowledge of science, while, for the research scientist, the primary objective is the generation of scientific knowledge.