The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
404 
2. EXPERIMENTAL METHODS AND MATERIALS 
2.1 Experimental design 
Experiment one: From April to August in 2006, the experiment 
was carried out at the loess plateau ecological experimental sta 
tion (E104°25\ N30°53') of the key laboratory of the nation 
arid agriculture at the Northern Mountain Yuzhong, lanzhou 
university. The soil type is yellow soft soil and the four culti- 
vars are Dingxi35, Gaoyuan602, Longchun8139 and Dingxi24. 
The density grads is 100 grains/m2, 200 grains / m2, 400 
grains / m2, 600 grains / m2, 800 grains / m2, 1600 grains / 
m2, 3200 grains / m2.The sample site is 2mx2m and in order 
to ensure the precision the part of the wheat provide to observe 
the biophysical parameters was apart from the spectral observa 
tion. 
Experiment two: In Dingxi arid meteorology and agriculture 
experiment station (35°32'N, 104°37'E) of CMA, China. And 
the four cultivars are Dingxi35 Gaoyuan602, Longchun8139 
and Dingxi38, the area is 3m><3m, the line is 12 meter, and the 
field management is the same to experiment one. 
2.2 Measurement 
The canopy and leaf spectral reflectance was measured using a 
portable ASD Field Spec Pro FR2500 spectroradiometer (Ana 
lytical Spectral Devices Inc., Boulder, CO, USA) with spectral 
range from 350 to 2500 nm (1 nm intervals). The spectral reso 
lution was 3, and 10 nm for the ranges 350-1000 and 1000- 
2500 nm, respectively. The optical sensor of the spectroradi 
ometer was mounted in the frame of a supplemental light 
source with a 50-mm distance from target leaf surface. The 
sight angle is 5° and 25°.A Spectralon white reference panel 
was used to optimize the instrument to 100% reflectance at all 
wavebands prior to canopy and leaf reflectance measurements. 
When measuring leaf reflectance, the sight angle is 5° and that 
is 25° for the canopy reflectance measurement. Spectral meas 
urements were collected around solar noon on clear days using 
the following protocol: canopy reference measurement was 
collected twenty-five times at five spots and the height of the 
sensor and the canopy was one meter. At the last, the average 
value was the reflectance of the spot, followed by one refer 
ence measurement collected from a white field reference panel. 
The white field reference panel was made of a lighter, more 
portable material than the Spectralon panel and enabled more 
frequent calibration measurements to be made within the field 
without damaging the coating of the Spectralon panel itself. 
Meanwhile, the leaf of the stem reflectance was collected ten 
times each spot and the interval was 0.1 meter then obtain the 
average value. 
Leaf area index (LAI) was recorded using the LAI-2000 plant 
canopy analyzer. Plant components were dried at 70 °C and 
weighed to determine the dry biomass. The chlorophyll meas 
ures by a SPAD502 and the plant height is determined syn 
chronously. 
2.3 Selection and definition of spectral indices 
Spectral indices were computed by chlorophyll absorption 
around 640~660nm and 430~450nm (Table 1). Furthermore, as 
we all know, the red edge parameter is another important index 
to the vegetation grown status. The quantitative describe the 
red edge feature are main following three: (1) the position of 
red edge(Xred), that is the wavelength of the maximum of the 
first derivative reflectance in red region((680-760nm); (2) the 
range of the red edge( DXred), that is the maximum of the first 
derivative reflectance in red region((680-760nm); (3) The area 
of the red edge (Sred), that is the area of the first derivative re 
flectance surrounded. In this paper, the first derivative reflec 
tance is calculated by difference, DA.= (Ri + 1) - (Ri-1) / 
(A,i+ 1) - (A.i — 1) , and the Ri is the reflectance when the 
wavelegth is i. some research indicated that there are two fac 
tors determined the position and the slope of the red edge, one 
is the chlorophyll, it cause the change of the spectral varies 
around 700nm and the other is scatter feature of the plant, it 
was determined by the structure of the canopy and leaf and so 
on(Boochs F,1990; Florler D N H,1983). 
Indices 
Reference 
Formulation 
NDVI 
Rouse etal.(1974) 
y DV/ Kr-K* *850-*650 
R mr + R red *850 + *650 
EVI 
Huete et al., (2002), 
jgyj — -> y, — R red 2.5 X * g50 — * 65Q 
*»r + 6 x R red — 7.5 x R hlue + 1 * 850 + 6 x * 650 — 7.5 x * 450 +1 
NDWI 
Gao (1996) 
NDWI ^»60 ~ 240 
^860 + ^1240 
RVI 
Pearson&Miller (1972) 
RVI=^L = ikl 
Rred R-650 
PVI 
Richardson&Wiegand 
(1977) 
PV j _ R nir - aRred -b *850 - a x * 650 - (a= 10.489,b=6.604) 
V(l + a 2 ) V0 + « 2 ) 
SAVI 
Huete(1988) 
SAVI - R ^~ R red (i + L y L=0.5 
Kir+Ked+L 
DVI 
Jordan(1969) 
DVI=R nir -R red =R85o-R65o 
^red 
D^red 
R670/R550 
R670/R440 
the position of red edge 
the maximum of the first derivative reflectance in red region((680- 
760nm) 
Table. 1 the camputed of the spectral indices