Variations Of Par Parameters And Validation Of Fpar/lai Model Of Warm Steppe In Hulunber

The variations of PAR (Photosynthetic active radiation) in Leymus chinensis meadow-steppe in Hulunber were studied as well as the validation of FPAR (Fraction of photosynthetic active radiation) /LAI (Leaf area index) model for Leymus chinensis was conducted. The results are as follows:1)The seasonal variations of both PAR and APAR (Absorbed photosynthesis active radiation) tended to decrease in the growth period from early June to late September. PAR fluctuated in a wider range between 25 mol/m2 and 58 mol/m2 and APAR fluctuated in a narrower range between 17 mol/m2 and 34 mol/m2. However, FPAR tended to increase. It ranged from 0.46 to 0.77 and the highest value of FPAR was 0.77, appearing in the last ten days of August.2)The changes of the incident PAR, reflectance PAR, transmittance PAR of canopy and reflectance PAR of soil in the whole day was a standard curve of sine in clear days. The diurnal variation of the reflectance ratio of canopy was higher in the morning and the evening and the lowest value appeard around 12:00 at the noon. The diurnal change of the reflectane ratio of soil varied in a wider range of variation in 0.4 on June compared with varying only in 0.08 on July and September. The diurnal variation of APAR was identical with the incident PAR's. The diurnal FPAR variation was a curve of cosine in clear day on June, July and in the middle of August, and its range of variation was 0.60. Compared with it, the range of variation was only 0.13 on September. The relatively correct PAR data were got by measuring on the ground as well as FPAR and it provided a reference for the evaluaiton of precision and validation of FPAR in grassland.3)Reflectance and transmittance in 400 to 700nm are both low . The reason of this phenomenon is that light was absorbed by chlorophyll a,chlorophyll b,lutein and carotene near 450nm(blue),660nm(red) and there are two absorption valleys(near 450nm, 660nm) and one small reflectance peak (around 550nm ) appearing at corresponding bands which were called blue edge,red valley and green peak. To 680nm as the center of the reflectivity minimum start the transition to the reflection from the 800nm peak, during the existence of the inflection point corresponding to the wavelength of "red edge". The high reflectivity of platform area rage from 800 to 1 350 nm have connection with the internal structure of leaves. The spectral characteristics from 1 300 to 2 500 nm were mainly influenced by water content of leaf. There will be two major reflection peaks in this range of bands which exist around 1 650 and 2 200nm because of the strong absorption of water moisture in 1 450 and 1 940 band.4)The feature of spectral curve of Leymus chinensis' canopy is similar to the leaf's. The spectral curve of Leymus chinensis' canopy looks seems as the curve of soil when the value of LAI is very small. The spectral curve' characteristic of canopy are becoming more and more obvious along with the increase of LAI. For Leymus chinensis measured at the same time but in different area, reflectance of canopy is not absolutely high corresponding the high LAI because of difference in soil types.5)The FPAR/LAI model based on warm steppe was validated by comparing and analyzing of the results of FPAR/LAI obtained respectively from the simulated by FPAR/LAI model and measure FPAR/LAI. Correlation coefficients were 0.8634, 0.8418 and 0.6408 respectively. It suggested that the model ass suitable.