CASI diurnal experiment over two sites carried out in June 2000 with a specific CASI mode of operation in order to allow for higher spatial resolution data with spectral bands centered at the PSII photosystem. CASI data were collected in 9 spectral bands at 680.47, 684.26, 688.06, 691.86, 695.66, 699.46, 703.26, 707.06, and 710.87 nm and 0.56x1.08m spatial resolution, resampled to 0.5x0.5 m.
Variation of CASI optical index R750/R710 and fluorescence measurement Fv/Fm in the diurnal experiment (top), and reflectance difference (bottom) obtained from the Acer saccharum M. site between 8.00am and 12.20pm acquired with CASI at 5m spatial resolution and 144 channels.
CASI diurnal mission carried out in July 1999 collecting data over two study sites at different times of the day, 8.00h, 9.30h, 12.20, and 16.12h along with ground truth CF measurements with PAM-2000. Airborne CASI data acquired at 5m spatial resolution and 144 channels
Reflectance difference obtained between the 8.20am, 9.02am and 1.37pm measurements in the diurnal experiment over a canopy of Acer saccharum M. seedlings using a fibre spectrometer. Reflectance difference between 8.20h and 13.30h is higher than reflectance difference between 8.20h and 9.00am, consistent with previous diurnal experiments in which the maximum in the 690-700nm region due to the effects of CF is higher in the early morning than in mid-day, when light saturation reduces the CF, and therefore its effects on the apparent reflectance.
Diurnal variations of Fv/Fm and the optical index R6852/(R675·690) calculated from CASI canopy reflectance in laboratory using Acer sacharum M. seedlings. The behaviour of CF during the day is tracked by the optical index derived from CASI reflectance achieving r2=0.95.
Time-decay fluorescence in apparent canopy reflectance. CASI reflectance measurements from Acer Saccharum M. seedlings in the laboratory taken after dark adaptation and after 3 minutes of illumination (top), and CASI reflectance bands 751.8 nm and 689 nm during the first 30 seconds of the study.
CASI canopy-reflectance measurements of Acer saccharum M. seedlings in laboratory. Data were collected from the plant material using the Schott RG695 filter with dark-adapted plant material and then without the filter, therefore allowing red light to reach the plant material. A reflectance change in the 730-750 nm can be detected due to the photosystem excitation by red light. The maximum reflectance difference of 3% is observed at 742 nm.
Canopy reflectance imagery collected in laboratory from Acer saccharum M. seedlings using the CASI hyperspectral imager at 2.5 m above the canopy, at a nominal bandwidth of 2.5 nm between 405 and 940 nm. Collimated illumination by a stablized 1000W light source at 45 inclination and a Spectralon reflectance panel enabled normalization to scene above-canopy apparent reflectance.
FRT Model simulating leaf reflectance with fluorescence (fluorescence efficiency=0.085, chl a+b content = 50 g.cm-2, leaf thickness = 0.075 mm, labeled as Ref_wFLOU), and without fluorescence (labeled as Ref_noFLUO).
Variation of Fv/Fm (top) and Ft (bottom) during the day of the experiment measured in leaf samples, compared to the variation of the reflectance difference at 740 nm (Rdiff@740) with and without the filter. The similar tendencies in solid curves, which are the least-squares best fit through the two sets of data, show that the Fv/Fm dark-adapted and Ft steady-state fluorescence are tracked by reflectance measurements.
Variation of the reflectance difference at 755 nm with (Rfl_wf) and without filter (Rfl_nf) with time. It demonstrates the fluorescence decay at 755 nm with time after the illumination of a dark-adapted leaf.
Reflectance measurements taken at t0 (r1) and t1(5 min) (r2) which demonstrates that fluorescence emission bands affect the reflectance measurements.
Single leaf reflectance measurements obtained with the Li-Cor 1800 apparatus and fiber spectrometer using the measurement protocol with the RG695 filter (thick line) and with no filter (thin line) from a dark-adapted Acer saccharum M. leaf sample. The additive effect of the broad 740 nm fluorescence signal superimposed on the reflectance spectrum is shown.
Transmittance of the Schott RG 695 high pass filter measured with the Li-Cor 1800 integrating sphere and 7.5nm Ocean Optics fiber spectrometer. The filter blocks out the excitation light at l < 695 nm and enables the measurements of leaf reflectance and transmittance without the influence of chlorophyll fluorescence
Schematic view of the Li-Cor 1800 integrating sphere coated internally with BaSO4, coupled to the Ocean Optics spectrometer. Ports A, B, and C enable the exchange of white and dark plugs as well as the light source. The optional long-pass filter placed at the exit aperture of the light source enables measurements of reflectance and transmittance at l > 700 nm while suppressing the fluorescence signal.
A series of laboratory and field measurements of spectral reflectance under artificial and natural light conditions demonstrate that effects of natural chlorophyll fluorescence are observable in the reflectance red edge spectral region. These are results from the progress made to link physiologically-based indicators to optical indices from hyperspectral remote sensing in the Bioindicators of Forest Sustainability Project.
This study is carried out on twelve sites of Acer saccharum M. in the Algoma Region, Ontario (Canada), where field measurements, laboratory-simulation experiments, and hyperspectral CASI imagery have been carried out in 1997, 1998, 1999 and 2000 campaigns. Leaf samples from the study sites have been used for reflectance and transmittance measurements with the Li-Cor Model 1800 integrating sphere apparatus coupled to an Ocean Optics Model ST1000 fibre spectrometer in which the same leaves are illuminated alternatively with and without fluorescence-exciting radiation.
A study of the diurnal change in leaf reflectance spectra, combined with fluorescence measurements with the PAM-2000 Fluorometer show that the difference spectra are consistent with observed diurnal changes in steady-state fluorescence. Small canopies of Acer saccharum M. have been used for laboratory measurements with the CASI hyperspectral sensor, and under natural light conditions with a fibre spectrometer in diurnal trials, in which the variation of measured reflectance is shown experimentally to be consistent with a fluorescence signature imposed on the inherent leaf reflectance signature. Such reflectance changes due to CF are measurable under natural illumination conditions, although airborne experiments with the CASI hyperspectral sensor produced promising but less convincing results in two diurnal experiments carried out in 1999 and 2000, where variations of reflectance due to the effect of CF were observed.