Monday, January 31, 2011
Friday, January 28, 2011
veg reflactance
FINE STRUCTURE IN THE SPECTRAL
REFLECTANCE OF VEGETATION AND SO I LS
V, C, VANDERBI LT
Purdue University/LARS
E, Re STONER
Earth Resources Laboratory/National
Aeronautics and Space Administration
L, Lt BIEHLj Bo F, ROBINSONj
R, A, WEISMILLER AND Ma E, BAUER
Purdue University/LARS
The spectral reflective response of
plants, soils, and rocks may contain in-
formation concentrated in relatively nar-
row spectral regions defined by the light
absorption properties of the constituent
atoms and molecules. The hope exists that
such information will be of value in re-
mote sensing in discriminating information
classes, in identifying growth stages and
stress conditions in crops, and in delin-
eating the chemical and physical proper-
ties of soils and rocks. Satellite sen-
sors measuring spectral regions possibly
as narrow as 0.02 pm, a spectral resolu-
tion significantly better than that (0.1
pm) of the Landsat multispectral scanner,
appear feasible .
Fine structure in crop spectra has
been reported by Collins who identified
a shift in the radiance of wheat measured
in the far red (near-infrared 0.73 pm)
wavelengths, a shift that occurs at the
onset of heading. Wiersma grouped spec-
tra from bare soil and vegetation and
found a significant amount of non-redun-
dant information in the near-infrared
wavelength region in bands 0.02 pm apart.
The paper addresses the key issue
raised by Wiersma; if there is information
in narrow wavelength bands in reflectance
spectra of bare soil and vegetation, is
that information attributable to proper-
ties of the soil, the vegetation, or both.
Four hundred eighty-one spectra repre-
senting soils from throughout the United
States were analyzed. More than 1000
wheat spectra from fourfields measured
at four growth stages, several view direc-
tions, and several illumination angles
were analyzed. The analyses involved the
correlation coefficient computed for the
spectral reflectance of adjacent wave-
lengths 0.02 pm apart.
The analysis results show clearly the
large water absorption bands at 1.4 and
1.9 um, prominent in soil and vegetation
U.S. Government work not protected by U.S. copyright.
spectra, The iron oxide absorption band
at 0.9 um is quite pronounced in the anal-
ysis results of the soils data. The vege-
tation analysis results show clearly the
transition wavelength region between the
visible and the near-infrared, anomalies
at 0.53 and 0.57 pm, and minor water ab-
sorption bands at 0.95 and 1.15 pm. At
three wavelengths, 0.85, 1.05, and 1.25 pm,
small anomalies in the results may indi-
cate fine structure in the reflectance
data but the finding is tenuous at best.
1980 Machine Processing of Remotely Sensed Data Symposium
REFLECTANCE OF VEGETATION AND SO I LS
V, C, VANDERBI LT
Purdue University/LARS
E, Re STONER
Earth Resources Laboratory/National
Aeronautics and Space Administration
L, Lt BIEHLj Bo F, ROBINSONj
R, A, WEISMILLER AND Ma E, BAUER
Purdue University/LARS
The spectral reflective response of
plants, soils, and rocks may contain in-
formation concentrated in relatively nar-
row spectral regions defined by the light
absorption properties of the constituent
atoms and molecules. The hope exists that
such information will be of value in re-
mote sensing in discriminating information
classes, in identifying growth stages and
stress conditions in crops, and in delin-
eating the chemical and physical proper-
ties of soils and rocks. Satellite sen-
sors measuring spectral regions possibly
as narrow as 0.02 pm, a spectral resolu-
tion significantly better than that (0.1
pm) of the Landsat multispectral scanner,
appear feasible .
Fine structure in crop spectra has
been reported by Collins who identified
a shift in the radiance of wheat measured
in the far red (near-infrared 0.73 pm)
wavelengths, a shift that occurs at the
onset of heading. Wiersma grouped spec-
tra from bare soil and vegetation and
found a significant amount of non-redun-
dant information in the near-infrared
wavelength region in bands 0.02 pm apart.
The paper addresses the key issue
raised by Wiersma; if there is information
in narrow wavelength bands in reflectance
spectra of bare soil and vegetation, is
that information attributable to proper-
ties of the soil, the vegetation, or both.
Four hundred eighty-one spectra repre-
senting soils from throughout the United
States were analyzed. More than 1000
wheat spectra from fourfields measured
at four growth stages, several view direc-
tions, and several illumination angles
were analyzed. The analyses involved the
correlation coefficient computed for the
spectral reflectance of adjacent wave-
lengths 0.02 pm apart.
The analysis results show clearly the
large water absorption bands at 1.4 and
1.9 um, prominent in soil and vegetation
U.S. Government work not protected by U.S. copyright.
spectra, The iron oxide absorption band
at 0.9 um is quite pronounced in the anal-
ysis results of the soils data. The vege-
tation analysis results show clearly the
transition wavelength region between the
visible and the near-infrared, anomalies
at 0.53 and 0.57 pm, and minor water ab-
sorption bands at 0.95 and 1.15 pm. At
three wavelengths, 0.85, 1.05, and 1.25 pm,
small anomalies in the results may indi-
cate fine structure in the reflectance
data but the finding is tenuous at best.
1980 Machine Processing of Remotely Sensed Data Symposium
veg reflactance
Vegetation has a unique spectral signature which enables it to be distinguished readily from other types of land cover in an optical/near-infrared image. The reflectance is low in both the blue and red regions of the spectrum, due to absorption by chlorophyll for photosynthesis. It has a peak at the green region which gives rise to the green colour of vegetation. In the near infrared (NIR) region, the reflectance is much higher than that in the visible band due to the cellular structure in the leaves. Hence, vegetation can be identified by the high NIR but generally low visible reflectances. This property has been used in early reconnaisance missions during war times for "camouflage detection".
The shape of the reflectance spectrum can be used for identification of vegetation type. For example, the reflectance spectra of vegetation 1 and 2 in the above figures can be distinguished although they exhibit the generally characteristics of high NIR but low visible reflectances. Vegetation 1 has higher reflectance in the visible region but lower reflectance in the NIR region. For the same vegetation type, the reflectance spectrum also depends on other factors such as the leaf moisture content and health of the plants.
The reflectance of vegetation in the SWIR region (e.g. band 5 of Landsat TM and band 4 of SPOT 4 sensors) is more varied, depending on the types of plants and the plant's water content. Water has strong absorption bands around 1.45, 1.95 and 2.50 µm. Outside these absorption bands in the SWIR region, reflectance of leaves generally increases when leaf liquid water content decreases. This property can be used for identifying tree types and plant conditions from remote sensing images. The SWIR band can be used in detecting plant drought stress and delineating burnt areas and fire-affected vegetation. The SWIR band is also sensitive to the thermal radiation emitted by intense fires, and hence can be used to detect active fires, especially during night-time when the background interference from SWIR in reflected sunlight is absent.
Typical Reflectance Spectrum of Vegetation. The labelled arrows indicate the common wavelength bands used in optical remote sensing of vegetation: A: blue band, B: green band; C: red band; D: near IR band;
The shape of the reflectance spectrum can be used for identification of vegetation type. For example, the reflectance spectra of vegetation 1 and 2 in the above figures can be distinguished although they exhibit the generally characteristics of high NIR but low visible reflectances. Vegetation 1 has higher reflectance in the visible region but lower reflectance in the NIR region. For the same vegetation type, the reflectance spectrum also depends on other factors such as the leaf moisture content and health of the plants.
The reflectance of vegetation in the SWIR region (e.g. band 5 of Landsat TM and band 4 of SPOT 4 sensors) is more varied, depending on the types of plants and the plant's water content. Water has strong absorption bands around 1.45, 1.95 and 2.50 µm. Outside these absorption bands in the SWIR region, reflectance of leaves generally increases when leaf liquid water content decreases. This property can be used for identifying tree types and plant conditions from remote sensing images. The SWIR band can be used in detecting plant drought stress and delineating burnt areas and fire-affected vegetation. The SWIR band is also sensitive to the thermal radiation emitted by intense fires, and hence can be used to detect active fires, especially during night-time when the background interference from SWIR in reflected sunlight is absent.
Typical Reflectance Spectrum of Vegetation. The labelled arrows indicate the common wavelength bands used in optical remote sensing of vegetation: A: blue band, B: green band; C: red band; D: near IR band;
emr interaction
http://www.epilogue.net/art/
http://www.crisp.nus.edu.sg/~research/tutorial/optical.htm
http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1395&context=lars_symp
http://www.crisp.nus.edu.sg/~research/tutorial/optical.htm
http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1395&context=lars_symp
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